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Long-term project viability is critically linked to purposeful economic development. Therefore, conservationists are increasingly looking for ways to link conservation to sustainable development, particularly in areas that are impoverished. Integrated conservation and development projects (ICDP) are one of the most popular mechanisms by which this could be accomplished. ICDPs combine conservation activities and local customs with aspects of economic development, including poverty reduction, job creation, health care, and food security. A major goal of ICDPs is for local people to become involved in conservation efforts and have access to opportunities and markets for which sustainable use of natural resources is more valuable than its destructive use. Zambia’s Community Markets for Conservation program (COMACO) illustrates on how this goal can be achieved (Lewis et al., 2011). Working around the Luangwa Valley’s national parks, COMACO helps food-insecure households and bushmeat hunters to meet their nutritional and income needs through sustainable production of honey, soy, Chama rice, groundnuts, and peanut butter (Figure 14.6). As additional incentive, COMACO connects participants to high-value markets where the villagers’ locally crafted products and sustainably cultivated produce can earn significantly higher prices than locally. Through this project, the area’s average household income has more than quadrupled, over 1,400 bushmeat hunters have adopted more sustainable lifestyles, and over 10,000 km2 of land have been dedicated to community-conserved areas where wildlife populations are now thriving.
Community-based natural resource management (CBNRM) represents another approach in which local landowners and community groups can benefit economically from biodiversity and conservation. In previous years, government officials managed biodiversity both inside and outside protected areas through top-down mechanisms with little to no local input. Gaining little economic benefit from the wildlife on their lands, local communities had few incentives to participate in conservation efforts; in some cases, they even became hostile to conservation projects that impeded their activities (Section 13.6.2). To overcome this imbalance, centralised management systems are increasingly transitioning to CBNRM models that involve collaborative management of natural resources on private and communal lands. By empowering local communities and strengthening accountability, government officials and conservation organizations hope that CBNRM projects can simultaneously counterbalance pressures on local wildlife and contribute to economic development in ways that will have long-lasting positive impacts.
Namibia hosts one of the most ambitious CBNRM projects to date. With seed money from external funders such as the US Agency for International Development (USAID), the Namibian government granted community groups the opportunity to manage the wildlife on their own lands. To obtain these rights, interested community groups needed to form a management committee and determine the boundaries of its land, after which the government designated the group’s land as a “community conservancy”. Participating conservancies then worked with tourist operators—who employed members from the local communities—to provide opportunities for wildlife viewing and hunting (Naidoo et al., 2016), while also allowing tourists to learn about Namibia’s cultural heritage at traditional villages. Revenues from these joint ventures were used to build and maintain even more tourist facilities, and train and pay game guards (also hired from the communal group) who monitor wildlife and human activities on the conservancies. These endeavours have been extremely successful (NACSO, 2015): from the program’s inception in 1996 to 2014, Namibia’s terrestrial protected area coverage increased from 14% to 20%. Wildlife populations also rebounded: for example, Namibia’s elephant population increased from 7,500 to 20,000. Local communities have since reaped the benefits (Störmer et al., 2019). For example, in just 2014, Namibia’s CBNRM projects generated US \$6 million in income and provided employment to 5,800 people (NACSO, 2015).
Unfortunately, maintaining programs, even successful ones, remains challenging over the long term. Consequently, many previous ICDPs and CBNRM projects have only been partially successful. This includes Zimbabwe’s iconic Communal Areas Management Programme for Indigenous Resources (CAMPFIRE) of the 1990s (Box 14.4), once considered a global model for conservation on unprotected lands. There are many reasons for these projects’ partial successes and failures, including funding limitations, project over-complexity, and political instabilities (Pooley et al., 2014). Although disappointing, these failures have offered valuable lessons that enabled conservation groups to adapt to the challenges of maintaining similar projects over the long term. Today, ICDPs and CBNRM are regarded as worthy of serious consideration, with successful programs across southern, East, West, and Central Africa (Roe et al., 2009). In addition to providing employment and food security, revenues from ICDPs and CBNRM projects have been used to build schools, clinics, and community centres; improve roads and sanitation; and establish crèches, community gardens, and nurseries (Arntzen et al., 2007; NACSO, 2015). In the end, ICDPs and CBNRM projects will be judged as successful when they can demonstrate that they can both protect wildlife and ensure improved livelihoods over the long term. To achieve these outcomes, a critical component of any ICDP or CBNRM project is the ongoing monitoring of biological, social, and economic factors to determine how effective the programs are in meeting their goals. Involving local people in these monitoring efforts may increase information sharing and help to determine how aware the people themselves are of the benefits and challenges each project presents (Braschler, 2009).
Box 14.4 Confronting Human-Wildlife Conflict in Zimbabwe
Steven Matema1,2
1African Conservation Trust, Applied Ecology Unit,
Durban, South Africa.
2African Wildlife Economy Institute,
Department of Animal Sciences,
Stellenbosch University, South Africa.
[email protected]
In Zimbabwe, several agro-pastoral communities live at the edge of protected areas. They thus come into conflict with wildlife species such as elephants, lions, chacma baboon (Papio ursinus, LC), leopard, spotted hyena (Crocuta crocuta, LC), bushpig (Potamochoerus africana, LC), and common warthog (Phacochoerus africanus, LC) on a regular basis. Zimbabwean law does not provide compensation for crop and livestock losses due to wildlife damage; farmers, thus, develop negative attitudes towards wildlife. Fences and the use of unpalatable buffer crops have not been as successful in mitigating human-wildlife conflict as wildlife conservationists had envisioned (Parker and Osborne, 2006). Instead, lethal control has been the predominant method for managing human-wildlife conflict outside of protected areas, causing a rapid decline in native wildlife populations.
Starting in 1975, the government began to experiment with “people-centred” human-wildlife conflict management strategies (Table 14.1) by adopting the principle that good environmental stewardship is contingent on conferring use and management rights to those directly affected by wildlife depredation. This was the basis for the Communal Areas Management Programme for Indigenous Resources (CAMPFIRE). Under CAMPFIRE, smallholder agro-pastoralists, Rural District Councils (RDC, the land authorities in rural areas), and private safari operators co-manage wildlife outside protected areas and share income from controlled safari hunting and tourism (Murphree, 2009; Taylor, 2009). CAMPFIRE led to a dramatic increase in wildlife populations outside of Zimbabwe’s protected areas: the elephant population increased, and the buffalo population stabilised or declined only slightly outside protected areas (Taylor, 2009). Many of the project’s benefits have also been sustained, despite Zimbabwe’s political volatility over time (Balint and Mashinya, 2008). Yet, in socio-economical terms, CAMPFIRE has largely failed: powerful politicians and local traditional leaders captured benefits, and natural resource governance arrangements have been politicised because political party-affiliated RDC councillors automatically chair local CAMPFIRE committees following the amendment of the Rural District Councils Act in 2002 (Matema and Andersson, 2015). Ongoing research in the Zambezi Valley also showed that trophy quality has declined since the early 2000s: the horn size of African buffalo (Syncerus caffer, NT) and elephant declined respectively by 42% (down from 1.35 m to 0.79 m) and 40% (down from 1.47 m to 0.91 m) between 2006 and 2014 (Matema et al., unpublished litt.). This suggests a decline in the number of adult animals and/or indiscriminate hunting of wildlife, indicating that CAMPFIRE may have also failed to reach its ultimate conservation goals.
Table 14.1 Policy and legislative changes for a people-centred approach to wildlife conservation in Zimbabwe, 1975–2005.
Year
Key event
Outcomes for conservation and human-wildlife conflict
1975
Parks and Wildlife Act enacted
Act gives authority to private landowners of white origin to exploit game for profit but leaves out black agro-pastoralists. Wildlife increases on private land. Human-wildlife conflict and negative attitudes toward wildlife by black agro-pastoralists persist.
1978
Wildlife Industries New Development for All (WINDFALL) program
Culling of meat from parks and distribution to neighbouring communities as a strategy to mitigate human-wildlife conflict improves attitudes towards wildlife. Revenue sent to district councils with no local participation, decision making, or community ownership.
1982
Parks and Wildlife Act amended
The amendment makes provision for authority to be granted to district councils to manage wildlife in rural areas on behalf of the communities.
1984
CAMPFIRE conceived by Department of Parks and Wildlife Management
Target is: collective ownership with defined rights of access to natural resources, appropriate and legitimate institutions, technical and financial assistance.
1989
Authority granted to the first two Rural District Councils
Implementation of CAMPFIRE. Local participation but devolution stops at Rural District Council level.
2005
Direct payment system introduced in CAMPFIRE
Communities receive income due to them from the safari operator directly into a community bank account, bypassing the Rural District Councils (another level of elite capture of income).
Sources: Murphree, 2009; Taylor, 2009.
Two major lessons were learnt from the CAMPFIRE experience. First, if community-based conservation is to be effective as a human-wildlife conflict mitigation strategy, attention needs to be paid to local and national political dynamics. Second, devolution—the transfer of decision power to local levels—is important. The enactment of Zimbabwe’s Indigenisation and Economic Empowerment Act (2008), which makes provision for rural communities to form Community Share Ownership Trusts to exploit natural resources in their areas, provided a model that CAMPFIRE could have adopted to achieve complete devolution. However, the political elite has used the 2008 Act to demand shares in, or a complete take-over of, wildlife conservancies owned by ranchers of white origin. Communities living next to these conservancies have been excluded in these take-overs with the concomitant escalation of human-human conflict about wildlife (Nyahunzvi, 2014), and negative implications for local tolerance of wildlife species that kill livestock and damage crops. To curb elite capture of income, global compacts are needed, such as the recent ban of imports of wildlife trophies into the USA until there is evidence that local people are equitably sharing revenue from CAMPFIRE. The CAMPFIRE model can work and create greater tolerance for wildlife so long as it buffers local people from income losses. That means compensation in lieu of retaliation on species damaging crops and killing livestock. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/14%3A_Conservation_on_Unprotected_Lands/14.03%3A_Linking_Conservation_to_Socio-Economic_Development.txt |
As a growing human population continues to encroach on the last remaining wildernesses, wildlife populations are facing increased competition for space and food. Inevitably, as animals are being displaced from degraded ecosystems, they will increasingly meet humans. Some of these interactions will be negative ranging from direct conflict (e.g. injury and even death to one or both participants) and indirect conflict (e.g. transmission of diseases) to opportunity costs (e.g. loss of income due to crop damage and livestock predation). Although human-wildlife conflict is not unique to Africa, Africans are generally very vulnerable due to high levels of poverty and dependence on land, which limits options for conflict mitigation. Managing human-wildlife conflict is thus an important issue to consider in the management of potentially dangerous species, especially near protected area borders.
Dealing with predators
When wildlife impedes human activities, the traditional solution is to either kill the animal or to exclude it from the area with a barrier such as a fence. Killing problem animals can take the form of pro-active lethal control to avoid losses, or retaliatory killings in response to losses. While there is a sense of instant gratification after killing a problem animal, it provides only a temporary solution at best, and may even give rise to a new set of challenges. For example, work on black-backed jackals (Canis mesomelas, LC) showed that killing territorial individuals may cause a breakdown in their local social structure, in turn allowing multiple roaming sub-adult animals to take advantage of the vacant territory (Minnie et al., 2016). Killing apex predators could also give rise mesopredator release, where medium-sized carnivores and omnivores (e.g. jackals and baboons) flourish in the absence of their natural enemies (Brashares et al., 2010). Indiscriminate poisoning and trapping also kills beneficial non-target animals that opportunistically scavenge, such as owls, vultures, and harmless ant-eating mammals (Brown, 2006; Ogada et al., 2015). Thus, while killing problem animals may seem an intuitive solution, it is seldom the best strategy.
Pastoralist communities are particularly vulnerable to predators. Because they are nomadic, pastoralists do not always have access to permanent or sturdy structures to protect their livestock and themselves. Consequently, conservation biologists are spending considerable energy on finding predatory-friendly approaches that offer lasting solutions for pastoralist communities. Among the most successful are schemes that provide compensation payments to pastoralists who forego retaliatory killings following livestock losses (Dickman et al. 2011). In Kenya, for example, compensation schemes reduced retaliatory killings of lions by 73–91% (Maclennan et al., 2009; Hazzah et al., 2014). Retaliatory killings can be reduced even more when compensation schemes are combined with other strategies; for example, one study that encouraged the use of mobile enclosures for livestock, communal herding, and “lion guardians” (the latter drawing on local knowledge and traditional values to mitigate conflict) saw a drop of 99% in retaliatory killings (Hazzah et al., 2014).
Non-lethal control of problem animals involved in human-wildlife conflict may provide more benefits than lethal control.
Livestock on commercial and smallholder farms are also vulnerable to predation when foraging away from protective structures. Non-lethal options to reduce livestock losses under these circumstances include predator-proof fences using native thorny plants, corralling pregnant females and calves during their vulnerable periods (Schiess-Meier et al., 2007), and setting up visual, chemical, or acoustic repellents in predation hotspots. Eliminating poor livestock husbandry (Woodroffe and Frank, 2005; Gusset et al., 2009; Newsome et al., 2015) and tardy disposal of deceased animals (Humphries et al., 2015) can also avoid situations where predators are attracted to domestic animals in the first place. But perhaps one of the most successful programs has been the use of livestock guarding animals, which could be dogs (Figure 14.7), donkeys, and other domesticated animals trained to protect livestock. A study from South Africa found that livestock depredation was eliminated on 91% of farms after the placement of guardian dogs, saving each of the 94 participant farms US \$3,189 per year (Rust et al., 2013); Namibian farmers reported equally encouraging results with guardian animals (Marker et al., 2005). While there is an upfront cost involved in obtaining a guardian animal, recent work found that their deployment is generally more efficient and cost-effective than the cost of lethal options (McManus et al., 2015).
The collaborations between farmers and conservation biologists to reduce livestock predation have benefited biodiversity conservation as well. Populations of African wild dogs (Lycaon pictus, EN) and lions are rebounding on some unprotected lands (Woodruffe, 2011; Blackburn et al., 2016), while farmers using guardian animals are also more tolerant of some predators on their properties (Rust et al., 2013). Not only do these farmers enjoy seeing native wildlife on their properties; some have even completely switched focus away from livestock to more profitable ecotourism (Sims-Castley et al., 2005) and wildlife ranching endeavours (Lindsey et al., 2013).
Dealing with crop raiders
Non-lethal management of crop-raiding animals is also a high priority. The traditional non-lethal method of dealing with potentially dangerous crop-raiding species (e.g. elephants) involves maintaining electric fences (Kioko et al., 2008), but this method is expensive and requires electricity. To overcome these challenges, conservationists and communities have developed several innovative strategies that may even supplement incomes. One such method is to establish buffer fences made of honey-producing beehives (Scheijen et al., 2019) or chilli plants (Parker and Osborn, 2006; Chang’a et al., 2016); tea plants have also been used successfully to keep crop-raiding gorillas (Gorilla spp.) at bay (Seiler and Robbins, 2016). Using a different approach, conservation biologists in Tanzania developed a harmless, low-cost alarm kit to deter elephants (Bale, 2016). This four-step system involves first shining bright flashing lights at an approaching elephant, followed by loud air horns, then launching a grenade filled with chilli powder, sand, and a loud firecracker, and, as a last resort, launching exploding fireworks toward the approaching elephant.
Concluding thoughts on human-wildlife conflict
One of the most effective mechanisms for dealing with human-wildlife conflict is to develop awareness and opportunities for at-risk people to benefit from potentially harmful animals.
Whether dealing with dangerous animals or crop raiders, one of the most effective mechanisms for dealing with human-wildlife conflict is to develop awareness and opportunities for at-risk people to benefit from potentially harmful animals (Blackburn et al., 2016). Studies in northern Ethiopia found that most people—even those who have been victims of human-wildlife conflict—have positive attitudes towards wildlife and believe that they can co-exist (Eshete et al., 2015). The reason for such positive attitudes is that a substantial portion of the affected people are aware of benefits from ecosystem services, including ecotourism opportunities. Such positive attitudes toward wildlife play a crucial role in the protection of a range of endemic species in this Global Biodiversity Hotspot, including the Walia ibex (Capra walie, EN) and Ethiopian wolf (Canis simensis, EN).
As discussed earlier, both ICDPs and CBNRM programs offer opportunities for local people to gain direct benefits from local wildlife, even potentially dangerous species. There are also research opportunities to further human-wildlife conflict mitigation beyond direct benefits to local people. For example, much progress has been made in understanding how lion (Tuqa et al., 2014) and elephant (Granados et al., 2012; Chiyo et al., 2014) behaviors relate to human activities; a logical next step would be to use this information to reduce conflict (e.g. Packer et al., 2005). An increasing number of resources are available to aid these and other efforts. The IUCN Human-Wildlife Conflict Task Force has taken the lead to collate much of this information; their library (http://www.hwctf.org/resources/document-library) is sorted by species and topic. They also provide free training manuals (e.g. Parker et al., 2007) and host regular workshops. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/14%3A_Conservation_on_Unprotected_Lands/14.04%3A_Confronting_Human-Wildlife_Conflict.txt |
1. Many species persist outside protected areas, in areas such as traditional farmland, sustainably logged forests, and unprotected rangelands. These areas can and must play a more important role in ongoing conservation efforts.
2. Traditional peoples that live on undeveloped land have beliefs that are compatible with biodiversity conservation. There are conservation strategies that can benefit traditional people and protect biodiversity.
3. Areas intensively used by humans can also contribute to conservation efforts. Biodiversity-friendly techniques are being developed and implemented for the agriculture, logging, and fisheries industries, many which have been adopted. Mines and other extractive industries can participate in biodiversity offset programs, and partner with conservation organizations to contribute to local biodiversity protection. But there remains a need to monitor the activities of extractive industries to ensure that cost-cutting measures do not lead to biodiversity losses.
4. Integrated conservation and development projects (ICDPs) and community-based natural resource management (CBNRM) projects link biodiversity conservation with economic development. There is however a need to ensure these approaches remain resilient to challenges that may threaten their long-term success.
5. Human-wildlife conflict, such as livestock predation and crop raiding, remains a major conservation challenge. Multiple mechanisms have been developed to help victims overcome or mitigate such losses. Some of these mechanisms have even allowed victims to benefit from the animals they previously thought of as nuisances.
14.06: Topics for Discussion
1. Imagine that the government informs you that a highly threatened species lives on land that you planned to develop. Would you be happy, angry, confused, or proud? What are your options in terms of the planned development? What would be a fair compromise that would protect your rights and interests, the rights of the public, and the well-being of the species?
2. Imagine your country builds an expensive dam to provide hydroelectricity and water for irrigation. It will take decades to pay back the costs of construction and lost ecosystem services; some of those costs may never be recovered. Who are the winners of such a project, and who are the losers? How are each of these groups (consider both people and wildlife groups) affected? What do you think can be done to make the project more worthwhile?
3. Do you think that the purchase of “green” (environmentally-responsible) products is an effective way to promote biodiversity conservation? Would you be willing to spend more money for timber, fuelwood, coffee, chocolate, palm oil, and other products that have been produced in a sustainable way, and if so, how much more? How could you determine whether the purchase of such products was really making a difference?
4. Think of a family (someone you know or heard of) that has been a victim of human-wildlife conflict or contracted a disease while being in nature. What happened? What did the family lose? Was the family compensated for their losses? How and by whom? If you had the opportunity to establish a plan to prevent or mitigate future conflicts, what would you do?
14.07: Suggested Readings
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Cox, R.L., and E.C. Underwood. 2011. The importance of conserving biodiversity outside of protected areas in Mediterranean ecosystems. PLoS ONE 6: e14508. https://doi.org/10.1371/journal.pone.0014508 Unprotected lands have the potential to contribute to an overall conservation strategy.
Hassanali, A., H. Herren, Z.R. Khan, et al. 2008. Integrated pest management: The push-pull approach for controlling insect pests and weeds of cereals, and its potential for other agricultural systems including animal husbandry. Philosophical Transactions of the Royal Society of London B 363: 611–21. https://doi.org/10.1098/rstb.2007.2173 Benefits of integrated pest management strategies extend beyond pest control and increased crop yields.
Hopcraft, J.G.C., S.A.R. Mduma, M. Borner, et al. 2015. Conservation and economic benefits of a road around the Serengeti. Conservation Biology 29: 932–36. https://doi.org/10.1111/cobi.12470 Compromises between conservation and development might contribute more to socio-economic developmental goals than the original plans.
Laurance, W.F., S. Sloan, L. Weng, et al. 2015. Estimating the environmental costs of Africa’s massive “development corridors”. Current Biology 25: 3202–08. https://doi.org/10.1016/j.cub.2015.10.046 Il-conceived development wastes resources and harms biodiversity.
Lewis, D., S.D. Bell, J. Fay, et al. 2011. Community Markets for Conservation (COMACO) links biodiversity conservation with sustainable improvements in livelihoods and food production. Proceedings of the National Academy of Sciences 108: 13957–62. https://doi.org/10.1073/pnas.1011538108 An example of a program that links conservation with socio-economic upliftment.
McManus, J.S., A.J. Dickman, D. Gaynor, et al. 2015. Dead or alive? Comparing costs and benefits of lethal and non-lethal human-wildlife conflict mitigation on livestock farms. Oryx 49: 687–95. https://doi.org/10.1017/S0030605313001610 Non-lethal methods provide more benefits than lethal methods in controlling predators of livestock.
Morgan, D., R. Mundry, C. Sanz, et al. 2018. African apes coexisting with logging: Comparing chimpanzee (Pan troglodytes troglodytes) and gorilla (Gorilla gorilla gorilla) resource needs and responses to forestry activities. Biological Conservation 218: 277–86. https://doi.org/10.1016/j.biocon.2017.10.026 Guidance for sustainable logging aimed at protecting apes.
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The field of conservation biology has set itself some imposing—but critical—goals: to describe Earth’s biological diversity, to protect what remains, and to restore what is damaged. To understand what a significant undertaking this is, consider the Living Planet Index (http://www.livingplanetindex.org) which shows that, already in 2014, Sub-Saharan Africa’s vertebrate populations were on average down 56% compared to 1970 levels (WWF, 2018). Declines were even more pronounced for freshwater vertebrates which showed a 75% decline. With wildlife declines showing no sign of halting, we are in a race against time to prevent catastrophic losses. Conservation biology is a truly crisis discipline (Soulé, 1985; Kareiva and Marvier, 2012), because decisions often need to be made under pressure, with limited resources, and constrained by tight deadlines. At the same time, the discipline needs to offer a long-term conservation vision that extends beyond the immediate crisis, despite unreliable commitments to seeing such plans through to completion.
Despite the challenges we face, there are many positive signs for cautious optimism. Some threatened species are recovering, the number of well-managed protected areas is increasing, and, in some cases, natural resources are being used more prudently on unprotected lands. We have also increased our capacity to restore degraded ecosystems to such a level that we are now reintroducing species that were once extinct in the wild. Our improved ability to protect biodiversity is in no small way attributable to the wide range of productive local, national, and international collaborative efforts that have been cultivated over the past few decades. It is also because the field of conservation biology has expanded for the better, by developing linkages with rural development, economics, the arts, social sciences, and government policy, to name a few.
Make no mistake, many challenges remain unaddressed and under-addressed, and new ones will surely also arise. These challenges all need to be faced head-on, because there is no “Planet B”: Earth is our one and only planet. There will be times when the biodiversity crisis will feel insurmountable. When that happens, it is important to remember that every individual human can play a role in saving our natural heritage. If just one-tenth of Sub-Saharan Africa’s 1 billion people use one less plastic item (e.g. plastic bags, drinking straws, food wrappers) a week, there would be a reduction of 100,000,000 plastic items each week. People operating at the regional and global scales, such as company executives and government officials, also have an important task—ensuring that mechanisms are in place for all citizens to contribute to ensuring that future generations will inherit a healthier environment. Below, we offer a few holistic strategies towards a sustainable future.
15.01: Achieving Sustainable Development
Economic policies that favour growth are based on the erroneous assumption that natural resources are unlimited. It is thus bound to fail at one point or another.
Efforts to preserve biological diversity are regularly perceived as in conflict with societal progress (Redpath et al., 2013). Perhaps the root of this conflict lies with the fact that most of the development we see today is unsustainable—that is, it risks depleting natural resources to a point where they will no longer be available for use or to provide ecosystem services. Moreover, governments and businesses often measure success in terms of economic growth, which occurs when an economy increasingly produces more goods and services (often measured as GDP). Economic policies that favour economic growth are generally based on an implicit but erroneous assumption that the supply of natural resources is unlimited. A society that aims for economic growth is therefore bound to fail at one point or another.
To overcome these perceptions and conflicts, scientists, policy makers, and conservation managers are increasingly highlighting the need for sustainable development—economic activities that satisfy both present and future needs without compromising the natural world (Figure 15.1). Sustainable development is closely linked to economic development, a multi-dimensional concept that describes economic activities that aim to improve income and health without necessarily increasing consumption of natural resources. We should thus all strive for sustainable development, which emphasises economic development without unsustainable economic growth.
Sustainable development aims to satisfies present and future needs without compromising the natural world.
There are many good examples across Africa that illustrate the progress made towards sustainable development. For instance, many governments are investing in national parks and their infrastructure (such as staff and facilities) to protect biological diversity and provide economic opportunities for local communities. Similarly, stakeholders in large projects are increasingly engaging with one another to mitigate the negative impacts of infrastructure developments. One prime example was the 2015 Pan-African Business and Biodiversity Forum (http://www.panbbf.org), where representatives from business, governments, civil society, academia, development organizations, and financial institutions from across Africa came together to discuss how sustainable development can benefit nature, people, and business.
Unfortunately, there are also people and organizations that are taking advantage of this positive energy by misusing the term “sustainable development” to greenwash industrial activities that are harming the environment. For instance, a plan to establish a palm oil plantation that would damage a forested wilderness should not be considered sustainable development simply because the company agrees to protect a small plot of forest adjacent to the damaged area (see biodiversity offsets, Section 10.3.3). Similarly, many environmentally-destructive companies try to mislead customers with “environmentally-friendly” (often green-coloured) imagery on packages which are otherwise no better than the standard manufactured products. It is, therefore, critical for scientists, policy makers, and citizens to carefully study the issues, understand why different groups make arguments, and make thoughtful decisions about which actions or policies will best meet seemingly contradictory demands. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/15%3A_An_Agenda_for_the_Future/15.00%3A_Prelude_to_An_Agenda_for_the_Future.txt |
Over the past several decades, we have experienced a boom in new technologies to make our lives easier, our work more efficient, and our lifestyles more sustainable. Conservation biologists have adopted many of these new technologies to great success (Pimm et al., 2015). Consider, for example, the use of unmanned aerial vehicles (UAVs) to monitor environmental changes (Box 15.1), freely-available satellite imagery to monitor ecosystems (Section 10.1.1) and wildlife (Section 11.1.1), and molecular methods to monitor for wildlife crimes (Section 12.3.1). Hand-held devices that capture and send field data in real time are also increasing in popularity, as they enable conservation and law enforcement agencies to learn of and respond to threats much quicker than before (Wilson et al., 2019). To better streamline these efforts, there are groups such as Wildlabs which specialise in connecting the conservation community with engineers and entrepreneurs who develop such new technologies.
Box 15.1 Not Just for War: Drones in Conservation
Meg Boeni and Richard Primack
Biology Department, Boston University,
Boston, MA, USA.
Many of us have experienced the difficulty of following a moving herd of zebras, elephants, or any other large mammal from a vehicle or on foot. But what if this could be done from the sky? Efforts, such as mapping threatened species habitat, monitoring deforestation, and even fighting forest fires, have been aided for over 40 years with an “eye in the sky” using satellite and other aerial imagery (Pettorelli et al., 2013). The recent emergence of drones, or unmanned aerial vehicles (UAVs), has begun to make it even easier to facilitate conservation efforts from above.
Drone technology was originally developed for military applications but is fast becoming a vital resource to conservation biologists and natural resource managers. The increased popularity of drones in conservation is due to several distinct advantages. They are cheaper than airplanes or satellites; basic models that can fly up to 150 m high are available for around US \$2,000. Because they operate from the ground, they are also less affected by weather conditions such as cloud cover. Drones can carry a range of sensors and equipment—video, thermal imaging, or sound—that allow them to detect organisms and ecological processes that would be impossible to study otherwise, especially at large scales. New organizations such as Conservation Drones have greatly facilitated discussions and innovations in this rapidly developing technology. Lastly, some governments are highly receptive to these new technologies. Leading the way is Rwanda, where regulators are setting the stage for an airport dedicated to civilian and commercial drones (Simmons, 2016).
While conservationists are just beginning to explore the flexibility and applicability of drones, they have already proven their worth in African conservation initiatives (Figure 15.A). With encouragement from national park officials, drones have been used to survey elephant populations in Burkina Faso (Vermuelen et al., 2013) and chimpanzee (Pan troglodytes, EN) nests and fruiting trees in Gabon (van Andel et al., 2015). In South Africa, drones assist anti-poaching patrols in remote areas of national parks (Mulero-Pázmány et al., 2014). There are even discussions of using drones to plant trees in reforestation efforts, and to directly manage wildlife, such as deploying noise-making drones to block an elephant herd from entering farming areas.
Despite progress, a range of obstacles still must be overcome. For example, drones are often prohibited from flying near government buildings (which often includes conservation infrastructure); many countries also continue to uphold strict and arduous legal requirements for drone use. It is also important to remember that drones will never replace the need for rangers and researchers on the ground. They do however hold great promise in their potential to overcome some of the fundamental challenges that conservation biologists have always faced.
While conservation biologists certainly benefit from new technologies, these advances sometimes pose new challenges. Hunters now use powerful guns and motorised vehicles where historically they used bows and arrows and walked on foot. Sea fishing industries have transformed from using small wind-powered and hand-powered boats to large motorised fleets with freezers that can stay at sea for months at a time. Some technologies are so powerful that they allow for the alteration of entire ecosystems in a relatively short span of time. Some of these transformations are intentional, such as the creation of dams and the conversion of new agricultural land; others, such as pollution, are negative by-products from human activities. The impacts of these developments on ecosystems and wildlife are enormous and ominous; they have also stimulated the growth, expansion, and evolution of conservation biology.
Renewable energy sources are needed to create a sustainable society. They must also be evaluated for their environmental impact, with systems developed to mitigate those impacts.
Technologies developed to achieve sustainable development may sometimes also present new conservation challenges. For example, to combat climate change, scientists and engineers are rushing to reduce our dependence on fossil fuels by developing carbon-neutral and energy efficient alternatives. As these renewable energy sources have become more assimilated into our everyday lives, their unintended consequences on the environment have also become better understood. We now know that large wind farms (Figure 15.2) pose a significant collision hazard to birds (Rushworth and Krüger, 2014) and bats (Frick et al., 2017), while large solar-panel arrays that concentrate sunlight can also expose wildlife to burning temperatures (Walston et al., 2016). The impacts of hydroelectric dams are cause for even more concern: in addition to harming local fisheries and freshwater biodiversity (Section 5.3.2), these and other artificial reservoirs also generate large amounts of greenhouse gases that contribute to climate change (Deemer et al., 2016). Bioenergy also seems to create more problems than solutions, since it has become an important driver of habitat loss (Kleiner, 2007; see also Box 6.1). Similarly, hydrological fracturing for natural gas extraction—not in itself a carbon-neutral energy alternative but claimed to do less damage than coal and petroleum—has turned out to be so damaging to the environment and human health that several governments have now banned the practice (Section 7.1.1).
Despite the challenges posed by emerging technologies, none have yet posed an insurmountable threat. For example, we have already solved the ozone crisis by banning harmful chemicals such as chlorofluorocarbons (CFCs) (Section 12.2.1). We have also come a long way toward a sustainable fossil-fuel free world by setting guidelines for reducing the impact of wind power generation on wildlife (Reid et al., 2015; Martin et al., 2017), reducing the negative impacts of bioenergy production (Correa et al., 2017), safeguarding nuclear power stations and reusing nuclear waste (Heard and Brook, 2017), and developing more affordable solar power (Randall, 2016). It is important, however, to note that none of these emerging threats were solved by people who defended the status quo or resisted change, but by individuals who were alert and rapidly responded to new challenges before they reached a crisis point.
Environmental challenges are not solved by defending the status quo or resisting change, but by being alert and rapidly responding to new challenges before they reach a crisis point. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/15%3A_An_Agenda_for_the_Future/15.02%3A_Dealing_with_Technological_Advances.txt |
Much of the Earth’s biodiversity is concentrated in the tropics, a sizeable portion of which occurs in Africa. While people living in the tropics may be willing and eager to preserve the wildlife around them, they are often unable to accomplish the task due to funding constraints (James et al., 2001; McClanahan and Rankin, 2016). Because many of these areas experience high levels of poverty and rapid rates of population growth, the little aid these areas receive are generally diverted to short-term socio-economic programs that ensure elected officials remain in power, rather than long-lasting sustainable solutions. This scenario is not limited to the tropics or to Africa. In fact, one of the biggest challenges facing conservation biologists across the world is inadequate funding—many areas lack basic operational funds for protected areas (Section 13.7.1), with even less for staff training, retaining top talent, keeping promises to local communities, and fulfilling the obligations set out in international treaties.
There are many organizations that continuously work to fill these funding deficits. Prominently active in Africa are multilateral organizations, such as the UN Environmental Programme (UNEP), as well as the World Bank in association with its partner organizations. A key World Bank partner organization is the Forest Carbon Partnership Facility which helps countries in their REDD+ (discussed below) preparedness. Another is the Global Environment Facility (GEF), established to channel money from industrialized countries to conservation and environmental projects in developing countries. From 1991 to 2016, the World Bank-GEF partnership allocated over US \$4 billion to more than 1,000 projects in Sub-Saharan Africa, with another \$25 billion acquired through co-financing partnerships (http://www.thegef.org/projects). Prominent projects include a US \$35 million project to reverse environmental damage at Central Africa’s Lake Victoria, a US \$16 million project to strengthen community conservancies in Mozambique, and a US \$13 million project to bolster management effectiveness at Zambia’s Kafue National Park.
Another significant development has been the rise of NGOs that directly fund and manage conservation activities. NGOs rely on several funding mechanisms to accomplish their goals, including membership dues, donations from wealthy individuals, sponsorships from corporations, and grants from foundations and multilateral consortiums. NGOs use these funds to advance scientific research and conservation training, to implement large-scale conservation projects, and to develop locally-adapted conservation strategies (Shackeroff and Campbell, 2007), often in collaboration with local communities (Rodríguez et al., 2007). For example, BirdLife International provides alternative environmentally friendly income streams by training local guides to help tourists find rare and elusive bird species (Biggs et al., 2011); other NGOs train park rangers and wildlife biologists, set up ecotourism lodges, and create opportunities to sell hand-made crafts.
Multilateral consortiums and nongovernmental conservation organizations (NGOs) have emerged as important supporters of local conservation projects.
Another innovative funding approach, namely debt-for-nature swaps, leverages the huge international debt owed by developing countries to protect biodiversity. Major lenders (usually commercial banks or industrialized-country governments) have financed massive loans around the world, some of which they may never see repaid. One opportunity for the creditors to recoup some of this money is to restructure or sell the debt at a steep discount. Working with funders, investors, and development organizations, conservation groups may then buy a portion of these debts or help debtor country restructure this debt, in exchange for environmental commitments (in some cases, creditors may even directly engage with the debtor country). These commitments usually involve the debtor countries using the savings to annually fund, in their own currency, conservation activities, including enacting certain policies, acquiring lands for conservation, managing protected areas, and implementing conservation education programs. In other words, freeing up money previously being spent to repay debt to now fund conservation activities. Some of the African countries that have benefitted from such debt swaps include Botswana, Cameroon, Ghana (Figure 15.3), Guinea Bissau, Mozambique, Seychelles, Tanzania, and Zambia (Sheikh, 2018). In one such example, The Nature Conservancy (TNC), the French government, and a group of creditors known as the Paris Club negotiated a US \$22 million debt restructuring deal with the Seychelles in exchange for the creation of a climate adaptation trust fund and increased marine protection. As part of the deal, the Seychelles agreed to increase its marine protected areas (MPA) network from 1% to 30% coverage (400,00km2), and to develop and implement a comprehensive spatial management plan for all its territorial waters (TNC, 2015).
Another new strategy to obtain conservation funding is payment for ecosystem services (PES) schemes. Through these programs, governments, conservation NGOs, and businesses develop markets from which landowners can receive direct payments for protecting and restoring ecosystems and ecosystems services. In a pilot project funded and coordinated by WWF and CARE Kenya, 514 farmers living upstream of Kenya’s Lake Naivasha received US \$20,000 in payments from water users downstream to restore and maintain riparian forests to improve flood control and water purification services (Chiramba et al., 2011).
To combat climate change, a major international initiative financially rewards communities for preserving their carbon stocks. This initiative, established by the UN in 2007 and called Reducing Emissions from Deforestation and Forest Degradation (REDD+, see also Section 10.4) receives its operational funds from individuals (such as people traveling on aeroplanes) and organizations seeking carbon credits to offset their carbon emissions. These funds are then used for results-based payments for conservation of carbon stocks such as forests and peatlands, the loss of which causes about 35% of Africa’s greenhouse gas emissions (WRI, 2018). Today, REDD+ has already supported carbon conservation projects in over 30 Sub-Saharan African countries (http://www.reddprojectsdatabase.org). Being a major component of the Paris Agreement (Section 12.2.1), many more projects will hopefully be supported in coming years.
How effective is conservation funding?
Despite all these conservation resources, conservation activities continue to be underfunded due to a mismatch between funding needs and availability (Watson et al., 2014; McClanahan and Rankin, 2016; Gill et al., 2017; Lindsey et al., 2018). Exacerbating these shortfalls, conservation budgets continue to be dwarfed by spending from competing human activities and well-funded special-interest groups. For example, while the US \$1.2–2.4 billion annually needed to secure Africa’s protected areas with lions (Lindsey et al., 2018) is an enormous amount of money, it is much less than the US \$26 billion in perverse subsidies that was paid to Africa’s fossil fuel industry in 2015 (Whitley and van der Burg, 2015), which in turn is dwarfed by the whopping US \$640 billion the USA budgets for military defence (DOD, 2017).
While conservation funding is increasing, it continues to be dwarfed by perverse subsidies and spending by well-funded special-interest groups.
Many conservation projects are also constrained by weak institutional capacity, inappropriate nepotism, and even corruption in governments and NGOs (Section 2.4). There is sometimes a tendency for conservation organizations to compete, causing them to duplicate efforts in parallel rather than cooperating efficiently. Others spend a large percentage of their funds on maintaining extensive headquarters in expensive cities; these expenses are sometimes justifiable because of work on policy or advocacy, but they are sometimes wasteful and can come at a great cost to efforts in the field. Consequently, donors are increasingly worried about how funds earmarked for conservation will be spent—will funds be used to protect biodiversity and reducing poverty, or will they be diverted to other purposes? Thus, while new projects are often more effective, due in part to lessons learned from past experiences (Pooley et al., 2014), there is also a tendency to restrict funding to short-term cycles, and to add additional rules to prevent inappropriate spending. These additional constraints are making funding applications and accounting processes increasingly cumbersome and time-consuming, requiring even more time in the office than in the field. By focusing on short-term outcomes to meet reporting requirements, they also restrict grantees’ ability to invest in organizational resilience and staff development, to adapt to changing circumstances, and to incorporate new ideas mid-cycle (Nelson et al., 2017).
Over the past few years, conservation groups have tried to develop several kinds of grassroots initiatives that can be low cost and self-sustaining. Among the most popular are privately protected areas, integrated conservation and development projects (ICDPs), and community-based natural resource management (CBNRM, Section 14.3) (Box 15.2). Other projects promote farming with native wildlife, such as snails (Carvalho et al., 2015) and cane rats (Thryonomys swinderianus, LC) (van Vliet et al. 2016) as a means to generate income while reducing pressure on wildlife targeted by the bushmeat trade (for a review on wildlife farming for conservation, see Tensen, 2016). To reduce human-wildlife conflict (Section 14.4), some communities have also found dual purpose in income-generating activities, such as beekeeping, and planting cash crops, such as tea and hot pepper plants, which also serve as barriers to nuisance animals.
Box 15.2 Supporting Self-Organised Action for Conservation in Africa
Duan Biggs1,2
1Environmental Futures Research Institute,
Griffith University,
Nathan, Queensland, Australia.
2School of Public Leadership & Department of Conservation Ecology,
Stellenbosch University, South Africa.
https://www.resilientconservation.org
The conservation of biodiversity, especially outside of protected areas, faces ongoing budget constraints. One strategy to overcome such constraints is to facilitate and support individuals, communities, and organizations to self-organise to achieve positive conservation outcomes. Two terms are especially relevant in this regard: emergence (the coming about of new conservation initiatives and activities, McCay, 2002) and robustness (the durability and sustainability of these initiatives over time, Cox et al., 2010).
Central to the emergence of robust self-organised conservation activities is the particular composition of actors around a site or region of conservation interest, as well as a context that supports experimentation and learning (Figure 15.B). For example, where community conservancies are able to try different income-generating activities (e.g. photographic tourism, trophy hunting) and learn from each other through supported networks, the conditions for emergence will be strengthened (Child, 1996; Naidoo et al., 2016).
Also important are governance structures that enable communities and societies to have a central voice in the formulation of rules and policies. In this way, decision-making structures are perceived to be legitimate, and people are more empowered to take ownership of decisions that have important implications for their livelihoods (Cox et al., 2010; Biggs et al., 2019). For example, the recent ban on the import of elephant hunting trophies from Africa into the USA reduced benefit flows to communities. In addition, this ban weakened the perceived legitimacy of decision-making structures as affected communities did not have a voice in deliberations over the ban.
The final critical element is known as “nested enterprises”, which means the presence of multiple overlapping institutions that support emerging conservation initiatives and activities. Successful nested enterprises include local community-based groups which are linked to national and international NGOs and have representation in local and national government (Biggs et al., 2019). For example, NGO support to community conservancies in Namibia plays an important role in aiding conservancies to access support for challenges such as human-wildlife conflict and finding partner organizations for tourism development.
Africa provides several notable examples where appropriate conditions have allowed for the emergence of self-organised conservation action on previously unprotected lands. A prominent example includes the development and expansion of privately protected area in Southern Africa (Box 2.3; Section 13.1.3). Another example is the development of community conservancy programs, which have substantially extended the conservation estate and delivered socio-economic benefits in Kenya (Ihwagi et al., 2016) and Namibia (Naidoo et al., 2016; Störmer et al., 2019). Zimbabwe’s CAMPFIRE program (Box 14.4) has also contributed to the expansion of conservation land on a large scale and remains partially successful despite Zimbabwe’s current political crisis (Balint and Mashinya, 2008; Biggs et al., 2019). In each of these cases the conservation benefits have been substantial. For example, in Zimbabwe, elephant numbers on communal land increased from 4,000 to over 20,000 in just over a decade, while in Namibia, over 160,000 km2 of land now has stronger protections due to conducive conditions for emergence of self-organized conservation.
Recent history has shown that the presence of structures that support the emergence of robust self-organised action for conservation can have substantial benefits to biodiversity and to people. But securing the future of such initiatives relies on striking a careful balance between letting local individuals, communities, and organizations “do their own thing”, and providing external support and guidance when needed.
Further aiding these efforts is ecotourism, which has become a very lucrative market over the past few decades. Consequently, several private landowners and communal groups have converted their agricultural land into areas that maintain wildlife (Section 13.1). Some of these landowners cater to low-impact activities, such as bird watching (Figure 15.4) and guided safaris, while others offer hunting opportunities for wealthy individuals from North America, Europe, and Asia (Clements et al., 2016; Naidoo et al., 2016). The commercialisation of large, dangerous, and rare animals is particularly significant since more land in Africa is currently managed for regulated trophy hunting than national parks (IUCN/PACO, 2009; Flack, 2011). Because many rare and sought-after species targeted by trophy hunters require healthy ecosystems to thrive, other aspects of biodiversity also benefit, including the numerous birds, fish, insects, and plants that are not being commercially exploited in such game reserves.
By reaping social and economic benefits from conservation, local communities have been inspired to take the lead in protecting biodiversity on their own lands.
Despite these conservation gains from the regulated hunting industry, legitimate concerns linger, including overcrowding and poor treatment of some animals, the ethics of trading and killing threatened species, and whether selective hunting and breeding complement or run counter to overall conservation objectives (Milner et al., 2007). The actual contribution of regulated hunting to society at large is also still being debated (IUCN/PACO, 2009; Murray, 2017), especially since some hunting concessions are established through land grabs and eco-colonialism (see Box 14.1). Similarly, there is also concerns that legal markets for threatened species may stimulate black markets and overharvesting (Lenzen et al., 2012; Hsiang and Sekar, 2016). Finding the balance between developing responsible trade opportunities in threatened species that can fund conservation activities, and risking overharvesting, is a highly emotional issue (e.g. Biggs et al., 2013a,b; Collins et al., 2013; Litchfield, 2013; Prince and Okita-Ouma, 2013) that conservation biologists will continue to grapple with in the coming years.
In the end, given the importance of nature to human well-being, it is unfortunate that conservationists continue to struggle to obtain funding and other resources. Research has shown that under-funded conservation activities run a high risk of failure (McCreless et al., 2013) while the rush to monetise nature risks weakening protection of species without immediate or realised value (Muradian et al., 2013; Balding and Williams, 2016). This contrasts with investments in protecting the natural world, which could save trillions of dollars and benefit millions of people (Costanza et al., 2014; Shindell et al., 2016). We look forward to the day when governments and individuals shift some funding from perverse subsidies to industries such as fossil fuels and unsustainable fisheries (Section 4.5.3) to supporting more conservation organizations and activities. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/15%3A_An_Agenda_for_the_Future/15.03%3A_Funding_Conservation_Activities.txt |
Productive partnerships are one of the most important components of any successful conservation undertaking. Throughout this textbook, we have seen how successful partnerships can ensure effective law enforcement, sustainable development, ecosystem protection, and threat mitigation. Yet, many conservation projects continue to fail due to a lack of collaboration between community groups, scientists, and government leaders. Other projects fail due to unproductive partnerships, such as those relying too much on foreign consultants who lack the necessary understanding of cultural intricacies and organizational objectives in recipient countries (Mcleod et al., 2015). When considering conservation’s funding deficits, it is critical to wisely use what limited funds we have by maximising each project’s prospects for success. Accomplishing this task starts with partnership composition.
Partnerships with local people
One of the most important groups to partner with is local people, particularly those individuals who are directly affected, positively and sometimes not so positively—hopefully only in the short term—by conservation projects (Redpath et al., 2013; Hall et al., 2014). Conservation projects are significantly more likely to achieve their long-term goals when they incorporate local histories and find ways to work with existing relationships between local people and their land (Waylen et al., 2010; Oldekop et al., 2016). When local people understand and buy into a project’s goals and purposes, they may not only become partners in conservation, but also take on leadership roles in, or become activists for, environmental causes.
When local people buy into a project’s goals and purposes, they may not only become partners in conservation, but also take on leadership roles in, or become activists for, environmental causes.
Environmental monitoring by volunteer citizen scientists provides one of the prominent success stories involving local partnerships (Figure 15.5). For example, using hand-held devices (e.g. smart phones) with GPS capabilities, local communities are now able to map natural resources in their forests (http://www.mappingforrights.org), wildlife distributions (Box 15.3), and poaching hotspots (Edwards and Plagányi, 2008), as well as forest loss (DeVries et al., 2016) and human-wildlife conflict (Larson et al., 2016). In Ethiopia, citizen scientists are empowered to perform tasks usually reserved for specialists, such as maintaining long-term demographic studies on birds (Şekercioğlu, 2011). Even people that lack confidence can contribute to these efforts, through platforms such as iNaturalist which have automated features to help users identify unknown organisms they may encounter.
Box 15.3 Tracking Species in Space and Time: Citizen Science in Africa
Phoebe Barnard1,2
1Biodiversity Futures Programme and Climate Change BioAdaptation,
South African National Biodiversity Institute,
Cape Town, South Africa.
2Current Address:
Conservation Biology Institute,
Corvallis, OR, &
University of Washington, Bothell,
Bothell, WA, USA.
[email protected]
Planners and managers all know that keeping their eye on the world around them is crucial for good decision-making. But even in the richest nations, it’s not always easy to gather enough data to get a detailed sense of environmental change in multiple dimensions—or even to keep track of what’s happening on the far side of a large national park, reserve, or mountain range.
In Africa, perhaps even more than the rest of the world, the need for biodiversity monitoring data far outstrips the capacity of professional scientists to deliver it. And yet, in Namibia, South Africa, Eswatini, Lesotho, Kenya, Tanzania, Zimbabwe and Botswana, the combination of public interest in biodiversity, technology, and recreation is giving rise to highly motivated “armies” of civil society volunteers (Figure 15.C). These citizen scientists not only help create remarkably detailed, high-quality datasets, but also make aspirations for ecological study a reality.
Bird data, as in so many regions, form the crux of dynamic citizen science in Africa. There are atlas projects such as the Second Southern African Bird Atlas Project, Tanzania Bird Atlas, Kenya Bird Map, and Nigerian Bird delivering important data on bird distributions in space and time across key parts of the African continent. The best of these are linked directly with academic research and applied conservation planning, policy and management, to enable adaptive responses to global change challenges (Barnard et al., 2016). In South Africa, IUCN Red Data books, environmental impact assessments (EIAs), systematic conservation plans, and national biodiversity assessments are now based partly on bird atlas data, as are dozens of high impact journal publications. These datasets can highlight places where bird ranges are shrinking or numbers are declining, such as the secretarybird (Sagittarius serpentarius, VU) across Southern Africa (Figure 15.D), or expanding rapidly, such as the invasive common mynah (Acridotheres tristis, LC).
Citizen science-based biodiversity monitoring works well in countries in which at least part of the population is mobile, interested, and moderately educated. Despite these being quite daunting obstacles in some areas, there are several important initiatives that enable new citizen scientists to contribute to biodiversity monitoring, even by those with very limited or no literacy. One such example is MammalMap, a major initiative that uses camera traps to track important and visible taxa across the continent.
Many of Africa’s most dynamic and productive citizen-science projects supporting conservation biology arise from the University of Cape Town’s Animal Demography Unit. The unit was founded in order to bring together civil society volunteerism, professional science, and conservation biology. The ADU, with its projects to monitor birds, frogs, butterflies, mammals, reptiles and other groups, deserves national and global investment as a powerful hub of cost-effective biodiversity monitoring.
Citizen science helps track biodiversity in space and time, providing important snapshots of the state of the environment during times of dizzying environmental change. It also builds love, knowledge, and custodianship of biodiversity among people who need to re-connect with nature and find meaning in their lives. These volunteers contribute their time, fuel and energy towards national, regional and global causes. This is a crucial cause for biodiversity in Africa, which needs investment in order to spread to all levels of society.
There are many benefits to local involvement in biodiversity monitoring. For example, field data collected by citizen scientists—which are often as accurate as those collected by specialists (Danielsen et al., 2014; Schuttler et al. 2018)—allow biologists to obtain information from more areas more regularly and more cheaply than would be the case if specialists collected that same data. Local involvement also ensures that conservation decisions and actions are more effective and quicker to implement (Danielsen et al. 2010) and improves engagement, creating stronger advocates for conservation (Granek et al., 2008).
Partnerships among conservation professionals
Conservation biologists need to be more deliberate in fostering appropriate inter-organizational partnerships. Such partnerships enable new information to spread quicker and enable conservationists to learn from each other and to know whom to contact when advice is sought. Strategic partnerships also enable specialisation among organizations that they need not “do it all”. It allows sharing of scarce resources (e.g. trained volunteers, temporary staff, and citizen scientists) from one organization to another when not being utilised at a time. It also facilitates better coordination of activities, particularly at large scales, which improves project efficiency (Kark et al., 2015) organizational resilience (Maciejewski and Cumming, 2015), and conservation outcomes (Bonebrake et al., 2019). Lastly, research in Uganda showed that involving a variety of partners, especially governmental authorities, from the outset results in faster project implementation (Twinamatsiko et al., 2014).
Professional partnerships enable new information to spread quicker and enable conservationists to learn from each other and to know whom to contact when advice is sought.
Prospective collaborators are generally already familiar with each other. However, at times appropriate collaborators may be outside one’s immediate network; this is especially true for conservation start-ups or people who have recently entered the field. In these cases, there are several effective strategies to foster new and effective partnerships. One of the best options is to attend professional meetings (Figure 15.6) such as those presented by the Society for Conservation Biology (SCB)’s Africa Section (https://conbio.org/groups/sections/africa). While this can be intimidating at first, it is worth thinking ahead of time how your own interests can be integrated with that of potential collaborators. At an organizational level, one can also contact a third party, such as the Africa Biodiversity Collaborative Group, which specialises in bringing appropriate partners together. Lastly, social media (e.g. Facebook, Twitter, ResearchGate) and biodiversity observation platforms (e.g. iNaturalist) serve to connect conservationists and naturalists from across the spectrum who wish to discuss their activities with other like-minded individuals in a more informal, less intimidating setting.
Like a marriage or friendship, professional partnerships also require constant maintenance (WWF, 2000). Project partners will invariably have different biases, objectives, and interests. They may also compete for the same funding sources, face historical legacies that complicate cooperation, or be confused about their roles in a project. It is therefore advisable for new partnerships to start small, and to take on little risk. For example, rather than initiating a project to save a high-priority species, it may be more conducive to gain experience by focussing on a less critical species or preparing a local sanctuary for a reintroduction. Once the foundation of the new partnership is set, steps can be taken towards expansion, for example by inviting new types of partners, and taking on more complex projects. More information on nurturing partnerships can be obtained by researching topics such as social-ecological system resilience, or by attending a course or workshop in organizational leadership fundamentals. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/15%3A_An_Agenda_for_the_Future/15.04%3A_Building_Lasting_Partnerships.txt |
Every year, conservation biologists acquire a vast body of knowledge from projects all over Africa and beyond. Yet, this information is often only communicated at small working groups and specialised meetings, published as technical papers in scientific journals with expensive subscription fees, or worse, not communicated at all. This leaves the general public detached from conservation work which, in turn, gives them (especially people living in urban centres) a sense that they live independent from nature and the knowledge gained by scientists. It also creates opportunities for wilful ignorance, where citizens can normalize the environmental damage caused by their activities. To avoid these scenarios, conservation biologists need to be more proactive in outreach and environmental education, which aims to raise the public’s awareness and knowledge about the environment so they can adjust to live more sustainably.
One of the best ways to raise the public’s environmental awareness is to involve them in local conservation projects, especially those that include fieldwork and site visits. Citizen science projects, as discussed above, present one of the most effective strategies. The public could also be invited to a guided tour where they are introduced to your organization’s activities or provided with volunteer opportunities for stewardship workdays at a local protected area. During such workdays, ordinary citizens might help with tasks, such as invasive plant control, nest box installation, and recording wildlife behaviors. An effective public relations program can also connect people who want to engage with conservation; such a program may involve conservation exhibits in public spaces, articles written by conservation biologists for local magazines and newspapers, or public presentations.
Children and youth are one of the most important audiences for environmental education and outreach efforts. Exposing children to the wonders of the natural world instils in them a personal sense of competence, ethics, and environmental awareness that will last a lifetime (Johnson et al., 2013). These children can also influence their parents’ attitudes and behavior towards environmental issues (Damerell et al., 2013). Ignoring children during outreach events, or recruiting ill-prepared teachers (Nkambwe and Essilfie, 2012), may however turn children against the environment, which they may see as a dangerous place detached from their own lives (Adams and Savahl, 2013). It could also lead to nature deficit disorder, a situation where spending less time in nature leads to behavioral problems (Louv, 2005). Consequently, many conservation organizations are now sponsoring and establishing schools to ensure young children are exposed to the importance of the environment. Others are working with children by hosting school groups, screening documentaries, publishing children’s books, and offering field programs and school outings to nearby protected areas.
Exposing children to the wonders of the natural world instils in them a personal sense of competence, ethics, and environmental awareness that will last a lifetime.
Environmental education and outreach cultivates the next cohort of conservation leaders. Today, young African conservationists can develop their leadership skills by pursuing funding opportunities to attend conferences and workshops, and fellowships to study at research institutes affiliated with local universities (Box 15.4). Some people might also be interested in the South African Wildlife College and College of African Wildlife Management, both which specialise in preparing students for a career in wildlife management. Several prestigious awards are also available that provide African youth conservation leaders with the resources they need to achieve their goals. Many conservation NGOs are also increasingly focussed on building leadership capacity through exposure to real-world conservation dilemmas. For example, the Zoological Society of London (ZSL), combat pangolin poaching in Central Africa through a specially designed mentoring program in which young conservationists shadow experiences professionals to learn best practices in field assessments, legal protection, and demand reduction.
Box 15.4 The Contribution of Education Towards Conservation in Africa
Shiiwua Manu1,2 and Samuel Ivande1,2
1AP Leventis Ornithological Research Institute (APLORI),
University of Jos Biological Conservatory,
Laminga, Jos-East LGA, Nigeria.
2Department of Zoology, University of Jos,
Nigeria.
https://aplori.org
Improving the capacity of local people to appropriately manage natural resources in their domain is vital and fundamental for the successful conservation of biodiversity. This is usually a core objective of several environmental conservation organizations. Approaches to achieve this have often ranged from organising awareness campaigns, establishing sustainable livelihood programs, delivering workshops to provide technical support and training to individuals, local groups, government agencies and policy officers.
One model to highlight is the A.P. Leventis Ornithological Research Institute (APLORI) model. APLORI, focused on academic training, founded a research institute and field station in 2001 to train graduate students at masters and doctorate levels in conservation biology, and to facilitate research in a tropical savannah environment (Figure 15.E). APLORI is in the Amurum Forest Reserve—one off Nigeria’s key Important Bird Areas—and was established following an understanding between the Leventis Foundation, the University of Jos, Nigeria Conservation Foundation, and the Laminga community of Jos East—the reserve’s host community.
One key vision of the institute is to train and equip the students who will eventually be in the driving seat of ecological and conservation research and policy in the region. To date, APLORI has trained 104 students at the master’s level, with about 37 of these graduates going on to pursue doctorate degrees. APLORI is also host to many research projects needing a West African base; so far it has supported tropical ecological research for over 25 researchers from various leading universities across Europe and America. This also ensures that students at APLORI benefit from the expertise of visiting researchers.
After 14 years of APLORI’s existence, its graduates have begun to occupy key positions working at the frontlines to advance ecological research in the region. Of the Institute’s 104 graduates, 88% are actively engaged in teaching and research and are influencing policy at various universities, NGOs, and governmental agencies across Africa at various levels. At least four of these graduates are in leadership positions in important NGOs in the region including BirdLife Africa, Flora & Fauna International in Liberia, and A.G. Leventis Foundation.
The involvement of these graduates has greatly advanced the scope and quality of ecological research in the region. This is evidenced by the over a hundred published articles in international journals. A review of the research projects and publications from the institute indicates that the research scope is steadily advancing from simple biodiversity inventories and distribution updates to more detailed studies of population trends and dynamics, as well as aspects of animal behavior, foraging, breeding, and genetic and molecular studies of tropical species and Palearctic migrants.
Much of APLORI’s research uses birds to better understand the tropical environment. For example, observing breeding and migratory movements of some Afrotropical species like Abdim’s stork (Ciconia abdimii, LC), black coucal (Centropus grillii, LC), rosy bee-eater (Merops malimbicus, LC), and the African cuckoo (Cuculus gularis, LC), have contributed to improve our knowledge of how seasonality influences their use of the Afrotropical landscape (Ivande et al., 2012; Cox et al., 2012, 2014). Similarly, studies of Palearctic migrants in the Afrotropics have revealed ecological flexibility in non-breeding habitat occupancy (Ivande and Cresswell, 2016) as well as high within-winter survival and site fidelity in species like whinchats (Saxicola rubetra, LC) which have returned to the very same winter territories every year (Wilson and Cresswell, 2006; Blackburn and Cresswell, 2015a,b). Constant Effort Site mist netting of birds, which was initiated at APLORI in 2002, has also improved our understanding of migratory passage times and survival in tropical environments (McGregor et al., 2007; Iwajomo et al., 2011) while other projects have used birds to highlight the effects of habitat fragmentation on biodiversity (Manu et al., 2005, 2007).
The location of APLORI in the Laminga community represents an effective model of successful community development projects associated with conservation projects in an area. For example, all APLORI’s field assistants and support staff are employed from the community thus ensuring improved livelihoods as well as conservation skills for these individuals. This is in addition to the other community projects including: establishment of community woodlots, repair of access roads, construction of a community borehole for water, a police post, and a piggery, all of which contribute to livelihoods in the community.
Certainly, Africa with its increasing population and the attending anthropogenic pressures still needs more skilled personnel to adequately manage and conserve its vast natural resources. The APLORI model highlights the vital contribution that quality academic training and education can make.
Reaching people who are not usually attracted to nature-based activities remains a challenge. One option is to blend conservation education and outreach with attractions and activities without an obvious conservation link. Sporting events have proven very successful in this regard. For example, an annual half marathon hosted inside South Africa’s Kruger National Park has become an important opportunity to attract new people to conservation while also raising conservation funds. Another example is the Maasai Olympics, held every second year in Kenya’s Amboseli-Tsavo ecosystem, which raises conservation awareness within the local community. Local NGOs such as the Korup Rainforest Conservation Society (KRCS) in Cameroon raises funds from membership fees; these fees are then used to host football games between local youths and park rangers, and to buy farm equipment awarded to the winners in exchange for environmental commitments. Music concerts at botanical gardens (Figure 15.7) and national parks (e.g. https://www.montybrett.com/baroque-in-the-bush) have also successfully exposed new audiences to environmental issues.
Africa is in desperate need of the next generation of conservation heroes who are up to the task of addressing a growing list of complex problems. We have learnt much over the past few decades about how to better protect the natural environment in the face of growing human populations, increased consumption, and socio-economic transformations. We have also developed strong foundations in environmental education and leadership that will help us reach more people and cultivate stronger leaders. But many ecosystems continue to be in a state of distress, many species are facing extinction, and many people continue to live indifferent to their environment. The time for action is now. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/15%3A_An_Agenda_for_the_Future/15.05%3A_Environmental_Education_and_Leadership.txt |
1. The field of conservation biology has set itself some imposing tasks: to describe Earth’s biological diversity, to protect what remains, and to restore what is damaged. It is also a crisis discipline because decisions often need to be made under pressure, with limited resources, and under tight deadlines. A long-term conservation vision is also needed that extends beyond the immediate crisis.
2. Efforts to preserve biodiversity while overcoming conflicting human needs can be accomplished by striving towards sustainable development—economic development that satisfies both present and future needs without unsustainable economic growth that is compromising the natural world.
3. New technologies have greatly aided conservation efforts but have also created new challenges. Emerging threats are never solved by people who defend the status quo or resist change, but by individuals who rapidly respond to new challenges as soon as they arise.
4. One of the biggest challenges facing conservation biologists is inadequate funding. Fortunately, an increasing number of mechanisms are being established to fill funding voids, including multilateral funding consortiums, debt-for-nature swaps, payments for ecosystem services, and a range of grassroots initiatives.
5. To avoid leaving urban citizens detached from nature, conservation biologists need to reach out and educate the public, and particularly children, about their work. This can be achieved through citizen science projects, field programs for the public, and writing materials suitable for adults and children for newspapers, magazines, and websites.
15.07: Topics for Discussion
1. Think of a very important conservation challenge facing your local area. How much funding do you think would be needed to address the problem? What types of funding sources would you pursue? What are the most important benefits you would highlight to the granting agency to convince them to fund the project?
2. Several initiatives have tried to generate rural income by offering trophy hunting and wildlife viewing opportunities. Do you think these two activities are compatible with each other? What ethical, economic, political, environmental, and social issues does each initiative raise?
3. The world is moving away from fossil fuels towards renewable, carbon-neutral energy solutions, prominently solar energy, wind energy, nuclear energy, hydropower, and bioenergy. Make a list of benefits and drawbacks of each renewable energy solution. Which renewable energy solution do you think is the best, and which is the worst? What do you think is the best way to generate energy in your region and why?
4. How has studying conservation biology changed your lifestyle or level of political activity? How do you think you can make the biggest difference in protecting biodiversity?
5. Which section of this textbook appealed to you the most and why?
15.08: Suggested Readings
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Pooley, S., J.A. Mendelsohn, and E.J. Milner-Gulland. 2014. Hunting down the chimera of multiple disciplinarily in conservation science. Conservation Biology 28: 22–32. https://doi.org/10.1111/cobi.12183 Projects combining conservation and development often fail due to their complexity, but it is important to learn from them so that mistakes are not repeated.
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Joseph, L.N., R.F. Maloney, and H.P. Possingham. 2009. Optimal allocation of resources among threatened species: A project prioritization protocol. Conservation Biology 23: 328–38. https://doi.org/10.1111/j.1523-1739.2008.01124.x Prioritising conservation spending can increase spending efficiency.
Kark, S., A. Tulloch, A. Gordon, et al. 2015. Cross-boundary collaboration: Key to the conservation puzzle. Current Opinion in Environmental Sustainability 12: 12–24. https://doi.org/10.1016/j.cosust.2014.08.005 Conservation collaborations have many benefits, but also drawbacks that need to be considered.
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Nkambwe, M., and V.N. Essilfie. 2012. Misalignment between policy and practice: Introducing environmental education in school curricula in Botswana. Educational Research and Reviews 7: 19–26.
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Pimm, S.L., S. Alibhai, R. Bergl, et al. 2015. Emerging technologies to conserve biodiversity. Trends in Ecology and Evolution 30: 685–96. https://doi.org/10.1016/j.tree.2015.08.008
Pooley, S., J.A. Mendelsohn, and E.J. Milner-Gulland. 2014. Hunting down the chimera of multiple disciplinarity in conservation science. Conservation Biology 28: 22–32. https://doi.org/10.1111/cobi.12183
Prins, H.H.T., and B. Okita-Ouma. 2013. Rhino poaching: Unique challenges. Science 340: 1167–68. https://doi.org/10.1126/science.340.6137.1167-b
Randall, T. 2016. World energy hits a turning point: Solar that’s cheaper than wind. Bloomberg http://bloom.bg/2iWLc7q
Redpath, S.M., J, Young, A. Evely, et al. 2013. Understanding and managing conservation conflicts. Trends in Ecology and Evolution 28: 100–09. https://doi.org/10.1016/j.tree.2012.08.021
Reid, T., S. Krüger, D.P. Whitfield, et al. 2015. Using spatial analyses of bearded vulture movements in southern Africa to inform wind turbine placement. Journal of Applied Ecology 52: 881–92. https://doi.org/10.1111/1365-2664.12468
Rodríguez, J.P., A.B. Taber, P. Daszak, et al. 2007. Globalization of conservation: A view from the South. Science 317: 755–56. https://doi.org/10.1126/science.1145560
Rushworth, I., and S. Krüger. 2014. Wind farms threaten southern Africa’s cliff-nesting vultures. Ostrich 8: 13–23. http://doi.org/10.2989/00306525.2014.913211
Schuttler, S.G., R.S. Sears, I. Orendain, et al. 2018. Citizen science in schools: Students collect valuable mammal data for science, conservation, and community engagement. BioScience 69: biy141. https://doi.org/10.1093/biosci/biy141
Şekercioğlu, Ç.H. 2011. Promoting community-based bird monitoring in the tropics: Conservation, research, environmental education, capacity-building, and local incomes. Biological Conservation 151: 69–73. https://doi.org/10.1016/j.biocon.2011.10.024
Shackeroff, J.M., and L.M. Campbell. 2007. Traditional ecological knowledge in conservation research: Problems and prospects for their constructive engagement. Conservation and Society 5: 343.
Sheikh, P.A. 2018. Debt-for-nature initiatives and the tropical forest conservation act (TFCA): Status and implementation (Washington: Congressional Research Services). http://www.policyarchive.org/handle/10207/1351
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Wilson, J.W., R. Bergl, L.J. Minter, et al. 2019. The African elephant Loxodonta spp. conservation programs of North Carolina Zoo: Two decades of using emerging technologies to advance in situ conservation efforts. International Zoo Yearbook 53: in press. https://doi.org/10.1111/izy.12216
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Searchable databases provide a convenient way to find information on species, places, and topics. With the help of citizen scientists, these databases are rapidly expanding. Below are a few online databases that are free to use. Many also allow users to contribute their own data.
Biodiversity A-Z
http://www.biodiversitya-z.org
A thesaurus for biodiversity terminology.
Conservation Training
https://www.conservationtraining.org
Free conservation-based training materials, provided by TNC.
Copenhagen databases of African vertebrates
https://macroecology.ku.dk/resources/african-vertebrates
Distribution maps for Africa’s mammals, birds, snakes, and amphibians.
eBird
http://ebird.org
Citizen science platform for the global birding community.
Encyclopaedia of Life
http://www.eol.org
Developing resource documenting the biology of all species known to science.
Evidensia
https://www.evidensia.eco
Comprehensive information on sustainability standards.
Global Biodiversity Information Facility
http://www.gbif.org
Free and open access to biodiversity data.
Global Register of Introduced and Invasive Species (GRIIS)
http://www.griis.org
Information about invasive species.
iNaturalist
http://www.inaturalist.org
A citizen science project that collects distribution data on all species.
Learning for Nature
https://learningfornature.org
e-Learning resource by the UNDP.
Mongabay
https://news.mongabay.com
A leading environmental news source.
Movebank
https://www.movebank.org
A free online database for animal tracking data
Protected Planet
https://www.protectedplanet.net
Comprehensive global spatial dataset on protected areas.
PADD tracker
http://www.padddtracker.org
Monitors protected area downgrading, downsizing, and degazettement.
Species+
https://www.speciesplus.net
Provides information on species covered by multilateral environmental agreements.
Vital Signs
http://vitalsigns.org
Collects and integrates data on agriculture, ecosystems, and human well-being.
16.01: Selected Environmental Organisations
Online search engines such as Google provide powerful tools to obtain information about conservation topics and opportunities. While much of the information obtained in this way is valuable, the growing popularity of the Internet has also allowed the rapid distribution of false and misleading information. You should, thus, carefully consider the source of the information you obtain online.
Similarly, it is also important to thoroughly research any conservation organizations with whom you are interested in working with. This task is particularly difficult in Africa, where most organizations have not yet been assessed for their effectiveness in carrying out conservation activities. As a starting point, you can see whether the organization that interests you is a member of an international affiliate body, such as the IUCN or World Association for Zoos and Aquariums, which sets strict standards for organizational memberships. Online databases such as GuideStar (https://www.guidestar.org), Charity Navigator (https://www.charitynavigator.org), Better Business Bureau (https://www.bbb.org), and Great Nonprofits (https://greatnonprofits.org) are also good options for organization vetting.
Below is a partial list of credible conservation organizations active on a regional scale in Africa.
Africa Biodiversity Collaborative Group (ABCG)
Washington, DC, USA
http://www.abcg.org
Tackles conservation challenges by strengthening collaborations.
African Conservation Foundation (ACF)
Nairobi, Kenya and Yaoundé, Cameroon
https://www.africanconservation.org
Saves Africa’s endangered wildlife by building local capacity.
African World Heritage Fund
Midrand, South Africa
https://awhf.net
Works to protect Africa’s World Heritage Sites.
African Parks
Johannesburg, South Africa
https://www.african-parks.org
Manages protected areas in collaboration with governments and communities.
African Wildlife Foundation (AWF)
Nairobi, Kenya
http://www.awf.org
Works to ensure that wildlife and wild lands thrive.
Albertine Rift Conservation Society (ARCOS)
Kampala, Uganda
http://www.arcosnetwork.org
Promotes biodiversity conservation in the Albertine Rift region.
Association for Tropical Biology and Conservation (ATBC)
Lawrence, KS, USA
http://tropicalbiology.org
Fosters scientific understanding and conservation of tropical environments.
BirdLife International
Nairobi, Kenya and Accra, Ghana
http://www.birdlife.org/africa
Strives to conserve birds and their habitats, with national partners across Africa.
Born Free Foundation
Horsham, UK
http://www.bornfree.org.uk
Protects threatened species in the wild.
Botanical Gardens Conservation International (BGCI)
Nairobi, Kenya
http://www.bgci.org
Guides, encourages, and supports botanical gardens.
Cambridge Conservation Initiative (CCI)
Cambridge, UK
http://www.cambridgeconservation.org
A partnership of conservation leaders working towards a sustainable future.
Centre for International Forestry Research (CIFOR)
Yaoundé, Cameroon and Nairobi, Kenya
https://www.cifor.org
Conducts research on forests and landscape management.
CGIAR (formerly Consultative Group for International Agricultural Research)
Montpellier, France
http://www.cgiar.org
The world’s largest agricultural innovation network.
CITES Secretariat of Wild Fauna and Flora
Geneva, Switzerland
https://cites.org
The official UN body tasked with regulating the global trade in endangered species.
Conservation International (CI)
Arlington, VA, USA
http://www.conservation.org
Saves nature through science, policy, and partnerships.
Conservation Leadership Programme
Cambridge, UK
http://www.conservationleadershipprogram.org
Supports leadership development of early career conservationists.
Convention on Biological Diversity (CBD) Secretariat
Montreal, Canada
https://www.cbd.int
The official UN body tasked with promoting the goals of the CBD.
Critical Ecosystem Partnership Fund (CEPF)
Arlington, VA, USA
http://www.cepf.net
Provides financial and technical support to conserve critical ecosystems.
Darwin Initiative
London, UK
http://www.darwininitiative.org.uk
Assists developing countries implement biodiversity convention commitments.
Earthwatch Institute
Boston, MA, USA
http://earthwatch.org
Helps citizen scientists contribute to field conservation projects.
East African Wild Life Society (EAWLS)
Nairobi, Kenya
https://eawildlife.org
Promotes conservation and sustainable use of the environment.
EcoHealth Alliance
New York, NY, USA
https://www.ecohealthalliance.org
Studies connections between humans, wildlife, and ecosystems.
The Environmental Foundation for Africa (EFA)
Freetown, Sierra Leone
http://www.efasl.org
Protects and restores the environment in West Africa.
Environmental Investigation Agency (EIA)
London, UK
https://eia-international.org
Activist organization focussed on exposing environmental crimes.
Environmental Law Alliance Worldwide (ELAW)
Eugene, OR, USA
http://elaw.org
Helps partners gain skills and build strong conservation organizations.
Fauna & Flora International (FFI)
Cambridge, UK
http://www.fauna-flora.org
Africa’s first conservation society; has been protecting African wildlife since 1903.
FitzPatrick Institute of African Ornithology
Cape Town, South Africa
http://www.fitzpatrick.uct.ac.za
Promotes and undertakes scientific studies on African birds.
Forest Carbon Partnership Facility
Washington. DC
http://www.forestcarbonpartnership.org
Assist countries with their REDD+ preparations to reduce emissions from forest loss.
Forest Stewardship Council (FSC)
Bonn, Germany
https://ic.fsc.org
Sets the standards for responsibly managed forests.
Frankfurt Zoological Society (FZS)
Frankfurt, Germany
https://fzs.org
Maintains wilderness areas and biodiversity.
Future for Nature
Arnhem, The Netherlands
http://futurefornature.org
Provides mentoring and other assistance to young conservationists.
Game Rangers Association of Africa (GRAA)
Johannesburg, South Africa
http://www.gameranger.org
Provides support, networks, and representation for rangers.
Global Environment Facility (GEF)
Washington, DC, USA
http://www.thegef.org
Provide grants for biodiversity and sustainable development projects.
Global Forest Watch (GFW)
Washington, DC, USA
http://www.globalforestwatch.org
Empower people to better protect forests.
Global Wildlife Conservation (GWC)
Austin, TX, USA
https://www.globalwildlife.org
Protects species and habitats through science-based field action.
Goldman Environmental Foundation
San Francisco, CA, USA
http://www.goldmanprize.org
Recognises environmental activists who have made an impact.
Greenpeace Africa
Johannesburg, South Africa
http://www.greenpeace.org/africa
Activist organization known for protests against environmental crime
High Seas Alliance
Washington, DC, USA
http://highseasalliance.org
Facilitates cooperation for protection of high seas.
ICLEI Africa
Cape Town, South Africa
http://africa.iclei.org
A network of governments committed to sustainable urban development.
International Fund for Animal Welfare (IFAW)
Nairobi, Kenya and Cape Town, South Africa
http://www.ifaw.org/africa
Rescues and protects animals around the world.
Intergovernmental Panel on Climate Change (IPCC)
Geneva, Switzerland
http://www.ipcc.ch
The UN’s authority on climate change.
Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES)
Bonn, Germany
https://www.ipbes.net
The UN’s authority on nature’s contributions to people (NCP), or ecosystem services.
The International Ecotourism Society (TIES)
Washington, DC, USA
http://www.ecotourism.org
Promotes responsible tourism practices.
International Institute for Environment and Development (IIED)
London, UK
https://www.iied.org
Promotes sustainable development to protect the environment.
International Institute of Tropical Agriculture (IITA)
Ibadan, Nigeria
http://www.iita.org
Works to enhance crop quality and productivity.
International Tropical Timber Organization (ITTO)
Yokohama, Japan
http://www.itto.int
Promotes sustainable management of tropical forest resources.
International Union for Conservation of Nature (IUCN)
Gland, Switzerland
https://www.iucn.org
Coordinates international conservation efforts and produces Red Lists.
International Criminal Police Organisation (INTERPOL)
Lyon, France
https://www.interpol.int/Crime-areas/Environmental-crime
Facilitate prosecution of international environmental crimes.
iSeal
London, UK
https://www.isealalliance.org
A membership organization for sustainability standards.
Jane Goodall Institute
Vienna, VA, USA
http://www.janegoodall.org
Inspiring people to conserve the natural world.
Leadership for Conservation in Africa (LCA)
Pretoria, South Africa
http://lcafrica.org
Influences business leaders to support investment in conservation.
Marine Stewardship Council (MSC)
London, UK
https://www.msc.org
Promotes sustainable fishing practices.
National Geographic Society (NGS)
Washington, DC, USA
https://www.nationalgeographic.org
One of the world’s largest scientific and educational institutions.
Natural Capital Coalition
London, UK
https://naturalcapitalcoalition.org
Collaboration of the global natural capital community.
The Nature Conservancy (TNC)
Arlington, VA, USA
https://www.nature.org
Conserves threatened species and their habitats, emphasising land preservation.
Oxpeckers Centre for Investigative Environmental Journalism
Johannesburg, South Africa
https://oxpeckers.org
Investigative journalists focusing on African environmental issues.
Pan-African Association of Zoos and Aquaria (PAAZA)
Johannesburg, South Africa
http://www.zoosafrica.com
Guides and accredits African Zoos and Aquaria.
Peace Parks Foundation
Stellenbosch, South Africa
http://www.peaceparks.org
Facilitates the establishment of transfrontier conservation areas.
The Pew Charitable Trusts
London, UK
http://www.pewtrusts.org
Advances scientific understanding of environmental problems.
Project Aware
Rancho Santa Margarita, CA, USA
https://www.projectaware.org
A movement of scuba divers protecting the planet’s oceans.
Rainforest Alliance
New York, NY, USA
http://www.rainforest-alliance.org
Advances sustainable forestry, agriculture, and ecotourism.
Rainforest Trust
London, UK
https://www.rainforesttrust.org
Protecting forests by aquiring land for conservation.
Rapid Response Facility (RRF)
Cambridge, UK
http://www.rapid-response.org
Provides emergency support to natural World Heritage sites.
Regional Partnership for Coastal and Marine Conservation (PRCM)
Dakar, Senegal
http://www.prcmarine.org
Working on marine conservation in West Africa.
Roundtable on Sustainable Palm Oil (RSPO)
Kuala Lumpur, Malaysia
http://www.rspo.org
Advances sustainable palm oil production.
Royal Botanic Gardens, Kew
Richmond, Surrey, UK
https://www.kew.org
A leading botanical research institute with an enormous plant collection.
Rufford Foundation
London, UK
https://www.rufford.org/
Funds conservation projects across the developing world.
Sahara Conservation Fund
St. Louis, MO, USA
https://www.saharaconservation.org
Conserves biodiversity of the Sahara Desert and bordering Sahelian grasslands.
SEED
Berlin, Germany
https://www.seed.uno
A global partnership that promotes sustainable development.
Society for Conservation Biology (SCB)
Arlington, VA, USA
http://conbio.org
The leading scientific society for conservation biology.
Society for Ecological Restoration (SER)
Washington, DC, USA
http://www.ser.org
Scientific society that promotes ecological restoration.
Species360 (formerly International Species Information System)
Bloomington, MN, USA
https://www.species360.org
Gathers and shares information about animals kept in zoos and aquaria.
Tropical Biology Association
Nairobi, Kenya
http://www.tropical-biology.org
Help scientists manage and conserve natural resources in tropical regions.
Tusk
New York, NY, USA
http://www.tusk.org
Supports and connects conservation initiatives and expertise.
United Nations Environment Programme (UNEP)
Nairobi, Kenya
http://www.unep.org
Coordinates the UN’s environmental activities.
West Africa Biodiversity and Climate Change (WA BiCC)
Accra, Ghana
https://www.wabicc.org
Improve conservation and climate-resilient growth across West Africa.
Western Indian Ocean Marine Science Association (WIOMSA)
Zanzibar, Tanzania
http://www.wiomsa.org
Scientific society that promotes marine sciences.
Wetlands International
Dakar, Senegal
http://africa.wetlands.org
Dedicated to the conservation and restoration of wetlands.
Whiteley Fund for Nature
London, UK
http://whitleyaward.org
Funds conservation leaders and projects in developing countries.
WildAid
San Francisco, CA, USA
http://wildaid.org
Working to end the illegal wildlife trade.
WILDLABS
Cambridge, UK
https://www.wildlabs.net
Platform that promotes technology-enabled conservation.
WildLeaks
Los Angeles, CA, USA
https://wildleaks.org
An online whistleblower platform for biodiversity crimes.
Wildlife Conservation Network (WCN)
San Francisco, CA, USA
https://wildnet.org
Supports community-based conservation projects.
Wildlife Conservation Society (WCS)
Bronx, NY, USA
http://www.wcs.org
One of the world’s leaders in biodiversity conservation and research.
Wildlife Trade Monitoring Network (TRAFFIC)
Cambridge, UK
http://www.traffic.org
Promotes sustainable wildlife trade and combats wildlife crime.
World Bank
Washington, DC, USA
http://www.worldbank.org
Provides loans to developing countries for economic development.
Worldwatch Institute
Washington DC, USA
http://www.worldwatch.org
Highlights links between the economy and environment.
World Association of Zoos and Aquariums (WAZA)
Gland, Switzerland
http://www.waza.org
Guides, encourages, and supports zoos and aquaria.
World Conservation Monitoring Centre (UNEP-WCMC)
Cambridge, UK
https://www.unep-wcmc.org
An UN agency that supports biodiversity assessments and policy.
World Resources Institute (WRI)
Washington, DC, USA
http://www.wri.org
Promotes sustainable development with sound environmental management.
World Wide Fund For Nature (WWF)
Gland, Switzerland
https://www.panda.org
One of the world’s largest conservation organizations.
Zoological Society of London (ZSL)
London, UK
https://www.zsl.org
Manages several projects to protect threatened species and ecosystems. | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/16%3A_Appendix/16.00%3A_Selected_Sources_of_Information.txt |
Funding limitations often hamper conservation activities. Because conservation funding is limited, there is much competition for the few options available. Below are 15 tips to make the writing of funding proposals less tedious, time-consuming, and depressing. The list is not meant to be exhaustive, and by no means a guarantee for funding—no tip can ever do that. But these generalities should give early-career conservationists a better chance for success.
1. Start early. Obtaining funding is a highly competitive endeavour, one you are more likely to fail in with a rushed job. It generally takes several months to put together a proposal that can convince assessors that your proposed work is well planned and feasible, and that your team is up to the task. To get there, you need to allow for enough time to put together a well-functioning team, develop and refine all your ideas, design a well-polished proposal, adapt it to specific grant requirements, conduct pilot studies, obtain external advice, address comments and concerns, and navigate institutional bureaucracy.
2. Be a team player. Assembling a good team is perhaps your most important decision towards funding success. Remember, your team will be your main support network during this process. They will brainstorm with you, look for funding opportunities, and help develop, edit, and critique your proposal. Make sure you assemble a team willing to contribute to these tasks—it is no fun doing the work alone, only for others to claim the funds and fame. Second, a carefully selected team confers reputation. As unfair as it may seem, funders invest in projects that maximise returns with minimal risk. They do this by funding established experts with a track record of successful grant management. This poses a significant barrier to early-career conservationists—how can you obtain funding without a track record, and vice versa? The best way to overcome this barrier is to assemble a team that includes reputable collaborators where each member provides a different set of skills to assure success. (Note that established researchers are also increasingly relying on collaborations due to the interdisciplinary nature of conservation.) Make sure you state somewhere in your proposal (generally in a personnel section) why your team is the best to do this work, and how each team member’s skills complement the others. Instead of viewing this as an impediment, see this requirement as an opportunity to learn from and network with experts—your project will most likely also be better off as a result.
3. Focus on the funder’s priorities. Funders will have set priorities from which they will not deviate. Thus, while you and your colleagues may believe that your idea is truly ground-breaking, trying to convince funders to adapt their priorities to fit your grand idea simply will not happen. Instead, either find a funder whose priorities align with yours, or adapt your proposal to fit within the funder’s stated priorities. In some cases, funders require that you state how your priorities align with theirs—make sure you do it, using the exact wording the funders used in their call for proposals.
4. Your assessor is not an expert. Funders usually appoint a small panel of assessors with a general understanding of the funder’s priorities to quickly and efficiently adjudicate and rank funding proposals against each other. Having assessments done by non-experts has implications for how a proposal is written. First, do not assume that the assessor has specific knowledge of your field, or that s/he will just “get” the value of your project. Your proposal needs to clearly explain your plan in simple terms so that a lay person on the street will also care. Second, while technical terms (i.e. jargon) may be fine in specialist journals, they should be avoided at all costs in funding proposals. That also includes abbreviations, which can frustrate an assessor who needs to remind him/herself of the abbreviation’s meaning.
5. Follow the guidelines. Before starting to write the proposal, read through the guidelines>. While doing this, draw up a checklist documenting every requirement (e.g. budgets, timelines, margin sizes, fonts) that needs to be addressed and adhered to. Follow this checklist while writing the proposal. Then, when you are done, go over the guidelines again to make sure you did not miss a “hidden” requirement. While it may be tempting to make a small tweak, say to fit within the page limit, even minor deviations to the guidelines will stand out to assessors who look at hundreds of proposals in quick succession.
6. Keep it simple. As mentioned earlier, funders like to invest in projects that maximum returns for minimum risk. One way to meet this requirement is to have a carefully selected team of collaborators in place. Equally important is to propose projects that are realistic, with simple and obtainable goals. Remember, most grants run on one-year cycles, and there is only so much one can accomplish in that timeframe. While you may think your overly ambitious project will impress assessors, more likely it will be viewed as a money drain and too risky to fund.
7. Be exciting. A grant is a reward for promising exciting work. Getting that award letter is undeniably an exciting moment in anyone’s career. But before that excitement, you are going to have to think hard about ways to first make the assessors excited. This is difficult, because there are many constraints to proposals. Foremost is the challenge of finding a balance between simplicity and excitement. It is also difficult to excite an anonymous assessor with a limited understand of your work. But this situation is hardly unique: businesses all over the world constantly work on strategies to impress anonymous customers who are also considering competitor products. Remember, you, as the salesman, have only one opportunity to sell your project—through that piece of paper your proposal is printed on. While a proposal should remain formal, a marketing strategy that includes a memorable title that provokes curiosity, and an attractive layout that shows thoughtfulness and organization, can do wonders for making your proposal stand out.
8. Get to the point. Another way to provoke excitement is to make sure you keep the assessor’s attention from the start. Because you have only seconds to make an impression, this effort starts with a memorable title. Also, do not start the proposal like a journal article with a long background overview. Instead, use those first few sentences to immediately draw the assessor’s attention to the significance of your work. As a good rule of thumb, use that first paragraph to point out what major societal problem you are addressing, why addressing it now is essential, and how you are proposing to solve it. Putting the most thought-provoking information upfront shows your assessor that you are confident and organised.
9. Develop testable hypotheses. You have a much better chance of success if your aims/objectives are immediately visible. So write them in bold text, in their own line. They also need to be written in a way to show they are objectively testable. Consider the aim of solving pesticide pollution. How would you define “solved”? Nobody using pesticides anymore? Nobody getting sick from pesticides? You see, lofty and ill-defined aims provide opportunities for confusion, a risk of appearing unrealistic, and probably a funding denial. To give the assessor assurance that your conclusions will be valid, there is an expectation (especially among assessors who are scientists) for applicants to state their main aims as testable hypotheses, followed by likely testable outcomes. It may require some thinking to frame an objective in an exciting way.
10. Be exact and specific. Science and research are about discovering objective facts and testable outcomes. It is important for you to show assessors that you grasp these concepts. Use your methods section to address each of your hypotheses, one at a time. As you do this, detail exactly how you will collect data free from bias, and what models/statistics you will use to ensure your results are reliable. To show clarity and understanding, either spell out potentially subjective and context-specific terms such as “larger”, “amazing”, and “plenty”, or better yet, avoid them altogether. Also avoid vague throw-away statements like “we will model the population”; those will only hurt your cause. Instead, use that space to describe in detail how you will model the population.
11. State your impact. Some of the greatest discoveries of our time originated from pure scientific studies (i.e. those without obvious and immediate practical benefits). Even so, funders and scientists are increasingly debating the merits of funding pure over applied scientific studies (i.e. studies that directly and immediately benefit the public). While there is undoubtedly a need for better balance in funding allocations, there currently seems to be a strong bias towards funding applied research. Hence, unless grant guidelines explicitly state not to mention it, you should use some space to explain how your work will benefit society at large. It is important to note that the assessors may not share your background or values. Thus, do not assume the value of your work is self-evident—you really need to spell it out.
12. State your outreach strategy. While funding agencies generally support the cause they fund, they also want to attach their name to that cause and be recognized for their contributions. Funding agencies attached to governments in turn want tax-funded projects to be publicly accessible rather than restricted to the collective memories of specialists. A good outreach campaign also prevents the public from feeling detached from science and conservation. It is thus becoming increasingly important (and sometimes mandated) to state what steps you will take to communicate your project’s results to the broader public.
13. You are not alone. As discussed in point 1, you should have a team of collaborators willing to help you. Do not be shy asking them for help; after all, they will also benefit from the funding and fame. It is also worth talking to co-workers who were previously successful getting the funds you target, as there are often unwritten nuances in how proposals should be framed. BUT you should also remember that your proposal is not the only one being assessed. There are likely hundreds of others. They will be ranked, and the most exciting proposals will be funded. You should think very carefully, every step of the way, how to make your proposal stand out from the crowd.
14. Call on external help. Once you and your team finished writing the proposal, ask friends and family who are not part of your team to read and comment on it. First prize is if you can get input from lay people who are not familiar with your work. Ask them if the proposed work excites them, and which parts they do not understand. If your proposal bores or confuses them, then you have more work to do to avoid boring and confusing the assessors. Every extra person willing to read your proposal provides an extra opportunity to test your message and improve your work.
15. Do not give up. Obtaining funding is not easy. It is increasingly the case that funding cuts forces more conservationists to compete for the same, if not smaller, pot of money. Funding success also depends on factors out of your control (e.g. quality and number of other proposals), leaving the chance of success to an element of luck. That does not mean applying for funding is a waste of time. Foremost, you will not succeed if you do not try. Funders may also provide comments on proposals, which enables you to improve it for the next round. Lastly, obtaining funding really is a numbers game. Do not put all your eggs in one basket by submitting your proposal to only one funder. Rather, identify several potential funders, tweak your proposal to fit their guidelines and priorities, and submit >to every one of them. If you have a worthy idea, and you use every failure as an opportunity to refine your message, you will eventually achieve success.
16.03: Environmental Calendar
Several decades ago, the UN initiated a global outreach effort to mark the anniversary dates of key environmental treaties as an opportunity for us to pause and reflect on the natural environment’s importance in our lives. Following this example, some environmental organizations has started devoting additional days to celebrate environmental issues not pertinently covered by UN treaties. Perhaps the most well-known being WWF’s Earth Hour, held every year or 29 March, during which businesses and the public turn off non-essential lights for one hour, from 8:30–9:30pm, as a symbol of their commitment to the environment. These celebrations have become an important tool to help raise public awareness of the plight of the natural world, and many organizations are taking actions to promote environmental issues through newspaper articles, radio interviews, festivals, important announcements, seminars, and guided walks. Below is a list of some prominent celebrations in the annual environmental calendar. You, your friends, and your organization may celebrate only some of these days, or all of them; it’s all up to personal choices.
Celebration
Date
Inaugural year
International Zebra Day
31 January
2016
World Wetlands Day
2 February
1997
World Pangolin Day
Third Saturday in February
2012
*World Wildlife Day
3 March
2014
International Day of Action for Rivers
14 March
1997
World Frog Day
20 March
2014?
*International Day of Forests
21 March
2013
*World Water Day
22 March
1993
Earth Hour
29 March
2008
Earth Day
22 April
1970
World Penguin Day
25 April
Unclear
*World Migratory Bird Day
Second Saturday in May
2006
*International Day for Biological Diversity
22 May
2000
World Turtle Day
23 May
2000
*World Environmental Day
5 June
1974
*World Oceans Day
8 June
1992
World Sea Turtle Day
16 June
2005
*World Day to Combat Desertification and Drought
17 June
1995
World Albatross Day
19 June
2020
World Giraffe Day
21 June
2014
*World Population Day
11 July
1989
World Chimpanzee Day
14 July
2018
World Snake Day
16 July
2013
World Ranger Day
31 July
2007
World Lion Day
10 August
2013
World Elephant Day
12 August
2012
World Lizard Day
14 August
Unclear
International Vulture Awareness Day
First Saturday in Sept.
2009
*International Day for the Preservation of the Ozone Layer
16 September
1995
World Rhino Day
22 September
2010
World Gorilla Day
24 September
2017
World Environmental Health Day
26 September
2011
World Animal Day
4 October
1925
*International Day for Preventing the Exploitation of the Environment in War and Armed Conflict
6 November
2002
World Fisheries Day
21 November
1998
International Cheetah Day
4 December
2011
*World Soil Day
5 December
2014
*International Mountain Day
11 December
2003
*Officially celebrated by the UN | textbooks/bio/Ecology/Conservation_Biology_in_Sub-Saharan_Africa_(Wilson_and_Primack)/16%3A_Appendix/16.02%3A_Obtaining_Conservation_Funding.txt |
Learning Outcomes
After studying this chapter, you should be able to:
• Describe what the environment is, and some of its major components.
• Identify the shared characteristics of the natural sciences
• Understand the process of scientific inquiry
• Compare inductive reasoning with deductive reasoning
• Describe the goals of basic science and applied science
• Define environmental science
• Understand why it is important to study environmental science
• Explain the concept of sustainability and its social, political, and cultural challenges
• Evaluate the main points of environmental ethics
• Describe the concept of environmental justice
• Differentiate between developed and developing countries
Thumbnail image - “Environmental Protection” by ejaugsburg is in the Public Domain, CC0
01: Environmental Science
What is Environmental Science?
Environmental science is the dynamic, interdisciplinary study of the interaction of living and non-living parts of the environment, with special focus on the impact of humans on the environment. The study of environmental science includes circumstances, objects, or conditions by which an organism or community is surrounded and the complex ways in which they interact.
Why Study Environmental Science?
The need for equitable, ethical, and sustainable use of Earth’s resources by a global population that nears the carrying capacity of the planet requires us not only to understand how human behaviors affect the environment, but also the scientific principles that govern interactions between the living and non-living. Our future depends on our ability to understand and evaluate evidence-based arguments about the environmental consequences of human actions and technologies, and to make informed decisions based on those arguments.
From global climate change to habitat loss driven by human population growth and development, Earth is becoming a different planet—right before our eyes. The global scale and rate of environmental change are beyond anything in recorded human history. Our challenge is to acquire an improved understanding of Earth’s complex environmental systems; systems characterized by interactions within and among their natural and human components that link local to global and short-term to long-term phenomena, and individual behavior to collective action. The complexity of environmental challenges demands that we all participate in finding and implementing solutions leading to long-term environmental sustainability.
Perspectives: A brief history of planet Earth:
Attribution
The Earth, Humans, and the Environment by Alexandra Geddes is licensed under CC BY 4.0. Modified from original by Matthew R. Fisher.
1.02: The Process of Science
Like other natural sciences, environmental science is a science that gathers knowledge about the natural world. The methods of science include careful observation, record keeping, logical and mathematical reasoning, experimentation, and submitting conclusions to the scrutiny of others. Science also requires considerable imagination and creativity; a well-designed experiment is commonly described as elegant or beautiful. Science has considerable practical implications and some science is dedicated to practical applications, such as the prevention of disease (figure 2). Other science proceeds largely motivated by curiosity. Whatever its goal, there is no doubt that science has transformed human existence and will continue to do so.
The Nature of Science
Biology is a science, but what exactly is science? What does the study of biology share with other scientific disciplines? Science (from the Latin scientia, meaning “knowledge”) can be defined as a process of gaining knowledge about the natural world.
Science is a very specific way of learning about the world. The history of the past 500 years demonstrates that science is a very powerful way of gaining knowledge about the world; it is largely responsible for the technological revolutions that have taken place during this time. There are areas of knowledge, however, that the methods of science cannot be applied to. These include such things as morality, aesthetics, or spirituality. Science cannot investigate these areas because they are outside the realm of material phenomena, the phenomena of matter and energy, and cannot be observed and measured.
The scientific method is a method of research with defined steps that include experiments and careful observation. The steps of the scientific method will be examined in detail later, but one of the most important aspects of this method is the testing of hypotheses. A hypothesis is an proposed explanatory statement, for a given natural phenomenon, that can be tested. Hypotheses, or tentative explanations, are different than a scientific theory. A scientific theory is a widely-accepted, thoroughly tested and confirmed explanation for a set of observations or phenomena. Scientific theory is the foundation of scientific knowledge. In addition, in many scientific disciplines (less so in biology) there are scientific laws, often expressed in mathematical formulas, which describe how elements of nature will behave under certain specific conditions, but they do not offer explanations for why they occur.
Natural Sciences
What would you expect to see in a museum of natural sciences? Frogs? Plants? Dinosaur skeletons? Exhibits about how the brain functions? A planetarium? Gems and minerals? Or maybe all of the above? Science includes such diverse fields as astronomy, computer sciences, psychology,biology, and mathematics. However, those fields of science related to the physical world and its phenomena and processes are considered natural sciences and include the disciplines of physics, geology, biology, and chemistry. Environmental science is a cross-disciplinary natural science because it relies of the disciplines of chemistry, biology, and geology.
Scientific Inquiry
One thing is common to all forms of science: an ultimate goal to know. Curiosity and inquiry are the driving forces for the development of science. Scientists seek to understand the world and the way it operates. Two methods of logical thinking are used: inductive reasoning and deductive reasoning.
Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. This type of reasoning is common in descriptive science. A life scientist such as a biologist makes observations and records them. These data can be qualitative (descriptive) or quantitative (consisting of numbers), and the raw data can be supplemented with drawings, pictures, photos, or videos. From many observations, the scientist can infer conclusions (inductions) based on evidence. Inductive reasoning involves formulating generalizations inferred from careful observation and the analysis of a large amount of data. Brain studies often work this way. Many brains are observed while people are doing a task. The part of the brain that lights up, indicating activity, is then demonstrated to be the part controlling the response to that task.
Deductive reasoning or deduction is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the opposite direction as compared to inductive reasoning. Deductive reasoning is a form of logical thinking that uses a general principle or law to forecast specific results. From those general principles, a scientist can extrapolate and predict the specific results that would be valid as long as the general principles are valid. For example, a prediction would be that if the climate is becoming warmer in a region, the distribution of plants and animals should change. Comparisons have been made between distributions in the past and the present, and the many changes that have been found are consistent with a warming climate. Finding the change in distribution is evidence that the climate change conclusion is a valid one.
Both types of logical thinking are related to the two main pathways of scientific study: descriptive science and hypothesis-based science. Descriptive (or discovery) science aims to observe, explore, and discover, while hypothesis-based science begins with a specific question or problem and a potential answer or solution that can be tested. The boundary between these two forms of study is often blurred, because most scientific endeavors combine both approaches. Observations lead to questions, questions lead to forming a hypothesis as a possible answer to those questions, and then the hypothesis is tested. Thus, descriptive science and hypothesis-based science are in continuous dialogue.
“Scientists have become the bearers of the torch of discovery in our quest for knowledge.” – Stephen Hawking and Leonard Mlodinov, in The Grand Design (2010), Bantam Books
Hypothesis Testing
Biologists study the living world by posing questions about it and seeking science-based responses. This approach is common to other sciences as well and is often referred to as the scientific method. The scientific method was used even in ancient times, but it was first documented by England’s Sir Francis Bacon (1561–1626) who set up inductive methods for scientific inquiry. The scientific method is not exclusively used by biologists but can be applied to almost anything as a logical problem-solving method.
The scientific process typically starts with an observation (often a problem to be solved) that leads to a question. Let’s think about a simple problem that starts with an observation and apply the scientific method to solve the problem. One Monday morning, a student arrives at class and quickly discovers that the classroom is too warm. That is an observation that also describes a problem: the classroom is too warm. The student then asks a question: “Why is the classroom so warm?”
Recall that a hypothesis is a suggested explanation that can be tested. To solve a problem, several hypotheses may be proposed. For example, one hypothesis might be, “The classroom is warm because no one turned on the air conditioning.” But there could be other responses to the question, and therefore other hypotheses may be proposed. A second hypothesis might be, “The classroom is warm because there is a power failure, and so the air conditioning doesn’t work.”
Once a hypothesis has been selected, a prediction may be made. A prediction is similar to a hypothesis but it typically has the format “If . . . then . . . .” For example, the prediction for the first hypothesis might be, “If the student turns on the air conditioning, then the classroom will no longer be too warm.”
A hypothesis must be testable to ensure that it is valid. For example, a hypothesis that depends on what a bear thinks is not testable, because it can never be known what a bear thinks. It should also be falsifiable, meaning that it can be disproven by experimental results. An example of an unfalsifiable hypothesis is “Botticelli’s Birth of Venus is beautiful.” There is no experiment that might show this statement to be false. To test a hypothesis, a researcher will conduct one or more experiments designed to eliminate one or more of the hypotheses. This is important. A hypothesis can be disproven, or eliminated, but it can never be proven. Science does not deal in proofs like mathematics. If an experiment fails to disprove a hypothesis, then we find support for that explanation, but this is not to say that down the road a better explanation will not be found, or a more carefully designed experiment will be found to falsify the hypothesis.
Each experiment will have one or more variables and one or more controls. Experimental variables are any part of the experiment that can vary or change during the experiment. Controlled variables are parts of the experiment that do not change. Lastly, experiments might have a control group: a group of test subjects that are as similar as possible to all other test subjects, with the exception that they don’t receive the experimental treatment (those that do receive it are known as the experimental group). For example, in a study testing a weight-loss drug, the control group would be test subjects that don’t receive the drug (but they might receive a placebo, such as sugar pill, instead). Look for these various things in the example that follows:
An experiment might be conducted to test the hypothesis that phosphate (a nutrient) promotes the growth of algae in freshwater ponds. A series of artificial ponds are filled with water and half of them are treated by adding phosphate each week, while the other half are treated by adding a non-nutritional mineral that is not used by algae. The experimental variable here is presence/absence of a nutrient (phosphate). One potential controlled variable would be the volume of water in each tank. The amount of water that algae have access to may influence the results, thus researchers want to control its influence on the results by making sure all test subjects get the same amount. The control group consists of the tanks that received a placebo (non-nutritional mineral) instead of the phosphate. If the ponds with phosphate show more algal growth, then we have found support for the hypothesis. If they do not, then we reject our hypothesis. Be aware that rejecting one hypothesis does not determine whether or not the other hypotheses can be accepted; it simply eliminates one hypothesis that is not valid (Figure \(3\)). Using the scientific method, the hypotheses that are inconsistent with experimental data are rejected.
In the example below, the scientific method is used to solve an everyday problem. Which part in the example below is the hypothesis? Which is the prediction? Based on the results of the experiment, is the hypothesis supported? If it is not supported, propose some alternative hypotheses.
1. My toaster doesn’t toast my bread.
2. Why doesn’t my toaster work?
3. There is something wrong with the electrical outlet.
4. If something is wrong with the outlet, my coffeemaker also won’t work when plugged into it.
5. I plug my coffeemaker into the outlet.
6. My coffeemaker works.
In practice, the scientific method is not as rigid and structured as it might at first appear. Sometimes an experiment leads to conclusions that favor a change in approach; often, an experiment brings entirely new scientific questions to the puzzle. Many times, science does not operate in a linear fashion; instead, scientists continually draw inferences and make generalizations, finding patterns as their research proceeds. Scientific reasoning is more complex than the scientific method alone suggests.
Basic and Applied Science
Is it valuable to pursue science for the sake of simply gaining knowledge, or does scientific knowledge only have worth if we can apply it to solving a specific problem or bettering our lives? This question focuses on the differences between two types of science: basic science and applied science.
Basic science or “pure” science seeks to expand knowledge regardless of the short-term application of that knowledge. It is not focused on developing a product or a service of immediate public or commercial value. The immediate goal of basic science is knowledge for knowledge’s sake, though this does not mean that in the end it may not result in an application.
In contrast, applied science aims to use science to solve real-world problems, such as improving crop yield, find a cure for a particular disease, or save animals threatened by a natural disaster. In applied science, the problem is usually defined for the researcher.
Some individuals may perceive applied science as “useful” and basic science as “useless.” A question these people might pose to a scientist advocating knowledge acquisition would be, “What for?” A careful look at the history of science, however, reveals that basic knowledge has resulted in many remarkable applications of great value. Many scientists think that a basic understanding of science is necessary before an application is developed; therefore, applied science relies on the results generated through basic science. Other scientists think that it is time to move on from basic science and instead to find solutions to actual problems. Both approaches are valid. It is true that there are problems that demand immediate attention; however, few solutions would be found without the help of the knowledge generated through basic science.
One example of how basic and applied science can work together to solve practical problems occurred after the discovery of DNA structure led to an understanding of the molecular mechanisms governing DNA replication. Strands of DNA, unique in every human, are found in our cells, where they provide the instructions necessary for life. During DNA replication, new copies of DNA are made, shortly before a cell divides to form new cells. Understanding the mechanisms of DNA replication (through basic science) enabled scientists to develop laboratory techniques that are now used to identify genetic diseases, pinpoint individuals who were at a crime scene, and determine paternity (all examples of applied science). Without basic science, it is unlikely that applied science would exist.
Another example of the link between basic and applied research is the Human Genome Project, a study in which each human chromosome was analyzed and mapped to determine the precise sequence of the DNA code and the exact location of each gene. (The gene is the basic unit of heredity; an individual’s complete collection of genes is his or her genome.) Other organisms have also been studied as part of this project to gain a better understanding of human chromosomes. The Human Genome Project (Figure \(5\)) relied on basic research carried out with non-human organisms and, later, with the human genome. An important end goal eventually became using the data for applied research seeking cures for genetic diseases.
Scientific Work is Transparent & Open to Critique
Whether scientific research is basic science or applied science, scientists must share their findings for other researchers to expand and build upon their discoveries. For this reason, an important aspect of a scientist’s work is disseminating results and communicating with peers. Scientists can share results by presenting them at a scientific meeting or conference, but this approach can reach only the limited few who are present. Instead, most scientists present their results in peer-reviewed articles that are published in scientific journals. Peer-reviewed articles are scientific papers that are reviewed, usually anonymously by a scientist’s colleagues, or peers. These colleagues are qualified individuals, often experts in the same research area, who judge whether or not the scientist’s work is suitable for publication. The process of peer review helps to ensure that the research described in a scientific paper or grant proposal is original, significant, logical, ethical, and thorough. Scientists publish their work so other scientists can reproduce their experiments under similar or different conditions to expand on the findings. The experimental results must be consistent with the findings of other scientists.
As you review scientific information, whether in an academic setting or as part of your day-to-day life, it is important to think about the credibility of that information. You might ask yourself: has this scientific information been through the rigorous process of peer review? Are the conclusions based on available data and accepted by the larger scientific community? Scientists are inherently skeptical, especially if conclusions are not supported by evidence (and you should be too).
Attribution
Concepts of Biology by OpenStax is licensed under CC BY 3.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/01%3A_Environmental_Science/1.01%3A_The_Earth_Humans__the_Environment.txt |
Taking The Long View: Sustainability in Evolutionary and Ecological Perspective
Of the different forms of life that have inhabited the Earth in its three to four billion year history, 99.9% are now extinct. Against this backdrop, the human enterprise with its roughly 200,000-year history barely merits attention. As the American novelist Mark Twain once remarked, if our planet’s history were to be compared to the Eiffel Tower, human history would be a mere smear on the very tip of the tower. But while modern humans (Homo sapiens) might be insignificant in geologic time, we are by no means insignificant in terms of our recent planetary impact. A 1986 study estimated that 40% of the product of terrestrial plant photosynthesis — the basis of the food chain for most animal and bird life — was being appropriated by humans for their use. More recent studies estimate that 25% of photosynthesis on continental shelves (coastal areas) is ultimately being used to satisfy human demand. Human appropriation of such natural resources is having a profound impact upon the wide diversity of other species that also depend on them.
Evolution normally results in the generation of new lifeforms at a rate that outstrips the extinction of other species; this results in strong biological diversity. However, scientists have evidence that, for the first observable time in evolutionary history, another species — Homo sapiens — has upset this balance to the degree that the rate of species extinction is now estimated at 10,000 times the rate of species renewal. Human beings, just one species among millions, are crowding out the other species we share the planet with. Evidence of human interference with the natural world is visible in practically every ecosystem from the presence of pollutants in the stratosphere to the artificially changed courses of the majority of river systems on the planet. It is argued that ever since we abandoned nomadic, gatherer-hunter ways of life for settled societies some 12,000 years ago, humans have continually manipulated their natural world to meet their needs. While this observation is a correct one, the rate, scale, and the nature of human-induced global change — particularly in the post-industrial period — is unprecedented in the history of life on Earth.
There are three primary reasons for this:
Firstly, mechanization of both industry and agriculture in the last century resulted in vastly improved labor productivity which enabled the creation of goods and services. Since then, scientific advance and technological innovation — powered by ever-increasing inputs of fossil fuels and their derivatives — have revolutionized every industry and created many new ones. The subsequent development of western consumer culture, and the satisfaction of the accompanying disposable mentality, has generated material flows of an unprecedented scale. The Wuppertal Institute estimates that humans are now responsible for moving greater amounts of matter across the planet than all natural occurrences (earthquakes, storms, etc.) put together.
Secondly, the sheer size of the human population is unprecedented. Every passing year adds another 90 million people to the planet. Even though the environmental impact varies significantly between countries (and within them), the exponential growth in human numbers, coupled with rising material expectations in a world of limited resources, has catapulted the issue of distribution to prominence. Global inequalities in resource consumption and purchasing power mark the clearest dividing line between the haves and the have-nots. It has become apparent that present patterns of production and consumption are unsustainable for a global population that is projected to reach between 12 billion by the year 2050. If ecological crises and rising social conflict are to countered, the present rates of over-consumption by a rich minority, and under-consumption by a large majority, will have to be brought into balance.
Thirdly, it is not only the rate and the scale of change but the nature of that change that is unprecedented. Human inventiveness has introduced chemicals and materials into the environment which either do not occur naturally at all, or do not occur in the ratios in which we have introduced them. These persistent chemical pollutants are believed to be causing alterations in the environment, the effects of which are only slowly manifesting themselves, and the full scale of which is beyond calculation. CFCs and PCBs are but two examples of the approximately 100,000 chemicals currently in global circulation. (Between 500 and 1,000 new chemicals are being added to this list annually.) The majority of these chemicals have not been tested for their toxicity on humans and other life forms, let alone tested for their effects in combination with other chemicals. These issues are now the subject of special UN and other intergovernmental working groups.
The Evolution of Sustainability Itself
Our Common Future (1987), the report of the World Commission on Environment and Development, is widely credited with having popularized the concept of sustainable development. It defines sustainable development in the following ways…
• …development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
• … sustainable development is not a fixed state of harmony, but rather a process of change in which the exploitation of resources, the orientation of the technological development, and institutional change are made consistent with future as well as present needs.
The concept of sustainability, however, can be traced back much farther to the oral histories of indigenous cultures. For example, the principle of inter-generational equity is captured in the Inuit saying, ‘we do not inherit the Earth from our parents, we borrow it from our children’. The Native American ‘Law of the Seventh Generation’ is another illustration. According to this, before any major action was to be undertaken its potential consequences on the seventh generation had to be considered. For a species that at present is only 6,000 generations old and whose current political decision-makers operate on time scales of months or few years at most, the thought that other human cultures have based their decision-making systems on time scales of many decades seems wise but unfortunately inconceivable in the current political climate.
Environmental Equity
While much progress is being made to improve resource efficiency, far less progress has been made to improve resource distribution. Currently, just one-fifth of the global population is consuming three-quarters of the earth’s resources (Figure \(1\)). If the remaining four-fifths were to exercise their right to grow to the level of the rich minority it would result in ecological devastation. So far, global income inequalities and lack of purchasing power have prevented poorer countries from reaching the standard of living (and also resource consumption/waste emission) of the industrialized countries.
Countries such as China, Brazil, India, and Malaysia are, however, catching up fast. In such a situation, global consumption of resources and energy needs to be drastically reduced to a point where it can be repeated by future generations. But who will do the reducing? Poorer nations want to produce and consume more. Yet so do richer countries: their economies demand ever greater consumption-based expansion. Such stalemates have prevented any meaningful progress towards equitable and sustainable resource distribution at the international level. These issue of fairness and distributional justice remain unresolved.
Concepts in Environmental Science
The ecological footprint (EF), developed by Canadian ecologist and planner William Rees, is basically an accounting tool that uses land as the unit of measurement to assess per capita consumption, production, and discharge needs. It starts from the assumption that every category of energy and material consumption and waste discharge requires the productive or absorptive capacity of a finite area of land or water. If we (add up) all the land requirements for all categories of consumption and waste discharge by a defined population, the total area represents the Ecological Footprint of that population on Earth whether or not this area coincides with the population’s home region.
Land is used as the unit of measurement for the simple reason that, according to Rees, “Land area not only captures planet Earth’s finiteness, it can also be seen as a proxy for numerous essential life support functions from gas exchange to nutrient recycling … land supports photosynthesis, the energy conduit for the web of life. Photosynthesis sustains all important food chains and maintains the structural integrity of ecosystems.”
What does the ecological footprint tell us? Ecological footprint analysis can tell us in a vivid, ready-to-grasp manner how much of the Earth’s environmental functions are needed to support human activities. It also makes visible the extent to which consumer lifestyles and behaviors are ecologically sustainable calculated that the ecological footprint of the average American is – conservatively – 5.1 hectares per capita of productive land. With roughly 7.4 billion hectares of the planet’s total surface area of 51 billion hectares available for human consumption, if the current global population were to adopt American consumer lifestyles we would need two additional planets to produce the resources, absorb the wastes, and provide general life-support functions.
The precautionary principle is an important concept in environmental sustainability. A 1998 consensus statement characterized the precautionary principle this way: “when an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically”. For example, if a new pesticide chemical is created, the precautionary principle would dictate that we presume, for the sake of safety, that the chemical may have potential negative consequences for the environment and/or human health, even if such consequences have not been proven yet. In other words, it is best to proceed cautiously in the face of incomplete knowledge about something’s potential harm.
Some Indicators of Global Environmental Stress
• Forests Deforestation remains a main issue. 1 million hectares of forest were lost every year in the decade 1980-1990. The largest losses of forest area are taking place in the tropical moist deciduous forests, the zone best suited to human settlement and agriculture. Recent estimates suggest that nearly two-thirds of tropical deforestation is due to farmers clearing land for agriculture. There is increasing concern about the decline in forest quality associated with intensive use of forests and unregulated access.
• Soil — As much as 10% of the earth’s vegetated surface is now at least moderately degraded. Trends in soil quality and management of irrigated land raise serious questions about longer-term sustainability. It is estimated that about 20% of the world’s 250 million hectares of irrigated land are already degraded to the point where crop production is seriously reduced.
• Fresh Water — Some 20% of the world’s population lacks access to safe water and 50% lacks access to safe sanitation. If current trends in water use persist, two-thirds of the world’s population could be living in countries experiencing moderate or high water stress by 2025.
• Marine fisheries — 25% of the world’s marine fisheries are being fished at their maximum level of productivity and 35% are overfished (yields are declining). In order to maintain current per capita consumption of fish, global fish harvests must be increased; much of the increase might come through aquaculture which is a known source of water pollution, wetland loss and mangrove swamp destruction.
• Biodiversity — Biodiversity is increasingly coming under threat from development, which destroys or degrades natural habitats, and from pollution from a variety of sources. The first comprehensive global assessment of biodiversity put the total number of species at close to 14 million and found that between 1% and 11% of the world’s species may be threatened by extinction every decade. Coastal ecosystems, which host a very large proportion of marine species, are at great risk with perhaps one-third of the world’s coasts at high potential risk of degradation and another 17% at moderate risk.
• Atmosphere — The Intergovernmental Panel on Climate Change has established that human activities are having a discernible influence on global climate. CO2 emissions in most industrialized countries have risen during the past few years and countries generally failed to stabilize their greenhouse gas emissions at 1990 levels by 2000 as required by the Climate Change convention.
• Toxic chemicals — About 100,000 chemicals are now in commercial use and their potential impacts on human health and ecological function represent largely unknown risks. Persistent organic pollutants are now so widely distributed by air and ocean currents that they are found in the tissues of people and wildlife everywhere; they are of particular concern because of their high levels of toxicity and persistence in the environment.
• Hazardous wastes — Pollution from heavy metals, especially from their use in industry and mining, is also creating serious health consequences in many parts of the world. Incidents and accidents involving uncontrolled radioactive sources continue to increase, and particular risks are posed by the legacy of contaminated areas left from military activities involving nuclear materials.
• Waste — Domestic and industrial waste production continues to increase in both absolute and per capita terms, worldwide. In the developed world, per capita waste generation has increased threefold over the past 20 years; in developing countries, it is highly likely that waste generation will double during the next decade. The level of awareness regarding the health and environmental impacts of inadequate waste disposal remains rather poor; poor sanitation and waste management infrastructure is still one of the principal causes of death and disability for the urban poor. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/01%3A_Environmental_Science/1.03%3A_Environment_and_Sustainability.txt |
Frontier Ethic
The ways in which humans interact with the land and its natural resources are determined by ethical attitudes and behaviors. Early European settlers in North America rapidly consumed the natural resources of the land. After they depleted one area, they moved westward to new frontiers. Their attitude towards the land was that of a frontier ethic. A frontier ethic assumes that the earth has an unlimited supply of resources. If resources run out in one area, more can be found elsewhere or alternatively human ingenuity will find substitutes. This attitude sees humans as masters who manage the planet. The frontier ethic is completely anthropocentric (human-centered), for only the needs of humans are considered.
Most industrialized societies experience population and economic growth that are based upon this frontier ethic, assuming that infinite resources exist to support continued growth indefinitely. In fact, economic growth is considered a measure of how well a society is doing. The late economist Julian Simon pointed out that life on earth has never been better, and that population growth means more creative minds to solve future problems and give us an even better standard of living. However, now that the human population has passed seven billion and few frontiers are left, many are beginning to question the frontier ethic. Such people are moving toward an environmental ethic, which includes humans as part of the natural community rather than managers of it. Such an ethic places limits on human activities (e.g., uncontrolled resource use), that may adversely affect the natural community.
Some of those still subscribing to the frontier ethic suggest that outer space may be the new frontier. If we run out of resources (or space) on earth, they argue, we can simply populate other planets. This seems an unlikely solution, as even the most aggressive colonization plan would be incapable of transferring people to extraterrestrial colonies at a significant rate. Natural population growth on earth would outpace the colonization effort. A more likely scenario would be that space could provide the resources (e.g. from asteroid mining) that might help to sustain human existence on earth.
Sustainable Ethic
A sustainable ethic is an environmental ethic by which people treat the earth as if its resources are limited. This ethic assumes that the earth’s resources are not unlimited and that humans must use and conserve resources in a manner that allows their continued use in the future. A sustainable ethic also assumes that humans are a part of the natural environment and that we suffer when the health of a natural ecosystem is impaired. A sustainable ethic includes the following tenets:
• The earth has a limited supply of resources.
• Humans must conserve resources.
• Humans share the earth’s resources with other living things.
• Growth is not sustainable.
• Humans are a part of nature.
• Humans are affected by natural laws.
• Humans succeed best when they maintain the integrity of natural processes sand cooperate with nature.
For example, if a fuel shortage occurs, how can the problem be solved in a way that is consistent with a sustainable ethic? The solutions might include finding new ways to conserve oil or developing renewable energy alternatives. A sustainable ethic attitude in the face of such a problem would be that if drilling for oil damages the ecosystem, then that damage will affect the human population as well. A sustainable ethic can be either anthropocentric or biocentric (life-centered). An advocate for conserving oil resources may consider all oil resources as the property of humans. Using oil resources wisely so that future generations have access to them is an attitude consistent with an anthropocentric ethic. Using resources wisely to prevent ecological damage is in accord with a biocentric ethic.
Land Ethic
Aldo Leopold, an American wildlife natural historian and philosopher, advocated a biocentric ethic in his book, A Sand County Almanac. He suggested that humans had always considered land as property, just as ancient Greeks considered slaves as property. He believed that mistreatment of land (or of slaves) makes little economic or moral sense, much as today the concept of slavery is considered immoral. All humans are merely one component of an ethical framework. Leopold suggested that land be included in an ethical framework, calling this the land ethic.
“The land ethic simply enlarges the boundary of the community to include soils, waters, plants and animals; or collectively, the land. In short, a land ethic changes the role of Homo sapiens from conqueror of the land-community to plain member and citizen of it. It implies respect for his fellow members, and also respect for the community as such.” (Aldo Leopold, 1949)
Leopold divided conservationists into two groups: one group that regards the soil as a commodity and the other that regards the land as biota, with a broad interpretation of its function. If we apply this idea to the field of forestry, the first group of conservationists would grow trees like cabbages, while the second group would strive to maintain a natural ecosystem. Leopold maintained that the conservation movement must be based upon more than just economic necessity. Species with no discernible economic value to humans may be an integral part of a functioning ecosystem. The land ethic respects all parts of the natural world regardless of their utility, and decisions based upon that ethic result in more stable biological communities.
“Anything is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends to do otherwise.” (Aldo Leopold, 1949)
Hetch Hetchy Valley
In 1913, the Hetch Hetchy Valley – located in Yosemite National Park in California – was the site of a conflict between two factions, one with an anthropocentric ethic and the other, a biocentric ethic. As the last American frontiers were settled, the rate of forest destruction started to concern the public.
The conservation movement gained momentum, but quickly broke into two factions. One faction, led by Gifford Pinchot, Chief Forester under Teddy Roosevelt, advocated utilitarian conservation (i.e., conservation of resources for the good of the public). The other faction, led by John Muir, advocated preservation of forests and other wilderness for their inherent value. Both groups rejected the first tenet of frontier ethics, the assumption that resources are limitless. However, the conservationists agreed with the rest of the tenets of frontier ethics, while the preservationists agreed with the tenets of the sustainable ethic.
The Hetch Hetchy Valley was part of a protected National Park, but after the devastating fires of the 1906 San Francisco earthquake, residents of San Francisco wanted to dam the valley to provide their city with a stable supply of water. Gifford Pinchot favored the dam.
“As to my attitude regarding the proposed use of Hetch Hetchy by the city of San Francisco…I am fully persuaded that… the injury…by substituting a lake for the present swampy floor of the valley…is altogether unimportant compared with the benefits to be derived from it’s use as a reservoir.
“The fundamental principle of the whole conservation policy is that of use, to take every part of the land and its resources and put it to that use in which it will serve the most people.” (Gifford Pinchot, 1913)
John Muir, the founder of the Sierra Club and a great lover of wilderness, led the fight against the dam. He saw wilderness as having an intrinsic value, separate from its utilitarian value to people. He advocated preservation of wild places for their inherent beauty and for the sake of the creatures that live there. The issue aroused the American public, who were becoming increasingly alarmed at the growth of cities and the destruction of the landscape for the sake of commercial enterprises. Key senators received thousands of letters of protest.
“These temple destroyers, devotees of ravaging commercialism, seem to have a perfect contempt for Nature, and instead of lifting their eyes to the God of the Mountains, lift them to the Almighty Dollar.” (John Muir, 1912)
Despite public protest, Congress voted to dam the valley. The preservationists lost the fight for the Hetch Hetchy Valley, but their questioning of traditional American values had some lasting effects. In 1916, Congress passed the “National Park System Organic Act,” which declared that parks were to be maintained in a manner that left them unimpaired for future generations. As we use our public lands, we continue to debate whether we should be guided by preservationism or conservationism.
The Tragedy of the Commons
In his essay, The Tragedy of the Commons, Garrett Hardin (1968) looked at what happens when humans do not limit their actions by including the land as part of their ethic. The tragedy of the commons develops in the following way: Imagine a pasture open to all (the ‘commons’). It is to be expected that each herdsman will try to keep as many cattle as possible on the commons. As rational beings, each herdsman seeks to maximize their gain. Adding more cattle increases their profit, and they do not suffer any immediate negative consequence because the commons are shared by all. The rational herdsman concludes that the only sensible course is to add another animal to their herd, and then another, and so forth. However, this same conclusion is reached by each and every rational herdsman sharing the commons. Therein lies the tragedy: each person is locked into a system that compels them to increase their herd, without limit, in a world that is limited. Eventually this leads to the ruination of the commons. In a society that believes in the freedom of the commons, freedom brings ruin to all because each person acts selfishly.
Hardin went on to apply the situation to modern commons: overgrazing of public lands, overuse of public forests and parks, depletion of fish populations in the ocean, use of rivers as a common dumping ground for sewage, and fouling the air with pollution.
The “Tragedy of the Commons” is applicable to what is arguably the most consequential environmental problem: global climate change. The atmosphere is a commons into which countries are dumping carbon dioxide from the burning of fossil fuels. Although we know that the generation of greenhouse gases will have damaging effects upon the entire globe, we continue to burn fossil fuels. As a country, the immediate benefit from the continued use of fossil fuels is seen as a positive component (because of economic growth). All countries, however, will share the negative long-term effects. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/01%3A_Environmental_Science/1.04%3A_Environmental_Ethics.txt |
Environmental Justice
Environmental Justice is defined as the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. It will be achieved when everyone enjoys the same degree of protection from environmental and health hazards and equal access to the decision-making process to have a healthy environment in which to live, learn, and work.
During the 1980’s minority groups protested that hazardous waste sites were preferentially sited in minority neighborhoods. In 1987, Benjamin Chavis of the United Church of Christ Commission for Racism and Justice coined the term environmental racism to describe such a practice. The charges generally failed to consider whether the facility or the demography of the area came first. Most hazardous waste sites are located on property that was used as disposal sites long before modern facilities and disposal methods were available. Areas around such sites are typically depressed economically, often as a result of past disposal activities. Persons with low incomes are often constrained to live in such undesirable, but affordable, areas. The problem more likely resulted from one of insensitivity rather than racism. Indeed, the ethnic makeup of potential disposal facilities was most likely not considered when the sites were chosen.
Decisions in citing hazardous waste facilities are generally made on the basis of economics, geological suitability and the political climate. For example, a site must have a soil type and geological profile that prevents hazardous materials from moving into local aquifers. The cost of land is also an important consideration. The high cost of buying land would make it economically unfeasible to build a hazardous waste site in Beverly Hills. Some communities have seen a hazardous waste facility as a way of improving their local economy and quality of life. Emelle County, Alabama had illiteracy and infant mortality rates that were among the highest in the nation. A landfill constructed there provided jobs and revenue that ultimately helped to reduce both figures.
In an ideal world, there would be no hazardous waste facilities, but we do not live in an ideal world. Unfortunately, we live in a world plagued by rampant pollution and dumping of hazardous waste. Our industrialized society has necessarily produced wastes during the manufacture of products for our basic needs. Until technology can find a way to manage (or eliminate) hazardous waste, disposal facilities will be necessary to protect both humans and the environment. By the same token, this problem must be addressed. Industry and society must become more socially sensitive in the selection of future hazardous waste sites. All humans who help produce hazardous wastes must share the burden of dealing with those wastes, not just the poor and minorities.
Indigenous People
Since the end of the 15th century, most of the world’s frontiers have been claimed and colonized by established nations. Invariably, these conquered frontiers were home to people indigenous to those regions. Some were wiped out or assimilated by the invaders, while others survived while trying to maintain their unique cultures and way of life. The United Nations officially classifies indigenous people as those “having an historical continuity with pre-invasion and pre-colonial societies,” and “consider themselves distinct from other sectors of the societies now prevailing in those territories or parts of them.” Furthermore, indigenous people are “determined to preserve, develop and transmit to future generations, their ancestral territories, and their ethnic identity, as the basis of their continued existence as peoples in accordance with their own cultural patterns, social institutions and legal systems.” A few of the many groups of indigenous people around the world are: the many tribes of Native Americans (i.e., Navajo, Sioux) in the contiguous 48 states, the Inuit of the arctic region from Siberia to Canada, the rainforest tribes in Brazil, and the Ainu of northern Japan.
Many problems face indigenous people including the lack of human rights, exploitation of their traditional lands and themselves, and degradation of their culture. In response to the problems faced by these people, the United Nations proclaimed an “International Decade of the World’s Indigenous People” beginning in 1994. The main objective of this proclamation, according to the United Nations, is “the strengthening of international cooperation for the solution of problems faced by indigenous people in such areas as human rights, the environment, development, health, culture and education.” Its major goal is to protect the rights of indigenous people. Such protection would enable them to retain their cultural identity, such as their language and social customs, while participating in the political, economic and social activities of the region in which they reside.
Despite the lofty U.N. goals, the rights and feelings of indigenous people are often ignored or minimized, even by supposedly culturally sensitive developed countries. In the United States many of those in the federal government are pushing to exploit oil resources in the Arctic National Wildlife Refuge on the northern coast of Alaska. The “Gwich’in,” an indigenous people who rely culturally and spiritually on the herds of caribou that live in the region, claim that drilling in the region would devastate their way of life. Thousands of years of culture would be destroyed for a few months’ supply of oil. Drilling efforts have been stymied in the past, but mostly out of concern for environmental factors and not necessarily the needs of the indigenous people. Curiously, another group of indigenous people, the “Inupiat Eskimo,” favor oil drilling in the Arctic National Wildlife Refuge. Because they own considerable amounts of land adjacent to the refuge, they would potentially reap economic benefits from the development of the region.
The heart of most environmental conflicts faced by governments usually involves what constitutes proper and sustainable levels of development. For many indigenous peoples, sustainable development constitutes an integrated wholeness, where no single action is separate from others. They believe that sustainable development requires the maintenance and continuity of life, from generation to generation and that humans are not isolated entities, but are part of larger communities, which include the seas, rivers, mountains, trees, fish, animals and ancestral spirits. These, along with the sun, moon and cosmos, constitute a whole. From the point of view of indigenous people, sustainable development is a process that must integrate spiritual, cultural, economic, social, political, territorial and philosophical ideals.
Attribution
Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/01%3A_Environmental_Science/1.05%3A_Environmental_Justice_and_Indigenous_Struggles.txt |
Summary
Science attempts to describe and understand the nature of the universe in whole or in part. Science has many fields; those fields related to the physical world and its phenomena are considered natural sciences. A hypothesis is a tentative explanation for an observation. A scientific theory is a well-tested and consistently verified explanation for a set of observations or phenomena. A scientific law is a description, often in the form of a mathematical formula, of the behavior of an aspect of nature under certain circumstances. Two types of logical reasoning are used in science. Inductive reasoning uses results to produce general scientific principles. Deductive reasoning is a form of logical thinking that predicts results by applying general principles. The common thread throughout scientific research is the use of the scientific method. Scientists present their results in peer-reviewed scientific papers published in scientific journals. Science can be basic or applied. The main goal of basic science is to expand knowledge without any expectation of short-term practical application of that knowledge. The primary goal of applied research, however, is to solve practical problems.
Sustainability refers to three simple concerns: the need to arrest environmental degradation and ecological imbalance, the need not to impoverish future generations and the need for quality of life and equity between current generations. Added up, these core concerns are an unmistakable call for transformation. Business-as-usual is no longer an option. The concept of ethics involves standards of conduct. These standards help to distinguish between behavior that is considered right and that which is considered wrong. The ways in which humans interact with the land and its natural resources are determined by ethical attitudes and behaviors. A frontier ethic assumes that the earth has an unlimited supply of resources. Environmental ethic includes humans as part of the natural community rather than managers of it. Sustainable ethic assumes that the earth’s resources are not unlimited and that humans must use and conserve resources in a manner that allows their continued use in the future. Countries are categorized by a variety of methods. During the Cold War period, the United States government categorized countries according to each government’s ideology and capitalistic development. Current classification models utilize economic (and sometimes other) factors in their determination. Environmental justice is achieved when everyone enjoys the same degree of protection from environmental and health hazards and equal access to the decision-making process to have a healthy environment. Many problems face indigenous people, including: lack of human rights, exploitation of their traditional lands and themselves, and degradation of their culture. Despite the lofty U.N. goals, the rights and feelings of indigenous people are often ignored or minimized, even by supposedly culturally sensitive developed countries.
Review Questions
1. Scientific research that produces knowledge without any immediate practical use is specifically known as…
1. Basic science
2. Applied science
3. Hypothesis-based science
4. Descriptive science
5. Retrospective science
2. Which one of the following fulfills the definition of a hypothesis?
1. Removing invasive species will result in greater biodiversity.
2. Introducing invasive species will harm an ecosystem.
3. Invasive species are non-native species that alter ecosystems.
4. Introducing invasive species will decrease biodiversity by displacing native species
5. Ecosystem productivity will decrease when invasive species are introduced.
3. Which one of the following is consistent with the frontier ethic?
1. Expanding the area covered by a wildlife sanctuary
2. Protecting a natural area as a national park
3. Sustainable logging of a forest
4. Transferring ownership of forestland from private ownership to the federal government
5. Extracting copper ore from mineral-rich deposit in a landscape rich in biodiversity
4. Which one of the following suggests that when the effects of a human activity are poorly understood, we must presume that some level of harm may exist to the environment, and thus must proceed with that activity carefully?
1. Sustainability ethic
2. Precautionary principle
3. Environmental harm dictum
4. Environmental injustice
5. Presumptive principle
5. Which one of the following demonstrates the concept of the “tragedy of the commons”?
1. Competing companies log as many trees as possible for financial gain until no trees are left
2. Public forest land is sold to a privately-owned investor group
3. Logging forests is dangerous work and ends up killing or injuring many workers
4. A careless hiker accidentally starts a wildfire that destroys hundreds of acres of forest
5. Government regulations lead to conditions that increase the risk of forest fire on public lands
6. The equal sharing of Earth’s resources is specifically known as…
1. Environmental justice
2. Sustainability
3. Environmental equity
4. Ecological footprinting
5. Mutualism
7. John Muir’s position on the proposed development in the Hetch Hetchy Valley of California in the early 1900s would best match which one of the following?
1. Frontier ethic
2. Sustainable ethic
3. Land ethic
4. Ethos ethic
5. Darwinian ethic
8. Which one of the following is an example of inductive reasoning?
1. Every lion you’ve seen on TV hunts gazelles, therefore all lions hunt gazelles.
2. All tigers are mammals. All mammals are vertebrates. Therefore, tigers are vertebrates.
3. Every lake contains water; therefore, Crater Lake contains water.
4. Only plants have flowers. Tulips are a plant because they have flowers.
5. The sun emits energy in the form of photons. Visible light is made of photos and thus light is a type of energy.
9. The fair treatment and meaningful involvement of all people regarding enforcement and implementation of environmental regulations and policies is known as what?
1. Quid pro quo
2. Environmental justice
3. Environmental equity
4. Habeas corpus
5. Ecologic inclusiveness
10. People and their culture that have existed continuously dating back to a time before their land was invaded or colonized by other societies are known as…
1. Endemic
2. Indigenous
3. Exotic
4. Incunable
5. Invidious
See Appendix for answers
1. What is science?
2. Describe the process of scientific method.
3. What are inductive reasoning and deductive reasoning?
4. Describe the goals of basic and applied science.
5. Give one example of the link between basic and applied research.
6. What are peer-reviewed articles?
7. Explain the following terms: hypothesis, falsifiability, scientific law.
8. Name some indicators of global environmental stress.
9. Define sustainability.
10. Explain the following terms: frontier ethic, land ethic, environmental ethic.
11. What are developed countries according to the World Bank classification?
12. Define environmental justice.
Attributions
EEA. (1997). Towards sustainable development for local authorities – approaches, experiences and sources. Retrieved from http://www.eea.europa.eu/publication...07-97-191-EN-C. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.
Kriebel, D., Tickner, J., Epstein, P., Lemons, J., Levins, R., Loechler, E. L., … Stoto, M. (2001). The precautionary principle in environmental science. Environmental Health Perspectives, 109(9), 871–876. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1240435/.
NSF. (2009). Transitions and tipping points in complex environmental systems. Retrieved September 24, 2015 from http://www.nsf.gov/geo/ere/ereweb/ac...ort_090809.pdf. Modified from original.
Nuckols, J. R., Ward, M. H., & Jarup, L. (2004). Using geographic information systems for exposure assessment in environmental epidemiology studies. Environmental Health Perspectives, 112(9), 1007–1015. doi:10.1289/ehp.6738.
Theis, T. & Tomkin, J. (Eds.). (2015). Sustainability: A comprehensive foundation. Retrieved from http://cnx.org/contents/[email protected]. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
University of California College Prep. (2012). AP environmental science. Retrieved from http://cnx.org/content/col10548/1.2/. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0 | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/01%3A_Environmental_Science/1.0S%3A_1.S%3A__Environmental_Science_%28Summary%29.txt |
Learning Outcomes
After studying this chapter, you should be able to:
• Describe matter and elements
• Describe the ways in which carbon is critical to life
• Describe the roles of cells in organisms
• Compare and contrast prokaryotic cells and eukaryotic cells
• Summarize the process of photosynthesis and explain its relevance to other living things
• 2.1: Matter
At its most fundamental level, life is made of matter. Matter is something that occupies space and has mass. All matter is composed of elements, substances that cannot be broken down or transformed chemically into other substances. Each element is made of atoms, each with a constant number of protons and unique properties. A total of 118 elements have been defined; however, only 92 occur naturally and fewer than 30 are found in living cells.
• 2.2: Energy
Virtually every task performed by living organisms requires energy. Nutrients and other molecules are imported into the cell to meet these energy demands. For example, energy is required for the synthesis and breakdown of molecules, as well as the transport of molecules into and out of cells. In addition, processes such as ingesting and breaking down food, exporting wastes and toxins, and movement of the cell all require energy.
• 2.3: A Cell is the Smallest Unit of Life
The atom is the smallest and most fundamental unit of matter. Atoms combine to form molecules, which are chemical structures consisting of at least two atoms held together by a chemical bond. In plants, animals, and many other types of organisms, molecules come together in specific ways to create structures called organelles. Organelles are small structures that exist within cells and perform specialized functions. As discussed in more detail below, all living things are made of one or more cell
• 2.4: Energy Enters Ecosystems Through Photosynthesis
The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms combine to form molecules, which are chemical structures consisting of at least two atoms held together by a chemical bond. In plants, animals, and many other types of organisms, molecules come together in specific ways to create structures called organelles. Organelles are small structures that exist within cells and perform specialized functions.
• 2.S: Matter, Energy, & Life (Summary)
Thumbnail image - This sage thrasher’s diet, like that of almost all organisms, depends on photosynthesis.
02: Matter Energy Life
Atoms, Molecules, & Compounds
At its most fundamental level, life is made of matter. Matter is something that occupies space and has mass. All matter is composed of elements, substances that cannot be broken down or transformed chemically into other substances. Each element is made of atoms, each with a constant number of protons and unique properties. A total of 118 elements have been defined; however, only 92 occur naturally and fewer than 30 are found in living cells. The remaining 26 elements are unstable and therefore do not exist for very long or are theoretical and have yet to be detected. Each element is designated by its chemical symbol (such as H, N, O, C, and Na), and possesses unique properties. These unique properties allow elements to combine and to bond with each other in specific ways.
An atom is the smallest component of an element that retains all of the chemical properties of that element. For example, one hydrogen atom has all of the properties of the element hydrogen, such as it exists as a gas at room temperature and it bonds with oxygen to create a water molecule. Hydrogen atoms cannot be broken down into anything smaller while still retaining the properties of hydrogen. If a hydrogen atom were broken down into subatomic particles, it would no longer have the properties of hydrogen. At the most basic level, all organisms are made of a combination of elements. They contain atoms that combine together to form molecules. In multicellular organisms, such as animals, molecules can interact to form cells that combine to form tissues, which make up organs. These combinations continue until entire multicellular organisms are formed.
All matter, whether it be a rock or an organism, is made of atoms. Often, these atoms combine to form molecules. Molecule are chemicals made from two or more atoms bonded together. Some molecules are very simple, like O2, which is comprised of just two oxygen atoms. Some molecules used by organisms, such as DNA, are made of many millions of atoms. All atoms contain protons, electrons, and neutrons (Figure \(1\) below). The only exception is hydrogen (H), which is made of one proton and one electron. A proton is a positively charged particle that resides in the nucleus (the core of the atom) of an atom and has a mass of 1 and a charge of +1. An electron is a negatively charged particle that travels in the space around the nucleus. In other words, it resides outside of the nucleus. It has a negligible mass and has a charge of –1. Neutrons, like protons, reside in the nucleus of an atom. They have a mass of 1 and no charge. The positive (protons) and negative (electrons) charges balance each other in a neutral atom, which has a net zero charge.
Each element contains a different number of protons and neutrons, giving it its own atomic number and mass number. The atomic number of an element is equal to the number of protons that element contains. The mass number is the number of protons plus the number of neutrons of that element. Therefore, it is possible to determine the number of neutrons by subtracting the atomic number from the mass number.
Isotopes are different forms of the same element that have the same number of protons, but a different number of neutrons. Some elements, such as carbon, potassium, and uranium, have naturally occurring isotopes. Carbon 12, the most common isotope of carbon, contains six protons and six neutrons. Therefore, it has a mass number of 12 (six protons and six neutrons) and an atomic number of 6 (which makes it carbon). Carbon 14 contains six protons and eight neutrons. Therefore, it has a mass number of 14 (six protons and eight neutrons) and an atomic number of 6, meaning it is still the element carbon. These two alternate forms of carbon are isotopes. Some isotopes are unstable and will lose protons, other subatomic particles, or energy to form more stable elements. These are called radioactive isotopes or radioisotopes.
EVOLUTION IN ACTION: Carbon dating
Carbon-14 (14C) is a naturally occurring radioisotope that is created in the atmosphere by cosmic rays. This is a continuous process, so more 14C is always being created. As a living organism develops, the relative level of 14C in its body is equal to the concentration of 14C in the atmosphere. When an organism dies, it is no longer ingesting 14C, so the ratio will decline. 14C decays to 14N by a process called beta decay; it gives off energy in this slow process. After approximately 5,730 years, only one-half of the starting concentration of 14C will have been converted to 14N. The time it takes for half of the original concentration of an isotope to decay to its more stable form is called its half-life.
Because the half-life of 14C is long, it is used to age formerly living objects, such as fossils. Using the ratio of the 14C concentration found in an object to the amount of 14C detected in the atmosphere, the amount of the isotope that has not yet decayed can be determined. Based on this amount, the age of the fossil can be calculated to about 50,000 years (Figure \(2\) below). Isotopes with longer half-lives, such as potassium-40, are used to calculate the ages of older fossils. Through the use of carbon dating, scientists can reconstruct the ecology and biogeography of organisms living within the past 50,000 years.
Chemical Bonds
How elements interact with one another depends on the number of electrons and how they are arranged. When an atom does not contain equal numbers of protons and electrons it is called an ion. Because the number of electrons does not equal the number of protons, each ion has a net charge. For example, if sodium loses an electron, it now has 11 protons and only 10 electrons, leaving it with an overall charge of +1. Positive ions are formed by losing electrons and are called cations. Negative ions are formed by gaining electrons and are called anions. Elemental anionic names are changed to end in -ide. As an example, when chlorine becomes an ion it is referred to as chloride.
Ionic and covalent bonds are strong bonds formed between two atoms. These bonds hold atoms together in a relatively stable state. Ionic bonds are formed between two oppositely charged ions (an anion and a cation). Because positive and negative charges attract, these ions are held together much like two oppositely charged magnets would stick together. Covalent bonds form when electrons are shared between two atoms. Each atom shares one of their electrons, which then orbits the nuclei of both atoms, holding the two atoms together. Covalent bonds are the strongest and most common form of chemical bond in organisms. Unlike most ionic bonds, covalent bonds do not dissociate in water.
Covalent bonds come in two varieties: polar and non-polar. A non-polar covalent bond occurs when electrons are shared equally between the two atoms. Polar covalent bonds form when the electrons are shared unequally. Why does this occur? Each element has a known electronegativity: a measure of their affinity for electrons. Some elements, such as oxygen, are very electronegative because they strongly attract electrons from other atoms. Hydrogen, meanwhile, has low electronegativity and thus weakly attracts electrons, in comparison. Polar covalent bonds form when the two atoms involved have significantly different electronegativities. In biological systems, this occurs when oxygen bonds with hydrogen and when nitrogen (also quite electronegative) bonds with hydrogen.
When oxygen and hydrogen bond, for example, the shared electrons are pulled more strongly toward oxygen and thus farther away from hydrogen’s nucleus. Because the electrons move farther away from hydrogen, it becomes slightly positively charged (δ+). The oxygen becomes slightly negatively charged as the electrons become closer to it (δ–). If two molecules with polar covalent bonds approach one another, they can interact due to the attraction of opposite electrical charges. For example, the slight positive charge of hydrogen in a water molecule can be attracted to the slight negative charge of oxygen in a different water molecule (Figure \(3\)). This interaction between two polar molecules is called a hydrogen bond. This type of bond is very common in organisms. Notably, hydrogen bonds give water the unique properties that sustain life. If it were not for hydrogen bonding, water would be a gas rather than a liquid at room temperature.
WATER IS CRUCIAL TO MAINTAINING LIFE
Do you ever wonder why scientists spend time looking for water on other planets? It is because water is essential to life; even minute traces of it on another planet can indicate that life could or did exist on that planet. Water is one of the more abundant molecules in living cells and the one most critical to life as we know it. Approximately 60–70 percent of your body is made up of water. Without it, life simply would not exist.
• Water is polar. The hydrogen and oxygen atoms within water molecules form polar covalent bonds. The shared electrons spend more time associated with the oxygen atom than they do with hydrogen atoms. There is no overall charge to a water molecule, but there is a slight positive charge on each hydrogen atom and a slight negative charge on the oxygen atom. Because of these charges, the slightly positive hydrogen atoms repel each other and form the unique shape. Each water molecule attracts other water molecules because of the positive and negative charges in the different parts of the molecule. Water also attracts other polar molecules (such as sugars) that can dissolve in water and are referred to as hydrophilic (“water-loving”).
• Water stabilizes temperature. The hydrogen bonds in water allow it to absorb and release heat energy more slowly than many other substances. Temperature is a measure of the motion (kinetic energy) of molecules. As the motion increases, energy is higher and thus temperature is higher. Water absorbs a great deal of energy before its temperature rises. Increased energy disrupts the hydrogen bonds between water molecules. Because these bonds can be created and disrupted rapidly, water absorbs an increase in energy and temperature changes only minimally. This means that water moderates temperature changes within organisms and in their environments.
• Water is an excellent solvent. Because water is polar, with slight positive and negative charges, ionic compounds and polar molecules can readily dissolve in it. Water is, therefore, what is referred to as a solvent—a substance capable of dissolving another substance. The charged particles will form hydrogen bonds with a surrounding layer of water molecules.
• Water is cohesive. Have you ever filled up a glass of water to the very top and then slowly added a few more drops? Before it overflows, the water actually forms a dome-like shape above the rim of the glass. This water can stay above the glass because of the property of cohesion. In cohesion, water molecules are attracted to each other (because of hydrogen bonding), keeping the molecules together at the liquid-air (gas) interface, although there is no more room in the glass. Cohesion gives rise to surface tension, the capacity of a substance to withstand rupture when placed under tension or stress. When you drop a small scrap of paper onto a droplet of water, the paper floats on top of the water droplet, although the object is denser (heavier) than the water. This occurs because of the surface tension that is created by the water molecules. Cohesion and surface tension keep the water molecules intact and the item floating on the top. It is even possible to “float” a steel needle on top of a glass of water if you place it gently, without breaking the surface tension. These cohesive forces are also related to the water’s property of adhesion, or the attraction between water molecules and other molecules. This is observed when water “climbs” up a straw placed in a glass of water. You will notice that the water appears to be higher on the sides of the straw than in the middle. This is because the water molecules are attracted to the straw and therefore adhere to it. Cohesive and adhesive forces are important for sustaining life. For example, because of these forces, water can flow up from the roots to the tops of plants to feed the plant.
Buffers, pH, Acids, and Bases
The pH of a solution is a measure of its acidity or alkalinity. The pH scale ranges from 0 to 14. A change of one unit on the pH scale represents a change in the concentration of hydrogen ions by a factor of 10, a change in two units represents a change in the concentration of hydrogen ions by a factor of 100. Thus, small changes in pH represent large changes in the concentrations of hydrogen ions. Pure water is neutral. It is neither acidic nor basic and has a pH of 7.0. Anything below 7.0 (ranging from 0.0 to 6.9) is acidic, and anything above 7.0 (from 7.1 to 14.0) is alkaline. The blood in your veins is slightly alkaline (pH = 7.4). The environment in your stomach is highly acidic (pH = 1 to 2). Orange juice is mildly acidic (pH = approximately 3.5), whereas baking soda is basic (pH = 9.0).
Acids are substances that provide hydrogen ions (H+) and lower pH, whereas bases provide hydroxide ions (OH–) and raise pH. The stronger the acid, the more readily it donates H+. For example, hydrochloric acid and lemon juice are very acidic and readily give up H+ when added to water. Conversely, bases are those substances that readily donate OH–. The OH– ions combine with H+ to produce water, which raises a substance’s pH. Sodium hydroxide and many household cleaners are very alkaline and give up OH– rapidly when placed in water, thereby raising the pH.
How is it that we can ingest or inhale acidic or basic substances and not die? Buffers are the key. Buffers readily absorb excess H+ or OH–, keeping the pH of the body carefully maintained in the aforementioned narrow range. Carbon dioxide is part of a prominent buffer system in the human body; it keeps the pH within the proper range. This buffer system involves carbonic acid (H2CO3) and bicarbonate (HCO3–) anion. If too much H+ enters the body, bicarbonate will combine with the H+ to create carbonic acid and limit the decrease in pH. Likewise, if too much OH– is introduced into the system, carbonic acid will combine with it to create bicarbonate and limit the increase in pH. While carbonic acid is an important product in this reaction, its presence is fleeting because the carbonic acid is released from the body as carbon dioxide gas each time we breathe. Without this buffer system, the pH in our bodies would fluctuate too much and we would fail to survive.
Biological Molecules
Besides water, the molecules necessary for life are organic. Organic molecules are those that contain carbon covalently bonded to hydrogen. In addition, they may contain oxygen, nitrogen, phosphorus, sulfur, and additional elements.There are four major classes of organic molecules: carbohydrates, lipids, proteins, and nucleic acids. Each is an important component of the cell and performs a wide array of functions.
It is often said that life is “carbon-based.” This means that carbon atoms, bonded to other carbon atoms or other elements, form the fundamental components of many of the molecules found uniquely in living things. Other elements play important roles in biological molecules, but carbon certainly qualifies as the “foundation” element for molecules in living things. It is the bonding properties of carbon atoms that are responsible for its important role.
Carbon can form four covalent bonds with other atoms or molecules. The simplest organic carbon molecule is methane (CH4), in which four hydrogen atoms bind to a carbon atom (Figure \(5\)). Carbohydrates include what are commonly referred to as simple sugars, like glucose, and complex carbohydrates such as starch. While many types of carbohydrates are used for energy, some are used for structure by most organisms, including plants and animals. For example, cellulose is a complex carbohydrate that adds rigidity and strength to the cell walls of plants. The suffix “-ose” denotes a carbohydrate, but note that not all carbohydrates were given that suffix when names (e.g., starch).
Lipids include a diverse group of compounds that are united by a common feature. Lipids are hydrophobic (“water-fearing”), or insoluble in water, because they are non-polar molecules (molecules that contain non-polar covalent bonds) . Lipids perform many different functions in a cell. Cells store energy for long-term use in the form of lipids called fats. Lipids also provide insulation from the environment for plants and animals. For example, they help keep aquatic birds and mammals dry because of their water-repelling nature. Lipids are also the building blocks of many hormones and are an important constituent of cellular membranes. Lipids include fats, oils, waxes, phospholipids, and steroids.
Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. They are all polymers of amino acids. The functions of proteins are very diverse because there are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order. Proteins can function as enzymes, hormones, contractile fibers, cytoskeleton rods, and much more. Enzymes are vital to life because they act as catalyst in biochemical reactions (like digestion). Each enzyme is specific for the substrate (a reactant that binds to an enzyme) upon which it acts. Enzymes can function to break molecular bonds, to rearrange bonds, or to form new bonds.
Nucleic acids are very large molecules that are important to the continuity of life. They carry the genetic blueprint of a cell and thus the instructions for its functionality. The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in all organisms, ranging from single-celled bacteria to multicellular mammals. The other type of nucleic acid, RNA, is mostly involved in protein synthesis. The DNA molecules never leave the nucleus, but instead use an RNA intermediary to communicate with the rest of the cell. Other types of RNA are also involved in protein synthesis and its regulation. DNA and RNA are made up of small building blocks known as nucleotides. The nucleotides combine with each other to form a polynucleotide: DNA or RNA. Each nucleotide is made up of three components: a nitrogenous base, a pentose (five-carbon) sugar, and a phosphate. DNA has a beautiful double-helical structure (Figure \(6\)).
Attribution
• Concepts of Biology by OpenStax is licensed under CC BY 4.0. Modified from original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/02%3A_Matter_Energy__Life/2.01%3A_Matter.txt |
Virtually every task performed by living organisms requires energy. Nutrients and other molecules are imported into the cell to meet these energy demands. For example, energy is required for the synthesis and breakdown of molecules, as well as the transport of molecules into and out of cells. In addition, processes such as ingesting and breaking down food, exporting wastes and toxins, and movement of the cell all require energy.
Scientists use the term bioenergetics to describe the concept of energy flow through living systems, such as cells. Cellular processes such as the building and breaking down of complex molecules occur through step-wise chemical reactions. Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed. Together, all of the chemical reactions that take place inside cells, including those that consume or generate energy, are referred to as the cell’s metabolism.
From where, and in what form, does this energy come? How do living cells obtain energy, and how do they use it? This section will discuss different forms of energy and the physical laws that govern energy transfer.
Energy
Thermodynamics refers to the study of energy and energy transfer involving physical matter. The matter relevant to a particular case of energy transfer is called a system, and everything outside of that matter is called the surroundings. For instance, when heating a pot of water on the stove, the system includes the stove, the pot, and the water. Energy is transferred within the system (between the stove, pot, and water). There are two types of systems: open and closed. In an open system, energy can be exchanged with its surroundings. The stovetop system is open because heat can be lost to the air. A closed system cannot exchange energy with its surroundings.
Biological organisms are open systems. Energy is exchanged between them and their surroundings as they use energy from the sun to perform photosynthesis or consume energy-storing molecules and release energy to the environment by doing work and releasing heat. Like all things in the physical world, energy is subject to physical laws. The laws of thermodynamics govern the transfer of energy in and among all systems in the universe. In general, energy is defined as the ability to do work, or to create some kind of change. Energy exists in different forms: electrical energy, light energy, mechanical energy, and heat energy are all different types of energy. To appreciate the way energy flows into and out of biological systems, it is important to understand two of the physical laws that govern energy.
The first law of thermodynamics states that the total amount of energy in the universe is constant and conserved. In other words, there has always been, and always will be, exactly the same amount of energy in the universe. Energy exists in many different forms. According to the first law of thermodynamics, energy may be transferred from place to place or transformed into different forms, but it cannot be created or destroyed. The transfers and transformations of energy take place around us all the time. Light bulbs transform electrical energy into light and heat energy. Gas stoves transform chemical energy from natural gas into heat energy. Plants perform one of the most biologically useful energy transformations on earth: that of converting the energy of sunlight to chemical energy stored within organic molecules (Figure \(2\) below).
The challenge for all living organisms is to obtain energy from their surroundings in forms that are usable to perform cellular work. Cells have evolved to meet this challenge. Chemical energy stored within organic molecules such as sugars and fats is transferred and transformed through a series of cellular chemical reactions into energy within molecules of ATP (adenosine triphosphate). Energy in ATP molecules is easily accessible to do work. Examples of the types of work that cells need to do include building complex molecules, transporting materials, powering the motion of cilia or flagella, and contracting muscles to create movement.
A living cell’s primary tasks of obtaining, transforming, and using energy to do work may seem simple. However, the second law of thermodynamics explains why these tasks are harder than they appear. All energy transfers and transformations are never completely efficient. In every energy transfer, some amount of energy is lost in a form that is unusable. In most cases, this form is heat energy.
Thermodynamically, heat energy is defined as the energy transferred from one system to another that is not work. For example, when a light bulb is turned on, some of the energy being converted from electrical energy into light energy is lost as heat energy. Likewise, some energy is lost as heat energy during cellular metabolic reactions.
An important concept in physical systems is that of order and disorder. The more energy that is lost by a system to its surroundings, the less ordered and more random the system is. Scientists refer to the measure of randomness or disorder within a system as entropy. High entropy means high disorder and low energy. Molecules and chemical reactions have varying entropy as well. For example, entropy increases as molecules at a high concentration in one place diffuse and spread out. The second law of thermodynamics says that energy will always be lost as heat in energy transfers or transformations. Living things are highly ordered, requiring constant energy input to be maintained in a state of low entropy.
Potential and Kinetic Energy
When an object is in motion, there is energy associated with that object. Think of a wrecking ball. Even a slow-moving wrecking ball can do a great deal of damage to other objects. Energy associated with objects in motion is called kinetic energy. A speeding bullet, a walking person, and the rapid movement of molecules in the air all have kinetic energy. Now what if that same motionless wrecking ball is lifted two stories above ground with a crane? If the suspended wrecking ball is not moving, is there energy associated with it? The answer is yes. The energy that was required to lift the wrecking ball did not disappear, but is now stored in the wrecking ball by virtue of its position and the force of gravity acting on it. This type of energy is called potential energy (Figure \(3\) below). If the ball were to fall, the potential energy would be transformed into kinetic energy until all of the potential energy was exhausted when the ball rested on the ground. Wrecking balls also swing like a pendulum; through the swing, there is a constant change of potential energy (highest at the top of the swing) to kinetic energy (highest at the bottom of the swing). Other examples of potential energy include the energy of water held behind a dam or a person about to skydive out of an airplane.
Potential energy is not only associated with the location of matter, but also with the structure of matter. Even a spring on the ground has potential energy if it is compressed; so does a rubber band that is pulled taut. On a molecular level, the bonds that hold the atoms of molecules together exist in a particular structure that has potential energy. The fact that energy can be released by the breakdown of certain chemical bonds implies that those bonds have potential energy. In fact, there is potential energy stored within the bonds of all the food molecules we eat, which is harnessed for use. The type of potential energy that exists within chemical bonds, and is released when those bonds are broken, is called chemical energy. Chemical energy is responsible for providing living cells with energy from food. The release of energy occurs when the molecular bonds within food molecules are broken. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/02%3A_Matter_Energy__Life/2.02%3A_Energy.txt |
Levels of Biological Organization
Living things are highly organized and structured, following a hierarchy of scale from small to large (Figure \(1\)). The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms combine to form molecules, which are chemical structures consisting of at least two atoms held together by a chemical bond. In plants, animals, and many other types of organisms, molecules come together in specific ways to create structures called organelles. Organelles are small structures that exist within cells and perform specialized functions. As discussed in more detail below, all living things are made of one or more cells.
In most multicellular organisms, cells combine to make tissues, which are groups of similar cells carrying out the same function. Organs are collections of tissues grouped together based on a common function. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. For example vertebrate animals have many organ systems, such as the circulatory system that transports blood throughout the body and to and from the lungs; it includes organs such as the heart and blood vessels. Organisms are individual living entities. For example, each tree in a forest is an organism.
All the individuals of a species living within a specific area are collectively called a population. A community is the set of different populations inhabiting a common area. For instance, all of the trees, flowers, insects, and other populations in a forest form the forest’s community. The forest itself is an ecosystem. An ecosystem consists of all the living things in a particular area together with the abiotic, or non-living, parts of that environment such as nitrogen in the soil or rainwater. At the highest level of organization, the biosphere is the collection of all ecosystems, and it represents the zones of life on Earth. It includes land, water, and portions of the atmosphere.
Cell Theory
Close your eyes and picture a brick wall. What is the basic building block of that wall? It is a single brick, of course. Like a brick wall, your body is composed of basic building blocks and the building blocks of your body are cells. Your body has many kinds of cells, each specialized for a specific purpose. Just as a home is made from a variety of building materials, the human body is constructed from many cell types. For example, bone cells help to support and protect the body. Cells of the immune system fight invading bacteria. And red blood cells carry oxygen throughout the body. Each of these cell types plays a vital role during the growth, development, and day-to-day maintenance of the body. In spite of their enormous variety, however, all cells share certain fundamental characteristics.
The microscopes we use today are far more complex than those used in the 1600s by Antony van Leeuwenhoek, a Dutch shopkeeper who had great skill in crafting lenses. Despite the limitations of his now-ancient lenses, van Leeuwenhoek observed the movements of single-celled organism and sperm, which he collectively termed “animalcules.” In a 1665 publication called Micrographia, experimental scientist Robert Hooke coined the term “cell” (from the Latin cella, meaning “small room”) for the box-like structures he observed when viewing cork tissue through a lens. In the 1670s, van Leeuwenhoek discovered bacteria and protozoa. Later advances in lenses and microscope construction enabled other scientists to see different components inside cells.
By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory, which states that all living things are composed of one or more cells, that the cell is the basic unit of life, and that all new cells arise from existing cells. These principles still stand today. There are many types of cells, and all are grouped into one of two broad categories: prokaryotic and eukaryotic. Animal, plant, fungal, and protist cells are classified as eukaryotic, whereas bacteria and archaea cells are classified as prokaryotic.
All cells share four common components: 1) a plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment; 2) cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found; 3) DNA, the genetic material of the cell; and 4) ribosomes, particles that synthesize proteins. However, prokaryotes differ from eukaryotic cells in several ways.
Components of Prokaryotic Cells
A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. We will shortly come to see that this is significantly different in eukaryotes. Prokaryotic DNA is found in the central part of the cell: a darkened region called the nucleoid (Figure \(1\)).
Unlike Archaea and eukaryotes, bacteria have a cell wall made of peptidoglycan (molecules comprised of sugars and amino acids) and many have a polysaccharide capsule. The cell wall acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration. The capsule enables the cell to attach to surfaces in its environment. Some prokaryotes have flagella, pili, or fimbriae. Flagella are used for locomotion. Pili are used to exchange genetic material during a type of reproduction called conjugation. Fimbriae are protein appendages used by bacteria to attach to other cells.
Eukaryotic Cells
A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments called organelles. There are many different types of organelles, each with a highly specialized function (see Figure \(3\)). The word eukaryotic means “true kernel” or “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.
Cell Size
At 0.1–5.0 µm in diameter, most prokaryotic cells are significantly smaller than eukaryotic cells, which have diameters ranging from 10–100 µm (Figure \(3\)). The small size of prokaryotes allows ions and organic molecules that enter them to quickly spread to other parts of the cell. Similarly, any wastes produced within a prokaryotic cell can quickly move out. However, larger eukaryotic cells have evolved different structural adaptations to enhance cellular transport. Indeed, the large size of these cells would not be possible without these adaptations. In general, cell size is limited because volume increases much more quickly than does cell surface area. As a cell becomes larger, it becomes more and more difficult for the cell to acquire sufficient materials to support the processes inside the cell, because the relative size of the surface area through which materials must be transported declines.
Animal Cells versus Plant Cells
Despite their fundamental similarities, there are some striking differences between animal and plant cells (Figure \(3\)). Animal cells have centrioles, centrosomes, and lysosomes, whereas plant cells do not. Plant cells have a rigid cell wall that is external to the plasma membrane, chloroplasts, plasmodesmata, and plastids used for storage, and a large central vacuole, whereas animal cells do not.
Chloroplasts
From an ecological perspective, chloroplasts are a particularly important type of organelle because they perform photosynthesis. Photosynthesis forms the foundation of food chains in most ecosystems. Chloroplasts are only found in eukaryotic cells such as plants and algae. During photosynthesis, carbon dioxide, water, and light energy are used to make glucose and molecular oxygen. One major difference between algae/plants and animals is that plants/algae are able to make their own food, like glucose, whereas animals must obtain food by consuming other organisms.
Chloroplasts have outer and inner membranes, but within the space enclosed by a chloroplast’s inner membrane is a set of interconnected and stacked, fluid-filled membrane sacs called thylakoids (Figure \(4\) below). Each stack of thylakoids is called a granum (plural = grana). The fluid enclosed by the inner membrane and surrounding the grana is called the stroma. Each structure within the chloroplast has an important function, which is enabled by its particular shape. A common theme in biology is that form and function are interrelated. For example, the membrane-rich stacks of the thylakoids provide ample surface area to embed the proteins and pigments that are vital to photosynthesis. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/02%3A_Matter_Energy__Life/2.03%3A_A_Cell_is_the_Smallest_Unit_of_Life.txt |
Cells run on the chemical energy found mainly in carbohydrate molecules, and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. The energy stored in the bonds to hold these molecules together is released when an organism breaks down food. Cells then use this energy to perform work, such as movement. The energy that is harnessed from photosynthesis enters the ecosystems of our planet continuously and is transferred from one organism to another. Therefore, directly or indirectly, the process of photosynthesis provides most of the energy required by living things on Earth. Photosynthesis also results in the release of oxygen into the atmosphere. In short, to eat and breathe humans depend almost entirely on the organisms that carry out photosynthesis.
Solar Dependence and Food Production
Some organisms can carry out photosynthesis, whereas others cannot. An autotroph is an organism that can produce its own food. The Greek roots of the word autotroph mean “self” (auto) “feeder” (troph). Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae (Figure \(1\)). Oceanic algae contribute enormous quantities of food and oxygen to global food chains. More specifically, plants are photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight.
Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. The Greek roots of the word heterotroph mean “other” (hetero) “feeder” (troph), meaning that their food comes from other organisms. Even if the organism being consumed is another animal, it traces its stored energy back to autotrophs and the process of photosynthesis. Humans are heterotrophs, as are all animals and fungi. Heterotrophs depend on autotrophs, either directly or indirectly. For example, a deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer (Figure \(2\)). Using this reasoning, all food eaten by humans can be traced back to autotrophs that carry out photosynthesis.
Summary of Photosynthesis
Photosynthesis requires sunlight, carbon dioxide, and water as starting reactants (Figure \(3\)). After the process is complete, photosynthesis releases oxygen and produces carbohydrate molecules, most commonly glucose. These sugar molecules contain the energy that living things need to survive. The complex reactions of photosynthesis can be summarized by the chemical equation shown in Figure \(4\) below.
Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. In plants, photosynthesis takes place primarily in the chloroplasts of leaves. Chloroplasts have a double (inner and outer) membrane. Within the chloroplast is a third membrane that forms stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane are molecules of chlorophyll, a pigment (a molecule that absorbs light) through which the entire process of photosynthesis begins.
The Two Parts of Photosynthesis
Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the aid of water. The light-dependent reactions release oxygen as a byproduct from the splitting of water. In the Calvin cycle, the chemical energy derived from the light-dependent reactions drives both the capture of carbon in carbon dioxide molecules and the subsequent assembly of sugar molecules.
The Global Significance of Photosynthesis
The process of photosynthesis is crucially important to the biosphere for the following reasons:
1. It creates O2, which is important for two reasons. The molecular oxygen in Earth’s atmosphere was created by photosynthetic organisms; without photosynthesis there would be no O2 to support cellular respiration (see chapter 3.2) needed by complex, multicellular life. Photosynthetic bacteria were likely the first organisms to perform photosynthesis, dating back 2-3 billion years ago. Thanks to their activity, and a diversity of present-day photosynthesizing organisms, Earth’s atmosphere is currently about 21% O2. Also, this O2 is vital for the creation of the ozone layer (see chapter 10.2), which protects life from harmful ultraviolet radiation emitted by the sun. Ozone (O3) is created from the breakdown and reassembly of O2.
2. It provides energy for nearly all ecosystems. By transforming light energy into chemical energy, photosynthesis provides the energy used by organisms, whether those organisms are plants, grasshoppers, wolves, or fungi. The only exceptions are found in very rare and isolated ecosystems, such as near deep sea hydrothermal vents where organisms get energy that originally came from minerals, not the sun.
3. It provides the carbon needed for organic molecules. Organisms are primarily made of two things: water and organic molecules, the latter being carbon based. Through the process of carbon fixation, photosynthesis takes carbon from CO2 and converts it into sugars (which are organic). Carbon in these sugars can be re-purposed to create the other types of organic molecules that organisms need, such as lipids, proteins, and nucleic acids. For example, the carbon used to make your DNA was once CO2 used by photosynthetic organisms (see section 3.1 for more information on food webs). | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/02%3A_Matter_Energy__Life/2.04%3A_Energy_Enters_Ecosystems_Through_Photosynthesis.txt |
Summary
Matter is anything that occupies space and has mass. It is made up of atoms of different elements. Elements that occur naturally have unique qualities that allow them to combine in various ways to create compounds or molecules. Atoms, which consist of protons, neutrons, and electrons, are the smallest units of an element that retain all of the properties of that element. Electrons can be donated or shared between atoms to create bonds, including ionic, covalent, and hydrogen bonds. The pH of a solution is a measure of the concentration of hydrogen ions in the solution. Living things are carbon-based because carbon plays such a prominent role in the chemistry of living things.
A cell is the smallest unit of life. Most cells are so small that they cannot be viewed with the naked eye. The unified cell theory states that all organisms are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. Directly or indirectly, the process of photosynthesis provides most of the energy required by living things on earth. Photosynthesis also results in the release of oxygen into the atmosphere. In short, to eat and breathe, humans depend almost entirely on the organisms that carry out photosynthesis.
Review Questions
1. You analyze a sample of carbon and determine that 6% of the carbon atoms in your sample have a mass number (atomic mass) greater than 12, (12 is the normal atomic mass of carbon). Based on these results, which of the following can you reasonably conclude?
1. 6% of the carbon sample is a different element
2. 6% of the sample is comprised of carbon isotopes
3. 6% of the sample is comprised of carbon ions
4. 94% of the sample is comprised of carbon radioisotopes
5. 94% of the sample contains covalent bonds
2. An atom that has an electrical charge due to having a number of electrons unequal to the number of protons is considered a(n)…
1. Isotope
2. Ion
3. Element
4. Molecule
5. Acid
3. The atomic number for the element fluorine is 9 and its mass number is 19. How many neutrons does a normal atom of fluorine have?
1. 0
2. 9
3. 10
4. 19
5. Impossible to determine with the information given
4. Which one of the following is not one of the four major classes of organic compounds?
1. Nucleic acids
2. Water
3. Proteins
4. Carbohydrates
5. Lipids
5. You are working as an astrobiologist for NASA and are asked to analyze the first ever samples returned to Earth from Mars. How would you recognize if organic molecules were present in the samples?
1. Test for isotopes of carbon
2. Look for the presence of hydrogen bonds
3. Search for chemicals with carbon to hydrogen bonds
4. Analyze the percentage of molecules with covalent bonds
5. Measure the pH of the samples
6. A micro-organism is viewed through a microscope and is determined to be made of a single cell that lacks organelles. From this information, which of the following can you conclude?
1. The organism belongs to Domain Bacteria
2. The organism belongs to Domain Eukarya
3. The organism belongs to Domain Archaea
4. The cell is prokaryotic
5. The cell is eukaryotic
7. Which one of the following terms describes the complete set of chemical reactions that occur within cells?
1. Metabolism
2. Cellular respiration
3. Calvin Cycle
4. Bioenergetics
5. Thermodynamics
8. Which one of the following is most strongly associated with kinetic energy?
1. Atomic force
2. Static position in a gravitational field
3. Chemical energy
4. Movement
5. Covalent bonds
9. Which one of the following would help remove more CO2 from the atmosphere?
1. Planting more trees
2. Burning less fossil fuels
3. Increase the number of heterotrophs
4. Decrease the number of autotrophs
5. All of the above.
10. Water is essential to life because it has many special properties. Which one of the following is a special property of water?
1. It is able to covalently bond to other water molecules
2. It is good at dissolving other substances
3. It easily heats up.
4. It easily cools.
5. It has a low surface tension
See Appendix for answers
1. What is matter?
2. What are elements?
3. Describe the interrelationship between protons, neutrons, and electrons, and the ways in which electrons can be donated or shared between atoms.
4. What is energy? Describe the two major types of energy.
5. Why is it often said that life is “carbon-based”?
6. Describe the roles of cells in organisms.
7. What is the cell theory?
8. Name examples of prokaryotic and eukaryotic organisms.
9. How are photosynthesis and cellular respiration complementary processes?
10. Why are carnivores, such as lions, dependent on photosynthesis to survive? | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/02%3A_Matter_Energy__Life/2.0S%3A_2.S%3A__Matter_Energy__Life_%28Summary%29.txt |
Learning Outcomes
• Describe the basic types of ecosystems on Earth
• Differentiate between food chains and food webs and recognize the importance of each
• Describe how organisms acquire energy in a food web and in associated food chains
• Discuss the biogeochemical cycles of water, carbon, nitrogen, phosphorus, and sulfur
• Explain how human activities have impacted these cycles
• 3.1: Energy Flow through Ecosystems
• 3.2: Biogeochemical Cycles
• 3.3: Terrestrial Biomes
There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. Biomes are large-scale environments that are distinguished by characteristic temperature ranges and amounts of precipitation. These two variables affect the types of vegetation and animal life that can exist in those areas.
• 3.4: Aquatic Biomes
Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water still absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach.
• 3.5: Chapter Resources
Thumbnail image - The (a) Karner blue butterfly and (b) wild lupine live in oak-pine barren habitats in North America. This habitat is characterized by natural disturbance in the form of fire and nutrient-poor soils that are low in nitrogen—important factors in the distribution of the plants that live in this habitat. Researchers interested in ecosystem ecology study the importance of limited resources in this ecosystem and the movement of resources (such as nutrients) through the biotic and abiotic portions of the ecosystem. Researchers also examine how organisms have adapted to their ecosystem. (credit: USFWS)
03: Ecosystems and the Biosphere
An ecosystem is a community of organisms and their abiotic (non-living) environment. Ecosystems can be small, such as the tide pools found near the rocky shores of many oceans, or large, such as those found in the tropical rainforest of the Amazon in Brazil (Figure \(1\)).
There are three broad categories of ecosystems based on their general environment: freshwater, marine, and terrestrial. Within these three categories are individual ecosystem types based on the environmental habitat and organisms present.
Freshwater ecosystems are the least common, occurring on only 1.8 percent of Earth’s surface. These systems comprise lakes, rivers, streams, and springs; they are quite diverse and support a variety of animals, plants, fungi, protists and prokaryotes.
Marine ecosystems are the most common, comprising 75 percent of Earth’s surface and consisting of three basic types: shallow ocean, deep ocean water, and deep ocean bottom. Shallow ocean ecosystems include extremely biodiverse coral reef ecosystems. Small photosynthetic organisms suspended in ocean waters, collectively known as phytoplankton, perform 40 percent of all photosynthesis on Earth. Deep ocean bottom ecosystems contain a wide variety of marine organisms. These ecosystems are so deep that light is unable to reach them.
Terrestrial ecosystems, also known for their diversity, are grouped into large categories called biomes. A biome is a large-scale community of organisms, primarily defined on land by the dominant plant types that exist in geographic regions of the planet with similar climatic conditions. Examples of biomes include tropical rainforests, savannas, deserts, grasslands, temperate forests, and tundras. Grouping these ecosystems into just a few biome categories obscures the great diversity of the individual ecosystems within them. For example, the saguaro cacti (Carnegiea gigantean) and other plant life in the Sonoran Desert, in the United States, are relatively diverse compared with the desolate rocky desert of Boa Vista, an island off the coast of Western Africa (Figure \(2\)).
Food Chains and Food Webs
A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. The levels in the food chain are producers, primary consumers, higher-level consumers, and finally decomposers. These levels are used to describe ecosystem structure and dynamics. There is a single path through a food chain. Each organism in a food chain occupies a specific trophic level (energy level), its position in the food chain or food web.
In many ecosystems, the base, or foundation, of the food chain consists of photosynthetic organisms (plants or phytoplankton), which are called producers. The organisms that consume the producers are herbivores called primary consumers. Secondary consumers are usually carnivores that eat the primary consumers. Tertiary consumers are carnivores that eat other carnivores. Higher-level consumers feed on the next lower trophic levels, and so on, up to the organisms at the top of the food chain. In the Lake Ontario food chain, shown in Figure \(3\), the Chinook salmon is the apex consumer at the top of this food chain.
One major factor that limits the number of steps in a food chain is energy. Energy is lost at each trophic level and between trophic levels as heat and in the transfer to decomposers (Figure \(4\) below). Thus, after a limited number of trophic energy transfers, the amount of energy remaining in the food chain may not be great enough to support viable populations at higher trophic levels.
There is a one problem when using food chains to describe most ecosystems. Even when all organisms are grouped into appropriate trophic levels, some of these organisms can feed at more than one trophic level. In addition, species feed on and are eaten by more than one species. In other words, the linear model of ecosystems, the food chain, is a hypothetical and overly simplistic representation of ecosystem structure. A holistic model—which includes all the interactions between different species and their complex interconnected relationships with each other and with the environment—is a more accurate and descriptive model for ecosystems. A food web is a concept that accounts for the multiple trophic (feeding) interactions between each species (Figure \(5\) below).
Two general types of food webs are often shown interacting within a single ecosystem. A grazing food web has plants or other photosynthetic organisms at its base, followed by herbivores and various carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter (dead organisms), including decomposers (which break down dead and decaying organisms) and detritivores(which consume organic detritus). These organisms are usually bacteria, fungi, and invertebrate animals that recycle organic material back into the biotic part of the ecosystem as they themselves are consumed by other organisms.
How Organisms Acquire Energy in a Food Web
All living things require energy in one form or another. At the cellular level, energy is used in most metabolic pathways (usually in the form of ATP), especially those responsible for building large molecules from smaller compounds. Living organisms would not be able to assemble complex organic molecules (proteins, lipids, nucleic acids, and carbohydrates) without a constant energy input.
Food-web diagrams illustrate how energy flows directionally through ecosystems. They can also indicate how efficiently organisms acquire energy, use it, and how much remains for use by other organisms of the food web. Energy is acquired by living things in two ways: autotrophs harness light or chemical energy and heterotrophs acquire energy through the consumption and digestion of other living or previously living organisms.
Photosynthetic and chemosynthetic organisms are autotrophs, which are organisms capable of synthesizing their own food (more specifically, capable of using inorganic carbon as a carbon source). Photosynthetic autotrophs (photoautotrophs) use sunlight as an energy source, and chemosynthetic autotrophs (chemoautotrophs) use inorganic molecules as an energy source. Autotrophs are critical for ecosystems because they occupy the trophic level containing producers. Without these organisms, energy would not be available to other living organisms, and life would not be possible.
Photoautotrophs, such as plants, algae, and photosynthetic bacteria, are the energy source for a majority of the world’s ecosystems. Photoautotrophs harness the Sun’s solar energy by converting it to chemical energy. The rate at which photosynthetic producers incorporate energy from the Sun is called gross primary productivity. However, not all of the energy incorporated by producers is available to the other organisms in the food web because producers must also grow and reproduce, which consumes energy. Net primary productivity is the energy that remains in the producers after accounting for these organisms’ metabolism and heat loss. The net productivity is then available to the primary consumers at the next trophic level.
Chemoautotrophs are primarily bacteria and archaea that are found in rare ecosystems where sunlight is not available, such as those associated with dark caves or hydrothermal vents at the bottom of the ocean (Figure \(6\)). Many chemoautotrophs in hydrothermal vents use hydrogen sulfide (H2S), which is released from the vents, as a source of chemical energy. This allows them to synthesize complex organic molecules, such as glucose, for their own energy and, in turn, supplies energy to the rest of the ecosystem.
One of the most important consequences of ecosystem dynamics in terms of human impact is biomagnification. Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each successive trophic level. These are substances that are lipid soluble and are stored in the fat reserves of each organism. Many substances have been shown to biomagnify, including classical studies with the pesticide dichlorodiphenyltrichloroethane (DDT), which were described in the 1960s bestseller Silent Spring by Rachel Carson. DDT was a commonly used pesticide before its dangers to apex consumers, such as the bald eagle, became known. DDT and other toxins are taken in by producers and passed on to successive levels of consumers at increasingly higher rates. As bald eagles feed on contaminated fish, their DDT levels rise. It was discovered that DDT caused the eggshells of birds to become fragile, which contributed to the bald eagle being listed as an endangered species under U.S. law. The use of DDT was banned in the United States in the 1970s.
Another substances that biomagnifies is polychlorinated biphenyl (PCB), which was used as coolant liquids in the United States until its use was banned in 1979. PCB was best studied in aquatic ecosystems where predatory fish species accumulated very high concentrations of the toxin that is otherwise exists at low concentrations in the environment. As illustrated in a study performed by the NOAA in the Saginaw Bay of Lake Huron of the North American Great Lakes (Figure \(7\) below), PCB concentrations increased from the producers of the ecosystem (phytoplankton) through the different trophic levels of fish species. The apex consumer, the walleye, has more than four times the amount of PCBs compared to phytoplankton. Also, research found that birds that eat these fish may have PCB levels that are at least ten times higher than those found in the lake fish.
Other concerns have been raised by the biomagnification of heavy metals, such as mercury and cadmium, in certain types of seafood. The United States Environmental Protection Agency recommends that pregnant women and young children should not consume any swordfish, shark, king mackerel, or tilefish because of their high mercury content. These individuals are advised to eat fish low in mercury: salmon, shrimp, pollock, and catfish. Biomagnification is a good example of how ecosystem dynamics can affect our everyday lives, even influencing the food we eat.
Suggested Supplementary Reading
Canales, M. et al. 2018. 6 Things that Make Like on Earth Possible [Infographic]. National Geographic. March. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/03%3A_Ecosystems_and_the_Biosphere/3.01%3A_Energy_Flow_through_Ecosystems.txt |
Energy flows directionally through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during energy transformation between trophic levels. Rather than flowing through an ecosystem, the matter that makes up organisms is conserved and recycled. The six most common elements associated with organic molecules—carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur—take a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath Earth’s surface. Geologic processes, such as weathering, erosion, water drainage, and the subduction of the continental plates, all play a role in the cycling of elements on Earth. Because geology and chemistry have major roles in the study of these processes, the recycling of inorganic matter between living organisms and their nonliving environment are called biogeochemical cycles.
The six aforementioned elements are used by organisms in a variety of ways. Hydrogen and oxygen are found in water and organic molecules, both of which are essential to life. Carbon is found in all organic molecules, whereas nitrogen is an important component of nucleic acids and proteins. Phosphorus is used to make nucleic acids and the phospholipids that comprise biological membranes. Lastly, sulfur is critical to the three-dimensional shape of proteins.
The cycling of these elements is interconnected. For example, the movement of water is critical for the leaching of sulfur and phosphorus into rivers, lakes, and oceans. Minerals cycle through the biosphere between the biotic and abiotic components and from one organism to another.
The Water Cycle
The hydrosphere is the area of Earth where water movement and storage occurs: as liquid water on the surface (rivers, lakes, oceans) and beneath the surface (groundwater) or ice, (polar ice caps and glaciers), and as water vapor in the atmosphere.The human body is about 60 percent water and human cells are more than 70 percent water. Of the stores of water on Earth, 97.5 percent is salt water (see Figure \(1\) below). Of the remaining water, more than 99 percent is groundwater or ice. Thus, less than one percent of freshwater is present in lakes and rivers. Many organisms are dependent on this small percentage, a lack of which can have negative effects on ecosystems. Humans, of course, have developed technologies to increase water availability, such as digging wells to harvest groundwater, storing rainwater, and using desalination to obtain drinkable water from the ocean. Although this pursuit of drinkable water has been ongoing throughout human history, the supply of fresh water continues to be a major issue in modern times.
The various processes that occur during the cycling of water are illustrated in Figure \(2\) below. The processes include the following:
• evaporation and sublimation
• condensation and precipitation
• subsurface water flow
• surface runoff and snowmelt
• streamflow
The water cycle is driven by the Sun’s energy as it warms the oceans and other surface waters. This leads to evaporation (liquid water to water vapor) of liquid surface water and sublimation (ice to water vapor) of frozen water, thus moving large amounts of water into the atmosphere as water vapor. Over time, this water vapor condenses into clouds as liquid or frozen droplets and eventually leads to precipitation (rain, snow, hail), which returns water to Earth’s surface. Rain reaching Earth’s surface may evaporate again, flow over the surface, or percolate into the ground. Most easily observed is surface runoff: the flow of freshwater over land either from rain or melting ice. Runoff can make its way through streams and lakes to the oceans.
In most natural terrestrial environments rain encounters vegetation before it reaches the soil surface. A significant percentage of water evaporates immediately from the surfaces of plants. What is left reaches the soil and begins to move down. Surface runoff will occur only if the soil becomes saturated with water in a heavy rainfall. Water in the soil can be taken up by plant roots. The plant will use some of this water for its own metabolism and some of that will find its way into animals that eat the plants, but much of it will be lost back to the atmosphere through a process known as transpiration: water enters the vascular system of plants through the roots and evaporates, or transpires, through the stomata (small microscope openings) of the leaves. Ecologists combine transpiration and evaporation into a single term that describes water returned to the atmosphere: evapotranspiration. Water in the soil that is not taken up by a plant and that does not evaporate is able to percolate into the subsoil and bedrock where it forms groundwater.
Groundwater is a significant, subsurface reservoir of fresh water. It exists in the pores between particles in dirt, sand, and gravel or in the fissures in rocks. Groundwater can flow slowly through these pores and fissures and eventually finds its way to a stream or lake where it becomes part of the surface water again. Many streams flow not because they are replenished from rainwater directly but because they receive a constant inflow from the groundwater below. Some groundwater is found very deep in the bedrock and can persist there for millennia. Most groundwater reservoirs, or aquifers, are the source of drinking or irrigation water drawn up through wells. In many cases these aquifers are being depleted faster than they are being replenished by water percolating down from above.
Rain and surface runoff are major ways in which minerals, including phosphorus and sulfur, are cycled from land to water. The environmental effects of runoff will be discussed later as these cycles are described.
The Carbon Cycle
Carbon is the second most abundant element in organisms, by mass. Carbon is present in all organic molecules (and some molecules that are not organic such as CO2), and its role in the structure of biomolecules is of primary importance. Carbon compounds contain energy, and many of these compounds from dead plants and algae have fossilized over millions of years and are known as fossil fuels. Since the 1800s, the use of fossil fuels has accelerated. Since the beginning of the Industrial Revolution the demand for Earth’s limited fossil fuel supplies has risen, causing the amount of carbon dioxide in our atmosphere to drastically increase. This increase in carbon dioxide is associated with climate change and is a major environmental concern worldwide.
The carbon cycle is most easily studied as two interconnected subcycles: one dealing with rapid carbon exchange among living organisms and the other dealing with the long-term cycling of carbon through geologic processes. The entire carbon cycle is shown in Figure \(3\) below.
The Biological Carbon Cycle
Organisms are connected in many ways, even among different ecosystems. A good example of this connection is the exchange of carbon between heterotrophs and autotrophs by way of atmospheric carbon dioxide. Carbon dioxide (CO2) is the basic building block that autotrophs use to build high-energy compounds such as glucose. The energy harnessed from the Sun is used by these organisms to form the covalent bonds that link carbon atoms together. These chemical bonds store this energy for later use in the process of respiration. Most terrestrial autotrophs obtain their carbon dioxide directly from the atmosphere, while marine autotrophs acquire it in the dissolved form (bicarbonate, HCO3).
Carbon is passed from producers to higher trophic levels through consumption. For example, when a cow (primary consumer) eats grass (producer), it obtains some of the organic molecules originally made by the plant’s photosynthesis. Those organic compounds can then be passed to higher trophic levels, such as humans, when we eat the cow. At each level, however, organisms are performing respiration, a process in which organic molecules are broken down to release energy. As these organic molecules are broken down, carbon is removed from food molecules to form CO2, a gas that enters the atmosphere. Thus, CO2 is a byproduct of respiration. Recall that CO2 is consumed by producers during photosynthesis to make organic molecules. As these molecules are broken down during respiration, the carbon once again enters the atmosphere as CO2. Carbon exchange like this potentially connects all organisms on Earth. Think about this: the carbon in your DNA was once part of plant; millions of years ago perhaps it was part of dinosaur.
The Biogeochemical Carbon Cycle
The movement of carbon through land, water, and air is complex, and, in many cases, it occurs much more slowly than the movement between organisms. Carbon is stored for long periods in what are known as carbon reservoirs, which include the atmosphere, bodies of liquid water (mostly oceans), ocean sediment, soil, rocks (including fossil fuels), and Earth’s interior.
As stated, the atmosphere is a major reservoir of carbon in the form of carbon dioxide that is essential to the process of photosynthesis. The level of carbon dioxide in the atmosphere is greatly influenced by the reservoir of carbon in the oceans. The exchange of carbon between the atmosphere and water reservoirs influences how much carbon is found in each. Carbon dioxide (CO2) from the atmosphere dissolves in water and reacts with water molecules to form ionic compounds. Some of these ions combine with calcium ions in the seawater to form calcium carbonate (CaCO3), a major component of the shells of marine organisms. These organisms eventually die and their shells form sediments on the ocean floor. Over geologic time, the calcium carbonate forms limestone, which comprises the largest carbon reservoir on Earth.
On land, carbon is stored in soil as organic carbon as a result of the decomposition of organisms or from weathering of terrestrial rock and minerals (the world’s soils hold significantly more carbon than the atmosphere, for comparison). Deeper underground are fossil fuels, the anaerobically decomposed remains of plants and algae that lived millions of years ago. Fossil fuels are considered a non-renewable resource because their use far exceeds their rate of formation. A non-renewable resource is either regenerated very slowly or not at all. Another way for carbon to enter the atmosphere is from land (including land beneath the surface of the ocean) by the eruption of volcanoes and other geothermal systems. Carbon sediments from the ocean floor are taken deep within Earth by the process of subduction: the movement of one tectonic plate beneath another. Carbon is released as carbon dioxide when a volcano erupts or from volcanic hydrothermal vents.
The Nitrogen Cycle
Getting nitrogen into living organisms is difficult. Plants and phytoplankton are not equipped to incorporate nitrogen from the atmosphere (where it exists as tightly bonded, triple covalent N2) even though this molecule comprises approximately 78 percent of the atmosphere. Nitrogen enters the living world through free-living and symbiotic bacteria, which incorporate nitrogen into their organic molecules through specialized biochemical processes. Certain species of bacteria are able to perform nitrogen fixation, the process of converting nitrogen gas into ammonia (NH3), which spontaneously becomes ammonium (NH4+). Ammonium is converted by bacteria into nitrites (NO2) and then nitrates (NO3). At this point, the nitrogen-containing molecules are used by plants and other producers to make organic molecules such as DNA and proteins. This nitrogen is now available to consumers.
Organic nitrogen is especially important to the study of ecosystem dynamics because many ecosystem processes, such as primary production, are limited by the available supply of nitrogen. As shown in Figure \(4\) below, the nitrogen that enters living systems is eventually converted from organic nitrogen back into nitrogen gas by bacteria (Figure \(4\)). The process of denitrification is when bacteria convert the nitrates into nitrogen gas, thus allowing it to re-enter the atmosphere.
Human activity can alter the nitrogen cycle by two primary means: the combustion of fossil fuels, which releases different nitrogen oxides, and by the use of artificial fertilizers (which contain nitrogen and phosphorus compounds) in agriculture, which are then washed into lakes, streams, and rivers by surface runoff. Atmospheric nitrogen (other than N2) is associated with several effects on Earth’s ecosystems including the production of acid rain (as nitric acid, HNO3) and greenhouse gas effects (as nitrous oxide, N2O), potentially causing climate change. A major effect from fertilizer runoff is saltwater and freshwater eutrophication, a process whereby nutrient runoff causes the overgrowth of algae, the depletion of oxygen, and death of aquatic fauna.
In marine ecosystems, nitrogen compounds created by bacteria, or through decomposition, collects in ocean floor sediments. It can then be moved to land in geologic time by uplift of Earth’s crust and thereby incorporated into terrestrial rock. Although the movement of nitrogen from rock directly into living systems has been traditionally seen as insignificant compared with nitrogen fixed from the atmosphere, a recent study showed that this process may indeed be significant and should be included in any study of the global nitrogen cycle.
The Phosphorus Cycle
Phosphorus is an essential nutrient for living processes. It is a major component of nucleic acids and phospholipids, and, as calcium phosphate, it makes up the supportive components of our bones. Phosphorus is often the limiting nutrient (necessary for growth) in aquatic, particularly freshwater, ecosystems.
Phosphorus occurs in nature as the phosphate ion (PO43-). In addition to phosphate runoff as a result of human activity, natural surface runoff occurs when it is leached from phosphate-containing rock by weathering, thus sending phosphates into rivers, lakes, and the ocean. This rock has its origins in the ocean. Phosphate-containing ocean sediments form primarily from the bodies of ocean organisms and from their excretions. However, volcanic ash, aerosols, and mineral dust may also be significant phosphate sources. This sediment then is moved to land over geologic time by the uplifting of Earth’s surface. (Figure below)
Phosphorus is also reciprocally exchanged between phosphate dissolved in the ocean and marine organisms. The movement of phosphate from the ocean to the land and through the soil is extremely slow, with the average phosphate ion having an oceanic residence time between 20,000 and 100,000 years.
Excess phosphorus and nitrogen that enter these ecosystems from fertilizer runoff and from sewage cause excessive growth of algae. The subsequent death and decay of these organisms depletes dissolved oxygen, which leads to the death of aquatic organisms such as shellfish and fish. This process is responsible for dead zones in lakes and at the mouths of many major rivers and for massive fish kills, which often occur during the summer months (see Figure \(6\) below).
A dead zone is an area in lakes and oceans near the mouths of rivers where large areas are periodically depleted of their normal flora and fauna. These zones are caused by eutrophication coupled with other factors including oil spills, dumping toxic chemicals, and other human activities. The number of dead zones has increased for several years, and more than 400 of these zones were present as of 2008. One of the worst dead zones is off the coast of the United States in the Gulf of Mexico: fertilizer runoff from the Mississippi River basin created a dead zone of over 8,463 square miles. Phosphate and nitrate runoff from fertilizers also negatively affect several lake and bay ecosystems including the Chesapeake Bay in the eastern United States.
The Sulfur Cycle
Sulfur is an essential element for the molecules of living things. As part of the amino acid cysteine, it is involved in the formation of proteins. As shown in Figure \(7\) below, sulfur cycles between the oceans, land, and atmosphere. Atmospheric sulfur is found in the form of sulfur dioxide (SO2), which enters the atmosphere in three ways: first, from the decomposition of organic molecules; second, from volcanic activity and geothermal vents; and, third, from the burning of fossil fuels by humans.
On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents. Atmospheric sulfur is found in the form of sulfur dioxide (SO2), and as rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid (H2SO4). Sulfur can also fall directly from the atmosphere in a process called fallout. Also, as sulfur-containing rocks weather, sulfur is released into the soil. These rocks originate from ocean sediments that are moved to land by the geologic uplifting of ocean sediments. Terrestrial ecosystems can then make use of these soil sulfates (SO42-), which enter the food web by being taken up by plant roots. When these plants decompose and die, sulfur is released back into the atmosphere as hydrogen sulfide (H2S) gas.
Sulfur enters the ocean in runoff from land, from atmospheric fallout, and from underwater geothermal vents. Some ecosystems rely on chemoautotrophs using sulfur as a biological energy source. This sulfur then supports marine ecosystems in the form of sulfates.
Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases larger amounts of hydrogen sulfide gas into the atmosphere. As rain falls through this gas, it creates the phenomenon known as acid rain, which damages the natural environment by lowering the pH of lakes, thus killing many of the resident plants and animals. Acid rain is corrosive rain caused by rainwater falling to the ground through sulfur dioxide gas, turning it into weak sulfuric acid, which causes damage to aquatic ecosystems. Acid rain also affects the man-made environment through the chemical degradation of buildings. For example, many marble monuments, such as the Lincoln Memorial in Washington, DC, have suffered significant damage from acid rain over the years. These examples show the wide-ranging effects of human activities on our environment and the challenges that remain for our future.
Suggested Supplementary Reading
Bruckner, M. 2018. The Gulf of Mexico Dead Zone. [Website] <https://serc.carleton.edu/microbelif...one/index.html>
Contributors and Attributions
• Biogeochemical Cycles by OpenStax is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/03%3A_Ecosystems_and_the_Biosphere/3.02%3A_Biogeochemical_Cycles.txt |
Figure \(1\). Each of the world’s eight major biomes is distinguished by characteristic temperatures and amount of precipitation. Polar ice caps and mountains are also shown.
There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. Biomes are large-scale environments that are distinguished by characteristic temperature ranges and amounts of precipitation. These two variables affect the types of vegetation and animal life that can exist in those areas. Because each biome is defined by climate, the same biome can occur in geographically distinct areas with similar climates (Figures 1 and 2).
Tropical rainforests are found in equatorial regions (Figure \(1\)) are the most biodiverse terrestrial biome. This biodiversity is under extraordinary threat primarily through logging and deforestation for agriculture. Tropical rainforests have also been described as nature’s pharmacy because of the potential for new drugs that is largely hidden in the chemicals produced by the huge diversity of plants, animals, and other organisms. The vegetation is characterized by plants with spreading roots and broad leaves that fall off throughout the year, unlike the trees of deciduous forests that lose their leaves in one season.
The temperature and sunlight profiles of tropical rainforests are stable in comparison to other terrestrial biomes, with average temperatures ranging from 20oC to 34oC (68oF to 93oF). Month-to-month temperatures are relatively constant in tropical rainforests, in contrast to forests farther from the equator. This lack of temperature seasonality leads to year-round plant growth rather than just seasonal growth. In contrast to other ecosystems, a consistent daily amount of sunlight (11–12 hours per day year-round) provides more solar radiation and therefore more opportunity for primary productivity.
The annual rainfall in tropical rainforests ranges from 125 to 660 cm (50–200 in) with considerable seasonal variation. Tropical rainforests have wet months in which there can be more than 30 cm (11–12 in) of precipitation, as well as dry months in which there are fewer than 10 cm (3.5 in) of rainfall. However, the driest month of a tropical rainforest can still exceed the annual rainfall of some other biomes, such as deserts.Tropical rainforests have high net primary productivity because the annual temperatures and precipitation values support rapid plant growth. However, the high amounts of rainfall leaches nutrients from the soils of these forests.
Tropical rainforests are characterized by vertical layering of vegetation and the formation of distinct habitats for animals within each layer. On the forest floor is a sparse layer of plants and decaying plant matter. Above that is an understory of short, shrubby foliage. A layer of trees rises above this understory and is topped by a closed upper canopy—the uppermost overhead layer of branches and leaves. Some additional trees emerge through this closed upper canopy. These layers provide diverse and complex habitats for the variety of plants, animals, and other organisms. Many species of animals use the variety of plants and the complex structure of the tropical wet forests for food and shelter. Some organisms live several meters above ground, rarely descending to the forest floor.
Figure \(4\). A MinuteEarth video about how trees create rainfall, and vice versa.
Subtropical deserts exist between 15o and 30o north and south latitude and are centered on the Tropic of Cancer and the Tropic of Capricorn (Figure \(6\) below). Deserts are frequently located on the downwind or lee side of mountain ranges, which create a rain shadow after prevailing winds drop their water content on the mountains. This is typical of the North American deserts, such as the Mohave and Sonoran deserts. Deserts in other regions, such as the Sahara Desert in northern Africa or the Namib Desert in southwestern Africa are dry because of the high-pressure, dry air descending at those latitudes. Subtropical deserts are very dry; evaporation typically exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60oC (140oF) and nighttime temperatures approaching 0oC (32oF). Subtropical deserts are characterized by low annual precipitation of fewer than 30 cm (12 in) with little monthly variation and lack of predictability in rainfall. Some years may receive tiny amounts of rainfall, while others receive more. In some cases, the annual rainfall can be as low as 2 cm (0.8 in) in subtropical deserts located in central Australia (“the Outback”) and northern Africa.
Figure \(6\). A MinuteEarth video about the global climate patterns which lead to subtropical deserts.
The low species diversity of this biome is closely related to its low and unpredictable precipitation. Despite the relatively low diversity, desert species exhibit fascinating adaptations to the harshness of their environment. Very dry deserts lack perennial vegetation that lives from one year to the next; instead, many plants are annuals that grow quickly and reproduce when rainfall does occur, then they die. Perennial plants in deserts are characterized by adaptations that conserve water: deep roots, reduced foliage, and water-storing stems (Figure \(6\) below). Seed plants in the desert produce seeds that can lie dormant for extended periods between rains. Most animal life in subtropical deserts has adapted to a nocturnal life, spending the hot daytime hours beneath the ground. The Namib Desert is the oldest on the planet, and has probably been dry for more than 55 million years. It supports a number of endemic species (species found only there) because of this great age. For example, the unusual gymnosperm Welwitschia mirabilisis the only extant species of an entire order of plants. There are also five species of reptiles considered endemic to the Namib.
In addition to subtropical deserts there are cold deserts that experience freezing temperatures during the winter and any precipitation is in the form of snowfall. The largest of these deserts are the Gobi Desert in northern China and southern Mongolia, the Taklimakan Desert in western China, the Turkestan Desert, and the Great Basin Desert of the United States.
The chaparral is also called scrub forest and is found in California, along the Mediterranean Sea, and along the southern coast of Australia (Figure \(7\) below). The annual rainfall in this biome ranges from 65 cm to 75 cm (25.6–29.5 in) and the majority of the rain falls in the winter. Summers are very dry and many chaparral plants are dormant during the summertime. The chaparral vegetation is dominated by shrubs and is adapted to periodic fires, with some plants producing seeds that germinate only after a hot fire. The ashes left behind after a fire are rich in nutrients like nitrogen and fertilize the soil, promoting plant regrowth. Fire is a natural part of the maintenance of this biome.
Temperate grasslands are found throughout central North America, where they are also known as prairies, and in Eurasia, where they are known as steppes (Figure \(8\) below). Temperate grasslands have pronounced annual fluctuations in temperature with hot summers and cold winters. The annual temperature variation produces specific growing seasons for plants. Plant growth is possible when temperatures are warm enough to sustain plant growth, which occurs in the spring, summer, and fall.
Annual precipitation ranges from 25.4 cm to 88.9 cm (10–35 in). Temperate grasslands have few trees except for those found growing along rivers or streams. The dominant vegetation tends to consist of grasses. The treeless condition is maintained by low precipitation, frequent fires, and grazing. The vegetation is very dense and the soils are fertile because the subsurface of the soil is packed with the roots and rhizomes (underground stems) of these grasses. The roots and rhizomes act to anchor plants into the ground and replenish the organic material (humus) in the soil when they die and decay.
Fires, which are a natural disturbance in temperate grasslands, can be ignited by lightning strikes. It also appears that the lightning-caused fire regime in North American grasslands was enhanced by intentional burning by humans. When fire is suppressed in temperate grasslands, the vegetation eventually converts to scrub and dense forests. Often, the restoration or management of temperate grasslands requires the use of controlled burns to suppress the growth of trees and maintain the grasses.
Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand (Figure \(9\) below). This biome is found throughout mid-latitude regions. Temperatures range between –30oC and 30oC (–22oF to 86oF) and drop to below freezing on an annual basis. These temperatures mean that temperate forests have defined growing seasons during the spring, summer, and early fall. Precipitation is relatively constant throughout the year and ranges between 75 cm and 150 cm (29.5–59 in).
Deciduous trees are the dominant plant in this biome with fewer evergreen conifers. Deciduous trees lose their leaves each fall and remain leafless in the winter. Thus, little photosynthesis occurs during the dormant winter period. Each spring, new leaves appear as temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical rainforests. In addition, temperate forests show far less diversity of tree species than tropical rainforest biomes.
The trees of the temperate forests leaf out and shade much of the ground. However, more sunlight reaches the ground in this biome than in tropical rainforests because trees in temperate forests do not grow as tall as the trees in tropical rainforests. The soils of the temperate forests are rich in inorganic and organic nutrients compared to tropical rainforests. This is because of the thick layer of leaf litter on forest floors and reduced leaching of nutrients by rainfall. As this leaf litter decays, nutrients are returned to the soil. The leaf litter also protects soil from erosion, insulates the ground, and provides habitats for invertebrates and their predators.
The boreal forest, also known as taiga or coniferous forest, is found roughly between 50oand 60o north latitude across most of Canada, Alaska, Russia, and northern Europe (Figure \(10\) below). Boreal forests are also found above a certain elevation (and below high elevations where trees cannot grow) in mountain ranges throughout the Northern Hemisphere. This biome has cold, dry winters and short, cool, wet summers. The annual precipitation is from 40 cm to 100 cm (15.7–39 in) and usually takes the form of snow; relatively little evaporation occurs because of the cool temperatures.
The long and cold winters in the boreal forest have led to the predominance of cold-tolerant cone-bearing plants. These are evergreen coniferous trees like pines, spruce, and fir, which retain their needle-shaped leaves year-round. Evergreen trees can photosynthesize earlier in the spring than deciduous trees because less energy from the Sun is required to warm a needle-like leaf than a broad leaf. Evergreen trees grow faster than deciduous trees in the boreal forest. In addition, soils in boreal forest regions tend to be acidic with little available nitrogen. Leaves are a nitrogen-rich structure and deciduous trees must produce a new set of these nitrogen-rich structures each year. Therefore, coniferous trees that retain nitrogen-rich needles in a nitrogen limiting environment may have had a competitive advantage over the broad-leafed deciduous trees.
The net primary productivity of boreal forests is lower than that of temperate forests and tropical wet forests. The aboveground biomass of boreal forests is high because these slow-growing tree species are long-lived and accumulate standing biomass over time. Species diversity is less than that seen in temperate forests and tropical rainforests. Boreal forests lack the layered forest structure seen in tropical rainforests or, to a lesser degree, temperate forests. The structure of a boreal forest is often only a tree layer and a ground layer. When conifer needles are dropped, they decompose more slowly than broad leaves; therefore, fewer nutrients are returned to the soil to fuel plant growth.
The Arctic tundra lies north of the subarctic boreal forests and is located throughout the Arctic regions of the Northern Hemisphere. Tundra also exists at elevations above the tree line on mountains. The average winter temperature is –34°C (–29.2°F) and the average summer temperature is 3°C–12°C (37°F –52°F). Plants in the Arctic tundra have a short growing season of approximately 50–60 days. However, during this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is low (15–25 cm or 6–10 in) with little annual variation in precipitation. And, as in the boreal forests, there is little evaporation because of the cold temperatures.
Plants in the Arctic tundra are generally low to the ground and include low shrubs, grasses, lichens, and small flowering plants (Figure \(11\) below). There is little species diversity, low net primary productivity, and low above-ground biomass. The soils of the Arctic tundra may remain in a perennially frozen state referred to as permafrost. The permafrost makes it impossible for roots to penetrate far into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. The melting of the permafrost in the brief summer provides water for a burst of productivity while temperatures and long days permit it. During the growing season, the ground of the Arctic tundra can be completely covered with plants or lichens.
Suggested Supplementary Reading
HHMI. 2018. Biome Viewer. [Interactive Website]. Howard Hughes Medical Institute. <https://www.hhmi.org/biointeractive/biomeviewer> | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/03%3A_Ecosystems_and_the_Biosphere/3.03%3A_Terrestrial_Biomes.txt |
Abiotic Factors Influencing Aquatic Biomes
Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water still absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach. While there are some abiotic and biotic factors in a terrestrial ecosystem that might obscure light (like fog, dust, or insect swarms), usually these are not permanent features of the environment. The importance of light in aquatic biomes is central to the communities of organisms found in both freshwater and marine ecosystems. In freshwater systems, stratification due to differences in density is perhaps the most critical abiotic factor and is related to the energy aspects of light. The thermal properties of water (rates of heating and cooling) are significant to the function of marine systems and have major impacts on global climate and weather patterns. Marine systems are also influenced by large-scale physical water movements, such as currents; these are less important in most freshwater lakes.
The ocean is categorized by several areas or zones (Figure \(1\)). All of the ocean’s open water is referred to as the pelagic zone. The benthic zone extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor. Within the pelagic realm is the photic zone, which is the portion of the ocean that light can penetrate (approximately 200 m or 650 ft). At depths greater than 200 m, light cannot penetrate; thus, this is referred to as the aphotic zone. The majority of the ocean is aphotic and lacks sufficient light for photosynthesis. The deepest part of the ocean, the Challenger Deep (in the Mariana Trench, located in the western Pacific Ocean), is about 11,000 m (about 6.8 mi) deep. To give some perspective on the depth of this trench, the ocean is, on average, 4267 m. These zones are relevant to freshwater lakes as well.
Marine Biomes
The ocean is the largest marine biome. It is a continuous body of salt water that is relatively uniform in chemical composition; it is a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second kind of marine biome. Estuaries, coastal areas where salt water and fresh water mix, form a third unique marine biome.
Ocean
The physical diversity of the ocean is a significant influence on plants, animals, and other organisms. The ocean is categorized into different zones based on how far light reaches into the water. Each zone has a distinct group of species adapted to the biotic and abiotic conditions particular to that zone.
The intertidal zone, which is the zone between high and low tide, is the oceanic region that is closest to land (Figure \(2\)). Generally, most people think of this portion of the ocean as a sandy beach. In some cases, the intertidal zone is indeed a sandy beach, but it can also be rocky or muddy. Organisms are exposed to air and sunlight at low tide and are underwater most of the time, especially during high tide. Therefore, living things that thrive in the intertidal zone are adapted to being dry for long periods of time. The shore of the intertidal zone is also repeatedly struck by waves, and the organisms found there are adapted to withstand damage from the pounding action of the waves (Figure \(2\)). The exoskeletons of shoreline crustaceans (such as the shore crab, Carcinus maenas) are tough and protect them from desiccation (drying out) and wave damage. Another consequence of the pounding waves is that few algae and plants establish themselves in the constantly moving rocks, sand, or mud.
The neritic zone (Figure \(1\)) extends from the intertidal zone to depths of about 200 m (or 650 ft) at the edge of the continental shelf. Because light can penetrate this depth, photosynthesis can occur. The water here contains silt and is well-oxygenated, low in pressure, and stable in temperature. Phytoplankton and floating Sargassum (a type of free-floating marine seaweed) provide a habitat for some sea life found in the neritic zone. Zooplankton, protists, small fishes, and shrimp are found in the neritic zone and are the base of the food chain for most of the world’s fisheries.
Beyond the neritic zone is the open ocean area known as the oceanic zone (Figure \(1\)). Within the oceanic zone there is thermal stratification where warm and cold waters mix because of ocean currents. Abundant plankton serve as the base of the food chain for larger animals such as whales and dolphins. Nutrients are scarce and this is a relatively less productive part of the marine biome. When photosynthetic organisms and the protists and animals that feed on them die, their bodies fall to the bottom of the ocean where they remain. The majority of organisms in the aphotic zone include sea cucumbers (phylum Echinodermata) and other organisms that survive on the nutrients contained in the dead bodies of organisms in the photic zone.
The deepest part of the ocean is the abyssal zone, which is at depths of 4000 m or greater. The abyssal zone (Figure \(1\)) is very cold and has very high pressure, high oxygen content, and low nutrient content. There are a variety of invertebrates and fishes found in this zone, but the abyssal zone does not have plants because of the lack of light. Cracks in the Earth’s crust called hydrothermal vents are found primarily in the abyssal zone. Around these vents chemosynthetic bacteria utilize the hydrogen sulfide and other minerals emitted as an energy source and serve as the base of the food chain found in the abyssal zone.
Beneath the water is the benthic zone (Figure \(1\)), which is comprised of sand, silt, and dead organisms. This is a nutrient-rich portion of the ocean because of the dead organisms that fall from the upper layers of the ocean. Because of this high level of nutrients, a diversity of sponges, sea anemones, marine worms, sea stars, fishes, and bacteria exist.
Coral Reefs
Coral reefs are characterized by high biodiversity and the structures created by invertebrates that live in warm, shallow waters within the photic zone of the ocean. They are mostly found within 30 degrees north and south of the equator. The Great Barrier Reef is a well-known reef system located several miles off the northeastern coast of Australia. The coral organisms (members of phylum Cnidaria) are colonies of saltwater polyps that secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, forming the underwater reef (Figure \(3\)).
Corals found in shallower waters (at a depth of approximately 60 m or about 200 ft) have a mutualistic relationship with photosynthetic unicellular algae. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor and, without this mutualism, it would not be possible for large corals to grow. Some corals living in deeper and colder water do not have a mutualistic relationship with algae; these corals attain energy and nutrients using stinging cells on their tentacles to capture prey. It is estimated that more than 4,000 fish species inhabit coral reefs. These fishes can feed on coral, other invertebrates, or the seaweed and algae that are associated with the coral.
Link to Learning: Watch this National Oceanic and Atmospheric Administration (NOAA) video to see marine ecologist Dr. Peter Etnoyer discusses his research on coral organisms.
EVOLUTION CONNECTION: Global Decline of Coral Reefs
It takes a long time to build a coral reef. The animals that create coral reefs have evolved over millions of years, continuing to slowly deposit the calcium carbonate that forms their characteristic ocean homes. Bathed in warm tropical waters, the coral animals and their symbiotic algal partners evolved to survive at the upper limit of ocean water temperature.
Together, climate change and human activity pose dual threats to the long-term survival of the world’s coral reefs. As global warming due to fossil fuel emissions raises ocean temperatures, coral reefs are suffering. The excessive warmth causes the reefs to expel their symbiotic, food-producing algae, resulting in a phenomenon known as bleaching. When bleaching occurs, the reefs lose much of their characteristic color as the algae and the coral animals die if loss of the symbiotic zooxanthellae is prolonged.
Rising levels of atmospheric carbon dioxide further threaten the corals in other ways; as CO2 dissolves in ocean waters, it lowers the pH and increases ocean acidity. As acidity increases, it interferes with the calcification that normally occurs as coral animals build their calcium carbonate homes.
When a coral reef begins to die, species diversity plummets as animals lose food and shelter. Coral reefs are also economically important tourist destinations, so the decline of coral reefs poses a serious threat to coastal economies.
Human population growth has damaged corals in other ways, too. As human coastal populations increase, the runoff of sediment and agricultural chemicals has increased, too, causing some of the once-clear tropical waters to become cloudy. At the same time, overfishing of popular fish species has allowed the predator species that eat corals to go unchecked.
Although a rise in global temperatures of 1–2˚C (a conservative scientific projection) in the coming decades may not seem large, it is very significant to this biome. When change occurs rapidly, species can become extinct before evolution leads to new adaptations. Many scientists believe that global warming, with its rapid (in terms of evolutionary time) and inexorable increases in temperature, is tipping the balance beyond the point at which many of the world’s coral reefs can recover.
Estuaries: Where the Ocean Meets Fresh Water
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity; mixing results in a diluted (brackish) saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives. Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies and is based on the rate of flow of its freshwater sources. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water.
The short-term and rapid variation in salinity due to the mixing of fresh water and salt water is a difficult physiological challenge for the plants and animals that inhabit estuaries. Many estuarine plant species are halophytes: plants that can tolerate salty conditions. Halophytic plants are adapted to deal with the salinity resulting from saltwater on their roots or from sea spray. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs. Other plants are able to pump oxygen into their roots. Animals, such as mussels and clams (phylum Mollusca), have developed behavioral adaptations that expend a lot of energy to function in this rapidly changing environment. When these animals are exposed to low salinity, they stop feeding, close their shells, and switch from aerobic respiration (in which they use gills) to anaerobic respiration (a process that does not require oxygen). When high tide returns to the estuary, the salinity and oxygen content of the water increases, and these animals open their shells, begin feeding, and return to aerobic respiration.
Freshwater Biomes
Freshwater biomes include lakes and ponds (standing water) as well as rivers and streams (flowing water). They also include wetlands, which will be discussed later. Humans rely on freshwater biomes to provide aquatic resources for drinking water, crop irrigation, sanitation, and industry. These various roles and human benefits are referred to as ecosystem services. Lakes and ponds are found in terrestrial landscapes and are, therefore, connected with abiotic and biotic factors influencing these terrestrial biomes.
Lakes and Ponds
Lakes and ponds can range in area from a few square meters to thousands of square kilometers. Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with deeper, cooler water. Light can penetrate within the photic zone of the lake or pond. Phytoplankton (small photosynthetic organisms such as algae and cyanobacteria that float in the water) are found here and carry out photosynthesis, providing the base of the food web of lakes and ponds. Zooplankton (very small animals that float in the water), such as rotifers and small crustaceans, consume these phytoplankton. At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom.
Nitrogen and phosphorus are important limiting nutrients in lakes and ponds. Because of this, they are determining factors in the amount of phytoplankton growth in lakes and ponds. When there is a large input of nitrogen and phosphorus (from sewage and runoff from fertilized lawns and farms, for example), the growth of algae skyrockets, resulting in a large accumulation of algae called an algal bloom. Algal blooms (Figure \(4\)) can become so extensive that they reduce light penetration in water. As a result, the lake or pond becomes aphotic and photosynthetic plants rooted in the lake bottom cannot survive. When the algae die and decompose, severe oxygen depletion of the water occurs. Fishes and other organisms that require oxygen are then more likely to die, and resulting dead zones are found across the globe. Lake Erie and the Gulf of Mexico represent freshwater and marine habitats where phosphorus control and storm water runoff pose significant environmental challenges.
Rivers and Streams
Rivers and streams are continuously moving bodies of water that carry large amounts of water from the source, or headwater, to a lake or ocean. The largest rivers include the Nile River in Africa, the Amazon River in South America, and the Mississippi River in North America.
Abiotic features of rivers and streams vary along the length of the river or stream. Streams begin at a point of origin referred to as source water. The source water is usually cold, low in nutrients, and clear. The channel (the width of the river or stream) is narrower than at any other place along the length of the river or stream. Because of this, the current is often faster here than at any other point of the river or stream.
The fast-moving water results in minimal silt accumulation at the bottom of the river or stream, therefore the water is clear. Photosynthesis here is mostly attributed to algae that are growing on rocks; the swift current inhibits the growth of phytoplankton. An additional input of energy can come from leaves or other organic material that falls into the river or stream from trees and other plants that border the water. When the leaves decompose, the organic material and nutrients in the leaves are returned to the water. Plants and animals have adapted to this fast-moving water. For instance, leeches (phylum Annelida) have elongated bodies and suckers on both ends. These suckers attach to the substrate, keeping the leech anchored in place. Freshwater trout species (phylum Chordata) are an important predator in these fast-moving rivers and streams.
As the river or stream flows away from the source, the width of the channel gradually widens and the current slows. This slow-moving water, caused by the gradient decrease and the volume increase as tributaries unite, has more sedimentation. Phytoplankton can also be suspended in slow-moving water. Therefore, the water will not be as clear as it is near the source. The water is also warmer. Worms (phylum Annelida) and insects (phylum Arthropoda) can be found burrowing into the mud. The higher order predator vertebrates (phylum Chordata) include waterfowl, frogs, and fishes. These predators must find food in these slow moving, sometimes murky, waters and, unlike the trout in the waters at the source, these vertebrates may not be able to use vision as their primary sense to find food. Instead, they are more likely to use taste or chemical cues to find prey.
Wetlands
Wetlands are environments in which the soil is either permanently or periodically saturated with water. Wetlands are different from lakes because wetlands are shallow bodies of water that may periodically dry out. Emergent vegetation consists of wetland plants that are rooted in the soil but have portions of leaves, stems, and flowers extending above the water’s surface. There are several types of wetlands including marshes, swamps, bogs, mudflats, and salt marshes (Figure \(5\)).
Contributors and Attributions
• Biology by OpenStax is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/03%3A_Ecosystems_and_the_Biosphere/3.04%3A_Aquatic_Biomes.txt |
Summary
Ecosystems exist underground, on land, at sea, and in the air. Organisms in an ecosystem acquire energy in a variety of ways, which is transferred between trophic levels as the energy flows from the base to the top of the food web, with energy being lost at each transfer. Mineral nutrients are cycled through ecosystems and their environment. Of particular importance are water, carbon, nitrogen, phosphorus, and sulfur. All of these cycles have major impacts on ecosystem structure and function. Ecosystems have been damaged by a variety of human activities that alter the natural biogeochemical cycles due to pollution, oil spills, and events causing global climate change. The health of the biosphere depends on understanding these cycles and how to protect the environment from irreversible damage. Earth has terrestrial and aquatic biomes. There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. Temperature and precipitation, and variations in both, are key abiotic factors that shape the composition of animal and plant communities in terrestrial biomes. Sunlight is an important factor in bodies of water, especially those that are very deep, because of the role of photosynthesis in sustaining certain organisms. Other important factors include temperature, water movement, and salt content. Aquatic biomes include both freshwater and marine environments. Like terrestrial biomes, aquatic biomes are influenced by abiotic factors. In the case of aquatic biomes the abiotic factors include light, temperature, flow regime, and dissolved solids.
Review Questions
1. Secondary consumers would eat which one following?
1. Producers
2. Plants
3. Herbivores
4. Carnivores
5. Tertiary consumers
2. If you are concerned about biomagnification of toxins, which one of the following would you most want to avoid eating?
1. Tuna (tertiary consumer)
2. Seaweed (producer)
3. Urchin (primary consumer)
4. Sculpin (secondary consumer)
5. Any photoautotroph
3. Which one of the following is not a biogeochemical cycle?
1. Energy cycle
2. Nitrogen cycle
3. Carbon cycle
4. Phosphorus cycle
5. Water cycle
4. Which one of the following would not increase the amount of water in the atmosphere?
1. Evaporation
2. Transpiration
3. Sublimation
4. Infiltration
5. Evapotranspiration
5. Which one of the following processes would remove nitrates from contaminated water by converting it into nitrogen gas?
1. Nitrification
2. Nitrogen fixation
3. Denitrification
4. Assimilation
5. Ammonification
6. What do deserts and chaparral have in common?
1. Dry and hot summers
2. Dominated by abundant evergreen shrubs
3. Both can exist as either the hot or cold variety
4. Very small amounts of rainfall consistently throughout the year
5. Very low biodiversity
7. Which one of the following would most likely live within the benthic realm of the ocean?
1. Squid
2. Tuna
3. Phytoplankton
4. Marine worm
5. Shark
8. What two variables most strongly contribute to the type of biome that exists in a particular area?
1. Precipitation levels and temperature
2. Type of producers and density of herbivores
3. Amount of sunlight and annual rainfall
4. Soil type and amount of O2
5. Distance from ocean and elevation
9. The conversion of nitrogen gas (N2) into ammonia (NH3) happens during which specific process?
1. Ammonification
2. Dentification
3. Nitrification
4. Nitrogenous cycling
5. Nitrogen fixation
10. Use your knowledge of the relative energy content among trophic levels to answer the following question: A larger human population could be supported if all humans derived their food from which trophic level?
1. Producers
2. Primary consumers
3. Secondary consumers
4. Tertiary consumers
5. Quaternary consumers
See Appendix for answers
Attributions
OpenStax College. (2013). Concepts of biology. Retrieved from http://cnx.org/contents/[email protected]. OpenStax CNX. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/03%3A_Ecosystems_and_the_Biosphere/3.05%3A_Chapter_Resources.txt |
Learning Outcomes
• Describe how ecologists measure population size and density
• Describe three different patterns of population distribution
• Give examples of how the carrying capacity of a habitat may change
• Explain how humans have expanded the carrying capacity of their habitat
• Discuss the long-term implications of unchecked human population growth
• 4.1: Population Demographics and Dynamics
Populations are dynamic entities. Their size and composition fluctuate in response to numerous factors, including seasonal and yearly changes in the environment, natural disasters such as forest fires and volcanic eruptions, and competition for resources between and within species. The study of populations is called demography.
• 4.2: Population Growth and Regulation
Population ecologists make use of a variety of methods to model population dynamics. An accurate model should be able to describe the changes occurring in a population and predict future changes.
• 4.3: The Human Population
Concepts of animal population dynamics can be applied to human population growth. Earth’s human population and their use of resources are growing rapidly, to the extent that some worry about the ability of Earth’s environment to sustain its human population. Long-term exponential growth carries with it the potential risks of famine, disease, and large-scale death, as well as social consequences of crowding such as increased crime.
• 4.4: Community Ecology
Populations typically do not live in isolation from other species. Populations that interact within a given habitat form a community. The number of species occupying the same habitat and their relative abundance is known as the diversity of the community. Areas with low species diversity, such as the glaciers of Antarctica, still contain a wide variety of living organisms, whereas the diversity of tropical rainforests is so great that it cannot be accurately assessed.
• 4.5: Chapter Resources
Thumbnail image - Asian carp jump out of the water in response to electrofishing. The Asian carp in the inset photograph were harvested from the Little Calumet River in Illinois in May, 2010, using rotenone, a toxin often used as an insecticide, in an effort to learn more about the population of the species. (credit main image: modification of work by USGS; credit inset: modification of work by Lt. David French, USCG)
04: Community Population Ecology
Imagine sailing down a river in a small motorboat on a weekend afternoon; the water is smooth, and you are enjoying the sunshine and cool breeze when suddenly you are hit in the head by a 20-pound silver carp. This is a risk now on many rivers and canal systems in Illinois and Missouri because of the presence of Asian carp. This fish—actually a group of species including the silver, black, grass, and big head carp—has been farmed and eaten in China for over 1,000 years. It is one of the most important aquaculture food resources worldwide. In the United States, however, Asian carp is considered a dangerous invasive species that disrupts ecological community structure to the point of threatening native species. The effects of invasive species (such as the Asian carp, kudzu vine, predatory snakehead fish, and zebra mussel) are just one aspect of what ecologists study to understand how populations interact within ecological communities, and what impact natural and human-induced disturbances have on the characteristics of communities.
Populations are dynamic entities. Their size and composition fluctuate in response to numerous factors, including seasonal and yearly changes in the environment, natural disasters such as forest fires and volcanic eruptions, and competition for resources between and within species. The study of populations is called demography.
Population Size and Density
Populations are characterized by their population size (total number of individuals) and their population density (number of individuals per unit area). A population may have a large number of individuals that are distributed densely, or sparsely. There are also populations with small numbers of individuals that may be dense or very sparsely distributed in a local area. Population size can affect potential for adaptation because it affects the amount of genetic variation present in the population. Density can have effects on interactions within a population such as competition for food and the ability of individuals to find a mate. Smaller organisms tend to be more densely distributed than larger organisms (Figure $1$).
Estimating Population Size
The most accurate way to determine population size is to count all of the individuals within the area. However, this method is usually not logistically or economically feasible, especially when studying large areas. Thus, scientists usually study populations by sampling a representative portion of each habitat and use this sample to make inferences about the population as a whole. The methods used to sample populations to determine their size and density are typically tailored to the characteristics of the organism being studied. For immobile organisms such as plants, or for very small and slow-moving organisms, a quadrat may be used. A quadrat is a square structure that is randomly located on the ground and used to count the number of individuals that lie within its boundaries. To obtain an accurate count using this method, the square must be placed at random locations within the habitat enough times to produce an accurate estimate.
For smaller mobile organisms, such as mammals, a technique called mark and recapture is often used. This method involves marking captured animals in and releasing them back into the environment to mix with the rest of the population. Later, a new sample is captured and scientists determine how many of the marked animals are in the new sample. This method assumes that the larger the population, the lower the percentage of marked organisms that will be recaptured since they will have mixed with more unmarked individuals. For example, if 80 field mice are captured, marked, and released into the forest, then a second trapping 100 field mice are captured and 20 of them are marked, the population size (N) can be determined using the following equation:
$N = \frac{(\text{number marked first catch} \times \text{total number of second catch})}{\text{number marked second catch}}$
Using our example, the equation would be:
$\frac{(80 \times 100)}{20} = 400$
These results give us an estimate of 400 total individuals in the original population. The true number usually will be a bit different from this because of chance errors and possible bias caused by the sampling methods.
Species Distribution
In addition to measuring size and density, further information about a population can be obtained by looking at the distribution of the individuals throughout their range. A species distribution pattern is the distribution of individuals within a habitat at a particular point in time—broad categories of patterns are used to describe them.
Individuals within a population can be distributed at random, in groups, or equally spaced apart (more or less). These are known as random, clumped, and uniform distribution patterns, respectively (Figure $2$). Different distributions reflect important aspects of the biology of the species. They also affect the mathematical methods required to estimate population sizes. An example of random distribution occurs with dandelion and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in favorable environments. A clumped distribution, may be seen in plants that drop their seeds straight to the ground, such as oak trees; it can also be seen in animals that live in social groups (schools of fish or herds of elephants). Uniform distribution is observed in plants that secrete substances inhibiting the growth of nearby individuals (such as the release of toxic chemicals by sage plants). It is also seen in territorial animal species, such as penguins that maintain a defined territory for nesting. The territorial defensive behaviors of each individual create a regular pattern of distribution of similar-sized territories and individuals within those territories. Thus, the distribution of the individuals within a population provides more information about how they interact with each other than does a simple density measurement. Just as lower density species might have more difficulty finding a mate, solitary species with a random distribution might have a similar difficulty when compared to social species clumped together in groups.
Life tables provide important information about the life history of an organism and the life expectancy of individuals at each age. They are modeled after actuarial tables used by the insurance industry for estimating human life expectancy. Life tables may include the probability of each age group dying before their next birthday, the percentage of surviving individuals dying at a particular age interval (their mortality rate, and their life expectancy at each interval. An example of a life table is shown in Table 1 from a study of Dall mountain sheep, a species native to northwestern North America. Notice that the population is divided into age intervals (column A).
As can be seen from the mortality rate data (column D), a high death rate occurred when the sheep were between six months and a year old, and then increased even more from 8 to 12 years old, after which there were few survivors. The data indicate that if a sheep in this population were to survive to age one, it could be expected to live another 7.7 years on average, as shown by the life-expectancy numbers in column E.
Table 1: Life Table of Dall Mountain Sheep
Age interval (years) Number dying in age interval out of 1000 born Number surviving at beginning of age interval out of 1000 born Mortality rate per 1000 alive at beginning of age interval Life expectancy or mean lifetime remaining to those attaining age interval
0–0.5 54 1000 54.0 7.06
0.5–1 145 946 153.3
1–2 12 801 15.0 7.7
2–3 13 789 16.5 6.8
3–4 12 776 15.5 5.9
4–5 30 764 39.3 5.0
5–6 46 734 62.7 4.2
6–7 48 688 69.8 3.4
7–8 69 640 107.8 2.6
8–9 132 571 231.2 1.9
9–10 187 439 426.0 1.3
10–11 156 252 619.0 0.9
11–12 90 96 937.5 0.6
12–13 3 6 500.0 1.2
13–14 3 3 1000 0.7
Another tool used by population ecologists is a survivorship curve, which is a graph of the number of individuals surviving at each age interval versus time. These curves allow us to compare the life histories of different populations (Figure $3$). There are three types of survivorship curves. In a type I curve, mortality is low in the early and middle years and occurs mostly in older individuals. Organisms exhibiting a type I survivorship typically produce few offspring and provide good care to the offspring increasing the likelihood of their survival. Humans and most mammals exhibit a type I survivorship curve. In type II curves, mortality is relatively constant throughout the entire life span, and mortality is equally likely to occur at any point in the life span. Many bird populations provide examples of an intermediate or type II survivorship curve. In type III survivorship curves, early ages experience the highest mortality with much lower mortality rates for organisms that make it to advanced years. Type III organisms typically produce large numbers of offspring, but provide very little or no care for them. Trees and marine invertebrates exhibit a type III survivorship curve because very few of these organisms survive their younger years, but those that do make it to an old age are more likely to survive for a relatively long period of time.
Contributors and Attributions
• Population Demography by OpenStax is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/04%3A_Community__Population_Ecology/4.01%3A_Population_Demographics_and_Dynamics.txt |
Population ecologists make use of a variety of methods to model population dynamics. An accurate model should be able to describe the changes occurring in a population and predict future changes. The two simplest models of population growth use deterministic equations (equations that do not account for random events) to describe the rate of change in the size of a population over time. The first of these models, exponential growth, describes populations that increase in numbers without any limits to their growth. The second model, logistic growth, introduces limits to reproductive growth that become more intense as the population size increases. Neither model adequately describes natural populations, but they provide points of comparison.
Exponential Growth
Charles Darwin, in developing his theory of natural selection, was influenced by the English clergyman Thomas Malthus. Malthus published his book in 1798 stating that populations with abundant natural resources grow very rapidly. However, they limit further growth by depleting their resources. The early pattern of accelerating population size is called exponential growth (Figure \(1\)).
The best example of exponential growth in organisms is seen in bacteria. Bacteria are prokaryotes that reproduce quickly, about an hour for many species. If 1000 bacteria are placed in a large flask with an abundant supply of nutrients (so the nutrients will not become quickly depleted), the number of bacteria will have doubled from 1000 to 2000 after just an hour. In another hour, each of the 2000 bacteria will divide, producing 4000 bacteria. After the third hour, there should be 8000 bacteria in the flask. The important concept of exponential growth is that the growth rate—the number of organisms added in each reproductive generation—is itself increasing; that is, the population size is increasing at a greater and greater rate. After 24 of these cycles, the population would have increased from 1000 to more than 16 billion bacteria. When the population size, N, is plotted over time, a J-shaped growth curve is produced (Figure \(1\)).
The bacteria-in-a-flask example is not truly representative of the real world where resources are usually limited. However, when a species is introduced into a new habitat that it finds suitable, it may show exponential growth for a while. In the case of the bacteria in the flask, some bacteria will die during the experiment and thus not reproduce; therefore, the growth rate is lowered from a maximal rate in which there is no mortality.
Logistic Growth
Extended exponential growth is possible only when infinite natural resources are available; this is not the case in the real world. Charles Darwin recognized this fact in his description of the “struggle for existence,” which states that individuals will compete, with members of their own or other species, for limited resources. The successful ones are more likely to survive and pass on the traits that made them successful to the next generation at a greater rate (natural selection). To model the reality of limited resources, population ecologists developed the logistic growth model.
Carrying Capacity and the Logistic Model
In the real world, with its limited resources, exponential growth cannot continue indefinitely. Exponential growth may occur in environments where there are few individuals and plentiful resources, but when the number of individuals gets large enough, resources will be depleted and the growth rate will slow down. Eventually, the growth rate will plateau or level off (Figure \(1\)). This population size, which is determined by the maximum population size that a particular environment can sustain, is called the carrying capacity, symbolized as K. In real populations, a growing population often overshoots its carrying capacity and the death rate increases beyond the birth rate causing the population size to decline back to the carrying capacity or below it. Most populations usually fluctuate around the carrying capacity in an undulating fashion rather than existing right at it.
A graph of logistic growth yields the S-shaped curve (Figure \(1\)). It is a more realistic model of population growth than exponential growth. There are three different sections to an S-shaped curve. Initially, growth is exponential because there are few individuals and ample resources available. Then, as resources begin to become limited, the growth rate decreases. Finally, the growth rate levels off at the carrying capacity of the environment, with little change in population number over time.
Examples of Logistic Growth
Yeast, a unicellular fungus used to make bread and alcoholic beverages, exhibits the classical S-shaped curve when grown in a test tube (Figure \(2\)a). Its growth levels off as the population depletes the nutrients that are necessary for its growth. In the real world, however, there are variations to this idealized curve. Examples in wild populations include sheep and harbor seals (Figure \(2\)b). In both examples, the population size exceeds the carrying capacity for short periods of time and then falls below the carrying capacity afterwards. This fluctuation in population size continues to occur as the population oscillates around its carrying capacity. Still, even with this oscillation the logistic model is confirmed.
Population Dynamics and Regulation
The logistic model of population growth, while valid in many natural populations and a useful model, is a simplification of real-world population dynamics. Implicit in the model is that the carrying capacity of the environment does not change, which is not the case. The carrying capacity varies annually. For example, some summers are hot and dry whereas others are cold and wet; in many areas, the carrying capacity during the winter is much lower than it is during the summer. Also, natural events such as earthquakes, volcanoes, and fires can alter an environment and hence its carrying capacity. Additionally, populations do not usually exist in isolation. They share the environment with other species, competing with them for the same resources (interspecific competition). These factors are also important to understanding how a specific population will grow.
Why Did the Woolly Mammoth Go Extinct?
Most populations of woolly mammoths went extinct about 10,000 years ago, soon after paleontologists believe humans began to colonize North America and northern Eurasia (Figure \(3\)). A mammoth population survived on Wrangel Island, in the East Siberian Sea, and was isolated from human contact until as recently as 1700 BC. We know a lot about these animals from carcasses found frozen in the ice of Siberia and other northern regions.
It is commonly thought that climate change and human hunting led to their extinction. A 2008 study estimated that climate change reduced the mammoth’s range from 3,000,000 square miles 42,000 years ago to 310,000 square miles 6,000 years ago.2 Through archaeological evidence of kill sites, it is also well documented that humans hunted these animals. A 2012 study concluded that no single factor was exclusively responsible for the extinction of these magnificent creatures.3 In addition to climate change and reduction of habitat, scientists demonstrated another important factor in the mammoth’s extinction was the migration of human hunters across the Bering Strait to North America during the last ice age 20,000 years ago.
The maintenance of stable populations was and is very complex, with many interacting factors determining the outcome. It is important to remember that humans are also part of nature. Once we contributed to a species’ decline using primitive hunting technology only.
Demographic-Based Population Models
Population ecologists have hypothesized that suites of characteristics may evolve in species that lead to particular adaptations to their environments. These adaptations impact the kind of population growth their species experience. Life history characteristics such as birth rates, age at first reproduction, the numbers of offspring, and even death rates evolve just like anatomy or behavior, leading to adaptations that affect population growth. Population ecologists have described a continuum of life-history “strategies” with K-selected species on one end and r-selected species on the other. K-selected species are adapted to stable, predictable environments. Populations of K-selected species tend to exist close to their carrying capacity. These species tend to have larger, but fewer, offspring and contribute large amounts of resources to each offspring. Elephants would be an example of a K-selected species. r-selected species are adapted to unstable and unpredictable environments. They have large numbers of small offspring. Animals that are r-selected do not provide a lot of resources or parental care to offspring, and the offspring are relatively self-sufficient at birth. Examples of r-selected species are marine invertebrates such as jellyfish and plants such as the dandelion. The two extreme strategies are at two ends of a continuum on which real species life histories will exist. In addition, life history strategies do not need to evolve as suites, but can evolve independently of each other, so each species may have some characteristics that trend toward one extreme or the other. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/04%3A_Community__Population_Ecology/4.02%3A_Population_Growth_and_Regulation.txt |
Concepts of animal population dynamics can be applied to human population growth. Humans are not unique in their ability to alter their environment. For example, beaver dams alter the stream environment where they are built. Humans, however, have the ability to alter their environment to increase its carrying capacity, sometimes to the detriment of other species. Earth’s human population and their use of resources are growing rapidly, to the extent that some worry about the ability of Earth’s environment to sustain its human population. Long-term exponential growth carries with it the potential risks of famine, disease, and large-scale death, as well as social consequences of crowding such as increased crime.
Human technology and particularly our harnessing of the energy contained in fossil fuels have caused unprecedented changes to Earth’s environment, altering ecosystems to the point where some may be in danger of collapse. Changes on a global scale including depletion of the ozone layer, desertification and topsoil loss, and global climate change are caused by human activities.
Human Population Growth
The fundamental cause of the acceleration of growth rate for humans in the past 200 years has been the reduced death rate due to changes in public health and sanitation. Clean drinking water and proper disposal sewage has drastically improved health in developed nations. Also, medical innovations such as the use of antibiotics and vaccines have decreased the ability of infectious disease to limit human population growth. In the past, diseases such as the bubonic plaque of the fourteenth century killed between 30 and 60 percent of Europe’s population and reduced the overall world population by as many as one hundred million people. Naturally, infectious disease continues to have an impact on human population growth, especially in poorer nations. For example, life expectancy in sub-Saharan Africa, which was increasing from 1950 to 1990, began to decline after 1985 largely as a result of HIV/AIDS mortality. The reduction in life expectancy caused by HIV/AIDS was estimated to be 7 years for 2005.
Technological advances of the industrial age have also supported population growth through urbanization and advances in agriculture. These advances in technology were possible, in part, due to the exploitation of fossil fuels.
Age Structure, Population Growth, and Economic Development
The age structure of a population is an important factor in population dynamics. Age structure is the proportion of a population in different age classes. Models that incorporate age structure allow better prediction of population growth, plus the ability to associate this growth with the level of economic development in a region. Countries with rapid growth have a pyramidal shape in their age structure diagrams, showing a preponderance of younger individuals, many of whom are of reproductive age (Figure \(3\)).
This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of less-than-optimal living conditions, and there is a high birth rate. Age structures of areas with slow growth, including developed countries such as the United States, still have a pyramidal structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals. Other developed countries, such as Italy, have zero population growth. The age structure of these populations is more conical, with an even greater percentage of middle-aged and older individuals. The actual growth rates in different countries are shown in Figure \(4\), with the highest rates tending to be in the less economically developed countries of Africa and Asia.
Long-Term Consequences of Exponential Human Population Growth
Many dire predictions have been made about the world’s population leading to a major crisis called the “population explosion.” In the 1968 book The Population Bomb, biologist Paul R. Ehrlich wrote,
“The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate.”
While these predictions obviously didn’t bear fruit, the laws of exponential population growth are still in effect, and unchecked human population growth cannot continue indefinitely. Efforts to moderate population control led to the one-child policy in China, which imposes fines on urban couples who have more than one child. Due to the fact that some couples wish to have a male heir, many Chinese couples continue to have more than one child. The effectiveness of the policy in limiting overall population growth is controversial, as is the policy itself. Moreover, there are stories of female infanticide having occurred in some of the more rural areas of the country. Family planning education programs in other countries have had highly positive effects on limiting population growth rates and increasing standards of living.
In spite of population control policies, the human population continues to grow. The United Nations estimates the future world population size to be 11.2 billion people by the year 2100. There is no way to know whether human population growth will moderate to the point where the crisis described by Dr. Ehrlich will be averted. Another consequence of population growth is the change and degradation of the natural environment. Many countries have attempted to reduce the human impact on climate change by limiting their emission of greenhouse gases. However, a global climate change treaty remains elusive, and many underdeveloped countries trying to improve their economic condition may be less likely to agree with such provisions without compensation if it means slowing their economic development. Furthermore, the role of human activity in causing climate change has become a hotly debated socio-political issue in some developed countries, including the United States, despite the overwhelming scientific evidence. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment to maintain the carrying capacity for the human species. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/04%3A_Community__Population_Ecology/4.03%3A_The_Human_Population.txt |
Populations typically do not live in isolation from other species. Populations that interact within a given habitat form a community. The number of species occupying the same habitat and their relative abundance is known as the diversity of the community. Areas with low species diversity, such as the glaciers of Antarctica, still contain a wide variety of living organisms, whereas the diversity of tropical rainforests is so great that it cannot be accurately assessed. Scientists study ecology at the community level to understand how species interact with each other and compete for the same resources.
Predation and Herbivory
Perhaps the classical example of species interaction is the predator-prey relationship. The narrowest definition of predation describes individuals of one population that kill and then consume the individuals of another population. Population sizes of predators and prey in a community are not constant over time, and they may vary in cycles that appear to be related. The most often cited example of predator-prey population dynamics is seen in the cycling of the lynx (predator) and the snowshoe hare (prey), using 100 years of trapping data from North America (Figure \(1\)). This cycling of predator and prey population sizes has a period of approximately ten years, with the predator population lagging one to two years behind the prey population. An apparent explanation for this pattern is that as the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare numbers begin to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, in part, to low predation pressure, starting the cycle anew.
Defense Mechanisms against Predation and Herbivory
Predation and predator avoidance are strong influenced by natural selection. Any heritable character that allows an individual of a prey population to better evade its predators will be represented in greater numbers in later generations. Likewise, traits that allow a predator to more efficiently locate and capture its prey will lead to a greater number of offspring and an increase in the commonness of the trait within the population. Such ecological relationships between specific populations lead to adaptations that are driven by reciprocal evolutionary responses in those populations. Species have evolved numerous mechanisms to escape predation (including herbivory, the consumption of plants for food). Defenses may be mechanical, chemical, physical, or behavioral.
Mechanical defenses, such as the presence of armor in animals or thorns in plants, discourage predation and herbivory by discouraging physical contact (Figure \(2\)a). Many animals produce or obtain chemical defenses from plants and store them to prevent predation. Many plant species produce secondary plant compounds that serve no function for the plant except that they are toxic to animals and discourage consumption. For example, the foxglove produces several compounds, including digitalis, that are extremely toxic when eaten (Figure \(2\)b). (Biomedical scientists have repurposed the chemical produced by foxglove as a heart medication, which has saved lives for many decades.)
Many species use their body shape and coloration to avoid being detected by predators. The tropical walking stick is an insect with the coloration and body shape of a twig, which makes it very hard to see when it is stationary against a background of real twigs (Figure \(3\)a). In another example, the chameleon can change its color to match its surroundings (Figure \(3\)b).
Some species use coloration as a way of warning predators that they are distasteful or poisonous. For example, the monarch butterfly caterpillar sequesters poisons from its food (plants and milkweeds) to make itself poisonous or distasteful to potential predators. The caterpillar is bright yellow and black to advertise its toxicity. The caterpillar is also able to pass the sequestered toxins on to the adult monarch, which is also dramatically colored black and red as a warning to potential predators. Fire-bellied toads produce toxins that make them distasteful to their potential predators (Figure \(4\)). They have bright red or orange coloration on their bellies, which they display to a potential predator to advertise their poisonous nature and discourage an attack. Warning coloration only works if a predator uses eyesight to locate prey and can learn—a naïve predator must experience the negative consequences of eating one before it will avoid other similarly colored individuals.
While some predators learn to avoid eating certain potential prey because of their coloration, other species have evolved mechanisms to mimic this coloration to avoid being eaten, even though they themselves may not be unpleasant to eat or contain toxic chemicals. In some cases of mimicry, a harmless species imitates the warning coloration of a harmful species. Assuming they share the same predators, this coloration then protects the harmless ones. Many insect species mimic the coloration of wasps, which are stinging, venomous insects, thereby discouraging predation (Figure \(5\)).
In other cases of mimicry, multiple species share the same warning coloration, but all of them actually have defenses. The commonness of the signal improves the compliance of all the potential predators. Figure \(6\) shows a variety of foul-tasting butterflies with similar coloration.
Competitive Exclusion Principle
Resources are often limited within a habitat and multiple species may compete to obtain them. Ecologists have come to understand that all species have an ecological niche: the unique set of resources used by a species, which includes its interactions with other species. The competitive exclusion principle states that two species cannot occupy the exact same niche in a habitat. In other words, different species cannot coexist in a community if they are competing for all the same resources. It is important to note that competition is bad for both competitors because it wastes energy. The competitive exclusion principle works because if there is competition between two species for the same resources, then natural selection will favor traits that lessen reliance on the shared resource, thus reducing competition. If either species is unable to evolve to reduce competition, then the species that most efficiently exploits the resource will drive the other species to extinction. An experimental example of this principle is shown in Figure \(7\) with two protozoan species: Paramecium aurelia and Paramecium caudatum. When grown individually in the laboratory, they both thrive. But when they are placed together in the same test tube (habitat), P. aurelia outcompetes P. caudatum for food, leading to the latter’s eventual extinction.
Symbiosis
Symbiotic relationships are close, long-term interactions between individuals of different species. Symbioses may be commensal, in which one species benefits while the other is neither harmed nor benefited; mutualistic, in which both species benefit; or parasitic, in which the interaction harms one species and benefits the other.
Commensalism occurs when one species benefits from a close prolonged interaction, while the other neither benefits or is harmed. Birds nesting in trees provide an example of a commensal relationship (Figure \(8\)). The tree is not harmed by the presence of the nest among its branches. The nests are light and produce little strain on the structural integrity of the branch, and most of the leaves, which the tree uses to get energy by photosynthesis, are above the nest so they are unaffected. The bird, on the other hand, benefits greatly. If the bird had to nest in the open, its eggs and young would be vulnerable to predators. Many potential commensal relationships are difficult to identify because it is difficult to prove that one partner does not derive some benefit from the presence of the other.
A second type of symbiotic relationship is called mutualism, in which two species benefit from their interaction. For example, termites have a mutualistic relationship with protists that live in the insect’s gut (Figure \(9\)a). The termite benefits from the ability of the protists to digest cellulose. However, the protists are able to digest cellulose only because of the presence of symbiotic bacteria within their cells that produce the cellulase enzyme. The termite itself cannot do this; without the protozoa, it would not be able to obtain energy from its food (cellulose from the wood it chews and eats). The protozoa benefit by having a protective environment and a constant supply of food from the wood chewing actions of the termite. In turn, the protists benefit from the enzymes provided by their bacterial endosymbionts, while the bacteria benefit from a doubly protective environment and a constant source of nutrients from two hosts. Lichen are a mutualistic relationship between a fungus and photosynthetic algae or cyanobacteria (Figure \(9\)b). The glucose produced by the algae provides nourishment for both organisms, whereas the physical structure of the lichen protects the algae from the elements and makes certain nutrients in the atmosphere more available to the algae. The algae of lichens can live independently given the right environment, but many of the fungal partners are unable to live on their own.
A parasite is an organism that feeds off another without immediately killing the organism it is feeding on. In parasitism, the parasite benefits, but the organism being fed upon, the host, is harmed. The host is usually weakened by the parasite as it siphons resources the host would normally use to maintain itself. Parasites may kill their hosts, but there is usually selection to slow down this process to allow the parasite time to complete its reproductive cycle before it or its offspring are able to spread to another host. Parasitism is a form of predation.
The reproductive cycles of parasites are often very complex, sometimes requiring more than one host species. A tapeworm causes disease in humans when contaminated and under-cooked meat such as pork, fish, or beef is consumed (Figure \(10\)). The tapeworm can live inside the intestine of the host for several years, benefiting from the host’s food, and it may grow to be over 50 feet long by adding segments. The parasite moves from one host species to a second host species in order to complete its life cycle.
Characteristics of Communities
Communities are complex systems that can be characterized by their structure (the number and size of populations and their interactions) and dynamics (how the members and their interactions change over time). Understanding community structure and dynamics allows us to minimize impacts on ecosystems and manage ecological communities we benefit from.
Ecologists have extensively studied one of the fundamental characteristics of communities: biodiversity. One measure of biodiversity used by ecologists is the number of different species in a particular area and their relative abundance. The area in question could be a habitat, a biome, or the entire biosphere. Species richness is the term used to describe the number of species living in a habitat or other unit. Species richness varies across the globe (Figure \(11\)). Species richness is related to latitude: the greatest species richness occurs near the equator and the lowest richness occurs near the poles. The exact reasons for this are not clearly understood. Other factors besides latitude influence species richness as well. For example, ecologists studying islands found that biodiversity varies with island size and distance from the mainland.
Relative abundance is the number individuals in a species relative to the total number of individuals in all species within a system. Foundation species, described below, often have the highest relative abundance of species.
Foundation species are considered the “base” or “bedrock” of a community, having the greatest influence on its overall structure. They are often primary producers, and they are typically an abundant organism. For example, kelp, a species of brown algae, is a foundation species that forms the basis of the kelp forests off the coast of California.
Foundation species may physically modify the environment to produce and maintain habitats that benefit the other organisms that use them. Examples include the kelp described above or tree species found in a forest. The photosynthetic corals of the coral reef also provide structure by physically modifying the environment (Figure \(12\)). The exoskeletons of living and dead coral make up most of the reef structure, which protects many other species from waves and ocean currents.
A keystone species is one whose presence has inordinate influence in maintaining the prevalence of various species in an ecosystem, the ecological community’s structure, and sometimes its biodiversity. Pisaster ochraceus, the intertidal sea star, is a keystone species in the northwestern portion of the United States (Figure \(13\)). Studies have shown that when this organism is removed from communities, mussel populations (their natural prey) increase, which completely alters the species composition and reduces biodiversity. Another keystone species is the banded tetra, a fish in tropical streams, which supplies nearly all of the phosphorus, a necessary inorganic nutrient, to the rest of the community. The banded tetra feeds largely on insects from the terrestrial ecosystem and then excretes phosphorus into the aquatic ecosystem. The relationships between populations in the community, and possibly the biodiversity, would change dramatically if these fish were to become extinct.
BIOLOGY IN ACTION
Invasive species are non-native organisms that, when introduced to an area out of its native range, alter the community they invade. In the United States, invasive species like the purple loosestrife (Lythrum salicaria) and the zebra mussel (Dreissena polymorpha) have drastically altered the ecosystems they invaded. Some well-known invasive animals include the emerald ash borer (Agrilus planipennis) and the European starling (Sturnus vulgaris). Whether enjoying a forest hike, taking a summer boat trip, or simply walking down an urban street, you have likely encountered an invasive species.
One of the many recent proliferations of an invasive species concerns the Asian carp in the United States. Asian carp were introduced to the United States in the 1970s by fisheries (commercial catfish ponds) and by sewage treatment facilities that used the fish’s excellent filter feeding abilities to clean their ponds of excess plankton. Some of the fish escaped, and by the 1980s they had colonized many waterways of the Mississippi River basin, including the Illinois and Missouri Rivers.
Voracious feeders and rapid reproducers, Asian carp may outcompete native species for food and could lead to their extinction. One species, the grass carp, feeds on phytoplankton and aquatic plants. It competes with native species for these resources and alters nursery habitats for other fish by removing aquatic plants. In some parts of the Illinois River, Asian carp constitute 95 percent of the community’s biomass. Although edible, the fish is bony and not desired in the United States.
The Great Lakes and their prized salmon and lake trout fisheries are being threatened by Asian carp. The carp are not yet present in the Great Lakes, and attempts are being made to prevent its access to the lakes through the Chicago Ship and Sanitary Canal, which is the only connection between the Mississippi River and Great Lakes basins. To prevent the Asian carp from leaving the canal, a series of electric barriers have been used to discourage their migration; however, the threat is significant enough that several states and Canada have sued to have the Chicago channel permanently cut off from Lake Michigan. Local and national politicians have weighed in on how to solve the problem. In general, governments have been ineffective in preventing or slowing the introduction of invasive species.
Community Dynamics
Community dynamics are the changes in community structure and composition over time, often following environmental disturbances such as volcanoes, earthquakes, storms, fires, and climate change. Communities with a relatively constant number of species are said to be at equilibrium. The equilibrium is dynamic with species identities and relationships changing over time, but maintaining relatively constant numbers. Following a disturbance, the community may or may not return to the equilibrium state.
Succession describes the sequential appearance and disappearance of species in a community over time after a severe disturbance. In primary succession, newly exposed or newly formed rock is colonized by living organisms. In secondary succession, a part of an ecosystem is disturbed and remnants of the previous community remain. In both cases, there is a sequential change in species until a more or less permanent community develops.
Primary Succession and Pioneer Species
Primary succession occurs when new land is formed, or when the soil and all life is removed from pre-existing land. An example of the former is the eruption of volcanoes on the Big Island of Hawaii, which results in lava that flows into the ocean and continually forms new land. From this process, approximately 32 acres of land are added to the Big Island each year. An example of pre-existing soil being removed is through the activity of glaciers. The massive weight of the glacier scours the landscape down to the bedrock as the glacier moves. This removes any original soil and leaves exposed rock once the glacier melts and retreats.
In both cases, the ecosystem starts with bare rock that is devoid of life. New soil is slowly formed as weathering and other natural forces break down the rock and lead to the establishment of hearty organisms, such as lichens and some plants, which are collectively known as pioneer species (Figure \(14\)) because they are the first to appear. These species help to further break down the mineral-rich rock into soil where other, less hardy but more competitive species, such as grasses, shrubs, and trees, will grow and eventually replace the pioneer species. Over time the area will reach an equilibrium state, with a set of organisms quite different from the pioneer species.
Secondary succession
A classic example of secondary succession occurs in forests cleared by wildfire, or by clearcut logging (Figure \(15\)). Wildfires will burn most vegetation, and unless the animals can flee the area, they are killed. Their nutrients, however, are returned to the ground in the form of ash. Thus, although the community has been dramatically altered, there is a soil ecosystem present that provides a foundation for rapid recolonization.
Before the fire, the vegetation was dominated by tall trees with access to the major plant energy resource: sunlight. Their height gave them access to sunlight while also shading the ground and other low-lying species. After the fire, though, these trees are no longer dominant. Thus, the first plants to grow back are usually annual plants followed within a few years by quickly growing and spreading grasses and other pioneer species. Due, at least in part, to changes in the environment brought on by the growth of grasses and forbs, over many years, shrubs emerge along with small trees. These organisms are called intermediate species. Eventually, over 150 years or more, the forest will reach its equilibrium point and resemble the community before the fire. This equilibrium state is referred to as the climax community, which will remain until the next disturbance. The climax community is typically characteristic of a given climate and geology. Although the community in equilibrium looks the same once it is attained, the equilibrium is a dynamic one with constant changes in abundance and sometimes species identities.
Contributors and Attributions
• Community Ecology by OpenStax is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/04%3A_Community__Population_Ecology/4.04%3A_Community_Ecology.txt |
Summary
Populations are individuals of a species that live in a particular habitat. Ecologists measure characteristics of populations: size, density, and distribution pattern. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time. Populations with unlimited resources grow exponentially—with an accelerating growth rate. When resources become limiting, populations follow a logistic growth curve in which population size will level off at the carrying capacity. Humans have increased their carrying capacity through technology, urbanization, and harnessing the energy of fossil fuels. Unchecked human population growth could have dire long-term effects on human welfare and Earth’s ecosystems. Communities include all the different species living in a given area. The variety of these species is referred to as biodiversity. Species may form symbiotic relationships such as commensalism, mutualism, or parasitism. Community structure is described by its foundation and keystone species. Communities respond to environmental disturbances by succession: the predictable appearance of different types of plant species, until a stable community structure is established.
Review Questions
1. You are working as a biologist and perform the “mark and recapture” technique to estimate the number of endangered lemurs living within a particular habitat. You initially capture 37 lemurs, marking them all before releasing them. Two months later, you capture 49 lemurs, of which 11 are those originally captured and marked. What is the estimated size of the lemur population, rounded to the nearest whole number?
1. 60
2. 86
3. 97
4. 165
5. 407
2. Which one of the following measuring techniques would best enable you to determine the distribution pattern of a population of zebra?
1. Track how many and which individuals use a central watering hole
2. Use a drone to capture aerial photographs of their habitat range
3. Employ a camera trap in the middle of their habitat
4. Use the mark-recapture method
5. Collect and analyze DNA from hair samples collected at 2 locations
3. A species that you are studying has a type III survivorship curve. Which one of the following describes this type of curve?
1. Survivorship rates are lowest during early parts of its lifecycle
2. Survivorship rates are lowest during the late parts of its lifecycle
3. Survivorship rates are highest during early parts of its lifecycle
4. Survivorship rates are consistent through the lifecycle
5. Survivorship rates are highest in the early and middle parts of its lifecycle
4. A population has unlimited resources and exhibits rapid and sustained population growth. This type of growth would be best described by which one of the following?
1. Exponential
2. Logistic
3. Sigmoidal
4. Parabolic
5. Inverse
5. What single factor has most strongly contributed to the rapid population growth in the human population witnessed over the last 150 years?
1. Increased fertility rates
2. Reduced death rates
3. Longer life spans
4. Economic growth
5. Increased morbidity
6. Which one of the following age groups would most likely to lead to rapid population growth in the future if it contained the greatest relative abundance within that population?
1. 0-15 years old
2. 16-30 years old
3. 31-45 years old
4. 46-60 years old
5. 61 years old and greater
7. Two species have the same ecological niche. If they lived in the same habitat, both would compete until one species became predominant and the other became locally extinct. This process is summarized by which one of the following?
1. Niche warfare
2. Competitive exclusion principle
3. Species selection principle
4. Exclusion through competition theorem
5. Exclusive ecological fractioning
8. Which form of symbiosis benefits one member of the interaction, but neither benefits nor harms the other member?
1. Parasitism
2. Commensalism
3. Sequentialism
4. Mutualism
5. Natural selection
9. Biologists examined the effects of reintroducing wolves into Yellowstone National Park of the United States. They found that by preying on elk, wolves altered the foraging behavior of the elk; the elk spent less time browsing near streambanks. This allowed the regrowth of important vegetation, which had large positive impacts on the ecosystem at large. When a relatively small number of individuals, like wolves, have disproportionate impacts on the ecosystem, they are referred to as a…
1. Foundation species
2. Portal species
3. Keystone species
4. Cornerstone species
5. Pivotal species
10. The 1980 volcanic explosion of Mt. St. Helens in the United States devasted the north side of the mountain and it’s forests. The forests were demolished and replaced with volcanic debris that formed the new soil, free of any remnants of the previous ecosystem (such as seeds stored in the soil). Such an event would lead to which one of the following processes?
1. Primary succession
2. Secondary succession
3. Tertiary succession
4. Quaternary succession
5. Pioneering succession
See Appendix for answers
Attributions
OpenStax College. (2013). Concepts of biology. Retrieved from http://cnx.org/contents/[email protected]. OpenStax CNX. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/04%3A_Community__Population_Ecology/4.05%3A_Chapter_Resources.txt |
Learning Outcomes
• Describe biodiversity
• Explain how species evolve through natural selection
• Identify benefits of biodiversity to humans
• Explain the effects of habitat loss, exotic species, and hunting on biodiversity
• Identify the early and predicted effects of climate change on biodiversity
• Explain the legislative framework for conservation
• Identify examples of the effects of habitat restoration
Thumbnail image - Habitat destruction through deforestation, especially of tropical rainforests as seen in this satellite view of Amazon rainforests in Brazil, is a major cause of the current decline in biodiversity. (credit: modification of work by Jesse Allen and Robert Simmon, NASA Earth Observatory)
05: Conservation Biodiversity
Earth is home to an impressive array of life forms. From single-celled organisms to creatures made of many trillions of cells, life has taken on many wonderful shapes and evolved countless strategies for survival. Recall that cell theory dictates that all living things are made of one or more cells. Some organisms are made of just a single cell, and are thus referred to as unicellular. Organisms containing more than one cell are said to be multicellular. Despite the wide range of organisms, there exists only two fundamental cell plans: prokaryotic and eukaryotic. The main difference these two cell plans is that eukaryotic cells have internal, membrane-bound structures called organelles (see chp 2.3). Thus, if you were to microscopically analyze the cells of any organism on Earth, you would find either prokaryotic or eukaryotic cells depending on the type of organism.
Biologists name, group, and classify organisms based on similarities in genetics and morphology. This branch of biological science is known as taxonomy. Taxonomists group organisms into categories that range from very broad to very specific (Figure \(1\)). The broadest category is called domain and the most specific is species (notice the similarities between the words specific and species). Currently, taxonomists recognize three domains: Bacteria, Archaea, and Eukarya. All life forms are classified within these three domains.
Domain Bacteria
Domain Bacteria includes prokaryotic, unicellular organisms (Figure \(2\)). They are incredibly abundant and found in nearly every imaginable type of habitat, including your body. While many people view bacteria only as disease-causing organisms, most species are actually either benign or beneficial to humans. While it is true that some bacteria may cause disease in people, this is more the exception than the rule.
Bacteria are well-known for their metabolic diversity. Metabolism is a general term describing the complex biochemistry that occurs inside of cells. Many species of bacteria are autotrophs, meaning they can create their own food source without having to eat other organisms. Most autotrophic bacteria do this by using photosynthesis, a process that converts light energy into chemical energy that can be utilized by cells. A well-known and ecologically-important group of photosynthetic bacteria is cyanobacteria. These are sometimes referred to a blue-green algae, but this name is not appropriate because, as you will see shortly, algae are organisms that belong to domain Eukarya. Cyanobacteria play important roles in food webs of aquatic systems, such as lakes.
Other species of bacteria are heterotrophs, meaning that they need to acquire their food by eating other organisms. This classification includes the bacteria that cause disease in humans (during an infection, the bacteria is eating you). However, most heterotrophic bacteria are harmless to humans. In fact, you have hundreds of species of bacteria living on your skin and in your large intestine that do you no harm. Beyond your body, heterotrophic bacteria play vital roles in ecosystems, especially soil-dwelling bacteria that decompose living matter and make nutrients available to plants.
Domain Archaea
Like bacteria, organisms in domain Archaea are prokaryotic and unicellular. Superficially, they look a lot like bacteria, and many biologists confused them as bacteria until a few decades ago. But hiding in their genes is a story that modern DNA analysis has recently revealed: archaeans are so different genetically that they belong in their own domain.
Many archaean species are found in some of the most inhospitable environments, areas of immense pressure (bottom of the ocean), salinity (such as the Great Salt Lake), or heat (geothermal springs). Organisms that can tolerate and even thrive in such conditions are known as extremophiles. (It should be noted that many bacteria are also extremophiles). Along with genetic evidence, the fact that a large percentage of archaeans are extremophiles suggests that they may be descendants of some of the most ancient lifeforms on Earth; life that originated on a young planet that was inhospitable by today’s standards.
For whatever reason, archaeans are not as abundant in and on the human body as bacteria, and they cause substantially fewer diseases. Research on archaeans continues to shed light on this interesting and somewhat mysterious domain.
Domain Eukarya
This domain is most familiar to use because it includes humans and other animals, along with plants, fungi, and a lesser-known group, the protists. Unlike the other domains, Domain Eukaryacontains multicellular organisms, in addition to unicellular species. The domain is characterized by the presence of eukaryotic cells. For this domain, you will be introduced to several of its kingdoms. Kingdom is the taxonomic grouping immediately below domain (see Figure \(1\)).
Kingdom Animalia is comprised of multicellular, heterotrophic organisms. This kingdom includes humans and other primates, insects, fish, reptiles, and many other types of animals. Kingdom Plantae includes multicellular, autotrophic organisms. Except for a few species that are parasites, plants use photosynthesis to meet their energy demands.
Kingdom Fungi includes multicellular and unicellular, heterotrophic fungi. Fungi are commonly mistaken for plants because some species of fungi grow in the ground. Fungi are fundamentally different from plants in that they do not perform photosynthesis and instead feed on the living matter of others. Another misconception is that all fungi are mushrooms. A mushroom is a temporary reproductive structure used by some fungal species, but not all. Some fungi take the form of molds and mildews, which are commonly seen on rotting food. Lastly, yeast are unicellular fungi. Many species of yeast are important to humans, especially baker’s and brewer’s yeast. Through their metabolism, these yeast produce CO2 gas and alcohol. The former makes bread rise and the latter is the source for all alcoholic beverages.
Protists refer to a highly disparate group that was formerly its own kingdom until recent genetic analysis indicated that it should be split in to many kingdoms (Figure \(4\)). As a group, protists are very diverse and include unicellular, multicellular, heterotrophic, and autotrophic organisms. The term ‘protist’ was used as a catchall for any eukaryote that was neither animal, plant, or fungus. Examples of protists include macroalgae such as kelps and seaweeds, microalgae such as diatoms and dinoflagellates, and important disease-causing microbes such as Plasmodium, the parasite that causes malaria. Sadly, malaria kills hundreds of thousands of people every year.
With this cursory and fundamental understanding of biological diversity, you are now better equipped to study the role of biodiversity in the biosphere and in human economics, health, and culture. Each life form, even the smallest microbe, is a fascinating and and complex living machine. This complexity means we will likely never fully understand each organism and the myriad ways they interact with each other, with us, and with their environment. Thus, it is wise to value biodiversity and take measures to conserve it.
Contributors and Attributions
• This work by Matthew R. Fisher is licensed under CC BY 4.0. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/05%3A_Conservation__Biodiversity/5.01%3A_Introduction_to_Biodiversity.txt |
What biological process is responsible for biodiversity?
All species —from the bacteria on our skin to the birds outside—evolved at some point from a different species. Although it may seem that living things today stay much the same from generation to generation, that is not the case because evolution is ongoing. Evolution is the process through which the characteristics of a species change over time, which can ultimately cause new species to arise.
The theory of evolution is the unifying theory of biology, meaning it is the framework within which biologists ask questions about the living world. Its power is that it provides direction for predictions about living things that are borne out in experiment after experiment. The Ukrainian-born American geneticist Theodosius Dobzhansky famously wrote that “nothing makes sense in biology except in the light of evolution.” He meant that the principle that all life has evolved and diversified from a common ancestor is the foundation from which we understand all other questions in biology.
Discovering How Populations Change
The theory of evolution by natural selection describes a mechanism for how species can change over time. That species change was suggested and debated well before Darwin. The view that species were unchanging was grounded in the writings of Plato, yet there were also ancient Greeks that expressed evolutionary ideas.
In the eighteenth century, ideas about the evolution of animals were reintroduced by the various naturalists. At the same time, James Hutton, the Scottish naturalist, proposed that geological change occurred gradually by the accumulation of small changes from processes (over long periods of time) just like those happening today. This contrasted with the predominant view that the geology of the planet was a consequence of catastrophic events occurring during a relatively brief past. Hutton’s view was later popularized by the geologist Charles Lyell in the nineteenth century. Lyell became a friend to Darwin and his ideas were very influential on Darwin’s thinking. Lyell argued that the greater age of Earth gave more time for gradual change in species, and the process provided an analogy for gradual change in species.
Charles Darwin and Natural Selection
Natural selection as a mechanism for evolution was independently conceived of and described by two naturalists, Charles Darwin and Alfred Russell Wallace, in the mid-nineteenth century. Importantly, each spent years exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world on H.M.S. Beagle, visiting South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, like Wallace’s later journeys in the Malay Archipelago, included stops at several island chains, the last being the Galápagos Islands (west of Ecuador). On these islands, Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galápagos Islands comprised several species that each had a unique beak shape (Figure \(2\)). He observed both that these finches closely resembled another finch species on the mainland of South America and that the group of species in the Galápagos formed a graded series of beak sizes and shapes, with very small differences between the most similar. Darwin imagined that the island species might be all species modified from one original mainland species. In 1860, he wrote, “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”
Wallace and Darwin both observed similar patterns in other organisms and independently conceived a mechanism to explain how and why such changes could take place. Darwin called this mechanism natural selection. Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, there exists variation in traits among individuals within a population, and these traits are inherited, or passed from parent to offspring. Second, more offspring are produced than are able to survive; in other words, resources for survival and reproduction are limited. And lastly, there is a competition for those resources in each generation. Out of these three principles, Darwin and Wallace reasoned that offspring with inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called “descent with modification.” In sum, we can define natural selection as a process the causes beneficial traits to become more common in a population over time, causing the population to evolve.
Papers by Darwin and Wallace (Figure \(3\)) presenting the idea of natural selection were read together in 1858 before the Linnaean Society in London. The following year Darwin’s book, On the Origin of Species, was published, which outlined in considerable detail his arguments for evolution by natural selection.
Natural selection can only take place if there is variation, or differences, among individuals in a population. Importantly, these differences must have some genetic basis, otherwise natural selection would not lead to change in the next generation because there would be no way to transmit those traits from one generation to the next.
Genetic diversity in a population comes from two main sources: mutation and sexual reproduction. Mutation, a permanent change in DNA sequence is the ultimate source of new genetic variation in any population. An individual that has a mutated gene might have a different trait than other individuals in the population. Without variation in traits, nature would not be able to select the traits that are best adapted for the organisms’ environment at that particular time.
Evolutionary change in action
The development of antibiotic resistant bacteria is an example of evolution through natural selection and it has been directly observed by scientists. How does this happen? Imagine a person that has a bacterial infection: their body is being attacked by billions of bacteria. Because there is genetic variation in populations, some individual bacteria may already possess traits that allow them to tolerate antibiotic drugs. When the infected person is prescribed antibiotics, the drug attacks and kills the entire population, except for those bacteria that can resist the drug. These bacteria survive because they had a trait that was beneficial and thus nature selected for it. The surviving population will all be resistant to the drug and continue to reproduce, multiple, and pass down that beneficial trait to all offspring. The population has now evolved because all individuals have the antibiotic-resistant trait, whereas before it was rare. It is important to realize that evolution occurs at the population level and is reliant upon genetic variation that was already present. Without that variation, there is nothing for nature to select for. The rise and spread of antibiotic resistant bacteria is an emerging environmental issue and will be discussed in a later chapter.
Attribution
“Discovering How Populations Change” by Open Stax is licensed under CC BY 4.0. Modified from the original by Matthew R Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/05%3A_Conservation__Biodiversity/5.02%3A_Origin_of_Biodiversity.txt |
The Biodiversity Crisis
Biologists estimate that species extinctions are currently 500–1000 times the normal, or background, rate seen previously in Earth’s history. The current high rates will cause a precipitous decline in the biodiversity of the planet in the next century or two. The loss of biodiversity will include many species we know today. Although it is sometimes difficult to predict which species will become extinct, many are listed as endangered (at great risk of extinction). However, many extinctions will affect species that biologist have not yet discovered. Most of these “invisible” species that will become extinct currently live in tropical rainforests like those of the Amazon basin. These rainforests are the most diverse ecosystems on the planet and are being destroyed rapidly by deforestation. Between 1970 and 2011, almost 20 percent of the Amazon rainforest was lost.
Biodiversity is a broad term for biological variety, and it can be measured at a number of organizational levels. Traditionally, ecologists have measured biodiversity by taking into account both the number of species and the number of individuals of each species (known as relative abundance). However, biologists are using different measures of biodiversity, including genetic diversity, to help focus efforts to preserve the biologically and technologically important elements of biodiversity.
Biodiversity loss refers to the reduction of biodiversity due to displacement or extinction of species. The loss of a particular individual species may seem unimportant to some, especially if it is not a charismatic species like the Bengal tiger or the bottlenose dolphin. However, the current accelerated extinction rate means the loss of tens of thousands of species within our lifetimes. Much of this loss is occurring in tropical rainforests like the one pictured in Figure \(1\), which are very high in biodiversity but are being cleared for timber and agriculture. This is likely to have dramatic effects on human welfare through the collapse of ecosystems.
Biologists recognize that human populations are embedded in ecosystems and are dependent on them, just as is every other species on the planet. Agriculture began after early hunter-gatherer societies first settled in one place and heavily modified their immediate environment. This cultural transition has made it difficult for humans to recognize their dependence on living things other than crops and domesticated animals on the planet. Today our technology smooths out the harshness of existence and allows many of us to live longer, more comfortable lives, but ultimately the human species cannot exist without its surrounding ecosystems. Our ecosystems provide us with food, medicine, clean air and water, recreation, and spiritual and aesthetical inspiration.
Types of Biodiversity
A common meaning of biodiversity is simply the number of species in a location or on Earth; for example, the American Ornithologists’ Union lists 2078 species of birds in North and Central America. This is one measure of the bird biodiversity on the continent. More sophisticated measures of diversity take into account the relative abundances of species. For example, a forest with 10 equally common species of trees is more diverse than a forest that has 10 species of trees wherein just one of those species makes up 95 percent of the trees. Biologists have also identified alternate measures of biodiversity, some of which are important in planning how to preserve biodiversity.
Genetic diversity is one alternate concept of biodiversity. Genetic diversity is the raw material for evolutionary adaptation in a species and is represented by the variety of genes present within a population. A species’ potential to adapt to changing environments or new diseases depends on this genetic diversity.
It is also useful to define ecosystem diversity: the number of different ecosystems on Earth or in a geographical area. The loss of an ecosystem means the loss of the interactions between species and the loss of biological productivity that an ecosystem is able to create. An example of a largely extinct ecosystem in North America is the prairie ecosystem (Figure \(2\)). Prairies once spanned central North America from the boreal forest in northern Canada down into Mexico. They are now all but gone, replaced by crop fields, pasture lands, and suburban sprawl. Many of the species survive, but the hugely productive ecosystem that was responsible for creating our most productive agricultural soils is now gone. As a consequence, their soils are now being depleted unless they are maintained artificially at great expense. The decline in soil productivity occurs because the interactions in the original ecosystem have been lost.
Current Species Diversity
Despite considerable effort, knowledge of the species that inhabit the planet is limited. A recent estimate suggests that only 13% of eukaryotic species have been named (Table 1). Estimates of numbers of prokaryotic species are largely guesses, but biologists agree that science has only just begun to catalog their diversity. . Given that Earth is losing species at an accelerating pace, science knows little about what is being lost.
Table 1. This table shows the estimated number of species by taxonomic group—including both described (named and studied) and predicted (yet to be named) species.
Estimated Numbers of Described and Predicted species
Source: Mora et al 2011 Source: Chapman 2009 Source: Groombridge and Jenkins 2002
Described Predicted Described Predicted Described Predicted
Animals 1,124,516 9,920,000 1,424,153 6,836,330 1,225,500 10,820,000
Photosynthetic protists 17,892 34,900 25,044 200,500
Fungi 44,368 616,320 98,998 1,500,000 72,000 1,500,000
Plants 224,244 314,600 310,129 390,800 270,000 320,000
Non-photosynthetic protists 16,236 72,800 28,871 1,000,000 80,000 600,000
Prokaryotes 10,307 1,000,000 10,175
Total 1,438,769 10,960,000 1,897,502 10,897,630 1,657,675 13,240,000
There are various initiatives to catalog described species in accessible and more organized ways, and the internet is facilitating that effort. Nevertheless, at the current rate of species description, which according to the State of Observed Species1 reports is 17,000–20,000 new species a year, it would take close to 500 years to describe all of the species currently in existence. The task, however, is becoming increasingly impossible over time as extinction removes species from Earth faster than they can be described.
Naming and counting species may seem an unimportant pursuit given the other needs of humanity, but it is not simply an accounting. Describing species is a complex process by which biologists determine an organism’s unique characteristics and whether or not that organism belongs to any other described species. It allows biologists to find and recognize the species after the initial discovery to follow up on questions about its biology. That subsequent research will produce the discoveries that make the species valuable to humans and to our ecosystems. Without a name and description, a species cannot be studied in depth and in a coordinated way by multiple scientists.
Patterns of Biodiversity
Biodiversity is not evenly distributed on the planet. Lake Victoria contained almost 500 species of cichlids (just one family of fishes that are present in the lake) before the introduction of an exotic species in the 1980s and 1990s caused a mass extinction. All of these species were found only in Lake Victoria, which is to say they were endemic. Endemic species are found in only one location. For example, the blue jay is endemic to North America, while the Barton Springs salamander is endemic to the mouth of one spring in Austin, Texas. Endemic species with highly restricted distributions, like the Barton Springs salamander, are particularly vulnerable to extinction.
Lake Huron contains about 79 species of fish, all of which are found in many other lakes in North America. What accounts for the difference in diversity between Lake Victoria and Lake Huron? Lake Victoria is a tropical lake, while Lake Huron is a temperate lake. Lake Huron in its present form is only about 7,000 years old, while Lake Victoria in its present form is about 15,000 years old. These two factors, latitude and age, are two of several hypotheses biogeographers have suggested to explain biodiversity patterns on Earth.
Biogeography is the study of the distribution of the world’s species both in the past and in the present. The work of biogeographers is critical to understanding our physical environment, how the environment affects species, and how changes in environment impact the distribution of a species.
There are three main fields of study under the heading of biogeography: ecological biogeography, historical biogeography (called paleobiogeography), and conservation biogeography. Ecological biogeography studies the current factors affecting the distribution of plants and animals. Historical biogeography, as the name implies, studies the past distribution of species. Conservation biogeography, on the other hand, is focused on the protection and restoration of species based upon the known historical and current ecological information.
One of the oldest observed patterns in ecology is that biodiversity typically increases as latitude declines. In other words, biodiversity increases closer to the equator (Figure \(3\)).
It is not yet clear why biodiversity increases closer to the equator, but hypotheses include the greater age of the ecosystems in the tropics versus temperate regions, which were largely devoid of life or drastically impoverished during the last ice age. The greater age provides more time for speciation, the evolutionary process of creating new species. Another possible explanation is the greater energy the tropics receive from the sun. But scientists have not been able to explain how greater energy input could translate into more species. The complexity of tropical ecosystems may promote speciation by increasing the habitat complexity, thus providing more ecological niches. Lastly, the tropics have been perceived as being more stable than temperate regions, which have a pronounced climate and day-length seasonality. The stability of tropical ecosystems might promote speciation. Regardless of the mechanisms, it is certainly true that biodiversity is greatest in the tropics. There are also high numbers of endemic species.
Importance of Biodiversity
Loss of biodiversity may have reverberating consequences on ecosystems because of the complex interrelations among species. For example, the extinction of one species may cause the extinction of another. Biodiversity is important to the survival and welfare of human populations because it has impacts on our health and our ability to feed ourselves through agriculture and harvesting populations of wild animals.
Human Health
Many medications are derived from natural chemicals made by a diverse group of organisms. For example, many plants produce compounds meant to protect the plant from insects and other animals that eat them. Some of these compounds also work as human medicines. Contemporary societies that live close to the land often have a broad knowledge of the medicinal uses of plants growing in their area. For centuries in Europe, older knowledge about the medical uses of plants was compiled in herbals—books that identified the plants and their uses. Humans are not the only animals to use plants for medicinal reasons. The other great apes, orangutans, chimpanzees, bonobos, and gorillas have all been observed self-medicating with plants.
Modern pharmaceutical science also recognizes the importance of these plant compounds. Examples of significant medicines derived from plant compounds include aspirin, codeine, digoxin, atropine, and vincristine (Figure \(4\)). Many medications were once derived from plant extracts but are now synthesized. It is estimated that, at one time, 25 percent of modern drugs contained at least one plant extract. That number has probably decreased to about 10 percent as natural plant ingredients are replaced by synthetic versions of the plant compounds. Antibiotics, which are responsible for extraordinary improvements in health and lifespans in developed countries, are compounds largely derived from fungi and bacteria.
In recent years, animal venoms and poisons have excited intense research for their medicinal potential. By 2007, the FDA had approved five drugs based on animal toxins to treat diseases such as hypertension, chronic pain, and diabetes. Another five drugs are undergoing clinical trials and at least six drugs are being used in other countries. Other toxins under investigation come from mammals, snakes, lizards, various amphibians, fish, snails, octopuses, and scorpions.
Aside from representing billions of dollars in profits, these medications improve people’s lives. Pharmaceutical companies are actively looking for new natural compounds that can function as medicines. It is estimated that one third of pharmaceutical research and development is spent on natural compounds and that about 35 percent of new drugs brought to market between 1981 and 2002 were from natural compounds.
Finally, it has been argued that humans benefit psychologically from living in a biodiverse world. The chief proponent of this idea is famed entomologist E. O. Wilson. He argues that human evolutionary history has adapted us to living in a natural environment and that built environments generate stresses that affect human health and well-being. There is considerable research into the psychologically regenerative benefits of natural landscapes that suggest the hypothesis may hold some truth.
Agricultural
Since the beginning of human agriculture more than 10,000 years ago, human groups have been breeding and selecting crop varieties. This crop diversity matched the cultural diversity of highly subdivided populations of humans. For example, potatoes were domesticated beginning around 7,000 years ago in the central Andes of Peru and Bolivia. The people in this region traditionally lived in relatively isolated settlements separated by mountains. The potatoes grown in that region belong to seven species and the number of varieties likely is in the thousands. Each variety has been bred to thrive at particular elevations and soil and climate conditions. The diversity is driven by the diverse demands of the dramatic elevation changes, the limited movement of people, and the demands created by crop rotation for different varieties that will do well in different fields.
Potatoes are only one example of agricultural diversity. Every plant, animal, and fungus that has been cultivated by humans has been bred from original wild ancestor species into diverse varieties arising from the demands for food value, adaptation to growing conditions, and resistance to pests. The potato demonstrates a well-known example of the risks of low crop diversity: during the tragic Irish potato famine (1845–1852 AD), the single potato variety grown in Ireland became susceptible to a potato blight—wiping out the crop. The loss of the crop led to famine, death, and mass emigration. Resistance to disease is a chief benefit to maintaining crop biodiversity and lack of diversity in contemporary crop species carries similar risks. Seed companies, which are the source of most crop varieties in developed countries, must continually breed new varieties to keep up with evolving pest organisms. These same seed companies, however, have participated in the decline of the number of varieties available as they focus on selling fewer varieties in more areas of the world replacing traditional local varieties.
The ability to create new crop varieties relies on the diversity of varieties available and the availability of wild forms related to the crop plant. These wild forms are often the source of new gene variants that can be bred with existing varieties to create varieties with new attributes. Loss of wild species related to a crop will mean the loss of potential in crop improvement. Maintaining the genetic diversity of wild species related to domesticated species ensures our continued supply of food.
Since the 1920s, government agriculture departments have maintained seed banks of crop varieties as a way to maintain crop diversity. This system has flaws because over time seed varieties are lost through accidents and there is no way to replace them. In 2008, the Svalbard Global seed Vault, located on Spitsbergen island, Norway, (Figure) began storing seeds from around the world as a backup system to the regional seed banks. If a regional seed bank stores varieties in Svalbard, losses can be replaced from Svalbard should something happen to the regional seeds. The Svalbard seed vault is deep into the rock of the arctic island. Conditions within the vault are maintained at ideal temperature and humidity for seed survival, but the deep underground location of the vault in the arctic means that failure of the vault’s systems will not compromise the climatic conditions inside the vault.
Although crops are largely under our control, our ability to grow them is dependent on the biodiversity of the ecosystems in which they are grown. That biodiversity creates the conditions under which crops are able to grow through what are known as ecosystem services—valuable conditions or processes that are carried out by an ecosystem. Crops are not grown, for the most part, in built environments. They are grown in soil. Although some agricultural soils are rendered sterile using controversial pesticide treatments, most contain a huge diversity of organisms that maintain nutrient cycles—breaking down organic matter into nutrient compounds that crops need for growth. These organisms also maintain soil texture that affects water and oxygen dynamics in the soil that are necessary for plant growth. Replacing the work of these organisms in forming arable soil is not practically possible. These kinds of processes are called ecosystem services. They occur within ecosystems, such as soil ecosystems, as a result of the diverse metabolic activities of the organisms living there, but they provide benefits to human food production, drinking water availability, and breathable air.
Other key ecosystem services related to food production are plant pollination and crop pest control. It is estimated that honeybee pollination within the United States brings in \$1.6 billion per year; other pollinators contribute up to \$6.7 billion. Over 150 crops in the United States require pollination to produce. Many honeybee populations are managed by beekeepers who rent out their hives’ services to farmers. Honeybee populations in North America have been suffering large losses caused by a syndrome known as colony collapse disorder, a new phenomenon with an unclear cause. Other pollinators include a diverse array of other bee species and various insects and birds. Loss of these species would make growing crops requiring pollination impossible, increasing dependence on other crops.
Finally, humans compete for their food with crop pests, most of which are insects. Pesticides control these competitors, but these are costly and lose their effectiveness over time as pest populations adapt. They also lead to collateral damage by killing non-pest species as well as beneficial insects like honeybees, and risking the health of agricultural workers and consumers. Moreover, these pesticides may migrate from the fields where they are applied and do damage to other ecosystems like streams, lakes, and even the ocean. Ecologists believe that the bulk of the work in removing pests is actually done by predators and parasites of those pests, but the impact has not been well studied. A review found that in 74 percent of studies that looked for an effect of landscape complexity (forests and fallow fields near to crop fields) on natural enemies of pests, the greater the complexity, the greater the effect of pest-suppressing organisms. Another experimental study found that introducing multiple enemies of pea aphids (an important alfalfa pest) increased the yield of alfalfa significantly. This study shows that a diversity of pests is more effective at control than one single pest. Loss of diversity in pest enemies will inevitably make it more difficult and costly to grow food. The world’s growing human population faces significant challenges in the increasing costs and other difficulties associated with producing food.
Wild Food Sources
In addition to growing crops and raising food animals, humans obtain food resources from wild populations, primarily wild fish populations. For about one billion people, aquatic resources provide the main source of animal protein. But since 1990, production from global fisheries has declined. Despite considerable effort, few fisheries on Earth are managed sustainability.
Fishery extinctions rarely lead to complete extinction of the harvested species, but rather to a radical restructuring of the marine ecosystem in which a dominant species is so over-harvested that it becomes a minor player, ecologically. In addition to humans losing the food source, these alterations affect many other species in ways that are difficult or impossible to predict. The collapse of fisheries has dramatic and long-lasting effects on local human populations that work in the fishery. In addition, the loss of an inexpensive protein source to populations that cannot afford to replace it will increase the cost of living and limit societies in other ways. In general, the fish taken from fisheries have shifted to smaller species and the larger species are overfished. The ultimate outcome could clearly be the loss of aquatic systems as food sources. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/05%3A_Conservation__Biodiversity/5.03%3A_Importance_of_Biodiversity.txt |
The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and the resources used by that population. The human population requires resources to survive and grow, and many of those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and introduction of exotic species. The first two of these are a direct result of human population growth and resource use. The third results from increased mobility and trade. A fourth major cause of extinction, anthropogenic (human-caused) climate change, has not yet had a large impact, but it is predicted to become significant during this century. Global climate change is also a consequence of human population needs for energy and the use of fossil fuels to meet those needs (Figure \(1\)). Environmental issues, such as toxic pollution, have specific targeted effects on species, but are not generally seen as threats at the magnitude of the others.
Habitat Loss
Humans rely on technology to modify their environment and make it habitable. Other species cannot do this. Elimination of their habitat—whether it is a forest, coral reef, grassland, or flowing river—will kill the individuals in the species. Remove the entire habitat and the species will become extinct, unless they are among the few species that do well in human-built environments. Human destruction of habitats (habitat generally refers to the part of the ecosystem required by a particular species) accelerated in the latter half of the twentieth century.
Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN), but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are removed for timber and to plant palm oil plantations (Figure \(2\)). Palm oil is used in many products including food products, cosmetics, and biodiesel in Europe. A 5-year estimate of global forest cover loss for the years from 2000 to 2005 was 3.1%. Much loss (2.4%) occurred in the tropics where forest loss is primarily from timber extraction. These losses certainly also represent the extinction of species unique to those areas.
BIOLOGY IN ACTION: Preventing Habitat Destruction with Wise Wood Choices
Most consumers do not imagine that the home improvement products they buy might be contributing to habitat loss and species extinctions. Yet the market for illegally harvested tropical timber is huge, and the wood products often find themselves in building supply stores in the United States. One estimate is that up to 10% of the imported timber in the United States, which is the world’s largest consumer of wood products, is illegally logged. In 2006, this amounted to \$3.6 billion in wood products. Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood.
How is it possible to determine if a wood product, such as flooring, was harvested sustainably or even legally? The Forest Stewardship Council (FSC) certifies sustainably harvested forest products. Looking for their certification on flooring and other hardwood products is one way to ensure that the wood has not been taken illegally from a tropical forest. There are certifications other than the FSC, but these are run by timber companies, thus creating a conflict of interest. Another approach is to buy domestic wood species. While it would be great if there was a list of legal versus illegal woods, it is not that simple. Logging and forest management laws vary from country to country; what is illegal in one country may be legal in another. Where and how a product is harvested and whether the forest from which it comes is being sustainably maintained all factor into whether a wood product will be certified by the FSC. It is always a good idea to ask questions about where a wood product came from and how the supplier knows that it was harvested legally.
Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently the target of habitat modification. Damming of rivers affects flow and access to habitat. Altering a flow regime can reduce or eliminate populations that are adapted to seasonal changes in flow. For example, an estimated 91% of riverways in the United States have been modified with damming or stream bank modification. Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in both aquatic and terrestrial habitats are at greater risk of population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost. This is of particular concern because amphibians have been declining in numbers and going extinct more rapidly than many other groups for a variety of possible reasons.
Overharvesting
Overharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated fisheries (including hunting of marine mammals and harvesting of crustaceans and other species) monitored by fisheries scientists that have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature.
Most fisheries are managed as a common resource, available to anyone willing to fish, even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons, in which fishers have little motivation to exercise restraint in harvesting a fishery when they do not own the fishery. The general outcome of harvests of resources held in common is their overexploitation. While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will drive toward fishing the population to extinction.
Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4000 species—despite making up only one percent of marine habitat. Most home marine aquaria house coral reef species that are wild-caught organisms—not cultured organisms. Although no marine species is known to have been driven extinct by the pet trade, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are also concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutans.
Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly. However, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many monkeys and the great apes living in the Congo basin.
Invasive Species
Exotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems. These new introductions are sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators.
Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, have characteristics that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. When this happens, the exotic species also becomes an invasive species. Invasive species can threaten other species through competition for resources, predation, or disease.
Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft (Figure \(4\)) from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.
Many introductions of aquatic species, both marine and freshwater, have occurred when ships have dumped ballast water taken on at a port of origin into waters at a destination port. Water from the port of origin is pumped into tanks on a ship empty of cargo to increase stability. The water is drawn from the ocean or estuary of the port and typically contains living organisms such as plant parts, microorganisms, eggs, larvae, or aquatic animals. The water is then pumped out before the ship takes on cargo at the destination port, which may be on a different continent. The zebra mussel was introduced to the Great Lakes from Europe prior to 1988 in ballast water. The zebra mussels in the Great Lakes have created millions of dollars in clean-up costs to maintain water intakes and other facilities. The mussels have also altered the ecology of the lakes dramatically. They threaten native mollusk populations, but have also benefited some species, such as smallmouth bass. The mussels are filter feeders and have dramatically improved water clarity, which in turn has allowed aquatic plants to grow along shorelines, providing shelter for young fish where it did not exist before. The European green crab, Carcinus maenas, was introduced to San Francisco Bay in the late 1990s, likely in ship ballast water, and has spread north along the coast to Washington. The crabs have been found to dramatically reduce the abundance of native clams and crabs with resulting increases in the prey species of those native crabs.
Invading exotic species can also be disease organisms. It now appears that the global decline in amphibian species recognized in the 1990s is, in some part, caused by the fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis (Figure \(5\)). There is evidence that the fungus is native to Africa and may have been spread throughout the world by transport of a commonly used laboratory and pet species: the African clawed frog, Xenopus laevis. It may well be that biologists themselves are responsible for spreading this disease worldwide. The North American bullfrog, Rana catesbeiana, which has also been widely introduced as a food animal but which easily escapes captivity, survives most infections of B. dendrobatidis and can act as a reservoir for the disease.
Early evidence suggests that another fungal pathogen, Geomyces destructans, introduced from Europe is responsible for white-nose syndrome, which infects cave-hibernating bats in eastern North America and has spread from a point of origin in western New York State (Figure \(6\)). The disease has decimated bat populations and threatens extinction of species already listed as endangered: the Indiana bat, Myotis sodalis, and potentially the Virginia big-eared bat, Corynorhinus townsendii virginianus. How the fungus was introduced is unknown, but one logical presumption would be that recreational cavers unintentionally brought the fungus on clothes or equipment from Europe.
Climate Change
Climate change, and specifically the anthropogenic warming trend presently underway, is recognized as a major extinction threat, particularly when combined with other threats such as habitat loss. Anthropogenic warming of the planet has been observed and is due to past and continuing emission of greenhouse gases, primarily carbon dioxide and methane, into the atmosphere caused by the burning of fossil fuels and deforestation. Scientists overwhelmingly agree the present warming trend is caused by humans and some of the likely effects include dramatic and dangerous climate changes in the coming decades. Scientists predict that climate change will alter regional climates, including rainfall and snowfall patterns, making habitats less hospitable to the species living in them. The warming trend will shift colder climates toward the north and south poles, forcing species to move (if possible) with their adapted climate norms.
The shifting ranges will impose new competitive regimes on species as they find themselves in contact with other species not present in their historic range. One such unexpected species contact is between polar bears and grizzly bears. Previously, these two species had separate ranges. Now, their ranges are overlapping and there are documented cases of these two species mating and producing viable offspring. Changing climates also throw off the delicate timing adaptations that species have to seasonal food resources and breeding times. Scientists have already documented many contemporary mismatches to shifts in resource availability and timing.
Other shifts in range have been observed. For example, one study indicates that European bird species ranges have moved 91 km (56.5 mi) northward, on average. The same study suggested that the optimal shift based on warming trends was double that distance, suggesting that the populations are not moving quickly enough. Range shifts have also been observed in plants, butterflies, other insects, freshwater fishes, reptiles, amphibians, and mammals.
Climate gradients will also move up mountains, eventually crowding species higher in altitude and eliminating the habitat for those species adapted to the highest elevations. Some climates will completely disappear. The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months. Seals are a critical source of protein for polar bears. A trend to decreasing sea ice coverage has occurred since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously predicted by climate models.
Finally, global warming will raise ocean levels due to meltwater from glaciers and the greater volume occupied by warmer water. Shorelines will be inundated, reducing island size, which will have an effect on some species, and a number of islands will disappear entirely. Additionally, the gradual melting and subsequent refreezing of the poles, glaciers, and higher elevation mountains—a cycle that has provided freshwater to environments for centuries—will be altered. This could result in an overabundance of salt water and a shortage of fresh water.
Suggested Supplementary Reading:
Hall. S. 2017. Could Genetic Engineering Save the Galápagos? Scientific American. December. p. 48-57.
This article explores the destructive nature of invasive species in the Galápagos Islands. Traditional efforts to eradicate invasive species, such as rats, can be expensive and cause ecological harm by the widespread distribution of poison. An alternate approach is genetic engineering in the form of a “gene drive”, an emerging technique that could be better – or worse – for the environment.
Contributors and Attributions
• Threats to Biodiversity by OpenStax is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/05%3A_Conservation__Biodiversity/5.04%3A_Threats_to_Biodiversity.txt |
Preserving biodiversity is an extraordinary challenge that must be met by greater understanding of biodiversity itself, changes in human behavior and beliefs, and various preservation strategies.
Change in Biodiversity through Time
The number of species on the planet, or in any geographical area, is the result of an equilibrium of two evolutionary processes that are ongoing: speciation and extinction. When speciation rates begin to outstrip extinction rates, the number of species will increase. Likewise, the reverse is true when extinction rates begin to overtake speciation rates. Throughout the history of life on Earth, as reflected in the fossil record, these two processes have fluctuated to a greater or lesser extent, sometimes leading to dramatic changes in the number of species on the planet as reflected in the fossil record (Figure \(1\)).
Paleontologists have identified five layers in the fossil record that appear to show sudden and dramatic losses in biodiversity. These are called mass extinctionsand are characterized by more than half of all species disappearing from the fossil record. There are many lesser, yet still dramatic, extinction events, but the five mass extinctions have attracted the most research into their causes. An argument can be made that the five mass extinctions are only the five most extreme events in a continuous series of large extinction events throughout the fossil record (since 542 million years ago). The most recent extinction in geological time, about 65 million years ago, saw the disappearance of most dinosaurs species (except birds) and many other species. Most scientists now agree the main cause of this extinction was the impact of a large asteroid in the present-day Yucatán Peninsula and the subsequent energy release and global climate changes caused by dust ejected into the atmosphere.
Recent and Current Extinction Rates
Many biologists say that we are currently experience a sixth mass extinction and it mostly has to do with the activities of humans. There are numerous recent extinctions of individual species that are recorded in human writings. Most of these are coincident with the expansion of the European colonies since the 1500s.
One of the earlier and popularly known examples is the dodo bird. The dodo bird lived in the forests of Mauritius, an island in the Indian Ocean. The dodo bird became extinct around 1662. It was hunted for its meat by sailors and was easy prey because the dodo, which did not evolve with humans, would approach people without fear. Introduced pigs, rats, and dogs brought to the island by European ships also killed dodo young and eggs (Figure \(2\)).
Steller’s sea cow became extinct in 1768; it was related to the manatee and probably once lived along the northwest coast of North America. Steller’s sea cow was discovered by Europeans in 1741, and it was hunted for meat and oil. A total of 27 years elapsed between the sea cow’s first contact with Europeans and extinction of the species. The last Steller’s sea cow was killed in 1768. In another example, the last living passenger pigeon died in a zoo in Cincinnati, Ohio, in 1914. This species had once migrated in the millions but declined in numbers because of overhunting and loss of habitat through the clearing of forests for farmland.
These are only a few of the recorded extinctions in the past 500 years. The International Union for Conservation of Nature (IUCN) keeps a list of extinct and endangered species called the Red List. The list is not complete, but it describes 380 vertebrates that became extinct after 1500 AD, 86 of which were driven extinct by overhunting or overfishing.
Estimates of Present-day Extinction Rates
Estimates of extinction rates are hampered by the fact that most extinctions are probably happening without being observed. The extinction of a bird or mammal is often noticed by humans, especially if it has been hunted or used in some other way. But there are many organisms that are less noticeable to humans (not necessarily of less value) and many that are undescribed.
The background extinction rate is estimated to be about 1 per million species years (E/MSY). One “species year” is one species in existence for one year. One million species years could be one species persisting for one million years, or a million species persisting for one year. If it is the latter, then one extinction per million species years would be one of those million species becoming extinct in that year. For example, if there are 10 million species in existence, then we would expect 10 of those species to become extinct in a year. This is the background rate.
One contemporary extinction-rate estimate uses the extinctions in the written record since the year 1500. For birds alone, this method yields an estimate of 26 E/MSY, almost three times the background rate. However, this value may be underestimated for three reasons. First, many existing species would not have been described until much later in the time period and so their loss would have gone unnoticed. Second, we know the number is higher than the written record suggests because now extinct species are being described from skeletal remains that were never mentioned in written history. And third, some species are probably already extinct even though conservationists are reluctant to name them as such. Taking these factors into account raises the estimated extinction rate to nearer 100 E/MSY. The predicted rate by the end of the century is 1500 E/MSY.
A second approach to estimating present-time extinction rates is to correlate species loss with habitat loss, and it is based on measuring forest-area loss and understanding species–area relationships. The species-area relationship is the rate at which new species are seen when the area surveyed is increased (Figure \(3\)). Likewise, if the habitat area is reduced, the number of species seen will also decline. This kind of relationship is also seen in the relationship between an island’s area and the number of species present on the island: as one increases, so does the other, though not in a straight line. Estimates of extinction rates based on habitat loss and species–area relationships have suggested that with about 90 percent of habitat loss an expected 50 percent of species would become extinct. Figure \(3\) shows that reducing forest area from 100 km2 to 10 km2, a decline of 90 percent, reduces the number of species by about 50 percent. Species–area estimates have led to estimates of present-day species extinction rates of about 1000 E/MSY and higher.
Conservation of Biodiversity
The threats to biodiversity have been recognized for some time. Today, the main efforts to preserve biodiversity involve legislative approaches to regulate human and corporate behavior, setting aside protected areas, and habitat restoration.
Changing Human Behavior
Legislation has been enacted to protect species throughout the world. The legislation includes international treaties as well as national and state laws. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) treaty came into force in 1975. The treaty, and the national legislation that supports it, provides a legal framework for preventing “listed” species from being transported across nations’ borders, thus protecting them from being caught or killed when the purpose involves international trade. The listed species that are protected by the treaty number some 33,000. The treaty is limited in its reach because it only deals with international movement of organisms or their parts. It is also limited by various countries’ ability or willingness to enforce the treaty and supporting legislation. The illegal trade in organisms and their parts is probably a market in the hundreds of millions of dollars.
Within many countries there are laws that protect endangered species and that regulate hunting and fishing. In the United States, the Endangered Species Act (ESA) was enacted in 1973. When an at-risk species is listed by the Act, the U.S. Fish & Wildlife Service is required by law to develop a management plan to protect the species and bring it back to sustainable numbers. The ESA, and others like it in other countries, is a useful tool, but it suffers because it is often difficult to get a species listed or to get an effective management plan in place once a species is listed.
The Migratory Bird Treaty Act (MBTA) is an agreement between the United States and Canada that was signed into law in 1918 in response to declines in North American bird species caused by hunting. The Act now lists over 800 protected species. It makes it illegal to disturb or kill the protected species or distribute their parts (much of the hunting of birds in the past was for their feathers). Examples of protected species include northern cardinals, the red-tailed hawk, and the American black vulture.
Global warming is expected to be a major driver of biodiversity loss. Many governments are concerned about the effects of anthropogenic global warming, primarily on their economies and food resources. Because greenhouse gas emissions do not respect national boundaries, the effort to curb them is international. The international response to global warming has been mixed. The Kyoto Protocol, an international agreement that came out of the United Nations Framework Convention on Climate Change that committed countries to reducing greenhouse gas emissions by 2012, was ratified by some countries, but spurned by others. Two countries that were especially important in terms of their potential impact that did not ratify the Kyoto protocol were the United States and China. Some goals for reduction in greenhouse gasses were met and exceeded by individual countries, but, worldwide, the effort to limit greenhouse gas production is not succeeding. A renegotiated 2016 treaty, called the Paris Agreement, once again brought nations together to take meaningful action on climate change. But like before, some nations are reluctant to participate. The newly-elected President Trump has indicated that he will withdraw the United States’ support of the agreement.
Conservation in Preserves
Establishment of wildlife and ecosystem preserves is one of the key tools in conservation efforts (Figure \(4\)). A preserve is an area of land set aside with varying degrees of protection for the organisms that exist within the boundaries of the preserve. In 2003, the IUCN World Parks Congress estimated that 11.5 percent of Earth’s land surface was covered by preserves of various kinds. This area is large but only represents 9 out of 14 recognized major biomes and research has shown that 12 percent of all species live outside preserves.
A biodiversity hotspot is a conservation concept developed by Norman Myers in 1988. Hotspots are geographical areas that contain high numbers of endemic species. The purpose of the concept was to identify important locations on the planet for conservation efforts, a kind of conservation triage. By protecting hotspots, governments are able to protect a larger number of species. The original criteria for a hotspot included the presence of 1500 or more species of endemic plants and 70 percent of the area disturbed by human activity. There are now 34 biodiversity hotspots (Figure \(5\)) that contain large numbers of endemic species, which include half of Earth’s endemic plants.
There has been extensive research into optimal preserve designs for maintaining biodiversity. The fundamental principles behind much of the research have come from the seminal theoretical work of Robert H. MacArthur and Edward O. Wilson published in 1967 on island biogeography.1This work sought to understand the factors affecting biodiversity on islands. Conservation preserves can be seen as “islands” of habitat within “an ocean” of non-habitat. In general, large preserves are better because they support more species, including species with large home ranges; they have more core area of optimal habitat for individual species; they have more niches to support more species; and they attract more species because they can be found and reached more easily. One large preserve is better than the same area of several smaller preserves because there is more core habitat unaffected by less hospitable ecosystems outside the preserve boundary. For this same reason, preserves in the shape of a square or circle will be better than a preserve with many thin “arms.” If preserves must be smaller, then providing wildlife corridors (narrow strips of protected land) between two preserves is important so that species and their genes can move between them. All of these factors are taken into consideration when planning the nature of a preserve before the land is set aside.
In addition to the physical specifications of a preserve, there are a variety of regulations related to the use of a preserve. These can include anything from timber extraction, mineral extraction, regulated hunting, human habitation, and nondestructive human recreation. Many of the decisions to include these other uses are made based on political pressures rather than conservation considerations. On the other hand, in some cases, wildlife protection policies have been so strict that subsistence-living indigenous populations have been forced from ancestral lands that fell within a preserve. In other cases, even if a preserve is designed to protect wildlife, if the protections are not or cannot be enforced, the preserve status will have little meaning in the face of illegal poaching and timber extraction. This is a widespread problem with preserves in the tropics.
Climate change will create inevitable problems with the location of preserves as the species within them migrate to higher latitudes as the habitat of the preserve becomes less favorable. Planning for the effects of global warming on future preserves, or adding new preserves to accommodate the changes expected from global warming is in progress, but will only be as effective as the accuracy of the predictions of the effects of global warming on future habitats.
Finally, an argument can be made that conservation preserves reinforce the cultural perception that humans are separate from nature, can exist outside of it, and can only operate in ways that do damage to biodiversity. Creating preserves reduces the pressure on human activities outside the preserves to be sustainable and non-damaging to biodiversity. Ultimately, the political, economic, and human demographic pressures will degrade and reduce the size of conservation preserves if the activities outside them are not altered to be less damaging to biodiversity.
Habitat Restoration
Habitat restoration is the process of bringing an area back to its natural state, before it was impacted through destructive human activities. It holds considerable promise as a mechanism for maintaining or restoring biodiversity. Reintroducing wolves, a top predator, to Yellowstone National Park in 1995 led to dramatic changes in the ecosystem that increased biodiversity. The wolves (Figure \(6\)) function to suppress elk and coyote populations and provide more abundant resources to the detritivores. Reducing elk populations has allowed revegetation of riparian (the areas along the banks of a stream or river) areas, which has increased the diversity of species in that habitat. Reduction of coyote populations by wolves has increased the prey species previously suppressed by coyotes. In this habitat, the wolf is a keystone species, meaning a species that is instrumental in maintaining diversity within an ecosystem. Removing a keystone species from an ecological community causes a collapse in diversity. The results from the Yellowstone experiment suggest that restoring a keystone species effectively can have the effect of restoring biodiversity in the community. Ecologists have argued for the identification of keystone species where possible and for focusing protection efforts on these species. It makes sense to return the keystone species to the ecosystems where they have been removed.
Other large-scale restoration experiments underway involve dam removal. In the United States, since the mid-1980s, many aging dams are being considered for removal rather than replacement because of shifting beliefs about the ecological value of free-flowing rivers. The measured benefits of dam removal include restoration of naturally fluctuating water levels (often the purpose of dams is to reduce variation in river flows), which leads to increased fish diversity and improved water quality. In the Pacific Northwest of the United States, dam removal projects are expected to increase populations of salmon, which is considered a keystone species because it transports nutrients to inland ecosystems during its annual spawning migrations. In other regions, such as the Atlantic coast, dam removal has allowed the return of other spawning anadromous fish species (species that are born in fresh water, live most of their lives in salt water, and return to fresh water to spawn). Some of the largest dam removal projects have yet to occur or have happened too recently for the consequences to be measured, such as Elwha Dam on the Olympic Peninsula of Washington State. The large-scale ecological experiments that these removal projects constitute will provide valuable data for other dam projects slated either for removal or construction.
The Role of Zoos and Captive Breeding
Zoos have sought to play a role in conservation efforts both through captive breeding programs and education (Figure \(7\)). The transformation of the missions of zoos from collection and exhibition facilities to organizations that are dedicated to conservation is ongoing. In general, it has been recognized that, except in some specific targeted cases, captive breeding programs for endangered species are inefficient and often prone to failure when the species are reintroduced to the wild. Zoo facilities are far too limited to contemplate captive breeding programs for the numbers of species that are now at risk. Education, on the other hand, is a potential positive impact of zoos on conservation efforts, particularly given the global trend to urbanization and the consequent reduction in contacts between people and wildlife. A number of studies have been performed to look at the effectiveness of zoos on people’s attitudes and actions regarding conservation and at present, the results tend to be mixed.
Suggested Supplemental Reading:
Paterniti. 2017. Should we Kill Animals to Save Them? National Geographic. October.
This article in National Geographic takes a closer look at whether or not sport hunting benefits wildlife conservation. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/05%3A_Conservation__Biodiversity/5.05%3A_Preserving_Biodiversity.txt |
Summary
Biodiversity exists at multiple levels of organization, and is measured in different ways depending on the goals of those taking the measurements. These include numbers of species, genetic diversity, chemical diversity, and ecosystem diversity. Humans use many compounds that were first discovered or derived from living organisms as medicines: secondary plant compounds, animal toxins, and antibiotics produced by bacteria and fungi. Ecosystems provide ecosystem services that support human agriculture: pollination, nutrient cycling, pest control, and soil development and maintenance. Loss of biodiversity threatens these ecosystem services and risks making food production more expensive or impossible. The core threats to biodiversity are human population growth and unsustainable resource use. Climate change is predicted to be a significant cause of extinction in the coming century. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. International treaties such as CITES regulate the transportation of endangered species across international borders. In the United States, the Endangered Species Act protects listed species but is hampered by procedural difficulties and a focus on individual species. The Migratory Bird Act is an agreement between Canada and the United States to protect migratory birds. Presently, 11 percent of Earth’s land surface is protected in some way. Habitat restoration has the potential to restore ecosystems to previous biodiversity levels before species become extinct. Examples of restoration include reintroduction of keystone species and removal of dams on rivers.
Review Questions
1. Bacteria that feed upon decaying organic matter in the soil would best be described as which one of the following?
1. Eukaryotic
2. Autotrophic
3. Fungi
4. Cyanobacteria
5. Heterotrophic
2. As Darwin recognized, populations evolve through natural selection when which of the following condition(s) are met?
1. Variation of traits among individuals
2. Competition for limited resources
3. More offspring are produced than can survive
4. All of the above
3. You are the world’s foremost expert on lizards. You have traveled the world extensively and have found that a particular species of lizard is found only in one desert near of the Chilean Andes. Which of following terms, with regard to its distribution, can be definitively applied to this species?
1. Endangered
2. Prokaryotic
3. Endemic
4. Disbursed
5. Clustered
4. Which one of the following is not a major cause of biodiversity loss?
1. Habitat loss
2. Climate change
3. Invasive Species
4. Zoonotic diseases
5. Overharvesting
5. Which one of the following statements is false?
1. There have been five mass extinctions preserved in the fossil record
2. Some bacteria are autotrophs
3. Current rates of extinction are higher than background extinction rates
4. Speciation is the process of creating new species
5. All living things can be classified into one of four taxonomic domains
6. During the middle of the 19th century, which scientist independently derived and proposed a theory of evolution that was similar to Darwin’s?
1. Gregor Mendel
2. Alfred Wallace
3. Isaac Newton
4. Rachel Carson
5. Niels Bohr
7. The study of the distribution of the world’s species both in the past and in the present is known by what term?
1. Geology
2. Biogeography
3. Biodiversity
4. Biogeomorphology
5. Ecological Succession
8. Which one of the following would be described as anthropogenic?
1. Water backing up behind a beaver dam
2. The dinosaurs going extinct
3. Logging a forest
4. A mudslide burying a stream
5. A volcanic eruption
9. By definition, what are you most likely to find in a biodiversity hotspot?
1. A large abundance of endangered species
2. A large number of endemic species
3. Mostly eukaryotic species
4. Extremophiles
5. Heat-loving microbes
10. You are working as a biologist for a team surveying biodiversity in the Amazon rainforest. You find a non-motile organism that grows in the soil, has eukaryotic cells, and is heterotrophic. Which one of the following could potentially describe this species?
1. Fungus
2. Animal
3. Bacteria
4. Plant
5. Archaea
See Appendix for answers
Attributions
OpenStax College. (2013). Concepts of biology. Retrieved from http://cnx.org/contents/[email protected]. OpenStax CNX. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/05%3A_Conservation__Biodiversity/5.06%3A_Chapter_Resources.txt |
Learning Outcomes
• Define environmental health
• Categorize environmental health risks
• Explain the concept of emerging diseases
• Summarize the principles of environmental toxicology
• Classify environmental contaminants
• 6.1: The Impacts of Environmental Conditions
Our industrialized society dumps huge amounts of pollutants and toxic wastes into the earth’s biosphere without fully considering the consequences. Such actions seriously degrade the health of the earth’s ecosystems, and this degradation ultimately affects the health and well-being of human populations.
• 6.2: Environmental Health
Environmental health is concerned with preventing disease, death and disability by reducing exposure to adverse environmental conditions and promoting behavioral change. It focuses on the direct and indirect causes of diseases and injuries, and taps resources inside and outside the health care system to help improve health outcomes.
• 6.3: Environmental Toxicology
Environmental toxicology is the scientific study of the health effects associated with exposure to toxic chemicals (Table 1) occurring in the natural, work, and living environments. The term also describes the management of environmental toxins and toxicity, and the development of protections for humans and the environment.
• 6.4: Bioremediation
Bioremediation is a waste management technique that involves the use of organisms such as plants, bacteria, and fungi to remove or neutralize pollutants from a contaminated site. According to the United States EPA, bioremediation is a “treatment that uses naturally occurring organisms to break down hazardous substances into less toxic or non toxic substances”.
• 6.5: Case Study - The Love Canal Disaster
One of the most famous and important examples of groundwater pollution in the U.S. is the Love Canal tragedy in Niagara Falls, New York. It is important because the pollution disaster at Love Canal, along with similar pollution calamities at that time (Times Beach, Missouri and Valley of Drums, Kentucky), helped to create Superfund, a federal program instituted in 1980 and designed to identify and clean up the worst of the hazardous chemical waste sites in the U.S.
• 6.S: Environmental Hazards & Human Health (Summary)
Thumbnail image - Bayee Waqo (12) was named after her grandmother Bayee Chumee (82). When her son and his wife both died of AIDS, Chumee took on the care of their daughter who was just two years old. Some years later, after repeated illness, the young girl was diagnosed HIV positive, and she has been on treatment since. At 82, Chumee is getting too weak for all the household chores, so her granddaughter helps by collecting firewood, fetching water, making coffee and baking bread.
06: Environmental Hazards Human Health
Our industrialized society dumps huge amounts of pollutants and toxic wastes into the earth’s biosphere without fully considering the consequences. Such actions seriously degrade the health of the earth’s ecosystems, and this degradation ultimately affects the health and well-being of human populations.
For most of human history, biological agents were the most significant factor in health. These included pathogenic (disease causing) organisms such as bacteria, viruses, protozoa, and internal parasites. In modern times, cardiovascular diseases, cancer, and accidents are the leading killers in most parts of the world. However, infectious diseases still cause about 22 million deaths a year, mostly in undeveloped countries. These diseases include: tuberculosis, malaria, pneumonia, influenza, whooping cough, dysentery and Acquired Immune Deficiency Syndrome (AIDS). Most of those affected are children. Malnutrition, unclean water, poor sanitary conditions and lack of proper medical care all play roles in these deaths. Compounding the problems of infectious diseases are factors such as drug-resistant pathogens, insecticide resistant carriers, and overpopulation. Overuse of antibiotics have allowed pathogens to develop a resistance to drugs. For example, tuberculosis (TB) was nearly eliminated in most parts of the world, but drug-resistant strains have now reversed that trend. Another example is malaria. The insecticide DDT (a chemical called dichlorodiphenyltrichloroethane) was widely used to control malaria-carrying mosquito populations in tropical regions. However, after many years the mosquitoes developed a natural resistance to DDT and again spread the disease widely. Anti-malarial medicines were also over-prescribed, which allowed the malaria pathogen to become drug-resistant.
Chemical agents also have significant effects on human health. Toxic heavy metals, dioxins, pesticides, and endocrine disrupters are examples of these chemical agents. Heavy metals (e.g., mercury, lead, & cadmium) are typically produced as by-products of mining and manufacturing processes. All of them biomagnify (become more concentrated in species with increasing food chain level). For example, mercury from polluted water can accumulate in swordfish to levels toxic to humans. When toxic heavy metals get into the body, they accumulate in tissues and may eventually cause sickness or death. Studies show that people with above-average lead levels in their bones have an increased risk of developing attention deficit disorder and aggressive behavior. Lead can also damage brain cells and affect muscular coordination.
ENVIRONMENTAL PERSISTENCE OF DDT
The pesticide DDT was widely used for decades. It was seen as an ideal pesticide because it is inexpensive and breaks down slowly in the environment. Unfortunately, the latter characteristic allows this chemical agent to biomagnify through the food chain. Populations of bird species at the top of the food chain, e.g., eagles and pelicans, are greatly affected by DDT in the environment. When these birds have sufficient levels of DDT, the shells of their eggs are so thin that they break, making reproduction impossible. After DDT was banned in the United States in 1972, affected bird populations made noticeable recoveries, including the iconic bald eagle. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/06%3A_Environmental_Hazards__Human_Health/6.01%3A_The_Impacts_of_Environmental_Conditions.txt |
Environmental health is concerned with preventing disease, death and disability by reducing exposure to adverse environmental conditions and promoting behavioral change. It focuses on the direct and indirect causes of diseases and injuries, and taps resources inside and outside the health care system to help improve health outcomes.
Table 1. Typical Environmental Health Issues: Determinants and Health Consequences.
Poverty, Health and Environment
Environmental health risks can be grouped into two broad categories. Traditional hazards are related to poverty and the lack of development and mostly affect developing countries and poor people. Their impact exceeds that of modern health hazards by 10 times in Africa, 5 times in Asian countries (except for China), and 2.5 times in Latin America and Middle East (Figure \(1\)). Water-related diseases caused by inadequate water supply and sanitation impose an especially large health burden in Africa, Asia, and the Pacific region. In India alone, over 700,000 children under 5 die annually from diarrhea. In Africa, malaria causes about 500,000 deaths annually. More than half of the world’s households use unprocessed solid fuels, particularly biomass (crop residues, wood, and dung) for cooking and heating in inefficient stoves without proper ventilation, exposing people—mainly poor women and children—to high levels of indoor air pollution(IAP). IAP causes about 2 million deaths in each year.
Modern hazards, caused by technological development, prevail in industrialized countries where exposure to traditional hazards is low. The contribution of modern environmental risks to the disease burden in most developing countries is similar to – and in quite a few countries, greater than – that in rich countries. Urban air pollution, for example, is highest in parts of China, India and some cities in Asia and Latin America. Poor people increasingly experience a “double burden” of traditional and modern environmental health risks. Their total burden of illness and death from all causes per million people is about twice that in rich countries, and the disease burden from environmental risks is 10 times greater.
Environmental Health and Child Survival
Worldwide, the top killers of children under five are acute respiratory infections (from indoor air pollution); diarrheal diseases (mostly from poor water, sanitation, and hygiene); and infectious diseases such as malaria. Children are especially susceptible to environmental factors that put them at risk of developing illness early in life. Malnutrition (the condition that occurs when body does not get enough nutrients) is an important contributor to child mortality—malnutrition and environmental infections are inextricably linked. The World Health Organization (WHO) recently concluded that about 50% of the consequences of malnutrition are in fact caused by inadequate water and sanitation provision and poor hygienic practices.
Poor Water and Sanitation Access
With 1.1 billion people lacking access to safe drinking water and 2.6 billion without adequate sanitation, the magnitude of the water and sanitation problem remains significant. Each year contaminated water and poor sanitation contribute to 5.4 billion cases of diarrhea worldwide and 1.6 million deaths, mostly among children under the age of five. Intestinal worms, which thrive in poor sanitary conditions, infect close to 90 percent of children in the developing world and, depending on the severity of the infection may lead to malnutrition, anemia, or stunted growth. About 6 million people are blind from trachoma, a disease caused by the lack of clean water combined with poor hygiene practices.
Indoor Air Pollution
Indoor air pollution—a much less publicized source of poor health—is responsible for more than 1.6 million deaths per year and for 2.7% of global burden of disease. It is estimated that half of the world’s population, mainly in developing countries, uses solid fuels (biomass and coal) for household cooking and space heating. Cooking and heating with such solid fuels on open fires or stoves without chimneys lead to indoor air pollution and subsequently, respiratory infections. Exposure to these health-damaging pollutants is particularly high among women and children in developing countries, who spend the most time inside the household. As many as half of the deaths attributable to indoor use of solid fuel are of children under the age of five.
Malaria
Approximately 40% of the world’s people—mostly those living in the world’s poorest countries—are at risk from malaria. Malaria is an infectious disease spread by mosquitoes but caused by a single-celled parasite called Plasmodium. Every year, more than 200 million people become infected with malaria and about 430,000 die, with most cases and deaths found in Sub-Saharan Africa. However, Asia, Latin America, the Middle East, and parts of Europe are also affected. Pregnant women are especially at high risk of malaria. Non-immune pregnant women risk both acute and severe clinical disease, resulting in fetal loss in up to 60% of such women and maternal deaths in more than 10%, including a 50% mortality rate for those with severe disease. Semi-immune pregnant women with malaria infection risk severe anemia and impaired fetal growth, even if they show no signs of acute clinical disease. An estimated 10,000 women and 200,000 infants die annually as a result of malaria infection during pregnancy.
Emerging Diseases
Emerging and re-emerging diseases have been defined as infectious diseases of humans whose occurrence during the past two decades has substantially increased or threatens to increase in the near future relative to populations affected, geographic distribution, or magnitude of impacts. Examples include Ebola virus, West Nile virus, Zika virus, sudden acute respiratory syndrome (SARS), H1N1 influenza; swine and avian influenza (swine, bird flu), HIV, and a variety of other viral, bacterial, and protozoal diseases.
A variety of environmental factors may contribute to re-emergence of a particular disease, including temperature, moisture, human food or animal feed sources, etc. Disease re-emergence may be caused by the coincidence of several of these environmental and/or social factors to allow optimal conditions for transmission of the disease.
Ebola, previously known as Ebola hemorrhagic fever, is a rare and deadly disease caused by infection with one of the Ebola virus strains. Ebola can cause disease in humans and nonhuman primates. The 2014 Ebola epidemic is the largest in history (with over 28,000 cases and 11,302 deaths), affecting multiple countries in West Africa. There were a small number of cases reported in Nigeria and Mali and a single case reported in Senegal; however, these cases were contained, with no further spread in these countries.
The HIV/AIDS epidemic has spread with ferocious speed. Virtually unknown 20 years ago, HIV has infected more than 60 million people worldwide. Each day, approximately 14,000 new infections occur, more than half of them among young people below age 25. Over 95 percent of PLWHA (People Living With HIV/AIDS) are in low- and middle- income countries. More than 20 million have died from AIDS, over 3 million in 2002 alone. AIDS is now the leading cause of death in Sub-Saharan Africa and the fourth-biggest killer globally. The epidemic has cut life expectancy by more than 10 years in several nations.
It seems likely that a wide variety of infectious diseases have affected human populations for thousands of years emerging when the environmental, host, and agent conditions were favorable. Expanding human populations have increased the potential for transmission of infectious disease as a result of close human proximity and increased likelihood for humans to be in “the wrong place at the right time” for disease to occur (eg, natural disasters or political conflicts). Global travel increases the potential for a carrier of disease to transmit infection thousands of miles away in just a few hours, as evidenced by WHO precautions concerning international travel and health.
Antibiotic Resistance
Antibiotics and similar drugs, together called antimicrobial agents, have been used for the last 70 years to treat patients who have infectious diseases. Since the 1940s, these drugs have greatly reduced illness and death from infectious diseases. However, these drugs have been used so widely and for so long that the infectious organisms the antibiotics are designed to kill have adapted to them, making the drugs less effective. Antibiotic resistance occurs when bacteria change in a way that reduces the effectiveness of drugs, chemicals, or other agents designed to cure or prevent infections. This is caused by the process of evolution through natural selection (Figure \(3\)). The antibiotic-resistant bacteria survive and continue to multiply, causing more harm.
New forms of antibiotic resistance can cross international boundaries and spread between continents with ease. Many forms of resistance spread with remarkable speed. Each year in the United States, at least 2 million people acquire serious infections with bacteria that are resistant to one or more of the antibiotics designed to treat those infections. At least 23,000 people die each year in the US as a direct result of these antibiotic-resistant infections. Many more die from other conditions that were complicated by an antibiotic-resistant infection. The use of antibiotics is the single most important factor leading to antibiotic resistance around the world.
Antibiotics are among the most commonly prescribed drugs used in human medicine, but up to 50% of all the antibiotics prescribed for people are not needed or are not optimally effective as prescribed.
During recent years, there has been growing concern over methicillin-resistant Staphylococcus aureus (MRSA), a bacterium that is resistant to many antibiotics. In the community, most MRSA infections are skin infections. In medical facilities, MRSA causes life-threatening bloodstream infections, pneumonia and surgical site infections.
Suggested Supplementary Reading:
Koch, B.J. et al. 2017. Food-animal production and the spread of antibiotic resistance: the role of ecology. Frontiers in Ecology and the Environment (15)6: 309-318.
Notable Excerpts:
“Antibiotic use in food animals is correlated with antibiotic resistance among bacteria affecting human populations.” p. 311
“Microbial genes encoding antibiotic resistance have moved between the food-animal and human health sectors, resulting in illnesses that could not be treated by antibiotics.” p. 312 | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/06%3A_Environmental_Hazards__Human_Health/6.02%3A_Environmental_Health.txt |
Environmental toxicology is the scientific study of the health effects associated with exposure to toxic chemicals (Table 1) occurring in the natural, work, and living environments. The term also describes the management of environmental toxins and toxicity, and the development of protections for humans and the environment.
2013 RANK
NAME
1 ARSENIC
2 LEAD
3 MERCURY
4 VINYL CHLORIDE
5 POLYCHLORINATED BIPHENYLS
6 BENZENE
7 CADMIUM
8 BENZO(A)PYRENE
9 POLYCYCLIC AROMATIC HYDROCARBONS
10 BENZO(B)FLUORANTHENE
11 CHLOROFORM
12 AROCLOR 1260
13 DDT, P,P’-
14 AROCLOR 1254
15 DIBENZO(A,H)ANTHRACENE
16 TRICHLOROETHYLENE
17 CHROMIUM, HEXAVALENT
18 DIELDRIN
19 PHOSPHORUS, WHITE
20 HEXACHLOROBUTADIENE
Routes of Exposure to Chemicals
In order to cause health problems, chemicals must enter your body. There are three main “routes of exposure,” or ways a chemical can get into your body.
• Breathing (inhalation): Breathing in chemical gases, mists, or dusts that are in the air.
• Skin or eye contact: Getting chemicals on the skin, or in the eyes. They can damage the skin, or be absorbed through the skin into the bloodstream.
• Swallowing (ingestion): This can happen when chemicals have spilled or settled onto food, beverages, cigarettes, beards, or hands.
Once chemicals have entered your body, some can move into your bloodstream and reach internal “target” organs, such as the lungs, liver, kidneys, or nervous system.
What Forms do Chemicals Take?
Chemical substances can take a variety of forms. They can be in the form of solids, liquids, dusts, vapors, gases, fibers, mists and fumes. The form a substance is in has a lot to do with how it gets into your body and what harm it can cause. A chemical can also change forms. For example, liquid solvents can evaporate and give off vapors that you can inhale. Sometimes chemicals are in a form that can’t be seen or smelled, so they can’t be easily detected.
What Health Effects Can Chemicals Cause?
An acute effect of a contaminant (The term “contaminant” means hazardous substances, pollutants, pollution, and chemicals) is one that occurs rapidly after exposure to a large amount of that substance. A chronic effect of a contaminant results from exposure to small amounts of a substance over a long period of time. In such a case, the effect may not be immediately obvious. Chronic effect are difficult to measure, as the effects may not be seen for years. Long-term exposure to cigarette smoking, low level radiation exposure, and moderate alcohol use are all thought to produce chronic effects.
For centuries, scientists have known that just about any substance is toxic in sufficient quantities. For example, small amounts of selenium are required by living organisms for proper functioning, but large amounts may cause cancer. The effect of a certain chemical on an individual depends on the dose (amount) of the chemical. This relationship is often illustrated by a dose-response curve which shows the relationship between dose and the response of the individual. Lethal doses in humans have been determined for many substances from information gathered from records of homicides, accidental poisonings, and testing on animals.
A dose that is lethal to 50% of a population of test animals is called the lethal dose-50% or LD-50. Determination of the LD-50 is required for new synthetic chemicals in order to give a measure of their toxicity. A dose that causes 50% of a population to exhibit any significant response (e.g., hair loss, stunted development) is referred to as the effective dose-50% or ED-50. Some toxins have a threshold amount below which there is no apparent effect on the exposed population.
Environmental Contaminants
The contamination of the air, water, or soil with potentially harmful substances can affect any person or community. Contaminants (Table 2) are often chemicals found in the environment in amounts higher than what would be there naturally. We can be exposed to these contaminants from a variety of residential, commercial, and industrial sources. Sometimes harmful environmental contaminants occur biologically, such as mold or a toxic algae bloom.
Table 2. Classification of Environmental Contaminants
Contaminant Definition
Carcinogen An agent which may produce cancer (uncontrolled cell growth), either by itself or in conjunction with another substance. Examples include formaldehyde, asbestos, radon, vinyl chloride, and tobacco.
Teratogen
A substance which can cause physical defects in a developing embryo. Examples include alcohol and cigarette smoke.
Mutagen A material that induces genetic changes (mutations) in the DNA. Examples include radioactive substances, x-rays and ultraviolet radiation.
Neurotoxicant
A substance that can cause an adverse effect on the chemistry, structure or function of the nervous system. Examples include lead and mercury.
Endocrine disruptor
A chemical that may interfere with the body’s endocrine (hormonal) system and produce adverse developmental, reproductive, neurological, and immune effects in both humans and wildlife. A wide range of substances, both natural and man-made, are thought to cause endocrine disruption, including pharmaceuticals, dioxin and dioxin-like compounds, arsenic, polychlorinated biphenyls (PCBs), DDT and other pesticides, and plasticizers such as bisphenol A (BPA).
An Overview of Some Common Contaminants
Arsenic is a naturally occurring element that is normally present throughout our environment in water, soil, dust, air, and food. Levels of arsenic can regionally vary due to farming and industrial activity as well as natural geological processes. The arsenic from farming and smelting tends to bind strongly to soil and is expected to remain near the surface of the land for hundreds of years as a long-term source of exposure. Wood that has been treated with chromated copper arsenate (CCA) is commonly found in decks and railing in existing homes and outdoor structures such as playground equipment. Some underground aquifers are located in rock or soil that has naturally high arsenic content.
Most arsenic gets into the body through ingestion of food or water. Arsenic in drinking water is a problem in many countries around the world, including Bangladesh, Chile, China, Vietnam, Taiwan, India, and the United States. Arsenic may also be found in foods, including rice and some fish, where it is present due to uptake from soil and water. It can also enter the body by breathing dust containing arsenic. Researchers are finding that arsenic, even at low levels, can interfere with the body’s endocrine system. Arsenic is also a known human carcinogen associated with skin, lung, bladder, kidney, and liver cancer.
Mercury is a naturally occurring metal, a useful chemical in some products, and a potential health risk. Mercury exists in several forms; the types people are usually exposed to are methylmercury and elemental mercury. Elemental mercury at room temperature is a shiny, silver-white liquid which can produce a harmful odorless vapor. Methylmercury, an organic compound, can build up in the bodies of long-living, predatory fish. To keep mercury out of the fish we eat and the air we breathe, it’s important to take mercury-containing products to a hazardous waste facility for disposal. Common products sold today that contain small amounts of mercury include fluorescent lights and button-cell batteries.
Although fish and shellfish have many nutritional benefits, consuming large quantities of fish increases a person’s exposure to mercury. Pregnant women who eat fish high in mercury on a regular basis run the risk of permanently damaging their developing fetuses. Children born to these mothers may exhibit motor difficulties, sensory problems and cognitive deficits. Figure \(1\) identifies the typical (average) amounts of mercury in commonly consumed commercial and sport-caught fish.
Bisphenol A (BPA) is a chemical synthesized in large quantities for use primarily in the production of polycarbonate plastics and epoxy resins. Polycarbonate plastics have many applications including use in some food and drink packaging, e.g., water and infant bottles, compact discs, impact-resistant safety equipment, and medical devices. Epoxy resins are used as lacquers to coat metal products such as food cans, bottle tops, and water supply pipes. Some dental sealants and composites may also contribute to BPA exposure. The primary source of exposure to BPA for most people is through the diet. Bisphenol A can leach into food from the protective internal epoxy resin coatings of canned foods and from consumer products such as polycarbonate tableware, food storage containers, water bottles, and baby bottles. The degree to which BPA leaches from polycarbonate bottles into liquid may depend more on the temperature of the liquid or bottle, than the age of the container. BPA can also be found in breast milk.
What can I do to prevent exposure to BPA?
Some animal studies suggest that infants and children may be the most vulnerable to the effects of BPA. Parents and caregivers, can make the personal choice to reduce exposures of their infants and children to BPA:
• Don’t microwave polycarbonate plastic food containers. Polycarbonate is strong and durable, but over time it may break down from over use at high temperatures.
• Plastic containers have recycle codes on the bottom. Some, but not all, plastics that are marked with recycle codes 3 or 7 may be made with BPA.
• Reduce your use of canned foods.
• When possible, opt for glass, porcelain or stainless steel containers, particularly for hot food or liquids.
• Use baby bottles that are BPA free.
Phthalates are a group of synthetic chemicals used to soften and increase the flexibility of plastic and vinyl. Polyvinyl chloride is made softer and more flexible by the addition of phthalates. Phthalates are used in hundreds of consumer products. Phthalates are used in cosmetics and personal care products, including perfume, hair spray, soap, shampoo, nail polish, and skin moisturizers. They are used in consumer products such as flexible plastic and vinyl toys, shower curtains, wallpaper, vinyl miniblinds, food packaging, and plastic wrap. Exposure to low levels of phthalates may come from eating food packaged in plastic that contains phthalates or breathing dust in rooms with vinyl miniblinds, wallpaper, or recently installed flooring that contain phthalates. We can be exposed to phthalates by drinking water that contains phthalates. Phthalates are suspected to be endocrine disruptors.
Lead is a metal that occurs naturally in the rocks and soil of the earth’s crust. It is also produced from burning fossil fuels such as coal, oil, gasoline, and natural gas; mining; and manufacturing. Lead has no distinctive taste or smell. The chemical symbol for elemental lead is Pb. Lead is used to produce batteries, pipes, roofing, scientific electronic equipment, military tracking systems, medical devices, and products to shield X-rays and nuclear radiation. It is used in ceramic glazes and crystal glassware. Because of health concerns, lead and lead compounds were banned from house paint in 1978; from solder used on water pipes in 1986; from gasoline in 1995; from solder used on food cans in 1996; and from tin-coated foil on wine bottles in 1996. The U.S. Food and Drug Administration has set a limit on the amount of lead that can be used in ceramics.
Lead and lead compounds are listed as “reasonably anticipated to be a human carcinogen”. It can affect almost every organ and system in your body. It can be equally harmful if breathed or swallowed. The part of the body most sensitive to lead exposure is the central nervous system, especially in children, who are more vulnerable to lead poisoning than adults. A child who swallows large amounts of lead can develop brain damage that can cause convulsions and death; the child can also develop blood anemia, kidney damage, colic, and muscle weakness. Repeated low levels of exposure to lead can alter a child’s normal mental and physical growth and result in learning or behavioral problems. Exposure to high levels of lead for pregnant women can cause miscarriage, premature births, and smaller babies. Repeated or chronic exposure can cause lead to accumulate in your body, leading to lead poisoning.
Formaldehyde is a colorless, flammable gas or liquid that has a pungent, suffocating odor. It is a volatile organic compound, which is an organic compound that easily becomes a vapor or gas. It is also naturally produced in small, harmless amounts in the human body. The primary way we can be exposed to formaldehyde is by breathing air containing it. Releases of formaldehyde into the air occur from industries using or manufacturing formaldehyde, wood products (such as particle-board, plywood, and furniture), automobile exhaust, cigarette smoke, paints and varnishes, and carpets and permanent press fabrics. Nail polish, and commercially applied floor finish emit formaldehyde.
In general, indoor environments consistently have higher concentrations than outdoor environments, because many building materials, consumer products, and fabrics emit formaldehyde. Levels of formaldehyde measured in indoor air range from 0.02–4 parts per million (ppm). Formaldehyde levels in outdoor air range from 0.001 to 0.02 ppm in urban areas.
Radiation
Radiation is energy given off by atoms and is all around us. We are exposed to radiation every day from natural sources like soil, rocks, and the sun. We are also exposed to radiation from man-made sources like medical X-rays and smoke detectors. We’re even exposed to low levels of radiation on cross-country flights, from watching television, and even from some construction materials. You cannot see, smell or taste radiation. Some types of radioactive materials are more dangerous than others. So it’s important to carefully manage radiation and radioactive substances to protect health and the environment.
Radon is a radioactive gas that is naturally-occurring, colorless, and odorless. It comes from the natural decay of uranium or thorium found in nearly all soils. It typically moves up through the ground and into the home through cracks in floors, walls and foundations. It can also be released from building materials or from well water. Radon breaks down quickly, giving off radioactive particles. Long-term exposure to these particles can lead to lung cancer. Radon is the leading cause of lung cancer among nonsmokers, according to the U.S. Environmental Protection Agency, and the second leading cause behind smoking. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/06%3A_Environmental_Hazards__Human_Health/6.03%3A_Environmental_Toxicology.txt |
Bioremediation is a waste management technique that involves the use of organisms such as plants, bacteria, and fungi to remove or neutralize pollutants from a contaminated site. According to the United States EPA, bioremediation is a “treatment that uses naturally occurring organisms to break down hazardous substances into less toxic or non toxic substances”.
Bioremediation is widely used to treat human sewage and has also been used to remove agricultural chemicals (pesticides and fertilizers) that leach from soil into groundwater. Certain toxic metals, such as selenium and arsenic compounds, can also be removed from water by bioremediation. Mercury is an example of a toxic metal that can be removed from an environment by bioremediation. Mercury is an active ingredient of some pesticides and is also a byproduct of certain industries, such as battery production. Mercury is usually present in very low concentrations in natural environments but it is highly toxic because it accumulates in living tissues. Several species of bacteria can carry out the biotransformation of toxic mercury into nontoxic forms. These bacteria, such as Pseudomonas aeruginosa, can convert Hg2+ to Hg, which is less toxic to humans.
Probably one of the most useful and interesting examples of the use of prokaryotes for bioremediation purposes is the cleanup of oil spills. The importance of prokaryotes to petroleum bioremediation has been demonstrated in several oil spills in recent years, such as the Exxon Valdez spill in Alaska (1989) (Figure \(1\)), the Prestige oil spill in Spain (2002), the spill into the Mediterranean from a Lebanon power plant (2006,) and more recently, the BP oil spill in the Gulf of Mexico (2010). To clean up these spills, bioremediation is promoted by adding inorganic nutrients that help bacteria already present in the environment to grow. Hydrocarbon-degrading bacteria feed on the hydrocarbons in the oil droplet, breaking them into inorganic compounds. Some species, such as Alcanivorax borkumensis, produce surfactants that solubilize the oil, while other bacteria degrade the oil into carbon dioxide. In the case of oil spills in the ocean, ongoing, natural bioremediation tends to occur, inasmuch as there are oil-consuming bacteria in the ocean prior to the spill. Under ideal conditions, it has been reported that up to 80 percent of the nonvolatile components in oil can be degraded within 1 year of the spill. Researchers have genetically engineered other bacteria to consume petroleum products; indeed, the first patent application for a bioremediation application in the U.S. was for a genetically modified oil-eating bacterium.
There are a number of cost/efficiency advantages to bioremediation, which can be employed in areas that are inaccessible without excavation. For example, hydrocarbon spills (specifically, oil spills) or certain chlorinated solvents may contaminate groundwater, which can be easier to treat using bioremediation than more conventional approaches. This is typically much less expensive than excavation followed by disposal elsewhere, incineration, or other off-site treatment strategies. It also reduces or eliminates the need for “pump and treat”, a practice common at sites where hydrocarbons have contaminated clean groundwater. Using prokaryotes for bioremediation of hydrocarbons also has the advantage of breaking down contaminants at the molecular level, as opposed to simply chemically dispersing the contaminant. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/06%3A_Environmental_Hazards__Human_Health/6.04%3A_Bioremediation.txt |
One of the most famous and important examples of groundwater pollution in the U.S. is the Love Canal tragedy in Niagara Falls, New York. It is important because the pollution disaster at Love Canal, along with similar pollution calamities at that time (Times Beach, Missouri and Valley of Drums, Kentucky), helped to create Superfund, a federal program instituted in 1980 and designed to identify and clean up the worst of the hazardous chemical waste sites in the U.S.
Love Canal is a neighborhood in Niagara Falls named after a large ditch (approximately 15 m wide, 3–12 m deep, and 1600 m long) that was dug in the 1890s for hydroelectric power. The ditch was abandoned before it actually generated any power and went mostly unused for decades, except for swimming by local residents. In the 1920s Niagara Falls began dumping urban waste into Love Canal, and in the 1940s the U.S. Army dumped waste from World War II there, including waste from the frantic effort to build a nuclear bomb. Hooker Chemical purchased the land in 1942 and lined it with clay. Then, the company put into Love Canal an estimated 21,000 tons of hazardous chemical waste, including the carcinogens benzene, dioxin, and PCBs in large metal barrels and covered them with more clay. In 1953, Hooker sold the land to the Niagara Falls school board for \$1, and included a clause in the sales contract that both described the land use (filled with chemical waste) and absolved them from any future damage claims from the buried waste. The school board promptly built a public school on the site and sold the surrounding land for a housing project that built 200 or so homes along the canal banks and another 1,000 in the neighborhood (Figure \(1\)). During construction, the canal’s clay cap and walls were breached, damaging some of the metal barrels.
Eventually, the chemical waste seeped into people’s basements, and the metal barrels worked their way to the surface. Trees and gardens began to die; bicycle tires and the rubber soles of children’s shoes disintegrated in noxious puddles. From the 1950s to the late 1970s, residents repeatedly complained of strange odors and substances that surfaced in their yards. City officials investigated the area, but did not act to solve the problem. Local residents allegedly experienced major health problems including high rates of miscarriages, birth defects, and chromosome damage, but studies by the New York State Health Department disputed that. Finally, in 1978 President Carter declared a state of emergency at Love Canal, making it the first human-caused environmental problem to be designated that way. The Love Canal incident became a symbol of improperly stored chemical waste. Clean up of Love Canal, which was funded by Superfund and completely finished in 2004, involved removing contaminated soil, installing drainage pipes to capture contaminated groundwater for treatment, and covering it with clay and plastic. In 1995, Occidental Chemical (the modern name for Hooker Chemical) paid \$102 million to Superfund for cleanup and \$27 million to Federal Emergency Management Association for the relocation of more than 1,000 families. New York State paid \$98 million to EPA and the US government paid \$8 million for pollution by the Army. The total clean up cost was estimated to be \$275 million.
The Love Canal tragedy helped to create Superfund, which has analyzed tens of thousands of hazardous waste sites in the U.S. and cleaned up hundreds of the worst ones. Nevertheless, over 1,000 major hazardous waste sites with a significant risk to human health or the environment are still in the process of being cleaned. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/06%3A_Environmental_Hazards__Human_Health/6.05%3A_Case_Study_-_The_Love_Canal_Disaster.txt |
Summary
Environmental health is concerned with preventing disease, death and disability by reducing exposure to adverse environmental conditions and promoting behavioral change. It focuses on the direct and indirect causes of diseases and injuries, and taps resources inside and outside the health care system to help improve health outcomes. Environmental health risks can be grouped into two broad categories. Traditional hazards related to poverty and lack of development affect developing countries and poor people most. Modern hazards, caused by development that lacks environmental safeguards, such as urban (outdoor) air pollution and exposure to agro-industrial chemicals and waste, prevail in industrialized countries, where exposure to traditional hazards is low. Each year contaminated water and poor sanitation contribute to 5.4 billion cases of diarrhea worldwide and 1.6 million deaths, mostly among children under the age of five. Indoor air pollution—a much less publicized source of poor health—is responsible for more than 1.6 million deaths per year and for 2.7 percent of global burden of disease.
Emerging and reemerging diseases have been defined as infectious diseases of humans whose occurrence during the past two decades has substantially increased or threatens to increase in the near future relative to populations affected, geographic distribution, or magnitude of impacts. Antibiotic resistance is a global problem. New forms of antibiotic resistance can cross international boundaries and spread between continents. Environmental toxicology is the scientific study of the health effects associated with exposure to toxic chemicals and systems occurring in the natural, work, and living environments; the management of environmental toxins and toxicity; and the development of protections for humans, animals, and plants. Environmental contaminants are chemicals found in the environment in amounts higher than what would be there naturally. We can be exposed to these contaminants from a variety of residential, commercial, and industrial sources.
Review Questions
1. The pesticide DDT is an example of which one of the following?
1. Biological agent
2. Atomic agent
3. Chemical agent
4. Capricious agent
5. Inorganic agent
2. From the perspective of human health, malnutrition is important because it…
1. Causes the majority of birth defects
2. Is the primary source of teratogens for most children
3. is an important contributor to child mortality
4. Is the second leading cause of death from emerging disease
5. Increases the occurrence of infectious cancers
3. Antibiotic resistance in organisms is the result of what process?
1. Differentiation
2. Evolution
3. Emergence
4. Succession
5. Fixation
4. Which one of the following is an example of an emerging disease?
1. Malaria
2. Ebola
3. Cancer
4. Heart disease
5. Leukemia
5. “Effective dose – 50%” describes which one of the following?
1. The dose that results in 50% mortality
2. The dose the results in 50% survival
3. The dose that is 50% less than the lethal dose
4. The dose that results in a significant response in 50% of subjects
5. The dose that is 50% more than the minimal dose
6. You are working as an environmental toxicologist for the government. Your results indicate that a particular chemical causes birth defects. Which one of the following best describes the effects of this chemical?
1. Teratogen
2. Carcinogen
3. Mutagen
4. Endocrine disruptor
5. Neurotoxicant
7. Which one of the following is most directly associated with radon?
1. Radiation
2. Endocrine disruption
3. Birth defects
4. Biological agents
5. Biomagnification
8. Which one of the following is an example of bioremediation?
1. Adding chemical dispersants following an oil spill
2. Growing large colonies of bacteria to produce antibiotic chemicals
3. Mimicking the processes of natural in a laboratory or industrial context
4. Removing invasive species that are overpopulating an ecosystem
5. Using plants to remove toxic metals from soils following a mining operation
9. Which one of the following is not a naturally-occurring element that may be hazardous to human health?
1. Lead
2. Radon
3. Phthalate
4. Mercury
5. Arsenic
10. Which one of the following is not true regarding the “Love Canal Disaster”?
1. It involved the improper storage of chemical waste
2. It was one of several incidents that led to the creation of the Superfund
3. A school was built on the contaminated site
4. Many homes had to be evacuated due to contamination from various biological agents
5. Many people living in the year reported serious health problems
See Appendix for answers
Attributions
EPA. (n.d.). Attachment 6: Useful terms and definitions for explaining risk. Accessed August 31, 2015 at http://www.epa.gov/superfund/community/pdfs/toolkit/risk_communication-attachment6.pdf. Modified from original.
OSHA. (n.d.). Understanding chemical hazards. Accessed August 25, 2015 fromhttps://www.osha.gov/dte/grant_mater...calHazards.pdf.Modified from original.
Theis, T. & Tomkin, J. (Eds.). (2015). Sustainability: A comprehensive foundation. Retrieved from http://cnx.org/contents/[email protected]. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
University of California College Prep. (2012). AP environmental science. Retrieved from http://cnx.org/content/col10548/1.2/. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
World Bank. (2003). Environmental health. Washington, DC. World Bank. Retrieved from https://openknowledge.worldbank.org/handle/10986/9734. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.
World Bank. (2008). Environmental health and child survival : Epidemiology, economics, experiences. Washington, DC: World Bank. World Bank. Retrieved from https://openknowledge.worldbank.org/handle/10986/6534. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.
World Bank. (2009). Environmental health and child survival. Retrieved from https://openknowledge.worldbank.org/...le/10986/11719. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/06%3A_Environmental_Hazards__Human_Health/6.0S%3A_6.S%3A_Environmental_Hazards__Human_Health_%28Summary%29.txt |
Learning Outcomes
• Understand how the water cycle operates
• Know the causes and effects of depletion in different water reservoirs
• Understand how we can work toward solving the water supply crisis
• Understand the major kinds of water pollutants and how they degrade water quality
• Understand how we can work toward solving the crisis involving water pollution
Thumbnail image - Great Lakes from Space. The Great Lakes hold 21% of the world’s surface fresh water. Lakes are an important surface water resource.
07: Water Availability and Use
Water, air, and food are the most important natural resources to people. Humans can live only a few minutes without oxygen, less than a week without water, and about a month without food. Water also is essential for our oxygen and food supply. Plants breakdown water and use it to create oxygen during the process of photosynthesis.
Water is the most essential compound for all living things. Human babies are approximately 75% water and adults are 60% water. Our brain is about 85% water, blood and kidneys are 83% water, muscles are 76% water, and even bones are 22% water. We constantly lose water by perspiration; in temperate climates we should drink about 2 quarts of water per day and people in hot desert climates should drink up to 10 quarts of water per day. Loss of 15% of body-water usually causes death.
Earth is truly the Water Planet. The abundance of liquid water on Earth’s surface distinguishes us from other bodies in the solar system. About 70% of Earth’s surface is covered by oceans and approximately half of Earth’s surface is obscured by clouds (also made of water) at any time. There is a very large volume of water on our planet, about 1.4 billion cubic kilometers (km3) (330 million cubic miles) or about 53 billion gallons per person on Earth. All of Earth’s water could cover the United States to a depth of 145 km (90 mi). From a human perspective, the problem is that over 97% of it is seawater, which is too salty to drink or use for irrigation. The most commonly used water sources are rivers and lakes, which contain less than 0.01% of the world’s water!
One of the most important environmental goals is to provide clean water to all people. Fortunately, water is a renewable resource and is difficult to destroy. Evaporation and precipitation combine to replenish our fresh water supply constantly; however, water availability is complicated by its uneven distribution over the Earth. Arid climate and densely populated areas have combined in many parts of the world to create water shortages, which are projected to worsen in the coming years due to population growth and climate change. Human activities such as water overuse and water pollution have compounded significantly the water crisis that exists today. Hundreds of millions of people lack access to safe drinking water, and billions of people lack access to improved sanitation as simple as a pit latrine. As a result, nearly two million people die every year from diarrheal diseases and 90% of those deaths occur among children under the age of 5. Most of these are easily prevented deaths.
Water Reservoirs and Water Cycle
Water is the only common substance that occurs naturally on earth in three forms: solid, liquid and gas. It is distributed in various locations, called water reservoirs. The oceans are by far the largest of the reservoirs with about 97% of all water but that water is too saline for most human uses (Figure \(1\)). Ice caps and glaciers are the largest reservoirs of fresh water but this water is inconveniently located, mostly in Antarctica and Greenland. Shallow groundwater is the largest reservoir of usable fresh water. Although rivers and lakes are the most heavily used water resources, they represent only a tiny amount of the world’s water. If all of world’s water was shrunk to the size of 1 gallon, then the total amount of fresh water would be about 1/3 cup, and the amount of readily usable fresh water would be 2 tablespoons.
The water (or hydrologic) cycle (that was covered in Chapter 3.2) shows the movement of water through different reservoirs, which include oceans, atmosphere, glaciers, groundwater, lakes, rivers, and biosphere. Solar energy and gravity drive the motion of water in the water cycle. Simply put, the water cycle involves water moving from oceans, rivers, and lakes to the atmosphere by evaporation, forming clouds. From clouds, it falls as precipitation (rain and snow) on both water and land. The water on land can either return to the ocean by surface runoff, rivers, glaciers, and subsurface groundwater flow, or return to the atmosphere by evaporation or transpiration (loss of water by plants to the atmosphere).
An important part of the water cycle is how water varies in salinity, which is the abundance of dissolved ions in water. The saltwater in the oceans is highly saline, with about 35,000 mg of dissolved ions per liter of seawater. Evaporation (where water changes from liquid to gas at ambient temperatures) is a distillation process that produces nearly pure water with almost no dissolved ions. As water vaporizes, it leaves the dissolved ions in the original liquid phase. Eventually, condensation (where water changes from gas to liquid) forms clouds and sometimes precipitation (rain and snow). After rainwater falls onto land, it dissolves minerals in rock and soil, which increases its salinity. Most lakes, rivers, and near-surface groundwater have a relatively low salinity and are called freshwater. The next several sections discuss important parts of the water cycle relative to fresh water resources.
Primary Fresh Water Resources: Precipitation
Precipitation levels are unevenly distributed around the globe, affecting fresh water availability (Figure \(3\)). More precipitation falls near the equator, whereas less precipitation tends to fall near 30 degrees north and south latitude, where the world’s largest deserts are located. These rainfall and climate patterns are related to global wind circulation cells. The intense sunlight at the equator heats air, causing it to rise and cool, which decreases the ability of the air mass to hold water vapor and results in frequent rainstorms. Around 30 degrees north and south latitude, descending air conditions produce warmer air, which increases its ability to hold water vapor and results in dry conditions. Both the dry air conditions and the warm temperatures of these latitude belts favor evaporation. Global precipitation and climate patterns are also affected by the size of continents, major ocean currents, and mountains.
Surface Water Resources: Rivers, Lakes, Glaciers
Flowing water from rain and melted snow on land enters river channels by surface runoff (Figure \(4\)) and groundwater seepage (Figure \(5\)). River discharge describes the volume of water moving through a river channel over time (Figure \(6\)). The relative contributions of surface runoff vs. groundwater seepage to river discharge depend on precipitation patterns, vegetation, topography, land use, and soil characteristics. Soon after a heavy rainstorm, river discharge increases due to surface runoff. The steady normal flow of river water is mainly from groundwater that discharges into the river. Gravity pulls river water downhill toward the ocean. Along the way the moving water of a river can erode soil particles and dissolve minerals. Groundwater also contributes a large amount of the dissolved minerals in river water. The geographic area drained by a river and its tributaries is called a drainage basin or watershed. The Mississippi River drainage basin includes approximately 40% of the U.S., a measure that includes the smaller drainage basins, such as the Ohio River and Missouri River that help to comprise it. Rivers are an important water resource for irrigation of cropland and drinking water for many cities around the world. Rivers that have had international disputes over water supply include the Colorado (Mexico, southwest U.S.), Nile (Egypt, Ethiopia, Sudan), Euphrates (Iraq, Syria, Turkey), Ganges (Bangladesh, India), and Jordan (Israel, Jordan, Syria).
In addition to rivers, lakes can also be an excellent source of freshwater for human use. They usually receive water from surface runoff and groundwater discharge. They tend to be short-lived on a geological time-scale because they are constantly filling in with sediment supplied by rivers. Lakes form in a variety of ways including glaciation, recent tectonic uplift (e.g., Lake Tanganyika, Africa), and volcanic eruptions (e.g., Crater Lake, Oregon). People also create artificial lakes (reservoirs) by damming rivers. Large changes in climate can result in major changes in a lake’s size. As Earth was coming out of the last Ice Age about 15,000 years ago, the climate in the western U.S. changed from cool and moist to warm and arid, which caused more than 100 large lakes to disappear. The Great Salt Lake in Utah is a remnant of a much larger lake called Lake Bonneville.
Groundwater Resources
Although most people in the world use surface water, groundwater is a much larger reservoir of usable fresh water, containing more than 30 times more water than rivers and lakes combined. Groundwater is a particularly important resource in arid climates, where surface water may be scarce. In addition, groundwater is the primary water source for rural homeowners, providing 98% of that water demand in the U.S.. Groundwater is water located in small spaces, called pore space, between mineral grains and fractures in subsurface earth materials (rock or sediment). Most groundwater originates from rain or snowmelt, which infiltrates the ground and moves downward until it reaches the saturated zone (where groundwater completely fills pore spaces in earth materials).
Other sources of groundwater include seepage from surface water (lakes, rivers, reservoirs, and swamps), surface water deliberately pumped into the ground, irrigation, and underground wastewater treatment systems (septic tanks). Recharge areas are locations where surface water infiltrates the ground rather than running into rivers or evaporating. Wetlands, for example, are excellent recharge areas. A large area of sub-surface, porous rock that holds water is an aquifer. Aquifers are commonly drilled, and wells installed, to provide water for agriculture and personal use.
Water Use in the U.S. and World
People need water, oftentimes large quantities, to produce the food, energy, and mineral resources they use. Consider, for example, these approximate water requirements for some things people in the developed world use every day: one tomato = 3 gallons; one kilowatt-hour of electricity from a thermoelectric power plant = 21 gallons; one loaf of bread = 150 gallons; one pound of beef = 1,600 gallons; and one ton of steel = 63,000 gallons. Human beings require only about 1 gallon per day to survive, but a typical person in a U.S. household uses approximately 100 gallons per day, which includes cooking, washing dishes and clothes, flushing the toilet, and bathing. The water demand of an area is a function of the population and other uses of water.
Global total water use is steadily increasing at a rate greater than world population growth (Figure \(10\)). During the 20th century global population tripled and water demand grew by a factor of six. The increase in global water demand beyond the rate of population growth is due to improved standard of living without an offset by water conservation. Increased production of goods and energy entails a large increase in water demand. The major global water uses are irrigation (68%), public supply (21%), and industry (11%). | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/07%3A_Water_Availability_and_Use/7.01%3A_Water_Cycle_and_Fresh_Water_Supply.txt |
Water Supply Problems: Resource Depletion
As groundwater is pumped from water wells, there usually is a localized drop in the water table around the well called a cone of depression. When there are a large number of wells that have been pumping water for a long time, the regional water table can drop significantly. This is called groundwater mining, which can force the drilling of deeper, more expensive wells that commonly encounter more saline groundwater. Rivers, lakes, and artificial lakes (reservoirs) can also be depleted due to overuse. Some large rivers, such as the Colorado in the U.S. and Yellow in China, run dry in some years. The case history of the Aral Sea discussed later in this chapter involves depletion of a lake. Finally, glaciers are being depleted due to accelerated melting associated with global warming over the past century.
Another water resource problem associated with groundwater mining is saltwater intrusion, where overpumping of fresh water aquifers near ocean coastlines causes saltwater to enter fresh water zones. The drop of the water table around a cone of depression in an unconfined aquifer can change the direction of regional groundwater flow, which could send nearby pollution toward the pumping well instead of away from it. Finally, problems of subsidence (gradual sinking of the land surface over a large area) and sinkholes (rapid sinking of the land surface over a small area) can develop due to a drop in the water table.
Water Supply Crisis
The water crisis refers to a global situation where people in many areas lack access to sufficient water, clean water, or both. This section describes the global situation involving water shortages, also called water stress. In general, water stress is greatest in areas with very low precipitation (major deserts), large population density (e.g., India), or both. Future global warming could worsen the water crisis by shifting precipitation patterns away from humid areas and by melting mountain glaciers that recharge rivers downstream. Melting glaciers will also contribute to rising sea level, which will worsen saltwater intrusion in aquifers near ocean coastlines.
According to a 2006 report by the United Nations Development Programme, 700 million people (11% of the world’s population) lived with water stress. Most of them live in the Middle East and North Africa. By 2025, the report projects that more than 3 billion people (about 40% of the world’s population) will live in water-stressed areas with the large increase coming mainly from China and India. The water crisis will also impact food production and our ability to feed the ever-growing population. We can expect future global tension and even conflict associated with water shortages and pollution. Historic and future areas of water conflict include the Middle East (Euphrates and Tigris River conflict among Turkey, Syria, and Iraq; Jordan River conflict among Israel, Lebanon, Jordan, and the Palestinian territories), Africa (Nile River conflict among Egypt, Ethiopia, and Sudan), Central Asia (Aral Sea conflict among Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, and Kyrgyzstan), and south Asia (Ganges River conflict between India and Pakistan).
Sustainable Solutions to the Water Supply Crisis?
The current and future water crisis described above requires multiple approaches to extending our fresh water supply and moving towards sustainability. Some of the longstanding traditional approaches include dams and aqueducts.
Reservoirs that form behind dams in rivers can collect water during wet times and store it for use during dry spells. They also can be used for urban water supplies. Other benefits of dams and reservoirs are hydroelectricity, flood control, and recreation. Some of the drawbacks are evaporative loss of water in arid climates, downstream river channel erosion, and impact on the ecosystem including a change from a river to lake habitat and interference with migration and spawning of fish.
Aqueducts can move water from where it is plentiful to where it is needed. Aqueducts can be controversial and politically difficult especially if the water transfer distances are large. One drawback is the water diversion can cause drought in the area from where the water is drawn. For example, Owens Lake and Mono Lake in central California began to disappear after their river flow was diverted to the Los Angeles aqueduct. Owens Lake remains almost completely dry, but Mono Lake has recovered more significantly due to legal intervention.
One method that can actually increase the amount of fresh water on Earth is desalination, which involves removing dissolved salt from seawater or saline groundwater. There are several ways to desalinate seawater including boiling, filtration, and electrodialysis. All of these procedures are moderately to very expensive and require considerable energy input, making the water produced much more expensive than fresh water from conventional sources. In addition, the process creates highly saline wastewater, which must be disposed of and creates significant environmental impact. Desalination is most common in the Middle East, where energy from oil is abundant but water is scarce.
Conservation means using less water and using it more efficiently. Around the home, conservation can involve both engineered features, such as high-efficiency clothes washers and low-flow showers and toilets, as well as behavioral decisions, such as growing native vegetation that require little irrigation in desert climates, turning off the water while you brush your teeth, and fixing leaky faucets.
Rainwater harvesting involves catching and storing rainwater for reuse before it reaches the ground. Another important technique is efficient irrigation, which is extremely important because irrigation accounts for a much larger water demand than public water supply. Water conservation strategies in agriculture include growing crops in areas where the natural rainfall can support them, more efficient irrigation systems such as drip systems that minimize losses due to evaporation, no-till farming that reduces evaporative losses by covering the soil, and reusing treated wastewater from sewage treatment plants. Recycled wastewater has also been used to recharge aquifers.
Suggested Supplementary Reading:
Weiss, K.R. 2018. Drying Lakes. National Geographic. March. p. 108-133.
This article documents how many lakes across the globe are drying up, the reasons why, and the effect on humans. Overuse and a warming climate threaten lakes that provide sustenance and jobs for humans, while also providing critical habitat for animals. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/07%3A_Water_Availability_and_Use/7.02%3A_Water_Supply_Problems_and_Solutions.txt |
The global water crisis also involves water pollution. For water to be useful for drinking and irrigation, it must not be polluted beyond certain thresholds. According to the World Health Organization, in 2008 approximately 880 million people in the world (or 13% of world population) did not have access to safe drinking water. At the same time, about 2.6 billion people (or 40% of world population) lived without improved sanitation, which is defined as having access to a public sewage system, septic tank, or even a simple pit latrine. Each year approximately 1.7 million people die from diarrheal diseases associated with unsafe drinking water, inadequate sanitation, and poor hygiene. Almost all of these deaths are in developing countries, and around 90% of them occur among children under the age of 5 (Figure $1$). Compounding the water crisis is the issue of social justice; poor people more commonly lack clean water and sanitation than wealthy people in similar areas. Globally, improving water safety, sanitation, and hygiene could prevent up to 9% of all disease and 6% of all deaths.
In addition to the global waterborne disease crisis, chemical pollution from agriculture, industry, cities, and mining threatens global water quality. Some chemical pollutants have serious and well-known health effects, whereas many others have poorly known long-term health effects. In the U.S. currently more than 40,000 water bodies fit the definition of “impaired” set by EPA, which means they could neither support a healthy ecosystem nor meet water quality standards. In Gallup public polls conducted over the past decade Americans consistently put water pollution and water supply as the top environmental concerns over issues such as air pollution, deforestation, species extinction, and global warming.
Any natural water contains dissolved chemicals, some of which are important human nutrients while others can be harmful to human health. The concentration of a water pollutant is commonly given in very small units such as parts per million (ppm) or even parts per billion (ppb). An arsenic concentration of 1 ppm means 1 part of arsenic per million parts of water. This is equivalent to one drop of arsenic in 50 liters of water. To give you a different perspective on appreciating small concentration units, converting 1 ppm to length units is 1 cm (0.4 in) in 10 km (6 miles) and converting 1 ppm to time units is 30 seconds in a year. Total dissolved solids (TDS) represent the total amount of dissolved material in water. Average TDS values for rainwater, river water, and seawater are about 4 ppm, 120 ppm, and 35,000 ppm, respectively.
Water Pollution Overview
Water pollution is the contamination of water by an excess amount of a substance that can cause harm to human beings and/or the ecosystem. The level of water pollution depends on the abundance of the pollutant, the ecological impact of the pollutant, and the use of the water. Pollutants are derived from biological, chemical, or physical processes. Although natural processes such as volcanic eruptions or evaporation sometimes can cause water pollution, most pollution is derived from human, land-based activities (Figure $2$). Water pollutants can move through different water reservoirs, as the water carrying them progresses through stages of the water cycle (Figure $3$). Water residence time (the average time that a water molecule spends in a water reservoir) is very important to pollution problems because it affects pollution potential. Water in rivers has a relatively short residence time, so pollution usually is there only briefly. Of course, pollution in rivers may simply move to another reservoir, such as the ocean, where it can cause further problems. Groundwater is typically characterized by slow flow and longer residence time, which can make groundwater pollution particularly problematic. Finally, pollution residence time can be much greater than the water residence time because a pollutant may be taken up for a long time within the ecosystem or absorbed onto sediment.
Pollutants enter water supplies from point sources, which are readily identifiable and relatively small locations, or nonpoint sources, which are large and more diffuse areas. Point sources of pollution include animal factory farms (Figure $4$) that raise a large number and high density of livestock such as cows, pigs, and chickens. Also, pipes included are pipes from a factories or sewage treatment plants. Combined sewer systems that have a single set of underground pipes to collect both sewage and storm water runoff from streets for wastewater treatment can be major point sources of pollutants. During heavy rain, storm water runoff may exceed sewer capacity, causing it to back up and spilling untreated sewage directly into surface waters (Figure $5$).
Nonpoint sources of pollution include agricultural fields, cities, and abandoned mines. Rainfall runs over the land and through the ground, picking up pollutants such as herbicides, pesticides, and fertilizer from agricultural fields and lawns; oil, antifreeze, animal waste, and road salt from urban areas; and acid and toxic elements from abandoned mines. Then, this pollution is carried into surface water bodies and groundwater. Nonpoint source pollution, which is the leading cause of water pollution in the U.S., is usually much more difficult and expensive to control than point source pollution because of its low concentration, multiple sources, and much greater volume of water.
Types of Water Pollutants
Oxygen-demanding waste is an extremely important pollutant to ecosystems. Most surface water in contact with the atmosphere has a small amount of dissolved oxygen, which is needed by aquatic organisms for cellular respiration. Bacteria decompose dead organic matter and remove dissolved oxygen (O2) according to the following reaction:
$\text{organic matter} + O_{2} \rightarrow CO_{2} + H_{2} O$
Too much decaying organic matter in water is a pollutant because it removes oxygen from water, which can kill fish, shellfish, and aquatic insects. The amount of oxygen used by aerobic (in the presence of oxygen) bacterial decomposition of organic matter is called biochemical oxygen demand (BOD). The major source of dead organic matter in many natural waters is sewage; grass and leaves are smaller sources. An unpolluted water body with respect to BOD is a turbulent river that flows through a natural forest. Turbulence continually brings water in contact with the atmosphere where the O2 content is restored. The dissolved oxygen content in such a river ranges from 10 to 14 ppm O2, BOD is low, and clean-water fish such as trout. A polluted water body with respect to oxygen is a stagnant deep lake in an urban setting with a combined sewer system. This system favors a high input of dead organic carbon from sewage overflows and limited chance for water circulation and contact with the atmosphere. In such a lake, the dissolved O2 content is ≤5 ppm O2, BOD is high, and low O2-tolerant fish, such as carp and catfish dominate.
Excessive plant nutrients, particularly nitrogen (N) and phosphorous (P), are pollutants closely related to oxygen-demanding waste. Aquatic plants require about 15 nutrients for growth, most of which are plentiful in water. N and P are called limiting nutrients, however, because they usually are present in water at low concentrations and therefore restrict the total amount of plant growth. This explains why N and P are major ingredients in most fertilizer. High concentrations of N and P from human sources (mostly agricultural and urban runoff including fertilizer, sewage, and phosphorus-based detergent) can cause cultural eutrophication, which leads to the rapid growth of aquatic producers, particularly algae. Thick mats of floating algae or rooted plants lead to a form of water pollution that damages the ecosystem by clogging fish gills and blocking sunlight. A small percentage of algal species produce toxins that can kill animals, including humans. Exponential growths of these algae are called harmful algal blooms. When the prolific algal layer dies, it becomes oxygen-demanding waste, which can create very low O2 concentrations in the water (< 2 ppm O2), a condition called hypoxia. This results in a dead zone because it causes death from asphyxiation to organisms that are unable to leave that environment. An estimated 50% of lakes in North America, Europe, and Asia are negatively impacted by cultural eutrophication. In addition, the size and number of marine hypoxic zones have grown dramatically over the past 50 years including a very large dead zone located offshore Louisiana in the Gulf of Mexico. Cultural eutrophication and hypoxia are difficult to combat, because they are caused primarily by nonpoint source pollution, which is difficult to regulate, and N and P, which are difficult to remove from wastewater.
Pathogens are disease-causing microorganisms, e.g., viruses, bacteria, parasitic worms, and protozoa, which cause a variety of intestinal diseases such as dysentery, typhoid fever, and cholera. Pathogens are the major cause of the water pollution crisis discussed at the beginning of this section. Unfortunately nearly a billion people around the world are exposed to waterborne pathogen pollution daily and around 1.5 million children mainly in underdeveloped countries die every year of waterborne diseases from pathogens. Pathogens enter water primarily from human and animal fecal waste due to inadequate sewage treatment. In many underdeveloped countries, sewage is discharged into local waters either untreated or after only rudimentary treatment. In developed countries untreated sewage discharge can occur from overflows of combined sewer systems, poorly managed livestock factory farms, and leaky or broken sewage collection systems. Water with pathogens can be remediated by adding chlorine or ozone, by boiling, or by treating the sewage in the first place.
Oil spills are another kind of organic pollution. Oil spills can result from supertanker accidents such as the Exxon Valdez in 1989, which spilled 10 million gallons of oil into the rich ecosystem of coastal Alaska and killed massive numbers of animals. The largest marine oil spill was the Deepwater Horizon disaster, which began with a natural gas explosion (Figure $6$) at an oil well 65 km offshore of Louisiana and flowed for 3 months in 2010, releasing an estimated 200 million gallons of oil. The worst oil spill ever occurred during the Persian Gulf war of 1991, when Iraq deliberately dumped approximately 200 million gallons of oil in offshore Kuwait and set more than 700 oil well fires that released enormous clouds of smoke and acid rain for over nine months.
During an oil spill on water, oil floats to the surface because it is less dense than water, and the lightest hydrocarbons evaporate, decreasing the size of the spill but polluting the air. Then, bacteria begin to decompose the remaining oil, in a process that can take many years. After several months only about 15% of the original volume may remain, but it is in thick asphalt lumps, a form that is particularly harmful to birds, fish, and shellfish. Cleanup operations can include skimmer ships that vacuum oil from the water surface (effective only for small spills), controlled burning (works only in early stages before the light, ignitable part evaporates but also pollutes the air), dispersants (detergents that break up oil to accelerate its decomposition, but some dispersants may be toxic to the ecosystem), and bioremediation (adding microorganisms that specialize in quickly decomposing oil, but this can disrupt the natural ecosystem).
Toxic chemicals involve many different kinds and sources, primarily from industry and mining. General kinds of toxic chemicals include hazardous chemicals and persistent organic pollutants that include DDT (pesticide), dioxin (herbicide by-product), and PCBs (polychlorinated biphenyls, which were used as a liquid insulator in electric transformers). Persistent organic pollutants (POPs) are long-lived in the environment, biomagnify through the food chain, and can be toxic. Another category of toxic chemicals includes radioactive materials such as cesium, iodine, uranium, and radon gas, which can result in long-term exposure to radioactivity if it gets into the body. A final group of toxic chemicals is heavy metals such as lead, mercury, arsenic, cadmium, and chromium, which can accumulate through the food chain. Heavy metals are commonly produced by industry and at metallic ore mines. Arsenic and mercury are discussed in more detail below.
Arsenic (As) has been famous as an agent of death for many centuries. Only recently have scientists recognized that health problems can be caused by drinking small arsenic concentrations in water over a long time. It enters the water supply naturally from weathering of arsenic-rich minerals and from human activities such as coal burning and smelting of metallic ores. The worst case of arsenic poisoning occurred in the densely populated impoverished country of Bangladesh, which had experienced 100,000s of deaths from diarrhea and cholera each year from drinking surface water contaminated with pathogens due to improper sewage treatment. In the 1970s the United Nations provided aid for millions of shallow water wells, which resulted in a dramatic drop in pathogenic diseases. Unfortunately, many of the wells produced water naturally rich in arsenic. Tragically, there are an estimated 77 million people (about half of the population) who inadvertently may have been exposed to toxic levels of arsenic in Bangladesh as a result. The World Health Organization has called it the largest mass poisoning of a population in history.
Mercury (Hg) is used in a variety of electrical products, such as dry cell batteries, fluorescent light bulbs, and switches, as well as in the manufacture of paint, paper, vinyl chloride, and fungicides. Mercury acts on the central nervous system and can cause loss of sight, feeling, and hearing as well as nervousness, shakiness, and death. Like arsenic, mercury enters the water supply naturally from weathering of mercury-rich minerals and from human activities such as coal burning and metal processing. A famous mercury poisoning case in Minamata, Japan involved methylmercury-rich industrial discharge that caused high Hg levels in fish. People in the local fishing villages ate fish up to three times per day for over 30 years, which resulted in over 2,000 deaths. During that time the responsible company and national government did little to mitigate, help alleviate, or even acknowledge the problem.
Hard water contains abundant calcium and magnesium, which reduces its ability to develop soapsuds and enhances scale (calcium and magnesium carbonate minerals) formation on hot water equipment. Water softeners remove calcium and magnesium, which allows the water to lather easily and resist scale formation. Hard water develops naturally from the dissolution of calcium and magnesium carbonate minerals in soil; it does not have negative health effects in people.
Groundwater pollution can occur from underground sources and all of the pollution sources that contaminate surface waters. Common sources of groundwater pollution are leaking underground storage tanks for fuel, septic tanks, agricultural activity, landfills, and fossil fuel extraction. Common groundwater pollutants include nitrate, pesticides, volatile organic compounds, and petroleum products. Another troublesome feature of groundwater pollution is that small amounts of certain pollutants, e.g., petroleum products and organic solvents, can contaminate large areas. In Denver, Colorado 80 liters of several organic solvents contaminated 4.5 trillion liters of groundwater and produced a 5 km long contaminant plume. A major threat to groundwater quality is from underground fuel storage tanks. Fuel tanks commonly are stored underground at gas stations to reduce explosion hazards. Before 1988 in the U.S. these storage tanks could be made of metal, which can corrode, leak, and quickly contaminate local groundwater. Now, leak detectors are required and the metal storage tanks are supposed to be protected from corrosion or replaced with fiberglass tanks. Currently there are around 600,000 underground fuel storage tanks in the U.S. and over 30% still do not comply with EPA regulations regarding either release prevention or leak detection. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/07%3A_Water_Availability_and_Use/7.03%3A_Water_Pollution.txt |
Resolution of the global water pollution crisis requires multiple approaches to improve the quality of our fresh water and move towards sustainability. The most deadly form of water pollution, pathogenic microorganisms that cause waterborne diseases, kills almost 2 million people in underdeveloped countries every year. The best strategy for addressing this problem is proper sewage (wastewater) treatment. Untreated sewage is not only a major cause of pathogenic diseases, but also a major source of other pollutants, including oxygen-demanding waste, nutrients (N and P, particularly), and toxic heavy metals. Wastewater treatment is done at a sewage treatment plant in urban areas and through a septic tank system in rural areas.
The main purpose of sewage (wastewater) treatment is to remove organic matter (oxygen-demanding waste) and kill bacteria. Special methods also can be used to remove nutrients and other pollutants. The numerous steps at a conventional sewage treatment plant include pretreatment (screening and removal of sand and gravel), primary treatment (settling or floatation to remove organic solids, fat, and grease), secondary treatment (aerobic bacterial decomposition of organic solids), tertiary treatment (bacterial decomposition of nutrients and filtration), disinfection (treatment with chlorine, ozone, ultraviolet light, or bleach to kill most microbes), and either discharge to surface waters (usually a local river) or reuse for some other purpose, such as irrigation, habitat preservation, and artificial groundwater recharge (Figure \(1\)).
The concentrated organic solid produced during primary and secondary treatment is called sludge, which is treated in a variety of ways including landfill disposal, incineration, use as fertilizer, and anaerobic bacterial decomposition, which is done in the absence of oxygen. Anaerobic decomposition of sludge produces methane gas, which can be used as an energy source. To reduce water pollution problems, separate sewer systems (where street runoff goes to rivers and only wastewater goes to a wastewater treatment plant) are much better than combined sewer systems, which can overflow and release untreated sewage into surface waters during heavy rain. Some cities such as Chicago, Illinois have constructed large underground caverns and also use abandoned rock quarries to hold storm sewer overflow. After the rain stops, the stored water goes to the sewage treatment plant for processing.
A septic tank system is an individual sewage treatment system for homes in typically rural settings. The basic components of a septic tank system (Figure \(2\)) include a sewer line from the house, a septic tank (a large container where sludge settles to the bottom and microorganisms decompose the organic solids anaerobically), and the drain field (network of perforated pipes where the clarified water seeps into the soil and is further purified by bacteria). Water pollution problems occur if the septic tank malfunctions, which usually occurs when a system is established in the wrong type of soil or maintained poorly.
For many developing countries, financial aid is necessary to build adequate sewage treatment facilities. The World Health Organization estimates an estimated cost savings of between \$3 and \$34 for every \$1 invested in clean water delivery and sanitation. The cost savings are from health care savings, gains in work and school productivity, and prevented deaths. Simple and inexpensive techniques for treating water at home include chlorination, filters, and solar disinfection. Another alternative is to use constructed wetlands technology (marshes built to treat contaminated water), which is simpler and cheaper than a conventional sewage treatment plant.
Bottled water is not a sustainable solution to the water crisis. Bottled water is not necessarily any safer than the U.S. public water supply, it costs on average about 700 times more than U.S. tap water, and every year it uses approximately 200 billion plastic and glass bottles that have a relatively low rate of recycling. Compared to tap water, it uses much more energy, mainly in bottle manufacturing and long-distance transportation. If you don’t like the taste of your tap water, then please use a water filter instead of bottled water!
CLEAN WATER ACT
During the early 1900s rapid industrialization in the U.S. resulted in widespread water pollution due to free discharge of waste into surface waters. The Cuyahoga River in northeast Ohio caught fire numerous times, including a famous fire in 1969 that caught the nation’s attention. In 1972 Congress passed one of the most important environmental laws in U.S. history, the Federal Water Pollution Control Act, which is more commonly called the Clean Water Act. The purpose of the Clean Water Act and later amendments is to maintain and restore water quality, or in simpler terms to make our water swimmable and fishable. It became illegal to dump pollution into surface water unless there was formal permission and U.S. water quality improved significantly as a result. More progress is needed because currently the EPA considers over 40,000 U.S. water bodies as impaired, most commonly due to pathogens, metals, plant nutrients, and oxygen depletion. Another concern is protecting groundwater quality, which is not yet addressed sufficiently by federal law. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/07%3A_Water_Availability_and_Use/7.04%3A_Water_Treatment.txt |
The Aral Sea is a lake located east of the Caspian Sea between Uzbekistan and Kazakhstan in central Asia. This area is part of the Turkestan desert, which is the fourth largest desert in the world; it is produced from a rain shadow effect by Afghanistan’s high mountains to the south. Due to the arid and seasonally hot climate there is extensive evaporation and limited surface waters in general. Summer temperatures can reach 60οC (140οF)! The water supply to the Aral Sea is mainly from two rivers, the Amu Darya and Syr Darya, which carry snow melt from mountainous areas.
In the early 1960s, the then-Soviet Union diverted the Amu Darya and Syr Darya Rivers for irrigation of one of the driest parts of Asia to produce rice, melons, cereals, and especially cotton. The Soviets wanted cotton or white gold to become a major export. They were successful, and, today Uzbekistan is one of the world’s largest exporters of cotton. Unfortunately, this action essentially eliminated any river inflow to the Aral Sea and caused it to disappear almost completely.
In 1960, Aral Sea was the fourth largest inland water body; only the Caspian Sea, Lake Superior, and Lake Victoria were larger. Since then, it has progressively shrunk due to evaporation and lack of recharge by rivers. Before 1965, the Aral Sea received 2060 km3 of fresh water per year from rivers and by the early 1980s it received none. By 2007, the Aral Sea shrank to about 10% of its original size and its salinity increased from about 1% dissolved salt to about 10% dissolved salt, which is 3 times more saline than seawater. These changes caused an enormous environmental impact. A once thriving fishing industry is dead as are the 24 species of fish that used to live there; the fish could not adapt to the more saline waters. The current shoreline is tens of kilometers from former fishing towns and commercial ports. Large shing boats lie in the dried up lakebed of dust and salt. A frustrating part of the river diversion project is that many of the irrigation canals were poorly built, allowing abundant water to leak or evaporate. An increasing number of dust storms blow salt, pesticides, and herbicides into nearby towns causing a variety of respiratory illnesses including tuberculosis.
The wetlands of the two river deltas and their associated ecosystems have disappeared. The regional climate is drier and has greater temperature extremes due to the absence of moisture and moderating influence from the lake. In 2003, some lake restoration work began on the northern part of the Aral Sea and it provided some relief by raising water levels and reducing salinity somewhat. The southern part of the Aral Sea has seen no relief and remains nearly completely dry. The destruction of the Aral Sea is one of the planet’s biggest environmental disasters and it is caused entirely by humans. Lake Chad in Africa is another example of a massive lake that has nearly disappeared for the same reasons as the Aral Sea. Aral Sea and Lake Chad are the most extreme examples of large lakes destroyed by unsustainable diversions of river water. Other lakes that have shrunk significantly due to human diversions of water include the Dead Sea in the Middle East, Lake Manchar in Pakistan, and Owens Lake and Mono Lake, both in California. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/07%3A_Water_Availability_and_Use/7.05%3A_Case_Study_-_The_Aral_Sea_-_Going_Going_Gone.txt |
Summary
Precipitation—a major control of fresh water availability—is unevenly distributed around the globe. More precipitation falls near the equator, and landmasses there are characterized by a tropical rainforest climate. Less precipitation tends to fall near 2030 north and south latitude, where the world’s largest deserts are located. The water crisis refers to a global situation where people in many areas lack access to sufficient water or clean water or both. The current and future water crisis requires multiple approaches to extending our fresh water supply and moving towards sustainability. Some of the longstanding traditional approaches include dams and aqueducts. Water pollution is the contamination of water by an excess amount of a substance that can cause harm to human beings and the ecosystem. The level of water pollution depends on the abundance of the pollutant, the ecological impact of the pollutant, and the use of the water. The most deadly form of water pollution, pathogenic microorganisms that cause waterborne diseases, kills almost 2 million people in underdeveloped countries every year. Resolution of the global water pollution crisis requires multiple approaches to improve the quality of fresh water. The best strategy for addressing this problem is proper sewage treatment. Untreated sewage is not only a major cause of pathogenic diseases, but also a major source of other pollutants, including oxygen-demanding waste, plant nutrients, and toxic heavy metals.
Review Questions
1. Approximately 97% of all water on Earth is found in what reservoir?
1. Oceans
2. Lakes
3. Streams
4. Groundwater
5. Glaciers and ice caps
2. The majority of freshwater, whether accessible to humans or not, is contained in what reservoir?
1. Ocean
2. Lakes
3. Streams
4. Groundwater
5. Glaciers and ice caps
3. You are studying a river and notice that it contains chemical waste. You have thoroughly searched the entire length of the stream and ruled out that the waste is directly entering the stream. Instead, the waste must by entering by one of its many tributary streams. Because these streams empty into the river you are studying, they must be within the same…
1. Watershed
2. Irrigation district
3. Riparian area
4. Aqueduct
5. Water zone
4. Adding water to a recharge area would have what practical effect?
1. Increased amount of groundwater
2. A more pronounced cone of depression
3. Depletion of an aquifer
4. Less infiltration
5. Greater precipitation
5. With removal of groundwater, which of the following may result?
1. subsidence
2. sinkholes
3. cone of depression
4. decreased water table
5. All of the above.
6. For individuals living in areas where no freshwater is available, which one of the following would produce water that could be used for drinking?
1. desalination
2. groundwater mining
3. sublimation
4. transpiration
5. saltation
7. Three carcinogens are equally harmful at equal concentrations. In a terrible industrial accident, 2 tons of each type of carcinogen were discharged into a river at the same time. The residence times of each pollutant is as follows: Chemical X = 2.8 days; Chemical Y = 3.5 days; Chemical Z = 17.2 hours. Which one possesses the greatest risk of exposure to the nearby community over the course of a week following the spill?
1. Chemical X
2. Chemical Y
3. Chemical Z
4. All chemicals provided equal likelihood of exposure
8. Fertilizers applied to residential lawns and gardens can end up in water bodies through the process of surface run-off or movement through ground water. This type of pollution would be considered…
1. Point source
2. Bioremediation
3. Non-point source
4. Throughput sourcing
5. Tangential
9. Which one of the following would most directly prevent a dead zone from forming in a water body that is already experiencing eutrophication?
1. Increase the O2 concentration in the water
2. Lower the nutrient levels
3. Increase the amount of algae and phytoplankton
4. Increase the amount of bacteria that decompose dead organic matter
5. Make the water more hypoxic
10. If you analyzed waste water directly after primary treatment, what would you notice?
1. Harmful bacteria and other biological agents have been killed or removed
2. The water is potable
3. Much of the dissolved solids have been removed
4. Many suspended solids have been removed
5. The water is mostly sludge
See Appendix for answers
Attributions
Theis, T. & Tomkin, J. (Eds.). (2015). Sustainability: A comprehensive foundation. Retrieved from http://cnx.org/contents/[email protected]. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. “Review Questions”is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/07%3A_Water_Availability_and_Use/7.06%3A_Chapter_Resources.txt |
Learning Outcomes
• Understand the major drivers of food insecurity
• Recognize the role of women in food and nutritional security
• Classify key food and nutritional sources
• Identify benefits and risks of genetic engineering
• 8.1: Food Security
Poverty—not food availability—is the major driver of food insecurity. Improvements in agricultural productivity are necessary to increase rural household incomes and access to available food but are insufficient to ensure food security. Evidence indicates that poverty reduction and food security do not necessarily move in tandem. The main problem is lack of economic (social and physical) access to food at national and household levels and inadequate nutrition (or hidden hunger).
• 8.2: Biotechnology and Genetic Engineering
The development of a new strain of crop is an example of agricultural biotechnology: a range of tools that include both traditional breeding techniques and more modern lab-based methods. Traditional methods date back thousands of years, whereas biotechnology uses the tools of genetic engineering developed over the last few decades. Genetic engineering is the name for the methods that scientists use to introduce new traits to an organism. This process results in genetically modified organisms.
• 8.3: Chapter Resources
Thumbnail image - By learning skills like composting, crop diversification, organic pesticide production, seed multiplication and agro-forestry farmers in Malawi are increasing their ability to feed their families over the long term.
08: Food Hunger
Progress continues in the fight against hunger, yet an unacceptably large number of people lack the food they need for an active and healthy life. The latest available estimates indicate that about 795 million people in the world – just over one in nine –still go to bed hungry every night, and an even greater number live in poverty (defined as living on less than \$1.25 per day). Poverty—not food availability—is the major driver of food insecurity. Improvements in agricultural productivity are necessary to increase rural household incomes and access to available food but are insufficient to ensure food security. Evidence indicates that poverty reduction and food security do not necessarily move in tandem. The main problem is lack of economic (social and physical) access to food at national and household levels and inadequate nutrition (or hidden hunger). Food security not only requires an adequate supply of food but also entails availability, access, and utilization by all—people of all ages, gender, ethnicity, religion, and socioeconomic levels.
From Agriculture to Food Security
Agriculture and food security are inextricably linked. The agricultural sector in each country is dependent on the available natural resources, as well as the politics that govern those resources. Staple food crops are the main source of dietary energy in the human diet and include things such as rice, wheat, sweet potatoes, maize, and cassava.
Food security
Food security is essentially built on four pillars: availability, access, utilization and stability. An individual must have access to sufficient food of the right dietary mix (quality) at all times to be food secure. Those who never have sufficient quality food are chronically food insecure.
When food security is analyzed at the national level, an understanding not only of national production is important, but also of the country’s access to food from the global market, its foreign exchange earnings, and its citizens’ consumer choices. Food security analyzed at the household level is conditioned by a household’s own food production and household members’ ability to purchase food of the right quality and diversity in the market place. However, it is only at the individual level that the analysis can be truly accurate because only through understanding who consumes what can we appreciate the impact of sociocultural and gender inequalities on people’s ability to meet their nutritional needs.The definition of food security is often applied at varying levels of aggregation, despite its articulation at the individual level. The importance of a pillar depends on the level of aggregation being addressed. At a global level, the important pillar is foodavailability. Does global agricultural activity produce sufficient food to feed all the world’s inhabitants? The answer today is yes, but it may not be true in the future given the impact of a growing world population, emerging plant and animal pests and diseases, declining soil productivity and environmental quality, increasing use of land for fuel rather than food, and lack of attention to agricultural research and development, among other factors.
The third pillar, food utilization, essentially translates the food available to a household into nutritional security for its members. One aspect of utilization is analyzed in terms of distribution according to need. Nutritional standards exist for the actual nutritional needs of men, women, boys, and girls of different ages and life phases (that is, pregnant women), but these “needs” are often socially constructed based on culture. For example, in South Asia evidence shows that women eat after everyone else has eaten and are less likely than men in the same household to consume preferred foods such as meats and fish. Hidden hunger commonly results from poor food utilization: that is, a person’s diet lacks the appropriate balance of macro- (calories) and micronutrients (vitamins and minerals). Individuals may look well nourished and consume sufficient calories but be deficient in key micronutrients such as vitamin A, iron, and iodine.
When food security is analyzed at the national level, an understanding not only of national production is important, but also of the country’s access to food from the global market, its foreign exchange earnings, and its citizens’ consumer choices. Food security analyzed at the household level is conditioned by a household’s own food production and household members’ ability to purchase food of the right quality and diversity in the market place. However, it is only at the individual level that the analysis can be truly accurate because only through understanding who consumes what can we appreciate the impact of sociocultural and gender inequalities on people’s ability to meet their nutritional needs.
Food stability is when a population, household, or individual has access to food at all times and does not risk losing access as a consequence of cyclical events, such as the dry season. When some lacks food stability, they have malnutrition, a lack of essential nutrients. This is economically costly because it can cost individuals 10 percent of their lifetime earnings and nations 2 to 3 percent of gross domestic product (GDP) in the worst-affected countries (Alderman 2005). Achieving food security is even more challenging in the context of HIV and AIDS. HIV affects people’s physical ability to produce and use food, reallocating household labor, increasing the work burden on women, and preventing widows and children from inheriting land and productive resources.
Obesity
Obesity means having too much body fat. It is not the same as overweight, which means weighing too much. Obesity has become a significant global health challenge, yet is preventable and reversible. Over the past 20 years, a global overweight/obesity epidemic has emerged, initially in industrial countries and now increasingly in low- and middle-income countries, particularly in urban settings, resulting in a triple burden of undernutrition, micronutrient deficiency, and overweight/obesity. There is significant variation by region; some have very high rates of undernourishment and low rates of obesity, while in other regions the opposite is true (Figure \(1\)).
However, obesity has increased to the extent that the number of overweight people now exceeds the number of underweight people worldwide. The economic cost of obesity has been estimated at \$2 trillion, accounting for about 5% of deaths worldwide. Almost 30% of the world’s population, or 2.1 billion people, are overweight or obese, 62% of whom live in developing countries.
Obesity accounts for a growing level and share of worldwide noncommunicable diseases, including diabetes, heart disease, and certain cancers that can reduce quality of life and increase public health costs of already under-resourced developing countries. The number of overweight children is projected to double by 2030. Driven primarily by increasing availability of processed, affordable, and effectively marketed food, the global food system is falling short with rising obesity and related poor health outcomes. Due to established health implications and rapid increase in prevalence, obesity is now a recognized major global health challenge.
Suggested Supplementary Reading:
McMillan, T. 2018. How China Plans to Feed 1.4 Billion Growing Appetites. National Geographic. February.
Contributors and Attributions
• Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/08%3A_Food__Hunger/8.01%3A_Food_Security.txt |
In the early 1990s, an emerging disease was destroying Hawaii’s production of papaya and threatening to decimate the \$11 million industry (Figure \(1\)). Fortunately, a man named Dennis Gonsalves, who was raised on a sugar plantation and then became a plant physiologist at Cornell University, would develop papaya plants genetically engineered to resist the deadly virus. By the end of the decade, the Hawaiian papaya industry and the livelihoods of many farmers were saved thanks to the free distribution of Dr. Gonsalves seeds.
The development of a new strain of crop is an example of agricultural biotechnology: a range of tools that include both traditional breeding techniques and more modern lab-based methods. Traditional methods date back thousands of years, whereas biotechnology uses the tools of genetic engineering developed over the last few decades. Genetic engineering is the name for the methods that scientists use to introduce new traits to an organism. This process results in genetically modified organisms, or GMO. For example, plants may be genetically engineered to produce characteristics to enhance the growth or nutritional profile of food crops. GMO that are crop species are commonly called genetically engineered crops, or GE crops for short
The History of Genetic Modification of Crops
Nearly all the fruits and vegetables found in your local market would not occur naturally. In fact, they exist only because of human intervention that began thousands of years ago. Humans created the vast majority of crop species by using traditional breeding practices on naturally-occurring, wild plants. These practices rely upon selective breeding (human assisted-breeding of individuals with desirable traits). Traditional breeding practices, although low-tech and simple to perform, have the practical outcome of modifying an organism’s genetic information, thus producing new traits.
An interesting example is maize (corn). Biologists have discovered that maize was developed from a wild plant called teosinte. Through traditional breeding practices, humans living thousands of years ago in what is now Southern Mexico began selecting for desirable traits until they were able to transform the plant into what is now known as maize. In doing so, they permanently (and unknowingly) altered its genetic instructions, allowing for new traits to emerge. Considering this history, we might ask the question: is there really such a thing as “non-GMO” maize?
This history of genetic modification is common to nearly all crop species. For example, cabbage, broccoli, Brussel sprouts, cauliflower, and kale were all developed from a single species of wild mustard plant (Figure \(2\)). Wild nightshade was the source of tomatoes, eggplant, tobacco, and potatoes, the latter developed by humans 7,000 – 10,000 years ago in South America.
Traditional Breeding v. Modern Genetic Engineering
To produce new traits in livestock, pets, crops, or other type of organism, there almost always has to be an underlying change in that organism’s genetic instructions. What many people might not understand is that traditional breeding practices do, in fact, result in permanent genetic changes and is therefore a type of genetic modification. This misunderstanding may arise because traditional breeding practices do not require sophisticated laboratory equipment or any knowledge of genetics, which some may see as a perquisite for genetic modification.
How do traditional breeding practices compare to modern genetic engineering? Both result in changes to an organism’s genetic information, but the magnitude of those changes varies amongst the two techniques (Figure \(3\)). Traditional breeding shuffles all of the genes between the two organisms being bred, which can number into the tens of thousands (maize, for example, has 32,000 genes). When mixing such a large number of genes, the results can be unpredictable. Modern genetic engineering is more precise in the sense that biologists can modify just a single gene. Also, genetic engineering can introduce a gene between two distantly-related species, such as inserting a bacterial gene into a plant. Such transfer might seem unusual, but it is not without its equivalent in nature. In a process called horizontal gene transfer, DNA from one species can be inserted into a different species. One recent study, for example, has found that humans contain about 150 genes from other species, including bacteria.
Potential Benefits of Genetic Engineering
Enhanced nutrition
Advances in biotechnology may provide consumers with foods that are nutritionally-enriched (Figure \(4\)), longer-lasting, or that contain lower levels of certain naturally occurring toxins present in some food plants. For example, developers are using biotechnology to try to reduce saturated fats in cooking oils, reduce allergens in foods, and increase disease-fighting nutrients in foods. Biotechnology may also be used to conserve natural resources, enable animals to more effectively use nutrients present in feed, decrease nutrient runoff into rivers and bays, and help meet the increasing world food and land demands.
Cheaper and More Manageable Production
Biotechnology may provide farmers with tools that can make production cheaper and more manageable. For example, some biotechnology crops can be engineered to tolerate specific herbicides, which make weed control simpler and more efficient. Other crops have been engineered to be resistant to specific plant diseases and insect pests, which can make pest control more reliable and effective, and/or can decrease the use of synthetic pesticides. These crop production options can help countries keep pace with demands for food while reducing production costs.
Improved pest control
Biotechnology has helped to make both pest control and weed management safer and easier while safeguarding crops against disease. For example, genetically engineered insect-resistant cotton has allowed for a significant reduction in the use of persistent, synthetic pesticides that may contaminate groundwater and the environment. In terms of improved weed control, herbicide-tolerant soybeans, cotton, and corn enable the use of reduced-risk herbicides that break down more quickly in soil and are non-toxic to wildlife and humans.
Potential Concerns about Genetically Engineered Crops
The complexity of ecological systems presents considerable challenges for experiments that assess the risks and benefits of GE crops. Assessing such risks is difficult, because both natural and human-modified systems are highly complex and fraught with uncertainties that may not be clarified until long after an experimental introduction has been concluded. Critics of GE crops warn that their cultivation should be carefully considered within broader ecosystems because of their potential benefits and hazards to the environment.
In addition to environmental risks, some people are concerned about potential health risks of GE crops because they feel that genetic modification alters the intrinsic properties, or essence, of an organism. As discussed above, however, it is known that both traditional breeding practices and modern genetic engineering produce permanent genetic modifications. Further, traditional breeding practices actually have a larger and more unpredictable impact on a species’ genetics because of its comparably crude nature. Considering this, it is wise that both new GE crops and traditionally produced crops should be studied for potential human health risks.
To address these various concerns, the US National Academies of Sciences, Engineering, and Medicine (NASEM) published a comprehensive, 500-page report in 2016 that summarized the current scientific knowledge regarding GE crops. The report, titled Genetically Engineered Crops: Experiences and Prospects, reviewed more than 900 research articles, in addition to public comments and expert testimony. Results from this seminal report, hereafter referred to as the “GE Crop Report” for brevity, is shared in the various subsections below.
Interbreeding with Native Species
Through interbreeding, or hybridization, GE crops might share their genetically-modified DNA with wild relatives. This could affect the genetics of those wild relatives and have unforeseen consequences on their populations, and could even have implications for the larger ecosystem. For example, if a gene engineered to confer herbicide resistance were to pass from a GE crop to a wild relative, it might transform the wild species into a ‘super weed’ – a species that could not be controlled by herbicide. Its rampant growth could then displace other wild species and the wildlife that depends on it, thus inflecting ecological harm.
NASEM’s GE Crop Report did find some evidence of genetic transfer between GE crops and wild relatives. However, there was no evidence of ecological harm from that transfer. Clearly, continued monitoring, especially for newly-developed crops, is warranted.
Consumers Right to Choose
The International Federation of Organic Agriculture Movement has made stringent efforts to keep GE crops out of organic production, yet some US organic farmers have found their corn (maize) crops, including seeds, contain detectable levels of genetically engineered DNA. The organic movement is firm in its opposition to any use of GE crops in agriculture, and organic standards explicitly prohibit their use (however, keep in mind that even “organic” maize has incurred significant genetic modification compared to its wild relative, teosinte). The farmers, whose seed is contaminated, have been under rigid organic certification, which assures that they did not use any kind of genetically modified materials on their farms.
Any trace of GE crops must have come from outside their production areas. While the exact origin is unclear at this time, it is likely that the contamination has been caused by pollen drift from GE crop fields in surrounding areas. However, the contamination may have also come from the seed supply. Seed producers, who intended to supply GE crop-free seed, have also been confronted with genetic contamination and cannot guarantee that their seed is 100% GE crop-free.
Long-Term Ecological Effects
An early study indicated the pollen from a particular type of genetically modified corn may be harmful to the caterpillars of monarch butterflies, This type of corn, known as Bt corn, is genetically modified to produce a bacterial protein that acts as an insecticide. This trait is favorable because it reduces the amount of insecticides used by farmers. Pollen from Bt corn can be harmful to caterpillars, but only at very high concentrations. These concentrations are seldom reached in nature and follow-up studies have found the effect of Bt corn to be negligible.
NASEM’s GE Crop Report documents that the validity of that initial monarch study was questioned by other scientists and this ultimately led to a large, multi-national study funded by the US and Canada. They found that the vast majority of Bt corn grown did not represent a risk to monarchs. However, one strain of Bt corn did, and it was consequently removed from the market.
The GE Crop Report also mentioned a separate threat to monarch: loss of milkweed, which is critical to the butterfly’s lifecycle. Some GE crops are engineered to resist the herbicide glyphosate. Farmers using these crops can spray their entire field with the herbicide, which kills milkweed but not their GE crop. This can lower the amount of milkweed growing within the habitat range of monarchs. The report concluded that more studies are needed to quantify the actual impact this may be having on monarch populations.
Human Health Risk
At least some of the genes used in GE crops may not have been used in the food supply before, so GM foods may pose a potential risk for human health, such as producing new allergens. But this is also true of crops generated by traditional breeding practices (because both produce genetic modifications and thus new traits).
Like other ‘controversial’ scientific issues, the scientific consensus on GE crops is quite clear: they are safe. The UN’s Food and Agriculture Organization has concluded that risks to human and animal health from the use of GMOs are negligible. NASEM’s GE Crop Report found “no substantiated evidence of a difference in risks to human health between current commercially available genetically engineered (GE) crops and conventionally bred crops, nor did it find conclusive cause-and-effect evidence of environmental problems from the GE crops.” The American Medical Association’s Council on Science and Public Health, in 2012, stated that “Bioengineered foods have been consumed for close to 20 years, and during that time, no overt consequences on human health have been reported and/or substantiated in the peer-reviewed literature.” Similar statements have been made by the US National Resource Council and the American Association for the Advancement of Science, which publishes the preeminent scholarly journal, Science.
The potential of GE crops to be allergenic is one of the potential adverse health effects and it should continue to be studied, especially because some scientific evidences indicates that animals fed GE crops have been harmed. NASEM’s GE Crop Report concluded that when developing new crops, it is the product that should be studied for potential health and environmental risks, not the process that achieved that product. What this means is, because both traditional breeding practices and modern genetic engineering produce new traits through genetic modification, they both present potential risks. Thus, for the safety of the environment and human health, both should be adequately studied.
Intellectual Property Rights
Intellectual property rights are one of the important factors in the current debate on GE crops. GE crops can be patented by Agri-businesses, which can lead to them controlling and potentially exploiting agricultural markets. Some accuse companies, such as Monsanto, of allegedly controlling seed production and pricing, much to the detriment of farmers. NASEM’s GE Crop Report recommends more research into how the concentration of seed-markets by a few companies, and the subsequent reduction of free market competition, may be affecting seed prices and farmers.
It should be noted that crops developed by traditional breeding can also be legally protected and controlled in ways similar to GE crops. Jim Myers, from Oregon State University notes that “In all but a few cases, all contemporary varieties developed by private breeders are [legally] protected, and most public varieties are protected as well.”
Are GE Crops the Solution We Need?
Significant resources, both financial and intellectual, have been allocated to answering the question: are GE crops safe? After many hundreds of scientific studies, the answer is yes. But a significant question still remains: are they necessary? Certainly, such as in instances like Hawaii’s papaya, which were threated with eradication due to an aggressive disease, genetic engineering was a quick and effective solution that would have been extremely difficult, if not impossible, to solve using traditional breeding practices.
However, in many cases, the early promises of GE crops – that they would improve nutritional quality of foods, confer disease resistance, and provide unparalleled advances in crop yields – have largely failed to come to fruition. NASEM’s GE Crop Report states that while GE crops have resulted in the reduction of agricultural loss from pests, reduced pesticide use, and reduced rates of injury from insecticides for farm workers, they have not increased the rate at which crop yields are advancing when compared to non-GE crops. Additionally, while there are some notable exceptions like golden rice or virus-resistant papayas, very few GE crops have been produced to increase nutritional capacity or to prevent plant disease that can devastate a farmer’s income and reduce food security. The vast majority of GE crops are developed for only two purposes: to introduce herbicide resistance or pest resistance.
Genetic engineering of crops represents in important tool in a world of rapidly changing climate and a burgeoning human population, but as you will see in the next chapter, it is only one of many tools that agriculturists can use to produce enough food for all humans while simultaneously working to conserve the environment.
Suggested Supplementary Reading:
Achenbach, J. 2015. “Why Do Many Reasonable People Doubt Science?” National Geographic Magazine. https://www.nationalgeographic.com/magazine/2015/03/science-doubters-climate-change-vaccinations-gmos/
NASEM. 2016.Genetically Engineered Crops: Experiences and Prospects. http://nas-sites.org/ge-crops/category/report/ | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/08%3A_Food__Hunger/8.02%3A_Biotechnology_and_Genetic_Engineering.txt |
Summary
Progress continues in the fight against hunger, yet an unacceptably large number of people still lack the food they need for an active and healthy life. About 795 million people in the world still go to bed hungry every night, and an even greater number live in poverty. Poverty is the major driver of food insecurity. Improvements in agricultural productivity are necessary to increase rural household incomes and access to available food but are insufficient to ensure food security. Food security is essentially built on four pillars: availability, access, utilization and stability. Women are crucial in the translation of the products of a vibrant agriculture sector into food and nutritional security for their households. They are often the farmers who cultivate food crops and produce commercial crops alongside the men in their households as a source of income. Over the past 20 years, a global obesity epidemic has emerged. Due to established health implications and rapid increase in prevalence, obesity is now a recognized major global health challenge, and no national success stories in curbing its growth have so far been reported. Genetic engineering is the name for methods that scientists use to introduce new traits or characteristics to an organism. Advocates say that application of genetic engineering in agriculture has resulted in benefits to farmers, producers, and consumers. Critics advise that the risks for the introduction of a GMO into each new ecosystem need to be examined on a case-by-case basis, alongside appropriate risk management measures.
Review Questions
1. Which one of the following is not one of the four pillars of food security?
1. Availability
2. Access
3. Utilization
4. Transformation
5. Stability
2. Which one of the following statements is false regarding selective breeding?
1. It results in genetic changes in the offspring
2. It is anthropogenic
3. Is reliant upon modern, lab-based methods
4. It can produce new traits over time
5. It was responsible for creating many common crops, such as maize (corn)
3. The US National Academy of Sciences, Engineering, and Medicine, along with other organizations such as the American Medical Association, have determined that GE crops…
1. Are safe to consume
2. Likely pose a risk to human health
3. Pose a serious risk to human health
4. Should be banned
5. Have not been scientifically studied and therefore they cannot make any recommendations.
4. Which one of the following regions has obesity rates that are lower than rates of undernourishment?
1. Middle East and North Africa
2. Latin America and Caribbean
3. Europe and Central Asia
4. South Asia
5. Potatoes, tomatoes, and tobacco were are developed by humans many thousands of years ago by the genetic modification of wild nightshade species. Specifically, these crops were developed using…
1. Selective breeding
2. Horizontal gene transfer
3. Epigenetics
4. Natural selection
5. Anthropogenesis
See Appendix for answers
Attributions
Bora, S., Ceccacci, I., Delgado, C. & Townsend, R. (2011). Food security and conflict. World Bank, Washington, DC. © World Bank. Retrieved from https://openknowledge.worldbank.org/...le/10986/11719. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.
CK12. (2015). Food and nutrients. Accessed August 31, 2015 at http://www.ck12.org/user:a3F1aWNrQHdlYmIub3Jn/section/Food-and-Nutrients/. Available under Creative Commons Attribution-NonCommercial 3.0 Unported License. (CC BY-NC 3.0). Modified from original.
Godheja, J. (2013). Impact of GMO’S on environment and human health. Recent Research In Science And Technology, 5(5). Retrieved from recent-science.com/index.php/rrst/article/view/17028. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.
Maghari, B. M., & Ardekani, A. M. (2011). Genetically Modified Foods and Social Concerns. Avicenna Journal of Medical Biotechnology, 3(3), 109–117.
World Bank; Food and Agriculture Organization; International Fund for Agricultural Development.(2009). Gender in agriculture sourcebook. Washington, DC: World Bank. © World Bank.Retrieved from https://openknowledge.worldbank.org/handle/10986/6603. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.
World Bank Group. (2015). Ending poverty and hunger by 2030: An agenda for the global food system. Washington, DC. © World Bank. Retrieved from https://openknowledge.worldbank.org/...le/10986/21771. Available under Creative Commons Attribution License 3.0 IGO (CC BY 3.0 IGO). Modified from original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/08%3A_Food__Hunger/8.03%3A_Chapter_Resources.txt |
Learning Outcomes
• Describe the components of soils
• Discuss how land use affects global ecosystem conditions
• Identify environmental effects of pesticides
• Recognize the relationship between exposure to POPs and human health
• Explain alternative practices in farming and soil management
• 9.1: Soil Profiles and Processes
The word “soil” has been defined differently by different scientific disciplines. In agriculture and horticulture, soil generally refers to the medium for plant growth, typically material within the upper meter or two. Soil consists predominantly of mineral matter, but also contains organic matter (humus) and living organisms. The pore spaces between mineral grains are filled with varying proportions of water and air.
• 9.2: Soil-Plant Interactions
Soil plays a key role in plant growth. Beneficial aspects to plants include providing physical support, water, heat, nutrients, and oxygen (Figure 1). Mineral nutrients from the soil can dissolve in water and then become available to plants. Although many aspects of soil are beneficial to plants, excessively high levels of trace metals (either naturally occurring or anthropogenically added) or applied herbicides can be toxic to some plants.
• 9.3: Conventional Agriculture
The prevailing agricultural system, variously called “conventional farming,” “modern agriculture,” or “industrial farming,” has delivered tremendous gains in productivity and efficiency. Food production worldwide has risen in the past 50 years; the World Bank estimates that between 70 percent and 90 percent of the recent increases in food production are the result of conventional agriculture rather than greater acreage under cultivation.
• 9.4: Pests and Pesticides
Pests are organisms that occur where they are not wanted or that cause damage to crops or humans or other animals. Thus, the term “pest” is a highly subjective term. A pesticide is a term for any substance intended for preventing, destroying, repelling, or mitigating any pest. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests.
• 9.5: Sustainable Agriculture
Sustainable agriculture means an integrated system of plant and animal production practices having a site-specific application,
• 9.S: Conventional & Sustainable Agriculture (Summary)
Thumbnail image - Women farmers planting a rice field in West Sumatra.
09: Conventional Sustainable Agriculture
What is Soil?
The word “soil” has been defined differently by different scientific disciplines. In agriculture and horticulture, soil generally refers to the medium for plant growth, typically material within the upper meter or two (Figure \(1\)). We will use this definition in this chapter. Soil consists predominantly of mineral matter, but also contains organic matter (humus) and living organisms. The pore spaces between mineral grains are filled with varying proportions of water and air.
In common usage, the term soil is sometimes restricted to only the dark topsoil in which we plant our seeds or vegetables. In a more broad definition, civil engineers use the term soil for any unconsolidated (soft when wet) material that is not considered bedrock. Under this definition, soil can be as much as several hundred feet thick! Ancient soils, sometimes buried and preserved in the subsurface, are referred to as paleosols (Figure \(2\)) and reflect past climatic and environmental conditions.
Importance of Soil
Soil is important to our society primarily because it provides the foundation of agriculture and forestry. Of course, soil is also a critical component for terrestrial ecosystems, and thus important to animals, plants, fungi, and microorganisms.
Soil plays a role in nearly all biogeochemical cycles on the Earth’s surface. Global cycling of key elements such as carbon (C), nitrogen (N), sulfur (S), and phosphorous (P) all pass through soil. In the hydrologic cycle, soil helps to mediate the flow of precipitation from the surface into the groundwater. Microorganisms living in soil can also be important components of biogeochemical cycles through the action of decomposition and other processes such as nitrogen fixation.
Soil Forming Factors
The fundamental factors that affect soil genesis can be categorized into five elements: climate, organisms, relief, parent material, and time. One could say that the relief, climate, and organisms dictate the local soil environment and act together to cause weathering and mixing of the soil parent material over time. As soil is formed it often has distinct layers, which are formally described as “horizons.” Upper horizons (labeled as the A and O horizons) are richer in organic material and so are important in plant growth, while deeper layers (such as the B and C horizons) retain more of the original features of the bedrock below (Figure \(3\)).
Climate
The role of climate in soil development includes aspects of temperature and precipitation. Soils in very cold areas with permafrost conditions tend to be shallow and weakly developed due to the short growing season. Organic rich surface horizons are common in low-lying areas due to limited decomposition. In warm, tropical soils, soils tend to be thicker, with extensive leaching and mineral alteration. In such climates, organic matter decomposition and chemical weathering occur at an accelerated rate.
Organisms
Animals, plants, and microorganisms all have important roles in soil development processes, in providing a supply of organic matter, and/or in nutrient cycling. Worms, nematodes, termites, ants, gophers, moles, etc. all cause considerable mixing of soil and help to blend soil, aerate and lighten the soil by creating pores (which help store water and air).
Plant life provides organic matter to soil and helps to recycle nutrients with uptake by roots in the subsurface. The type of plant life that occurs in a given area, such as types of trees or grasses, depends on the climate, along with parent material and soil type. With the annual dropping of leaves and needles, trees tend to add organic matter to soil surfaces, helping to create a thin, organic-rich A or O horizon over time. Grasses, on the other hand, have a considerable root and surface masses that add to the soil each fall for annuals and short-lived perennials. For this reason, grassland soils have much thicker A horizons with higher organic matter contents, and are more agriculturally productive than forest soils.
Relief (Topography and Drainage)
The local landscape can have a surprisingly strong effect on the soils that form on site. The local topography (relief) can have important microclimatic effects as well as affecting rates of soil erosion. In comparison to flat regions, areas with steep slopes overall have more soil erosion, more runoff of rainwater, and less water infiltration, all of which lead to more limited soil development in very hilly or mountainous areas. In the northern hemisphere, south-facing slopes are exposed to more direct sunlight angles and are thus warmer and drier than north-facing slopes. The cooler, moister north-facing slopes have a more dynamic plant community due to less evapotranspiration and, consequently, experience less erosion because of plant rooting of soil and have thicker soil development.
Soil drainage affects organic matter accumulation and preservation, and local vegetation types. Well-drained soils, generally on hills or sideslopes, are more brownish or reddish due to conversion of ferrous iron (Fe2+) to minerals with ferric (Fe3+) iron. More poorly drained soils, in lowland, alluvial plains or upland depressions, tend more be more greyish, greenish-grey (gleyed), or dark colored, due to iron reduction (to Fe2+) and accumulation and preservation of organic matter in areas tending towards anoxic. Areas with poor drainage also tend to be lowlands into which soil material may wash and accumulate from surrounding uplands, often resulting in overthickened A or O horizons. In contrast, steeply sloping areas in highlands may experience erosion and have thinner surface horizons.
Parent Material
The parent material of a soil is the material from which the soil has developed, whether it be river sands, shoreline deposits, glacial deposits, or various types of bedrock. In youthful soils, the parent material has a clear connection to the soil type and has significant influence. Over time, as weathering processes deepen, mix, and alter the soil, the parent material becomes less recognizable as chemical, physical, and biological processes take their effect. The type of parent material may also affect the rapidity of soil development. Parent materials that are highly weatherable (such as volcanic ash) will transform more quickly into highly developed soils, whereas parent materials that are quartz-rich, for example, will take longer to develop. Parent materials also provide nutrients to plants and can affect soil internal drainage (e.g. clay is more impermeable than sand and impedes drainage).
Time
In general, soil profiles tend to become thicker (deeper), more developed, and more altered over time. However, the rate of change is greater for soils in youthful stages of development. The degree of soil alteration and deepening slows with time and at some point, after tens or hundreds of thousands of years, may approach an equilibrium condition where erosion and deepening (removals and additions) become balanced. Young soils (< 10,000 years old) are strongly influenced by parent material and typically develop horizons and character rapidly. Moderate age soils (roughly 10,000 to 500,000 years old) are slowing in profile development and deepening, and may begin to approach equilibrium conditions. Old soils (>500,000 years old) have generally reached their limit as far as soil horizonation and physical structure, but may continue to alter chemically or mineralogically.
Soil development is not always continual. Geologic events can rapidly bury soils (landslides, glacier advance, lake transgression), can cause removal or truncation of soils (rivers, shorelines) or can cause soil renewal with additions of slowly deposited sediment that add to the soil (wind or floodplain deposits). Biological mixing can sometimes cause soil regression, a reversal or bump in the road for the normal path of increasing development over time. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/09%3A_Conventional__Sustainable_Agriculture/9.01%3A_Soil_Profiles_and_Processes.txt |
Soil plays a key role in plant growth. Beneficial aspects to plants include providing physical support, water, heat, nutrients, and oxygen (Figure \(1\)). Mineral nutrients from the soil can dissolve in water and then become available to plants. Although many aspects of soil are beneficial to plants, excessively high levels of trace metals (either naturally occurring or anthropogenically added) or applied herbicides can be toxic to some plants.
The ratio of solids/water/air in soil is also critically important to plants for proper oxygenation levels and water availability. Too much porosity with air space, such as in sandy or gravelly soils, can lead to less available water to plants, especially during dry seasons when the water table is low. Too much water, in poorly drained regions, can lead to anoxic conditions in the soil, which may be toxic to some plants.
Nutrient Uptake by Plants
Several elements obtained from soil are considered essential for plant growth. Macronutrients, including C, H, O, N, P, K, Ca, Mg, and S, are needed by plants in significant quantities. C, H, and O are mainly obtained from the atmosphere or from rainwater. These three elements are the main components of most organic compounds, such as proteins, lipids, carbohydrates, and nucleic acids. The other six elements (N, P, K, Ca, Mg, and S) are obtained by plant roots from the soil and are variously used for protein synthesis, chlorophyll synthesis, energy transfer, cell division, enzyme reactions, and homeostasis (the process regulating the conditions within an organism).
Micronutrients are essential elements that are needed only in small quantities, but can still be limiting to plant growth since these nutrients are not so abundant in nature. Micronutrients include iron (Fe), manganese (Mn), boron (B), molybdenum (Mo), chlorine (Cl), zinc (Zn), and copper (Cu). There are some other elements that tend to aid plant growth but are not absolutely essential.
Micronutrients and macronutrients are desirable in particular concentrations and can be detrimental to plant growth when concentrations in soil solution are either too low (limiting) or too high (toxicity). Mineral nutrients are useful to plants only if they are in an extractable form in soil solutions, such as a dissolved ion rather than in solid mineral. Many nutrients move through the soil and into the root system as a result of concentration gradients, moving by diffusion from high to low concentrations. However, some nutrients are selectively absorbed by the root membranes, enabling concentrations to become higher inside the plant than in the soil.
9.03: Conventional Agriculture
The prevailing agricultural system, variously called “conventional farming,” “modern agriculture,” or “industrial farming,” has delivered tremendous gains in productivity and efficiency. Food production worldwide has risen in the past 50 years; the World Bank estimates that between 70 percent and 90 percent of the recent increases in food production are the result of conventional agriculture rather than greater acreage under cultivation. U.S. consumers have come to expect abundant and inexpensive food.
Conventional farming systems vary from farm to farm and from country to country. However, they share many characteristics such as rapid technological innovation, large capital investments in equipment and technology, large-scale farms, single crops (monocultures); uniform high-yield hybrid crops, dependency on agribusiness, mechanization of farm work, and extensive use of pesticides, fertilizers, and herbicides. In the case of livestock, most production comes from systems where animals are highly concentrated and confined.
Both positive and negative consequences have come with the bounty associated with industrial farming. Some concerns about conventional agriculture are presented below.
Ecological Concerns
Agriculture profoundly affects many ecological systems. Negative effects of current practices include the following:
Decline in soil productivity can be due to wind and water erosion of exposed topsoil, soil compaction, loss of soil organic matter, water holding capacity, and biological activity; and salinization (increased salinity) of soils in highly-irrigated farming areas. Converting land to desert (desertification) can be caused by overgrazing of livestock and is a growing problem, especially in parts of Africa.
Agricultural practices have been found to contribute to non-point source water pollutants that include salts, fertilizers (nitrates and phosphorus, especially), pesticides, and herbicides. Pesticides from every chemical class have been detected in groundwater and are commonly found in groundwater beneath agricultural areas. They are also widespread in the nation’s surface waters. Eutrophication and “dead zones” due to nutrient runoff affect many rivers, lakes, and oceans. Reduced water quality impacts agricultural production, drinking water supplies, and fishery production. Water scarcity (discussed in the previous chapter) in many places is due to overuse of surface and ground water for irrigation with little concern for the natural cycle that maintains stable water availability.
Other environmental ills include over 400 insects and mite pests and more than 70 fungal pathogens that have become resistant to one or more pesticides. Pesticides have also placed stresses on pollinators and other beneficial insect species. This, along with habitat loss due to converting wildlands into agricultural fields, has affected entire ecosystems (such as the practice of converting tropical rainforests into grasslands for raising cattle).
Agriculture’s link to global climate change is just beginning to be appreciated. Destruction of tropical forests and other native vegetation for agricultural production has a role in elevated levels of carbon dioxide and other greenhouse gases. Recent studies have found that soils may be large reservoirs of carbon.
Economic and Social Concerns
Economically, the U.S. agricultural sector includes a history of increasingly large federal expenditures. Also observed is a widening disparity among the income of farmers and the escalating concentration of agribusiness—industries involved with manufacture, processing, and distribution of farm products—into fewer and fewer hands. Market competition is limited and farmers have little control over prices of their goods, and they continue to receive a smaller and smaller portion of consumer dollars spent on agricultural products.
Economic pressures have led to a tremendous loss to the number of farms, particularly small farms, and farmers during the past few decades. More than 155,000 farms were lost from 1987 to 1997. Economically, it is very difficult for potential farmers to enter the business today because of the high cost of doing business. Productive farmland also has been swallowed up by urban and suburban sprawl—since 1970, over 30 million acres have been lost to development.
Impacts on Human Health
Many potential health hazards are tied to farming practices. The general public may be affected by the sub-therapeutic use of antibiotics in animal production and the contamination of food and water by pesticides and nitrates. These are areas of active research to determine the levels of risk. The health of farm workers is also of concern, as their risk of exposure is much higher.
Philosophical Considerations
Historically, farming played an important role in our development and identity as a nation. From strongly agrarian roots, we have evolved into a culture with few farmers. Less than two percent of Americans now produce food for all U.S. citizens. Can sustainable and equitable food production be established when most consumers have so little connection to the natural processes that produce their food? What intrinsically American values have changed and will change with the decline of rural life and farmland ownership?
World population continues to grow. According to recent United Nations population projections, the world population will grow to 9.7 billion in 2050 and 11.2 billion in 2100. The rate of population increase is especially high in many developing countries. In these countries, the population factor, combined with rapid industrialization, poverty, political instability, and large food imports and debt burden, make long-term food security especially urgent. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/09%3A_Conventional__Sustainable_Agriculture/9.02%3A_Soil-Plant_Interactions.txt |
Pests are organisms that occur where they are not wanted or that cause damage to crops or humans or other animals. Thus, the term “pest” is a highly subjective term. A pesticide is a term for any substance intended for preventing, destroying, repelling, or mitigating any pest. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, and various other substances used to control pests. By their very nature, most pesticides create some risk of harm—pesticides can cause harm to humans, animals, and/or the environment because they are designed to kill or otherwise adversely affect living things. At the same time, pesticides are useful to society because they can kill potential disease-causing organisms and control insects, weeds, worms, and fungi.
Pest Control is a Common Tool
The management of pests is an essential part of agriculture, public health, and maintenance of power lines and roads. Chemical pest management has helped to reduce losses in agriculture and to limit human exposure to disease vectors, such as mosquitoes, saving many lives. Chemical pesticides can be effective, fast acting, adaptable to all crops and situations. When first applied, pesticides can result in impressive production gains of crops. However, despite these initial gains, excessive use of pesticides can be ecologically unsound, leading to the destruction of natural enemies, the increase of pesticide resistance, and outbreaks of secondary pests.
These consequences have often resulted in higher production costs as well as environmental and human health costs– side-effects which have been unevenly distributed. Despite the fact that the lion’s share of chemical pesticides are applied in developed countries, 99 percent of all pesticide poisoning cases occur in developing countries where regulatory, health and education systems are weakest. Many farmers in developing countries overuse pesticides and do not take proper safety precautions because they do not understand the risks and fear smaller harvests. Making matters worse, developing countries seldom have strong regulatory systems for dangerous chemicals; pesticides banned or restricted in industrialized countries are used widely in developing countries. Farmers’ perceptions of appropriate pesticide use vary by setting and culture. Prolonged exposure to pesticides has been associated with several chronic and acute health effects like non-Hodgkin’s lymphoma, leukemia, as well as cardiopulmonary disorders, neurological and hematological symptoms, and skin diseases.
HUMAN HEALTH, ENVIRONMENTAL, AND ECONOMIC EFFECTS OF PESTICIDE USE IN POTATO PRODUCTION IN ECUADOR
The International Potato Center (CIP) conducted an interdisciplinary and inter-institutional research intervention project dealing with pesticide impacts on agricultural production, human health, and the environment in Carchi, Ecuador. Carchi is the most important potato-growing area in Ecuador, where smallholder farmers dominate production. They use tremendous amounts of pesticides for the control of the Andean potato weevil and the late blight fungus. Virtually all farmers apply class 1b highly toxic pesticides using hand pump backpack sprayers.
The study found that the health problems caused by pesticides are severe and are affecting a high percentage of the rural population. Despite the existence of technology and policy solutions, government policies continue to promote the use of pesticides. The study conclusions concurred with those by the pesticide industry, “that any company that could not ensure the safe use of highly toxic pesticides should remove them from the market and that it is almost impossible to achieve safe use of highly toxic pesticides among small farmers in developing countries.”
Source: Yanggen et al. 2003.
Persistent Organic Pollutants
Persistent organic pollutants (POPs) are a group of organic chemicals, such as DDT, that have been widely used as pesticides or industrial chemicals and pose risks to human health and ecosystems. POPs have been produced and released into the environment by human activity. They have the following three characteristics:
• Persistent: POPs are chemicals that last a long time in the environment. Some may resist breakdown for years and even decades while others could potentially break down into other toxic substances.
• Bioaccumulative: POPs can accumulate in animals and humans, usually in fatty tissues and largely from the food they consume. As these compounds move up the food chain, they concentrate to levels that could be thousands of times higher than acceptable limits.
• Toxic: POPs can cause a wide range of health effects in humans, wildlife and fish. They have been linked to effects on the nervous system, reproductive and developmental problems, suppression of the immune system, cancer, and endocrine disruption. The deliberate production and use of most POPs has been banned around the world, with some exemptions made for human health considerations (e.g., DDT for malaria control) and/or in very specific cases where alternative chemicals have not been identified. However, the unintended production and/or the current use of some POPs continue to be an issue of global concern. Even though most POPs have not been manufactured or used for decades, they continue to be present in the environment and thus potentially harmful. The same properties that originally made them so effective, particularly their stability, make them difficult to eradicate from the environment.
POPs and Health
The relationship between exposure to environmental contaminants such as POPs and human health is complex. There is mounting evidence that these persistent, bioaccumulative and toxic chemicals (PBTs) cause long-term harm to human health and the environment. Drawing a direct link, however, between exposure to these chemicals and health effects is complicated, particularly since humans are exposed on a daily basis to many different environmental contaminants through the air they breathe, the water they drink, and the food they eat. Numerous studies link POPs with a number of adverse effects in humans. These include effects on the nervous system, problems related to reproduction and development, cancer, and genetic impacts. Moreover, there is mounting public concern over the environmental contaminants that mimic hormones in the human body (endocrine disruptors).
As with humans, animals are exposed to POPs in the environment through air, water and food. POPs can remain in sediments for years, where bottom-dwelling creatures consume them and who are then eaten by larger fish. Because tissue concentrations can increase or biomagnify at each level of the food chain, top predators (like largemouth bass or walleye) may have a million times greater concentrations of POPs than the water itself. The animals most exposed to PBT contaminants are those higher up the food web such as marine mammals including whales, seals, polar bears, and birds of prey in addition to fish species such as tuna, swordfish and bass (Figure \(2\)). Once POPs are released into the environment, they may be transported within a specific region and across international boundaries transferring among air, water, and land.
“Grasshopper Effect”
While generally banned or restricted, POPs make their way into and throughout the environment on a daily basis through a cycle of long-range air transport and deposition called the “grasshopper effect.”The “grasshopper” processes, illustrated in Figure \(3\), begin with the release of POPs into the environment. When POPs enter the atmosphere, they can be carried with wind currents, sometimes for long distances.
Through atmospheric processes, they are deposited onto land or into water ecosystems where they accumulate and potentially cause damage. From these ecosystems, they evaporate, again entering the atmosphere, typically traveling from warmer temperatures toward cooler regions. They condense out of the atmosphere whenever the temperature drops, eventually reaching highest concentrations in circumpolar countries. Through these processes, POPs can move thousands of kilometers from their original source of release in a cycle that may last decades. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/09%3A_Conventional__Sustainable_Agriculture/9.04%3A_Pests_and_Pesticides.txt |
Sustainable agriculture” was addressed by Congress in the 1990 “Farm Bill”. Under that law, “the term sustainable agriculture means an integrated system of plant and animal production practices having a site-specific application that will, over the long term:
• satisfy human food and fiber needs;
• enhance environmental quality and the natural resource base upon which the agricultural economy depends;
• make the most efficient use of nonrenewable resources and on-farm resources and integrate, where appropriate, natural biological cycles and controls;
• sustain the economic viability of farm operations; and
• enhance the quality of life for farmers and society as a whole.”
Organic Farming is Good for Farmers, Consumers and the Environment
Organic agriculture is an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. Organic food is produced by farmers who emphasize the use of renewable resources and the conservation of soil and water to enhance environmental quality for future generations. Organic meat, poultry, eggs, and dairy products come from animals that are given no antibiotics or growth hormones. Organic food is produced without using most conventional pesticides, fertilizers made with synthetic ingredients or sewage sludge, or GMOs.
Organic production, with the corresponding practices to maintain soil fertility and soil health is therefore a more benign alternative to conventional, high-value horticulture. The organic food movement has been endorsed by the UN’s Food and Agricultural Organization, which maintains in a 2007 report that organic farming fights hunger, tackles climate change, and is good for farmers, consumers, and the environment. The strongest benefits of organic agriculture are its use of resources that are independent of fossil fuels, are locally available, incur minimal environmental stresses, and are cost effective.
IPM is a Combination of Common-Sense Practices
Integrated Pest Management (IPM) refers to a mix of farmer-driven, ecologically-based pest control practices that seeks to reduce reliance on synthetic chemical pesticides. It involves (a) managing pests (keeping them below economically damaging levels) rather than seeking to eradicate them; (b) relying, to the extent possible, on non-chemical measures to keep pest populations low; and (c) selecting and applying pesticides, when they have to be used, in a way that minimizes adverse effects on beneficial organisms, humans, and the environment. It is commonly understood that applying an IPM approach does not necessarily mean eliminating pesticide use, although this is often the case because pesticides are often over-used for a variety of reasons.
The IPM approach regards pesticides as mainly short-term corrective measures when more ecologically based control measures are not working adequately (sometimes referred to as using pesticides as the “last resort”). In those cases when pesticides are used, they should be selected and applied in such a manner as to minimize the amount of disruption that they cause to the environment, such as using products that are non-persistent and applying them in the most targeted way possible).
Biological Control
Biological control (biocontrol) is the use of one biological species to reduce populations of a different species. There has been a substantial increase in commercialization of biocontrol products, such as beneficial insects, cultivated predators and natural or non-toxic pest control products. Biocontrol is being mainstreamed to major agricultural commodities, such as cotton, corn and most commonly vegetable crops. Biocontrol is also slowly emerging in vector control in public health and in areas that for a long time mainly focused on chemical vector control in mosquito/malaria—and black fly/onchocerciasis—control programs. Successful and commercialized examples of biocontrol include ladybugs to depress aphid populations, parasitic wasps to reduce moth populations, use of the bacterium Bacillus thuringenensis to kill mosquito and moth larvae, and introduction of fungi, such as Trichoderma, to suppress fungal-caused plant diseases, leaf beetle (Galerucella calmariensis) to suppress purple loosestrife, a noxious weed (Figure \(1\)). In all of these cases, the idea is not to completely destroy the pathogen or pest, but rather to reduce the damage below economically significant values.
Intercropping Promotes Plant Interactions
Intercropping means growing two or more crops in close proximity to each other during part or all of their life cycles to promote soil improvement, biodiversity, and pest management. Incorporating intercropping principles into an agricultural operation increases diversity and interaction between plants, arthropods, mammals, birds and microorganisms resulting in a more stable crop-ecosystem and a more efficient use of space, water, sunlight, and nutrients (Figure \(2\)). This collaborative type of crop management mimics nature and is subject to fewer pest outbreaks, improved nutrient cycling and crop nutrient uptake, and increased water infiltration and moisture retention. Soil quality, water quality and wildlife habitat all benefit.
Organic Farming Practices Reduce Unnecessary Input Use
In modern agricultural practices, heavy machinery is used to prepare the seedbed for planting, to control weeds, and to harvest the crop. The use of heavy equipment has many advantages in saving time and labor, but can cause compaction of soil and disruption of the natural soil organisms. The problem with soil compaction is that increased soil density limits root penetration depth and may inhibit proper plant growth.
Alternative practices generally encourage minimal tillage or no tillage methods. With proper planning, this can simultaneously limit compaction, protect soil organisms, reduce costs (if performed correctly), promote water infiltration, and help to prevent topsoil erosion (Figure \(3\)).
Tillage of fields does help to break up clods that were previously compacted, so best practices may vary at sites with different soil textures and composition. Another aspect of soil tillage is that it may lead to more rapid decomposition of organic matter due to greater soil aeration. Over large areas of farmland, this has the unintended consequence of releasing more carbon and nitrous oxides (greenhouse gases) into the atmosphere, thereby contributing to global warming effects. In no-till farming, carbon can actually become sequestered into the soil. Thus, no-till farming may be advantageous to sustainability issues on the local scale and the global scale. No-till systems of conservation farming have proved a major success in Latin America and are being used in South Asia and Africa.
Crop Rotation
Crop rotations are planned sequences of crops over time on the same field. Rotating crops provides productivity benefits by improving soil nutrient levels and breaking crop pest cycles. Farmers may also choose to rotate crops in order to reduce their production risk through diversification or to manage scarce resources, such as labor, during planting and harvesting timing. This strategy reduces the pesticide costs by naturally breaking the cycle of weeds, insects and diseases. Also, grass and legumes in a rotation protect water quality by preventing excess nutrients or chemicals from entering water supplies.
AN ALTERNATIVE TO SPRAYING: BOLLWORM CONTROL IN SHANDONG
Farmers in Shandong (China) have been using innovative methods to control bollworm infestation in cotton when this insect became resistant to most pesticides. Among the control measures implemented were:
1. The use of pest resistant cultivars and interplanting of cotton with wheat or maize.
2. Use of lamps and poplar twigs to trap and kill adults to lessen the number of adults.
3. If pesticides were used, they were applied on parts of cotton plant’s stem rather than by spraying the whole field (to protect natural enemies of the bollworm).
These and some additional biological control tools have proved to be effective in controlling insect populations and insect resistance, protecting surroundings and lowering costs.
The Future of the Sustainable Agriculture Concept
Many in the agricultural community have adopted the sense of urgency and direction pointed to by the sustainable agriculture concept. Sustainability has become an integral component of many government, commercial, and non-profit agriculture research efforts, and it is beginning to be woven into agricultural policy. Increasing numbers of farmers and ranchers have embarked on their own paths to sustainability, incorporating integrated and innovative approaches into their own enterprises. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/09%3A_Conventional__Sustainable_Agriculture/9.05%3A_Sustainable_Agriculture.txt |
Summary
In agriculture and horticulture, soil generally refers to the medium for plant growth, typically material within the upper meter or two. Soil plays a key role in plant growth. Beneficial aspects to plants include providing physical support, heat, water, nutrients, and oxygen. Heat, light, and oxygen are also obtained by the atmosphere, but the roots of many plants also require oxygen. The prevailing agricultural system has delivered tremendous gains in productivity and efficiency. Food production worldwide has risen in the past 50 years. On the other hand, agriculture profoundly affects many ecological systems. Negative effects of current practices include ecological concerns, economic and social concerns and human health concerns. Pesticides from every chemical class have been detected in groundwater and are commonly found in groundwater beneath agricultural areas. Despite impressive production gains, excessive use of pesticides has proven to be ecologically unsound, leading to the destruction of natural enemies, the increase of pest resistance pest resurgence and outbreaks of secondary pests. These consequences have often resulted in higher production costs and lost markets due to undesirable pesticide residue levels, as well as environmental and human health costs. Alternative and sustainable practices in farming and land use include organic agriculture, integrated pest management and biological control.
Review Questions
1. Which of the following is not one of the five soil-forming factors?
1. Climate
2. Organisms
3. Relief
4. Transpiration rate
5. Time
2. You analyze a soil sample for a farmer that has been dealing with fertility issues on her land. You find that it is deficient in all of the soil-derived macronutrients. Which one of the following is macronutrient derived from the soil?
1. carbon
2. nitrogen
3. hydrogen
4. iron
5. oxygen
3. The farmer adjacent to your land plants a single crop (soybean) over their entire 100 hectare field. This practice is known as a…
1. Monoculture
2. Crop plot
3. Agriplot
4. Rotational farming
5. Millibar
4. Salinization is bad for farmers because it results in…
1. Pesticide resistance
2. Increased salts in the soil
3. Nutrient-poor soils
4. Blight
5. Desertification
5. Besides being long-lasting, persistent organic pollutants share which of the following characteristics:
1. accumulate in higher trophic levels and are toxic
2. accumulate in lower trophic levels and are toxic
3. accumulate in higher trophic levels and are infectious biological agents
4. accumulate in lower trophic levels and are infectious biological agents
5. Are toxic and infectious
6. The grasshopper effect explains which one of the following phenomena?
1. The mass migration patterns of insects that are similar to, and include, grasshoppers
2. The lowering of nutrient capacity in soils due to the action of certain types of organisms
3. The long-range movement of certain types of pollutants across different regions of the Earth
4. The long-range atmospheric distribution of soil following tilling by farm equipment
5. The spread of invasive species through international trade in potted plants
7. An important goal of integrated pest management is to reduce the amount of pests while also…
1. Reducing the amount of genetically modified crops grown
2. Reducing the amount of fertilizer used
3. Introducing species that prey upon and destroy pest species
4. Integrating market-based strategies for maximization of profits
5. Reducing the amount of synthetic chemical pesticides used
8. Which one of the following describes the use of organisms to control pests?
1. Bioremediation
2. Intercropping
3. Species niche partitioning
4. Vector control
5. Biological control
9. What practice allows farmers to improve soil fertility, diversify their crops, and reduce pesticide costs by naturally breaking the cycle of weeds, insects, and diseases?
1. Monoculture
2. Biological control
3. Crop sharing
4. Crop rotation
5. Soil tilling
10. Which one of the following is more indicative of conventional agriculture, and not sustainable agriculture?
1. Biological control
2. Intercropping
3. Monocultures
4. Integrated pest management
5. Minimal tillage
See Appendix for answers | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/09%3A_Conventional__Sustainable_Agriculture/9.0S%3A_9.S%3A_Conventional__Sustainable_Agriculture_%28Summary%29.txt |
Learning Outcomes
• Identify sources of air pollution
• List common air pollutants
• Explain how the greenhouse effect causes the atmosphere to retain heat
• Explain how we know that humans are responsible for recent climate change
• List some effects of climate change
• Identify some climate change policies and adaptation measures
• 10.1: Atmospheric Pollution
Air pollution occurs in many forms but can generally be thought of as gaseous and particulate contaminants that are present in the earth’s atmosphere. Chemicals discharged into the air that have a direct impact on the environment are called primary pollutants. These primary pollutants sometimes react with other chemicals in the air to produce secondary pollutants.
• 10.2: Ozone Depletion
The ozone depletion process begins when CFCs (chlorofluorocarbons) and other ozone-depleting substances (ODS) are emitted into the atmosphere. CFC molecules are extremely stable, and they do not dissolve in rain. After a period of several years, ODS molecules reach the stratosphere, about 10 kilometers above the Earth’s surface. CFCs were used by industry as refrigerants, degreasing solvents, and propellants.
• 10.3: Acid Rain
Acid rain is a term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amounts of nitric and sulfuric acids. The precursors, or chemical forerunners, of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) resulting from fossil fuel combustion.
• 10.4: Climate Change
Earth’s temperature depends on the balance between energy entering and leaving the planet. When incoming energy from the sun is absorbed, Earth warms. When the sun’s energy is reflected back into space, Earth avoids warming. When energy is released from Earth into space, the planet cools. Many factors, both natural and human, can cause changes in Earth’s energy balance.
• 10.5: Chapter Resources
Thumbnail image - Traffic congestion is a daily reality of India’s urban centers. Slow speeds and idling vehicles produce, per trip, 4 to 8 times more pollutants and consume more carbon footprint fuels, than free flowing traffic. This 2008 image shows traffic congestion in Delhi.
10: Air Pollution Climate Change Ozone Depletion
Air pollution occurs in many forms but can generally be thought of as gaseous and particulate contaminants that are present in the earth’s atmosphere. Chemicals discharged into the air that have a direct impact on the environment are called primary pollutants. These primary pollutants sometimes react with other chemicals in the air to produce secondary pollutants.
Air pollution is typically separated into two categories: outdoor air pollution and indoor air pollution. Outdoor air pollution involves exposures that take place outside of the built environment. Examples include fine particles produced by the burning of coal, noxious gases such as sulfur dioxide, nitrogen oxides and carbon monoxide; ground-level ozone and tobacco smoke. Indoor air pollution involves exposures to particulates, carbon oxides, and other pollutants carried by indoor air or dust. Examples include household products and chemicals, out-gassing of building materials, allergens (cockroach and mouse dropping, mold, pollen), and tobacco smoke.
Sources of Air Pollution
A stationary source of air pollution refers to an emission source that does not move, also known as a point source. Stationary sources include factories, power plants, and dry cleaners. The term area source is used to describe many small sources of air pollution located together whose individual emissions may be below thresholds of concern, but whose collective emissions can be significant. Residential wood burners are a good example of a small source, but when combined with many other small sources, they can contribute to local and regional air pollution levels. Area sources can also be thought of as non-point sources, such as construction of housing developments, dry lake beds, and landfills.
A mobile source of air pollution refers to a source that is capable of moving under its own power. In general, mobile sources imply “on-road” transportation, which includes vehicles such as cars, sport utility vehicles, and buses. In addition, there is also a “non-road” or “off-road” category that includes gas-powered lawn tools and mowers, farm and construction equipment, recreational vehicles, boats, planes, and trains.
Agricultural sources arise from operations that raise animals and grow crops, which can generate emissions of gases and particulate matter. For example, animals confined to a barn or restricted area produce large amounts of manure. Manure emits various gases, particularly ammonia into the air. This ammonia can be emitted from the animal houses, manure storage areas, or from the land after the manure is applied. In crop production, the misapplication of fertilizers, herbicides, and pesticides can potentially result in aerial drift of these materials and harm may be caused.
Unlike the above mentioned sources of air pollution, air pollution caused by natural sourcesis not caused by people or their activities. An erupting volcano emits particulate matter and gases, forest and prairie fires can emit large quantities of “pollutants”, dust storms can create large amounts of particulate matter, and plants and trees naturally emit volatile organic compounds which can form aerosols that can cause a natural blue haze. Wild animals in their natural habitat are also considered natural sources of “pollution”.
Six Common Air Pollutants
The most commonly found air pollutants are particulate matter, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm health and the environment, and cause property damage. Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats. The U.S. Environmental Protection Agency (EPA) regulates them by developing criteria based on considerations of human and environmental health.
1. Ground-level ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC. Breathing ozone can trigger a variety of health problems, particularly for children, the elderly, and people of all ages who have lung diseases such as asthma. Ground level ozone can also have harmful effects on sensitive vegetation and ecosystems. (Ground-level ozone should not be confused with the ozone layer, which is high in the atmosphere and protects Earth from ultraviolet light; ground-level ozone provides no such protection).
2. Particulate matter, also known as particle pollution, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects.
3. Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes. Nationally and, particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources. CO can cause harmful health effects by reducing oxygen delivery to the body’s organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death.
4. Nitrogen dioxide (NO2) is one of a group of highly reactive gasses known as “oxides of nitrogen,” or nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. EPA’s National Ambient Air Quality Standard uses NO2 as the indicator for the larger group of nitrogen oxides. NO2 forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment. In addition to contributing to the formation of ground-level ozone, and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.
5. Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as “oxides of sulfur.” The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment. SO2 is linked with a number of adverse effects on the respiratory system.
6. Lead is a metal found naturally in the environment as well as in manufactured products. The major sources of lead emissions have historically been from fuels in on-road motor vehicles (such as cars and trucks) and industrial sources. As a result of regulatory efforts in the U.S. to remove lead from on-road motor vehicle gasoline, emissions of lead from the transportation sector dramatically declined by 95 percent between 1980 and 1999, and levels of lead in the air decreased by 94 percent between 1980 and 1999. Today, the highest levels of lead in air are usually found near lead smelters. The major sources of lead emissions to the air today are ore and metals processing and piston-engine aircraft operating on leaded aviation gasoline.
Indoor Air Pollution (Major concerns in developed countries)
Most people spend approximately 90 percent of their time indoors. However, the indoor air we breathe in homes and other buildings can be more polluted than outdoor air and can increase the risk of illness. There are many sources of indoor air pollution in homes. They include biological contaminants such as bacteria, molds and pollen, burning of fuels and environmental tobacco smoke, building materials and furnishings, household products, central heating and cooling systems, and outdoor sources. Outdoor air pollution can enter buildings and become a source of indoor air pollution.
Sick building syndrome is a term used to describe situations in which building occupants have health symptoms that are associated only with spending time in that building. Causes of sick building syndrome are believed to include inadequate ventilation, indoor air pollution, and biological contaminants. Usually indoor air quality problems only cause discomfort. Most people feel better as soon as they remove the source of the pollution. Making sure that your building is well-ventilated and getting rid of pollutants can improve the quality of your indoor air.
Secondhand Smoke (Environmental Tobacco Smoke)
Secondhand smoke is the combination of smoke that comes from a cigarette and smoke breathed out by a smoker. When a non-smoker is around someone smoking, they breathe in secondhand smoke.
Secondhand smoke is dangerous to anyone who breathes it in. There is no safe amount of secondhand smoke. It contains over 7,000 harmful chemicals, at least 250 of which are known to damage human health. It can also stay in the air for several hours after somebody smokes. Even breathing secondhand smoke for a short amount of time can hurt your body.
Over time, secondhand smoke can cause serious health issues in non-smokers. The only way to fully protect non-smokers from the dangers of secondhand smoke is to not allow smoking indoors. Separating smokers from nonsmokers (like “no smoking” sections in restaurants)‚ cleaning the air‚ and airing out buildings does not completely get rid of secondhand smoke.
Source: Smokefree.gov | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/10%3A_Air_Pollution_Climate_Change__Ozone_Depletion/10.01%3A_Atmospheric_Pollution.txt |
The ozone depletion process begins when CFCs (chlorofluorocarbons) and other ozone-depleting substances (ODS) are emitted into the atmosphere. CFC molecules are extremely stable, and they do not dissolve in rain. After a period of several years, ODS molecules reach the stratosphere, about 10 kilometers above the Earth’s surface. CFCs were used by industry as refrigerants, degreasing solvents, and propellants.
Ozone (O3) is constantly produced and destroyed in a natural cycle, as shown in Figure \(1\). However, the overall amount of ozone is essentially stable. This balance can be thought of as a stream’s depth at a particular location. Although individual water molecules are moving past the observer, the total depth remains constant. Similarly, while ozone production and destruction are balanced, ozone levels remain stable. This was the situation until the past several decades. Large increases in stratospheric ODS, however, have upset that balance. In effect, they are removing ozone faster than natural ozone creation reactions can keep up. Therefore, ozone levels fall.
Policies to Reduce Ozone Destruction
One success story in reducing pollutants that harm the atmosphere concerns ozone-destroying chemicals. In 1973, scientists calculated that CFCs could reach the stratosphere and break apart. This would release chlorine atoms, which would then destroy ozone. Based only on their calculations, the United States and most Scandinavian countries banned CFCs in spray cans in 1978. More confirmation that CFCs break down ozone was needed before more was done to reduce production of ozone-destroying chemicals. In 1985, members of the British Antarctic Survey reported that a 50% reduction in the ozone layer had been found over Antarctica in the previous three springs.
Two years after the British Antarctic Survey report, the “Montreal Protocol on Substances that Deplete the Ozone Layer” was ratified by nations all over the world. The Montreal Protocolcontrols the production and consumption of 96 chemicals that damage the ozone layer (Figure \(3\)). CFCs have been mostly phased out since 1995, although they were used in developing nations until 2010. Some of the less hazardous substances will not be phased out until 2030. The Protocol also requires that wealthier nations donate money to develop technologies that will replace these chemicals.
Because CFCs take many years to reach the stratosphere and can survive there a long time before they break down, the ozone hole will probably continue to grow for some time before it begins to shrink. The ozone layer will reach the same levels it had before 1980 around 2068 and 1950 levels in one or two centuries.
Health and Environmental Effects of Ozone Layer Depletion
There are three types of UV light: UVA, UVB, and UVC. Reductions in stratospheric ozone levels will lead to higher levels of UVB reaching the Earth’s surface. The sun’s output of UVB does not change; rather, less ozone means less protection, and hence more UVB reaches the Earth. Studies have shown that in the Antarctic, the amount of UVB measured at the surface can double during the annual ozone hole.
Laboratory and epidemiological studies demonstrate that UVB causes non-melanoma skin cancers and plays a major role in malignant melanoma development. In addition, UVB has been linked to cataracts, a clouding of the eye’s lens. All sunlight contains some UVB, even with normal stratospheric ozone levels. Therefore, it is always important to protect your skin and eyes from the sun. Ozone layer depletion increases the amount of UVB and the risk of health effects.
UVB is generally harmful to cells, and therefore all organisms. UVB cannot penetrate into an organism very far and thus tends to only impact skin cells. Microbes like bacteria, however, are composed of only one cell and can therefore be harmed by UVB, | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/10%3A_Air_Pollution_Climate_Change__Ozone_Depletion/10.02%3A_Ozone_Depletion.txt |
Acid rain is a term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amounts of nitric and sulfuric acids. The precursors, or chemical forerunners, of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion. Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. The result is a mild solution of sulfuric acid and nitric acid. When sulfur dioxide and nitrogen oxides are released from power plants and other sources, prevailing winds blow these compounds across state and national borders, sometimes over hundreds of miles.
Acid rain is measured using a scale called “pH.” The lower a substance’s pH, the more acidic it is. Pure water has a pH of 7.0. However, normal rain is slightly acidic because carbon dioxide (CO2) dissolves into it forming weak carbonic acid, giving the resulting mixture a pH of approximately 5.6 at typical atmospheric concentrations of CO2. As of 2000, the most acidic rain falling in the U.S. has a pH of about 4.3.
Effects of Acid Rain
Acid rain causes acidification of lakes and streams and contributes to the damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation’s cultural heritage. Prior to falling to the earth, sulfur dioxide (SO2) and nitrogen oxide (NOx) gases and their particulate matter derivatives—sulfates and nitrates—contribute to visibility degradation and harm public health.
The ecological effects of acid rain are most clearly seen in the aquatic, or water, environments, such as streams, lakes, and marshes. Most lakes and streams have a pH between 6 and 8, although some lakes are naturally acidic even without the effects of acid rain. Acid rain primarily affects sensitive bodies of water, which are located in watersheds whose soils have a limited ability to neutralize acidic compounds (called “buffering capacity”). Lakes and streams become acidic (i.e., the pH value goes down) when the water itself and its surrounding soil cannot buffer the acid rain enough to neutralize it. In areas where buffering capacity is low, acid rain releases aluminum from soils into lakes and streams; aluminum is highly toxic to many species of aquatic organisms. Acid rain causes slower growth, injury, or death of forests. Of course, acid rain is not the only cause of such conditions. Other factors contribute to the overall stress of these areas, including air pollutants, insects, disease, drought, or very cold weather. In most cases, in fact, the impacts of acid rain on trees are due to the combined effects of acid rain and these other environmental stressors.
Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals(such as bronze) and the deterioration of paint and stone (such as marble and limestone). These effects significantly reduce the societal value of buildings, bridges, cultural objects (such as statues, monuments, and tombstones), and cars (Figure \(2\)).
Sulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions contribute to visibility impairment, meaning we cannot see as far or as clearly through the air. The pollutants that cause acid rain—sulfur dioxide (SO2) and nitrogen oxides (NOx)—damage human health. These gases interact in the atmosphere to form fine sulfate and nitrate particles that can be transported long distances by winds and inhaled deep into people’s lungs. Fine particles can also penetrate indoors. Many scientific studies have identified a relationship between elevated levels of fine particles and increased illness and premature death from heart and lung disorders, such as asthma and bronchitis. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/10%3A_Air_Pollution_Climate_Change__Ozone_Depletion/10.03%3A_Acid_Rain.txt |
Earth’s Temperature is a Balancing Act
Earth’s temperature depends on the balance between energy entering and leaving the planet. When incoming energy from the sun is absorbed, Earth warms. When the sun’s energy is reflected back into space, Earth avoids warming. When energy is released from Earth into space, the planet cools. Many factors, both natural and human, can cause changes in Earth’s energy balance, including:
• Changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphere;
• Variations in the sun’s energy reaching Earth;
• Changes in the reflectivity of Earth’s atmosphere and surface.
Scientists have pieced together a picture of Earth’s climate, dating back hundreds of thousands of years, by analyzing a number of indirect measures of climate such as ice cores, tree rings, glacier size, pollen counts, and ocean sediments. Scientists have also studied changes in Earth’s orbit around the sun and the activity of the sun itself.
The historical record shows that the climate varies naturally over a wide range of time scales. In general, climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas (GHG) concentrations. Recent changes in climate, however, cannot be explained by natural causes alone. Research indicates that natural causes are very unlikely to explain most observed warming, especially warming since the mid-20th century. Rather, it is extremely likely that human activities, especially our combustion of fossil fuels, explains most of that warming. The scientific consensus is clear: through alterations of the carbon cycle, humans are changing the global climate by increasing the effects of something known as the greenhouse effect.
The Greenhouse Effect Causes the Atmosphere to Retain Heat
Gardeners that live in moderate or cool environments use greenhouses because they trap heat and create an environment that is warmer than outside temperatures. This is great for plants that like heat, or are sensitive to cold temperatures, such as tomato and pepper plants. Greenhouses contain glass or plastic that allow visible light from the sun to pass. This light, which is a form of energy, is absorbed by plants, soil, and surfaces and heats them. Some of that heat energy is then radiated outwards in the form of infrared radiation, a different form of energy. Unlike with visible light, the glass of the greenhouse blocks the infrared radiation, thereby trapping the heat energy, causing the temperature within the greenhouse to increase.
The same phenomenon happens inside a car on a sunny day. Have you ever noticed how much hotter a car can get compared to the outside temperature? Light energy from the sun passes through the windows and is absorbed by the surfaces in the car such as seats and the dashboard. Those warm surfaces then radiate infrared radiation, which cannot pass through the glass. This trapped infrared energy causes the air temperatures in the car to increase. This process is commonly known as the greenhouse effect.
The greenhouse effect also happens with the entire Earth. Of course, our planet is not surrounded by glass windows. Instead, the Earth is wrapped with an atmosphere that contains greenhouse gases (GHGs). Much like the glass in a greenhouse, GHGs allow incoming visible light energy from the sun to pass, but they block infrared radiation that is radiated from the Earth towards space (Figure \(1\)). In this way, they help trap heat energy that subsequently raises air temperature. Being a greenhouse gas is a physical property of certain types of gases; because of their molecular structure they absorb wavelengths of infrared radiation, but are transparent to visible light. Some notable greenhouse gases are water vapor (H2O), carbon dioxide (CO2), and methane (CH4). GHGs act like a blanket, making Earth significantly warmer than it would otherwise be. Scientists estimate that average temperature on Earth would be -18º C without naturally-occurring GHGs.
What is Global Warming?
Global warming refers to the recent and ongoing rise in global average temperature near Earth’s surface. It is caused mostly by increasing concentrations of greenhouse gases in the atmosphere. Global warming is causing climate patterns to change. However, global warming itself represents only one aspect of climate change.
What is Climate Change?
Climate change refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer.
The Main Greenhouse Gasses
The most important GHGs directly emitted by humans include CO2 and methane. Carbon dioxide (CO2) is the primary greenhouse gas that is contributing to recent global climate change. CO2 is a natural component of the carbon cycle, involved in such activities as photosynthesis, respiration, volcanic eruptions, and ocean-atmosphere exchange. Human activities, primarily the burning of fossil fuels and changes in land use, release very large amounts of CO2 to the atmosphere, causing its concentration in the atmosphere to rise.
Atmospheric CO2 concentrations have increased by 45% since pre-industrial times, from approximately 280 parts per million (ppm) in the 18th century to 408 ppm in 2018. The current CO2 level is higher than it has been in at least 800,000 years, based on evidence from ice cores that preserve ancient atmospheric gases. Human activities currently release over 30 billion tons of CO2 into the atmosphere every year. While some some volcanic eruptions released large quantities of CO2 in the distant past, the U.S. Geological Survey (USGS) reports that human activities now emit more than 135 times as much CO2 as volcanoes each year. This human-caused build-up of CO2 in the atmosphere is like a tub filling with water, where more water flows from the faucet than the drain can take away.
Methane (CH4) is produced through both natural and human activities. For example, wetlands, agricultural activities, and fossil fuel extraction and transport all emit CH4. Methane is more abundant in Earth’s atmosphere now than at any time in at least the past 650,000 years. Due to human activities, CH4 concentrations increased sharply during most of the 20th century and are now more than two and-a-half times pre-industrial levels. In recent decades, the rate of increase has slowed considerably.
Other Greenhouse Gasses
Water vapor is the most abundant greenhouse gas and also the most important in terms of its contribution to the natural greenhouse effect, despite having a short atmospheric lifetime. Some human activities can influence local water vapor levels. However, on a global scale, the concentration of water vapor is controlled by temperature, which influences overall rates of evaporation and precipitation. Therefore, the global concentration of water vapor is not substantially affected by direct human emissions.
Ground-level ozone (O3), which also has a short atmospheric lifetime, is a potent greenhouse gas. Chemical reactions create ozone from emissions of nitrogen oxides and volatile organic compounds from automobiles, power plants, and other industrial and commercial sources in the presence of sunlight (as discussed in section 10.1). In addition to trapping heat, ozone is a pollutant that can cause respiratory health problems and damage crops and ecosystems.
Changes in the Sun’s Energy Affect how Much Energy Reaches Earth
Climate can be influenced by natural changes that affect how much solar energy reaches Earth. These changes include changes within the sun and changes in Earth’s orbit. Changes occurring in the sun itself can affect the intensity of the sunlight that reaches Earth’s surface. The intensity of the sunlight can cause either warming (during periods of stronger solar intensity) or cooling (during periods of weaker solar intensity). The sun follows a natural 11-year cycle of small ups and downs in intensity, but the effect on Earth’s climate is small. Changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis can also affect the amount of sunlight reaching Earth’s surface.
Changes in the sun’s intensity have influenced Earth’s climate in the past. For example, the so-called “Little Ice Age” between the 17th and 19th centuries may have been partially caused by a low solar activity phase from 1645 to 1715, which coincided with cooler temperatures. The Little Ice Age refers to a slight cooling of North America, Europe, and probably other areas around the globe. Changes in Earth’s orbit have had a big impact on climate over tens of thousands of years. These changes appear to be the primary cause of past cycles of ice ages, in which Earth has experienced long periods of cold temperatures (ice ages), as well as shorter interglacial periods (periods between ice ages) of relatively warmer temperatures.
Changes in solar energy continue to affect climate. However, solar activity has been relatively constant, aside from the 11-year cycle, since the mid-20th century and therefore does not explain the recent warming of Earth. Similarly, changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis affect temperature on relatively long timescales (tens of thousands of years), and therefore cannot explain the recent warming.
Changes in Reflectivity Affect How Much Energy Enters Earth’s System
When sunlight energy reaches Earth it can be reflected or absorbed. The amount that is reflected or absorbed depends on Earth’s surface and atmosphere. Light-colored objects and surfaces, like snow and clouds, tend to reflect most sunlight, while darker objects and surfaces, like the ocean and forests, tend to absorb more sunlight. The term albedo refers to the amount of solar radiation reflected from an object or surface, often expressed as a percentage. Earth as a whole has an albedo of about 30%, meaning that 70% of the sunlight that reaches the planet is absorbed. Sunlight that is absorbed warms Earth’s land, water, and atmosphere.
Albedo is also affected by aerosols. Aerosols are small particles or liquid droplets in the atmosphere that can absorb or reflect sunlight. Unlike greenhouse gases (GHGs), the climate effects of aerosols vary depending on what they are made of and where they are emitted. Those aerosols that reflect sunlight, such as particles from volcanic eruptions or sulfur emissions from burning coal, have a cooling effect. Those that absorb sunlight, such as black carbon (a part of soot), have a warming effect.
Natural changes in albedo, like the melting of sea ice or increases in cloud cover, have contributed to climate change in the past, often acting as feedbacks to other processes. Volcanoes have played a noticeable role in climate. Volcanic particles that reach the upper atmosphere can reflect enough sunlight back to space to cool the surface of the planet by a few tenths of a degree for several years. Volcanic particles from a single eruption do not produce long-term change because they remain in the atmosphere for a much shorter time than GHGs.
Human changes in land use and land cover have changed Earth’s albedo. Processes such as deforestation, reforestation, desertification, and urbanization often contribute to changes in climate in the places they occur. These effects may be significant regionally, but are smaller when averaged over the entire globe.
Scientific Consensus: Global Climate Change is Real
The Intergovernmental Panel on Climate Change (IPCC) was created in 1988 by the United Nations Environment Programme and the World Meteorological Organization. It is charged with the task of evaluating and synthesizing the scientific evidence surrounding global climate change. The IPCC uses this information to evaluate current impacts and future risks, in addition to providing policymakers with assessments. These assessments are released about once every every six years. The most recent report, the 5th Assessment, was released in 2013. Hundreds of leading scientists from around the world are chosen to author these reports. Over the history of the IPCC, these scientists have reviewed thousands of peer-reviewed, publicly available studies. The scientific consensus is clear: global climate change is real and humans are very likely the cause for this change.
Additionally, the major scientific agencies of the United States, including the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), also agree that climate change is occurring and that humans are driving it. In 2010, the US National Research Council concluded that “Climate change is occurring, is very likely caused by human activities, and poses significant risks for a broad range of human and natural systems”. Many independent scientific organizations have released similar statements, both in the United States and abroad. This doesn’t necessarily mean that every scientist sees eye to eye on each component of the climate change problem, but broad agreement exists that climate change is happening and is primarily caused by excess greenhouse gases from human activities. Critics of climate change, driven by ideology instead of evidence, try to suggest to the public that there is no scientific consensus on global climate change. Such an assertion is patently false.
Current Status of Global Climate Change and Future Changes
Greenhouse gas concentrations in the atmosphere will continue to increase unless the billions of tons of anthropogenic emissions each year decrease substantially. Increased concentrations are expected to:
• Increase Earth’s average temperature,
• Influence the patterns and amounts of precipitation,
• Reduce ice and snow cover, as well as permafrost,
• Raise sea level,
• Increase the acidity of the oceans.
These changes will impact our food supply, water resources, infrastructure, ecosystems, and even our own health. The magnitude and rate of future climate change will primarily depend on the following factors:
• The rate at which levels of greenhouse gas concentrations in our atmosphere continue to increase,
• How strongly features of the climate (e.g., temperature, precipitation, and sea level) respond to the expected increase in greenhouse gas concentrations,
• Natural influences on climate (e.g., from volcanic activity and changes in the sun’s intensity) and natural processes within the climate system (e.g., changes in ocean circulation patterns).
Past and Present-day GHG Emissions Will Affect Climate Far into the Future
Many greenhouse gases stay in the atmosphere for long periods of time. As a result, even if emissions stopped increasing, atmospheric greenhouse gas concentrations would continue to remain elevated for hundreds of years. Moreover, if we stabilized concentrations and the composition of today’s atmosphere remained steady (which would require a dramatic reduction in current greenhouse gas emissions), surface air temperatures would continue to warm. This is because the oceans, which store heat, take many decades to fully respond to higher greenhouse gas concentrations. The ocean’s response to higher greenhouse gas concentrations and higher temperatures will continue to impact climate over the next several decades to hundreds of years.
Future Temperature Changes
Climate models project the following key temperature-related changes:
Key Global Projections
• Average global temperatures are expected to increase by 2°F to 11.5°F by 2100, depending on the level of future greenhouse gas emissions, and the outcomes from various climate models.
• By 2100, global average temperature is expected to warm at least twice as much as it has during the last 100 years.
• Ground-level air temperatures are expected to continue to warm more rapidly over land than oceans.
• Some parts of the world are projected to see larger temperature increases than the global average.
Future Precipitation and Storm Events
Patterns of precipitation and storm events, including both rain and snowfall are likely to change. However, some of these changes are less certain than the changes associated with temperature. Projections show that future precipitation and storm changes will vary by season and region. Some regions may have less precipitation, some may have more precipitation, and some may have little or no change. The amount of rain falling in heavy precipitation events is likely to increase in most regions, while storm tracks are projected to shift towards the poles. Climate models project the following precipitation and storm changes:
• Global average annual precipitation through the end of the century is expected to increase, although changes in the amount and intensity of precipitation will vary by region.
• The intensity of precipitation events will likely increase on average. This will be particularly pronounced in tropical and high-latitude regions, which are also expected to experience overall increases in precipitation.
• The strength of the winds associated with tropical storms is likely to increase. The amount of precipitation falling in tropical storms is also likely to increase.
• Annual average precipitation is projected to increase in some areas and decrease in others.
Future Ice, Snowpack, and Permafrost
Arctic sea ice is already declining drastically. The area of snow cover in the Northern Hemisphere has decreased since 1970. Permafrost temperature has increased over the last century, making it more susceptible to thawing. Over the next century, it is expected that sea ice will continue to decline, glaciers will continue to shrink, snow cover will continue to decrease, and permafrost will continue to thaw.
For every 2°F of warming, models project about a 15% decrease in the extent of annually averaged sea ice and a 25% decrease in September Arctic sea ice. The coastal sections of the Greenland and Antarctic ice sheets are expected to continue to melt or slide into the ocean. If the rate of this ice melting increases in the 21st century, the ice sheets could add significantly to global sea level rise. Glaciers are expected to continue to decrease in size. The rate of melting is expected to continue to increase, which will contribute to sea level rise.
Future Sea Level Change
Warming temperatures contribute to sea level rise by expanding ocean water, melting mountain glaciers and ice caps, and causing portions of the Greenland and Antarctic ice sheets to melt or flow into the ocean. Since 1870, global sea level has risen by about 8 inches. Estimates of future sea level rise vary for different regions, but global sea level for the next century is expected to rise at a greater rate than during the past 50 years. The contribution of thermal expansion, ice caps, and small glaciers to sea level rise is relatively well-studied, but the impacts of climate change on ice sheets are less understood and represent an active area of research. Thus, it is more difficult to predict how much changes in ice sheets will contribute to sea level rise. Greenland and Antarctic ice sheets could contribute an additional 1 foot of sea level rise, depending on how the ice sheets respond.
Regional and local factors will influence future relative sea level rise for specific coastlines around the world. For example, relative sea level rise depends on land elevation changes that occur as a result of subsidence (sinking) or uplift (rising), in addition to things such as local currents, winds, salinity, water temperatures, and proximity to thinning ice sheets. Assuming that these historical geological forces continue, a 2-foot rise in global sea level by 2100 would result in the following relative sea level rise:
• 2.3 feet at New York City
• 2.9 feet at Hampton Roads, Virginia
• 3.5 feet at Galveston, Texas
• 1 foot at Neah Bay in Washington state
Future Ocean Acidification
Ocean acidification is the process of ocean waters decreasing in pH. Oceans become more acidic as carbon dioxide (CO2) emissions in the atmosphere dissolve in the ocean. This change is measured on the pH scale, with lower values being more acidic. The pH level of the oceans has decreased by approximately 0.1 pH units since pre-industrial times, which is equivalent to a 25% increase in acidity. The pH level of the oceans is projected to decrease even more by the end of the century as CO2 concentrations are expected to increase for the foreseeable future. Ocean acidification adversely affects many marine species, including plankton, mollusks, shellfish, and corals. As ocean acidification increases, the availability of calcium carbonate will decline. Calcium carbonate is a key building block for the shells and skeletons of many marine organisms. If atmospheric CO2 concentrations double, coral calcification rates are projected to decline by more than 30%. If CO2 concentrations continue to rise at their current rate, corals could become rare on tropical and subtropical reefs by 2050.
Spread of Disease
This rise in global temperatures will increase the range of disease-carrying insects and the viruses and pathogenic parasites they harbor. Thus, diseases will spread to new regions of the globe. This spread has already been documented with dengue fever, a disease the affects hundreds of millions per year, according to the World Health Organization. Colder temperatures typically limit the distribution of certain species, such as the mosquitoes that transmit malaria, because freezing temperatures destroy their eggs.
Not only will the range of some disease-causing insects expand, the increasing temperatures will also accelerate their lifecycles, which allows them to breed and multiply quicker, and perhaps evolve pesticide resistance faster. In addition to dengue fever, other diseases are expected to spread to new portions of the world as the global climate warms. These include malaria, yellow fever, West Nile virus, zika virus, and chikungunya.
Climate change affects everyone
Our lives are connected to the climate. Human societies have adapted to the relatively stable climate we have enjoyed since the last ice age which ended several thousand years ago. A warming climate will bring changes that can affect our water supplies, agriculture, power and transportation systems, the natural environment, and even our own health and safety.
Carbon dioxide can stay in the atmosphere for nearly a century, on average, so Earth will continue to warm in the coming decades. The warmer it gets, the greater the risk for more severe changes to the climate and Earth’s system. Although it’s difficult to predict the exact impacts of climate change, what’s clear is that the climate we are accustomed to is no longer a reliable guide for what to expect in the future.
We can reduce the risks we will face from climate change. By making choices that reduce greenhouse gas pollution, and preparing for the changes that are already underway, we can reduce risks from climate change. Our decisions today will shape the world our children and grandchildren will live in.
You Can Take Action
You can take steps at home, on the road, and in your office to reduce greenhouse gas emissions and the risks associated with climate change. Many of these steps can save you money. Some, such as walking or biking to work, can even improve your health! You can also get involved on a local or state level to support energy efficiency, clean energy programs, or other climate programs.
Suggested Supplementary Reading:
Intergovernmental Panel on Climate Change. 2013. 5th Assessment: Summary for Policymakers. <http://www.ipcc.ch/pdf/assessment-re..._SPM_FINAL.pdf>
NASA. 2018. Global Climate Change: Vital Signs of the Planet. Website. <https://climate.nasa.gov/>
This website by NASA provides a multi-media smorgasbord of engaging content. Learn about climate change using data collected by NASA satellites and more. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/10%3A_Air_Pollution_Climate_Change__Ozone_Depletion/10.04%3A_Climate_Change.txt |
Summary
Air pollution can be thought of as gaseous and particulate contaminants that are present in the earth’s atmosphere. Chemicals discharged into the air that have a direct impact on the environment are called primary pollutants. These primary pollutants sometimes react with other chemicals in the air to produce secondary pollutants. The commonly found air pollutants, known as criteria pollutants, are particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm health and the environment, and cause property damage. The historical record shows that the climate system varies naturally over a wide range of time scales. In general, climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas concentrations. Recent climate changes, however, cannot be explained by natural causes alone. Natural causes are very unlikely to explain most observed warming, especially warming since the mid-20th century. Rather, human activities can explain most of that warming.
The primary human activity affecting the amount and rate of climate change is greenhouse gas emissions from the burning of fossil fuels. Greenhouse gas concentrations in the atmosphere will continue to increase unless the billions of tons of our annual emissions decrease substantially. Increased concentrations are expected to increase Earth’s average temperature, influence the patterns and amounts of precipitation, reduce ice and snow cover, as well as permafrost, raise sea level and increase the acidity of the oceans. These changes will impact our food supply, water resources, infrastructure, ecosystems, and even our own health. Acid rain is a term referring to a mixture of wet and dry deposition from the atmosphere containing higher than normal amounts of nitric and sulfuric acids. The precursors of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion. Acid rain causes acidification of lakes and streams, contributes to the damage of trees and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, contributes to the corrosion of metals and damages human health. The ozone depletion process begins when CFCs and other ozone-depleting substances (ODS) are emitted into the atmosphere. Reductions in stratospheric ozone levels lead to higher levels of UVB reaching the Earth’s surface. The sun’s output of UVB does not change; rather, less ozone means less protection, and hence more UVB reaches the Earth. Ozone layer depletion increases the amount of UVB tat lead to negative health and environmental effects.
Review Questions
1. Ground-level ozone…
1. Protects us from radiation
2. Is a primary pollutant
3. Is a secondary pollutant
4. Reduces visibility but is mostly harmless to human health
5. Is emitted from motor vehicles
2. Secondary pollutants are pollutants…
1. Emitted from non-point sources
2. That are created from the reaction of primary pollutants and other chemicals
3. That are less hazardous than primary pollutants
4. That have reduced ability to stay aloft in the atmosphere
5. Emitted by Class 2 polluters
3. Depletion of the stratospheric ozone layer occurs when molecules of ozone are destroyed by chemicals such as…
1. CFC
2. DDT
3. O3
4. PCB
5. CH4
4. What is the function of the stratospheric ozone layer?
1. Provides the biosphere with a source of elemental oxygen
2. Protects against ultraviolet light
3. Shields the Earth from high-energy cosmic rays
4. Protects organisms from infrared radiation
5. Creates UVB radiation for vitamin D synthesis
5. Anthropogenic causes of acid rain are primarily due to which one of the following?
1. Destruction of the ozone layer
2. Emissions of sulfur dioxide and nitrogen oxides from the combustion of fossil fuels
3. Emissions of carbon dioxide from the combustion of fossil fuels
4. Industrial emissions of acids
5. Acids formed in the contrails of airplanes
6. The scientific consensus regarding global climate change is that these changes are…
1. Caused by natural, Earth-based phenomena such as volcanoes
2. Poorly understood and no scientific conclusions can be made at this time
3. Primarily caused by human activities
4. Caused by eccentricity in Earth’s orbit and by changes in solar intensity
5. No greater or different than changes seen in the medieval times
7. Greenhouse gases are known to raise air temperatures by…
1. absorbing infrared radiation
2. creating heat through chemical reactions with atmospheric pollutants
3. absorbing incoming visible light from the sun
4. trapping high energy molecules and atomic particles
5. releasing heat stored in high-altitude catalytic cycles
8. Changes in reflectivity of visible light affect how much energy enters Earth’s system. What term is used by scientists to describe the reflectivity of a surface?
1. Contrastivity
2. Libido
3. Mirror-effect
4. Alluvium
5. Albedo
9. What is the primary cause of ocean acidification?
1. Atmospheric CO2 dissolving in ocean water
2. Increases in acid rain
3. Increased erosion of acid-containing rocks
4. Water draining into the ocean has a higher pH from industrial pollutants
5. All of the above
10. Which one of the following is not a predicted consequence of global climate change?
1. Spread of diseases carried by insects, such as malaria
2. Rise in sea levels
3. Increases in the global average air and ocean temperatures
4. Intensity of precipitation events will likely increase on average.
5. All of the above
See Appendix for answers
Attributions
CK12. (2015). Reducing ozone destruction. Accessed August 31, 2015 at http://www.ck12.org/book/CK-12-Earth...section/13.32/. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.
EPA. (n.d.). Climate change. Accessed August 31, 2015 at http://www.epa.gov/climatechange/. Modified from original.
University of California College Prep. (2012). AP environmental science. Retrieved from http://cnx.org/content/col10548/1.2/. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/10%3A_Air_Pollution_Climate_Change__Ozone_Depletion/10.05%3A_Chapter_Resources.txt |
Learning Outcomes
• Outline the history of human energy use
• Understand the challenges to continued reliance on fossil energy
• Outline environmental impacts of energy use
• Understand the global capacity for each non-renewable energy source
• Evaluate the different energy sources based on their environmental impact
• Understand the key factors in the growth of renewable energy sources
Thumbnail image - Wind farm near Copenhagen, Denmark. In 2014 wind power met 39% of electricity demand in Denmark.
11: Conventional Sustainable Energy
Energy for lighting, heating and cooling our buildings, manufacturing products, and powering our transportation systems comes from a variety of natural sources. The earth’s core provides geothermal energy. The gravitational pull of moon and sun create tides. The sun emits light (electromagnetic radiation), which creates wind, powers the water (hydrologic) cycle, and enables photosynthesis. Plants, algae, and cyanobacteria utilize solar energy to grow and create biomass that can be burned and used for biofuels, such as wood, biodiesel, bioethanol. Over the course of millions of years, biomass from photosynthetic organisms can create energy-rich fossil fuels through the geologic process of burial and transformation through heat and pressure.
Each of these types of energy can be defined as renewable or non-renewable. Renewable energy sources can be replenished within human lifespans. Examples include solar, wind, and biomass energy. Non-renewable energy is finite and cannot be replenished within a human timescale. Examples include nuclear energy and fossil fuels, which take millions of years to form. All energy sources have and some environmental and health cost, and the distribution of energy is not equally distributed among all nations.
Environmental and Health Challenges of Energy Use
The environmental impacts of energy use on humans and the planet can happen anywhere during the life cycle of the energy source. The impacts begin with the extraction of the resource. They continue with the processing, purification or manufacture of the source; its transportation to place of energy generation, and ends with the disposal of waste generated during use.
Extraction of fossil fuels can be used as a case study because its use has significant impacts on the environment. As we mine deeper into mountains, farther out at sea, or farther into pristine habitats, we risk damaging fragile environments, and the results of accidents or natural disasters during extraction processes can be devastating. Fossils fuels are often located far from where they are utilized so they need to be transported by pipeline, tankers, rail or trucks. These all present the potential for accidents, leakage and spills. When transported by rail or truck energy must be expended and pollutants are generated. Processing of petroleum, gas and coal generates various types of emissions and wastes, as well as utilizes water resources. Production of energy at power plants results in air, water, and, often, waste emissions. Power plants are highly regulated in the Unites States by federal and state law under the Clean Air and Clean Water Acts, while nuclear power plants are regulated by the Nuclear Regulatory Commission.
Geopolitical Challenges of Fossil Fuels
The use of fossil fuels has allowed much of the global population to reach a higher standard of living. However, this dependence on fossil fuels results in many significant impacts on society. Our modern technologies and services, such as transportation and plastics depend in many ways on fossil fuels. If supplies become limited or extremely costly, our economies are vulnerable. If countries do not have fossil fuel reserves of their own, they incur even more risk. The United States has become more and more dependent on foreign oil since 1970 when our own oil production peaked. The United States imported over half of the crude oil and refined petroleum products that we consumed during 2009. Just over half of these imports came from the Western Hemisphere (Figure \(2\)).
The major holder of oil reserves is the Organization of Petroleum Exporting Countries, (OPEC) (Figure \(3\)). As of 2018, there were 15 member countries in OPEC: Algeria, Angola, Congo, Ecuador, Equatorial Guinea, Gabon, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. OPEC attempts to influence the amount of oil available to the world by assigning a production quota to each member except Iraq, for which no quota is presently set.
Overall compliance with these quotas is mixed since the individual countries make the actual production decisions. All of these countries have a national oil company but also allow international oil companies to operate within their borders. They can restrict the amounts of production by those oil companies. Therefore, the OPEC countries have a large influence on how much of world demand is met by OPEC and non-OPEC supply. A recent example of this is the price increases that occurred during the year 2011 after multiple popular uprisings in Arab countries, including Libya.
This pressure has lead the United States to developing policies that would reduce reliance on foreign oil such as developing additional domestic sources and obtaining it from non-Middle Eastern countries such as Canada, Mexico, Venezuela, and Nigeria. However, since fossil fuel reserves create jobs and provide dividends to investors, a lot is at stake in a nation that has oil reserves. Oil wealth may be shared with the country’s inhabitants or retained by the oil companies and dictatorships, such as in Nigeria prior to the 1990s. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/11%3A_Conventional__Sustainable_Energy/11.01%3A_Challenges_and_Impacts_of_Energy_Use.txt |
Fossil Fuels
Fossil fuels comes from the organic matter of plants, algae, and cyanobacteria that was buried, heated, and compressed under high pressure over millions of years. The process transformed the biomass of those organisms into the three types of fossil fuels: oil, coal, and natural gas.
Petroleum (oil)
Thirty seven percent of the world’s energy consumption and 43% of the United States energy consumption comes from oil. Scientists and policy-makers often discuss the question of when the world will reach peak oil production, the point at which oil production is at its greatest and then declines. It is generally thought that peak oil will be reached by the middle of the 21st Century, although making such estimates is difficult because a lot of variables must be considered. Currently world reserves are 1.3 trillion barrels, or 45 years left at current level of production..
Environmental Impacts of Oil Extraction and Refining
Oil is usually found one to two miles (1.6 – 3.2 km) below the Earth’s surface, whether that is on land or ocean. Once oil is found and extracted it must be refined, which separates and prepares the mix of crude oil into the different types for gas, diesel, tar, and asphalt. Oil refining is one of top sources of air pollution in the United States for volatile organic hydrocarbons and toxic emissions, and the single largest source of carcinogenic benzene. When petroleum is burned as gasoline or diesel, or to make electricity or to power boilers for heat, it produces a number of emissions that have a detrimental effect on the environment and human health:
• Carbon dioxide (CO2) is a greenhouse gas and a source of climate change.
• Sulfur dioxide (SO2) causes acid rain, which damages plants and animals that live in water, and it increases or causes respiratory illnesses and heart diseases, particularly in vulnerable populations like children and the elderly.
• Nitrous oxides (NOx) and Volatile Organic Carbons (VOCs) contribute to ozone at ground level, which is an irritant and causes damage to the lungs.
• Particulate Matter (PM) produces hazy conditions in cities and scenic areas, and combines with ozone to contribute to asthma and chronic bronchitis, especially in children and the elderly. Very small, or “fine PM,” is also thought to penetrate the respiratory system more deeply and cause emphysema and lung cancer.
• Lead can have severe health impacts, especially for children.
There are other domestic sources of oil that are being considered as conventional resources and are being depleted. These include tar sands – deposits of moist sand and clay with 1-2 percent bitumen (thick and heavy petroleum rich in carbon and poor in hydrogen). These are removed by strip mining (see section below on coal). Another source is oil shale, which is sedimentary rock filled with organic matter that can be processed to produce liquid petroleum. Extracted by strip mining or creating subsurface mines, oil shale can be burned directly like coal or baked in the presence of hydrogen to extract liquid petroleum. However, the net energy values are low and they are expensive to extract and process. Both of these resources have severe environmental impacts due to strip mining, carbon dioxide, methane and other air pollutants similar to other fossil fuels.
As the United States tries to extract more oil from its own dwindling resources, they are drilling even deeper into the earth and increasing the environmental risks. The largest United States oil spill to date began in April 2010 when an explosion occurred on Deepwater Horizon Oil Rig killing 11 employees and spilling nearly 200 million gallons of oil before the resulting leak could be stopped. Wildlife, ecosystems, and people’s livelihood were adversely affected. A lot of money and huge amounts of energy were expended on immediate clean-up efforts. The long-term impacts are still not known. The National Commission on the Deepwater Horizon Oil Spill and Offshore Drilling was set up to study what went wrong.
The Global Dependence of Transportation on Oil
Two-thirds of oil consumption is devoted to transportation, providing fuel for cars, trucks, trains and airplanes. For the United States and most developed societies, transportation is woven into the fabric of our lives, a necessity as central to daily operations as food or shelter. The concentration of oil reserves in a few regions or the world makes much of the world dependent on imported energy for transportation. The rise in the price of oil in the last decade makes dependence on imported energy for transportation an economic as well as an energy issue. The United States, for example, now spends upwards of \$350 billion annually on imported oil, a drain of economic resources that could be used to stimulate growth, create jobs, build infrastructure and promote social advances at home.
Coal
Unlike oil, coal is a solid. Due to its relatively low cost and abundance, coal is used to generate about half of the electricity consumed in the United States. Coal is the largest domestically produced source of energy. Coal production has doubled in the United States over the last sixty year (Figure \(1\)). Current world reserves are estimated at 826,000 million tonnes, with nearly 30% of that in the United States. It is a major fuel resource that the United States controls domestically.
Coal is plentiful and inexpensive, when looking only at the market cost relative to the cost of other sources of electricity, but its extraction, transportation, and use produces a multitude of environmental impacts that the market cost does not truly represent. Coal emits sulfur dioxide, nitrogen oxide, and mercury, which have been linked to acid rain, smog, and health issues. Burning of coal emits higher amounts of carbon dioxide per unit of energy than the use of oil or natural gas. Coal accounted for 35% of the total United States emissions of carbon dioxide released into the Earth’s atmosphere in 2010. Ash generated from combustion contributes to water contamination. Some coal mining has a negative impact on ecosystems and water quality, and alters landscapes and scenic views (such as with mountaintop mining).
There are also significant health effects and risks to coal miners and those living in the vicinity of coal mines. Traditional underground mining is risky to mine workers due to the risk of entrapment or death. Over the last 15 years, the U.S. Mine Safety and Health Administration has published the number of mine worker fatalities and it has varied from 18-48 per year. Twenty-nine miners died on April 6, 2010 in an explosion at the Upper Big Branch coal mine in West Virginia, contributing to the uptick in deaths between 2009 and 2010. In other countries, with less safety regulations, accidents occur more frequently. In May 2011, for example, three people died and 11 were trapped in a coalmine in Mexico for several days. There is also risk of getting black lung disease (pneumoconiosis). This is a disease of the lungs caused by the inhalation of coal dust over a long period of time. It causes coughing and shortness of breath. If exposure is stopped the outcome is good. However, the complicated form may cause shortness of breath that gets increasingly worse.
Mountaintop mining (MTM), while less hazardous to workers, has particularly detrimental effects on land resources. MTM is a surface mining practice involving the removal of mountaintops to expose coal seams, and disposing of the associated mining waste in adjacent valleys. This form of mining is very damaging to the environment because it literally removes the tops of mountains, destroying the existing habitat. Additionally, the debris from MTM is dumped into valleys burying streams and other important habitat.
Natural Gas
Natural gas meets 20% of world energy needs and 25% of United States needs. Natural gas is mainly composed of methane (CH4) and is a very potent greenhouse gas. There are two types of natural gas. Biogenic gas is found at shallow depths and arises from anaerobic decay of organic matter by bacteria, like landfill gas. Thermogenic gas comes from the compression of organic matter and deep heat underground. They are found with petroleum in reservoir rocks and with coal deposits, and these fossil fuels are extracted together.
Natural gas is released into the atmosphere from coal mines, oil and gas wells, and natural gas storage tanks, pipelines, and processing plants. These leaks are the source of about 25% of total U.S. methane emissions, which translates to three percent of total U.S. greenhouse gas emissions. When natural gas is produced but cannot be captured and transported economically, it is “flared,” or burned at well sites, which converts it to CO2. This is considered to be safer and better than releasing methane into the atmosphere because CO2 is a less potent greenhouse gas than methane.
In the last few years a new reserve of natural gas has been identified: shale resources. The United States possesses 2,552 trillion cubic feet (Tcf) (72.27 trillion cubic meters) of potential natural gas resources, with shale resources accounting for 827 Tcf (23.42 tcm). As natural gas prices increased it has become more economical to extract the gas from shale. Figure \(3\) shows the past and forecasted U.S. natural gas production and the various sources. The current reserves are enough to last about 110 years at the 2009 rate of U.S. consumption (about 22.8 Tcf per year -645.7 bcm per year).
Natural gas is a preferred fossil fuel when considering its environmental impacts. Specifically, when burned, much less carbon dioxide (CO2), nitrogen oxides, and sulfur dioxide are omitted than from the combustion of coal or oil. It also does not produce ash or toxic emissions.
Natural gas production can result in the production of large volumes of contaminated water. This water has to be properly handled, stored, and treated so that it does not pollute land and water supplies. Extraction of shale gas is more problematic than traditional sources due to a process nicknamed fracking, or fracturing of wells, since it requires large amounts of water (Figure \(4\)). The technique uses high-pressure fluids to fracture the normally hard shale deposits and release gas and oil trapped inside the rock. To promote the flow of gas out of the rock, small particles of solids are included in the fracturing liquids to lodge in the shale cracks and keep them open after the liquids are depressurized. The considerable use of water may affect the availability of water for other uses in some regions and this can affect aquatic habitats. If mismanaged, hydraulic fracturing fluid can be released by spills, leaks, or various other exposure pathways. The fluid contains potentially hazardous chemicals such as hydrochloric acid, glutaraldehyde, petroleum distillate, and ethylene glycol. The risks of fracking have been highlighted in popular culture in the documentary, Gasland (2010).
The raw gas from a well may contain many other compounds besides the methane that is being sought, including hydrogen sulfide, a very toxic gas. Natural gas with high concentrations of hydrogen sulfide is usually flared which produces CO2, carbon monoxide, sulfur dioxide, nitrogen oxides, and many other compounds. Natural gas wells and pipelines often have engines to run equipment and compressors, which produce additional air pollutants and noise.
Contributions of Coal and Natural Gas to Electricity Generation
At present the fossil fuels used for electricity generation in the US are predominantly coal (44%) and natural gas (23%); petroleum accounts for approximately 1%. Coal electricity traces its origins to the early 20th Century, when it was the natural fuel for steam engines given its abundance, high energy density and low cost. gatural Gas is a later addition to the fossil electricity mix, arriving in significant quantities after World War II and with its greatest growth since 1990. Of the two fuels, coal emits almost twice the carbon dioxide as natural gas for the same heat output, making it significantly greater contributor to global warming and climate change.
The Future of Natural Gas and Coal
The future development of coal and natural gas depend on the degree of public and regulatory concern for carbon emissions, and the relative price and supply of the two fuels. Supplies of coal are abundant in the United States, and the transportation chain from mines to power plants is well established. The primary unknown factor is the degree of public and regulatory pressure that will be placed on carbon emissions. Strong regulatory pressure on carbon emissions would favor retirement of coal and addition of natural gas power plants. This trend is reinforced by the recent dramatic expansion of shale gas reserves in the United States due to advances in drilling technology. Shale natural gas production has increased 48% annually in the years 2006 – 2010, with more increases expected. Greater United States production of shale gas will gradually reduce imports and could eventually make the United States a net exporter of natural gas.
Nuclear Power
Nuclear power is energy released from the radioactive decay of elements, such as uranium, which releases large amounts of energy. Nuclear power plants produce no carbon dioxide and, therefore, are often considered an alternative fuel (fuels other than fossil fuels). Currently, world production of electricity from nuclear power is about 19.1 trillion KWh, with the United States producing and consuming about 22% of that. Nuclear power provides about 9% of the electricity in the United States (Figure \(7\)).
There are environmental challenges with nuclear power. Mining and refining uranium ore and making reactor fuel demands a lot of energy. Also, nuclear power plants are very expensive and require large amounts of metal, concrete, and energy to build. The main environmental challenge for nuclear power is the wastes including uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. These materials have long radioactive half-lives and thus remain a threat to human health for thousands of years. The half life of a radioactive element is the time it takes for 50% of the material to radioactively decay. The U.S. Nuclear Regulatory Commission regulates the operation of nuclear power plants and the handling, transportation, storage, and disposal of radioactive materials to protect human health and the environment.
By volume, the waste produced from mining uranium, called uranium mill tailings, is the largest waste and contains the radioactive element radium, which decays to produce radon, a radioactive gas. High-level radioactive waste consists of used nuclear reactor fuel. This fuel is in a solid form consisting of small fuel pellets in long metal tubes and must be stored and handled with multiple containment, first cooled by water and later in special outdoor concrete or steel containers that are cooled by air. There is no long-term storage facility for this fuel in the United States.
There are many other regulatory precautions governing permitting, construction, operation, and decommissioning of nuclear power plants due to risks from an uncontrolled nuclear reaction. The potential for contamination of air, water and food is high should an uncontrolled reaction occur. Even when planning for worst-case scenarios, there are always risks of unexpected events. For example, the March 2011 earthquake and subsequent tsunami that hit Japan resulted in reactor meltdowns at the Fukushima Daiichi Nuclear Power Station, causing massive damage to the surrounding area.
Debating Nuclear Energy
From a sustainability perspective, nuclear electricity presents an interesting dilemma. On the one hand, nuclear electricity produces no carbon emissions, a major sustainable advantage in a world facing anthropogenic climate change. On the other hand, nuclear electricity produces dangerous waste that i) must be stored out of the environment for thousands of years, ii) can produce bomb-grade plutonium and uranium that could be diverted by terrorists or others to destroy cities and poison the environment, and iii) threatens the natural and built environment through accidental leaks of long-lived radiation. Thoughtful scientists, policy makers, and citizens must weigh the benefit of this source of carbon-free electricity against the environmental risk of storing spent fuel, the societal risk of nuclear proliferation, and the impact of accidental or deliberate release of radiation. There are very few examples of humans having the power to permanently change the dynamics of the earth. Global climate change from carbon emissions is one example, and radiation from the explosion of a sufficient number of nuclear weapons is another. Nuclear electricity touches both of these opportunities, on the positive side for reducing carbon emissions and on the negative side for the risk of nuclear proliferation.
Nuclear electricity came on the energy scene remarkably quickly. Following the development of nuclear technology at the end of World War II for military ends, nuclear energy quickly acquired a new peacetime path for inexpensive production of electricity. Eleven years after the end of World War II, a very short time in energy terms, the first commercial nuclear reactor produced electricity at Calder Hall in Sellafield, England. The number of nuclear reactors grew steadily to more than 400 by 1990, four years after the Chernobyl disaster in 1986 and eleven years following Three Mile Island in 1979. Since 1990, the number of operating reactors has remained approximately flat, with new construction balancing decommissioning due to public and government reluctance to proceed with nuclear electricity expansion plans.
The outcome of this debate will determine whether the world experiences a nuclear renaissance that has been in the making for several years. The global discussion has been strongly impacted by the unlikely nuclear accident in Fukushima, Japan in March 2011. The Fukushima nuclear disaster was caused by an earthquake and tsunami that disabled the cooling system for a nuclear energy complex consisting of operating nuclear reactors and storage pools for underwater storage of spent nuclear fuel ultimately causing a partial meltdown of some of the reactor cores and release of significant radiation. This event, 25 years after Chernobyl, reminds us that safety and public confidence are especially important in nuclear energy; without them expansion of nuclear energy will not happen. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/11%3A_Conventional__Sustainable_Energy/11.02%3A_Non-Renewable_Energy_Sources.txt |
Hydropower
Hydropower (hydroelectric) relies on water to spin turbines and create electricity. It is considered a clean and renewable source of energy because it does not directly produce pollutants and because the source of power is regenerated. Hydropower provides 35% of the United States’ renewable energy consumption.
Hydropower dams and the reservoirs they create can have environmental impacts. For example, migration of fish to their upstream spawning areas can be obstructed by dams. In areas where salmon must travel upstream to spawn, such as along the Columbia River in Washington and Oregon, the dams block their way. This problem can be partially alleviated by using “fish ladders” that help salmon get around the dams. Fish traveling downstream, however, can get killed or injured as water moves through turbines in the dam. Reservoirs and operation of dams can also affect aquatic habitats due to changes in water temperatures, water depth, chemistry, flow characteristics, and sediment loads, all of which can lead to significant changes in the ecology and physical characteristics of the river both upstream and downstream. As reservoirs fill with water it may cause natural areas, farms, cities, and archeological sites to be inundated and force populations to relocate.
Small hydropower systems
Large-scale dam hydropower projects are often criticized for their impacts on wildlife habitat, fish migration, and water flow and quality. However, small run-of- the-river projects are free from many of the environmental problems associated with their large-scale relatives because they use the natural flow of the river, and thus produce relatively little change in the stream channel and flow. The dams built for some run-of-the-river projects are very small and impound little water, and many projects do not require a dam at all. Thus, effects such as oxygen depletion, increased temperature, decreased flow, and impeded upstream migration are not problems for many run-of-the-river projects.
Small hydropower projects offer emissions-free power solutions for many remote communities throughout the world, such as those in Nepal, India, China, and Peru, as well as for highly industrialized countries like the United States. Small hydropower systems are those that generate between .01 to 30 MW of electricity. Hydropower systems that generate up to 100 kilowatts (kW) of electricity are often called micro hydropower systems (Figure \(2\)). Most of the systems used by home and small business owners would qualify as microhydropower systems. In fact, a 10 kW system generally can provide enough power for a large home, a small resort, or a hobby farm.
Municipal Solid Waste
Municipal solid waste (MSW) is commonly known as garbage and can create electricity by burning it directly or by burning the methane produced as it decays. Waste to energy processes are gaining renewed interest as they can solve two problems at once: disposal of waste and production of energy from a renewable resource. Many of the environmental impacts are similar to those of a coal plant: air pollution, ash generation, etc. Because the fuel source is less standardized than coal and hazardous materials may be present in MSW, incinerators and waste-to-energy power plants need to clean the gases of harmful materials. The U.S. EPA regulates these plants very strictly and requires anti-pollution devices to be installed. Also, while incinerating at high temperature many of the toxic chemicals may break down into less harmful compounds. The ash from these plants may contain high concentrations of various metals that were present in the original waste. If ash is clean enough it can be “recycled” as an MSW landfill cover or to build roads, cement block and artificial reefs
Biofuel
Biomass refers to material made by organisms, such as cells and tissues. In terms of energy production, biomass is almost always derived from plants, and to a lesser extent, algae. For biomass to be a sustainable option, it usually needs to come from waste material, such as lumber mill sawdust, paper mill sludge, yard waste, or oat hulls from an oatmeal processing plant, material that would otherwise just rot. Livestock manure and human waste could also be considered biomass. The use of biomass can help mitigate climate change because when burned it adds no new carbon to the atmosphere. Thinking back to the carbon cycle (chapter 3), you will recall that photosynthesis removes CO2 through the process of carbon fixation. When biomass is burnt, CO2 is created, but this is equal to the amount of CO2captured during carbon fixation. Thus, biomass is a carbon neutral energy source because it doesn’t add new CO2 to the carbon cycle. Each type of biomass must be evaluated for its environmental and social impact in order to determine if it is really advancing sustainability and reducing environmental impacts. For example, cutting down large swaths of forests just for energy production is not a sustainable option because our energy demands are so great that we would quickly deforest the world, destroying critical habitat.
Burning Wood
Using wood, and charcoal made from wood, for heating and cooking can replace fossil fuels and may result in lower CO2 emissions. If wood is harvested from forests or woodlots that have to be thinned or from urban trees that fall down or needed be cut down anyway, then using it for biomass does not impact those ecosystems. However, wood smoke contains harmful pollutants like carbon monoxide and particulate matter. For home heating, it is most efficient and least polluting when using a modern wood stove or fireplace insert that are designed to release small amounts of particulates. However, in places where wood and charcoal are major cooking and heating fuels such as in undeveloped countries, the wood may be harvested faster than trees can grow resulting in deforestation.
Biomass can be used in small power plants. For instance, Colgate College has had a wood-burning boiler since the mid-1980’s and in one year it processed approximately 20,000 tons of locally and sustainably harvested wood chips, the equivalent of 1.17 million gallons (4.43 million liters) of fuel oil, avoiding 13,757 tons of emissions and saving the university over \$1.8 million in heating costs. The University’s steam-generating wood-burning facility now satisfies more than 75% of the campus’s heat and domestic hot water needs.
Landfill Gas or Biogas
Landfill gas (biogas) is a sort of man-made “biogenic” gas as discussed above. Methane is formed as a result of biological processes in sewage treatment plants, waste landfills, anaerobic composting, and livestock manure management systems. This gas is captured and burned to produce heat or electricity. The electricity may replace electricity produced by burning fossil fuels and result in a net reduction in CO2 emissions. The only environmental impacts are from the construction of the plant itself, similar to that of a natural gas plant.
Bioethanol and Biodiesel
Bioethanol and biodiesel are liquid biofuels manufactured from plants, typically crops. Bioethanol can be easily fermented from sugar cane juice, as is done in Brazil. Bioethanol can also be fermented from broken down corn starch, as is mainly done in the United States. The economic and social effects of growing plants for fuels need to be considered, since the land, fertilizers, and energy used to grow biofuel crops could be used to grow food crops instead. The competition of land for fuel vs. food can increase the price of food, which has a negative effect on society. It could also decrease the food supply increasing malnutrition and starvation globally. Also, in some parts of the world, large areas of natural vegetation and forests have been cut down to grow sugar cane for bioethanol and soybeans and palm-oil trees to make biodiesel. This is not sustainable land use. Biofuels may be derived from parts of plants not used for food, such as stalks, thus reducing that impact. Biodiesel can be made from used vegetable oil and has been produced on a very local basis. Compared to petroleum diesel, biodiesel combustion produces less sulfur oxides, particulate matter, carbon monoxide, and unburned and other hydrocarbons, but it produces more nitrogen oxide.
Liquid biofuels typically replace petroleum and are used to power vehicles. Although ethanol-gasoline mixtures burn cleaner than pure gasoline, they also are more volatile and thus have higher “evaporative emissions” from fuel tanks and dispensing equipment. These emissions contribute to the formation of harmful, ground level ozone and smog. Gasoline requires extra processing to reduce evaporative emissions before it is blended with ethanol.
Geothermal Energy
Five percent of the United States’ renewable energy comes from geothermal energy: using the heat of Earth’s subsurface to provide endless energy. Geothermal systems utilize a heat-exchange system that runs in the subsurface about 20 feet (5 meters) below the surface where the ground is at a constant temperature. The system uses the earth as a heat source (in the winter) or a heat sink (in the summer). This reduces the energy consumption required to generate heat from gas, steam, hot water, and conventional electric air-conditioning systems.The environmental impact of geothermal energy depends on how it is being used. Direct use and heating applications have almost no negative impact on the environment.
Geothermal power plants do not burn fuel to generate electricity so their emission levels are very low. They release less than 1% of the carbon dioxide emissions of a fossil fuel plant. Geothermal plants use scrubber systems to clean the air of hydrogen sulfide that is naturally found in the steam and hot water. They emit 97% less acid rain-causing sulfur compounds than are emitted by fossil fuel plants. After the steam and water from a geothermal reservoir have been used, they are injected back into the earth.
Solar Energy
Solar power converts the energy of light into electrical energy and has minimal impact on the environment, depending on where it is placed. In 2009, 1% of the renewable energy generated in the United States was from solar power (1646 MW) out of the 8% of the total electricity generation that was from renewable sources. The manufacturing of photovoltaic (PV) cells generates some hazardous waste from the chemicals and solvents used in processing. Often solar arrays are placed on roofs of buildings or over parking lots or integrated into construction in other ways. However, large systems may be placed on land and particularly in deserts where those fragile ecosystems could be damaged if care is not taken. Some solar thermal systems use potentially hazardous fluids (to transfer heat) that require proper handling and disposal. Concentrated solar systems may need to be cleaned regularly with water, which is also needed for cooling the turbine-generator. Using water from underground wells may affect the ecosystem in some arid locations.
Wind
Wind energy is a renewable energy source that is clean and has very few environmental challenges. Wind turbines are becoming a more prominent sight across the United States, even in regions that are considered to have less wind potential. Wind turbines (often called windmills) do not release emissions that pollute the air or water (with rare exceptions), and they do not require water for cooling. The U.S. wind industry had 40,181 MW of wind power capacity installed at the end of 2010, with 5,116 MW installed in 2010 alone, providing more than 20% of installed wind power around the globe. According to the American Wind Energy Association, over 35% of all new electrical generating capacity in the United States since 2006 was due to wind, surpassed only by natural gas.
Because a wind turbine has a small physical footprint relative to the amount of electricity it produces, many wind farms are located on crop and pasture land. They contribute to economic sustainability by providing extra income to farmers and ranchers, allowing them to stay in business and keep their property from being developed for other uses. For example, energy can be produced by installing wind turbines in the Appalachian mountains of the United States instead of engaging in mountain top removal for coal mining. Offshore wind turbines on lakes or the ocean may have smaller environmental impacts than turbines on land.
Wind turbines do have a few environmental challenges. There are aesthetic concerns to some people when they see them on the landscape. A few wind turbines have caught on fire, and some have leaked lubricating fluids, though this is relatively rare. Some people do not like the sound that wind turbine blades make. Turbines have been found to cause bird and bat deaths particularly if they are located along their migratory path. This is of particular concern if these are threatened or endangered species. There are ways to mitigate that impact and it is currently being researched. There are some small impacts from the construction of wind projects or farms, such as the construction of service roads, the production of the turbines themselves, and the concrete for the foundations. However, overall analysis has found that turbines make much more energy than the amount used to make and install them.
Interest in Renewable Energy
Strong interest in renewable energy in the modern era arose in response to the oil shocks of the 1970s, when the Organization of Petroleum Exporting Countries (OPEC) imposed oil embargos and raised prices in pursuit of geopolitical objectives. The shortages of oil, especially gasoline for transportation, and the eventual rise in the price of oil by a factor of approximately 10 from 1973 to 1981 disrupted the social and economic operation of many developed countries and emphasized their precarious dependence on foreign energy supplies. The reaction in the United States was a shift away from oil and gas to plentiful domestic coal for electricity production and the imposition of fuel economy standards for vehicles to reduce consumption of oil for transportation. Other developed countries without large fossil reserves, such as France and Japan, chose to emphasize nuclear (France to the 80% level and Japan to 30%) or to develop domestic renewable resources such as hydropower and wind (Scandinavia), geothermal (Iceland), solar, biomass and for electricity and heat. As oil prices collapsed in the late 1980s interest in renewables, such as wind and solar that faced significant technical and cost barriers, declined in many countries, while other renewables, such as hydropower and biomass, continued to experience growth.
The increasing price and volatility of oil prices since 1998, and the increasing dependence of many developed countries on foreign oil (60% of United States and 97% of Japanese oil was imported in 2008) spurred renewed interest in renewable alternatives to ensure energy security. A new concern, not known in previous oil crises, added further motivation: our knowledge of the emission of greenhouse gases and their growing contribution to climate change. An additional economic motivation, the high cost of foreign oil payments to supplier countries (approximately \$350 billion/year for the United States at 2011 prices), grew increasingly important as developed countries struggled to recover from the economic recession of 2008. These energy security, carbon emission, and climate change concerns drive significant increases in fuel economy standards, fuel switching of transportation from uncertain and volatile foreign oil to domestic electricity and biofuels, and production of electricity from low carbon sources.
Physical Origin of Renewable Energy
Although renewable energy is often classified as hydro, solar, wind, biomass, geothermal, wave and tide, all forms of renewable energy arise from only three sources: the light of the sun, the heat of the earth’s crust, and the gravitational attraction of the moon and sun. Sunlight provides by far the largest contribution to renewable energy. The sun provides the heat that drives the weather, including the formation of high- and low-pressure areas in the atmosphere that make wind. The sun also generates the heat required for vaporization of ocean water that ultimately falls over land creating rivers that drive hydropower, and the sun is the energy source for photosynthesis, which creates biomass. Solar energy can be directly captured for water and space heating, for driving conventional turbines that generate electricity, and as excitation energy for electrons in semiconductors that drive photovoltaics. The sun is also responsible for the energy of fossil fuels, created from the organic remains of plants and sea organisms compressed and heated in the absence of oxygen in the earth’s crust for tens to hundreds of millions of years. The time scale for fossil fuel regeneration, however, is too long to consider them renewable in human terms.
Geothermal energy originates from heat rising to the surface from earth’s molten iron core created during the formation and compression of the early earth as well as from heat produced continuously by radioactive decay of uranium, thorium and potassium in the earth’s crust. Tidal energy arises from the gravitational attraction of the moon and the more distant sun on the earth’s oceans, combined with rotation of the earth. These three sources – sunlight, the heat trapped in earth’s core and continuously generated in its crust, and gravitational force of the moon and sun on the oceans – account for all renewable energy.
Capacity and Geographical Distribution
Although renewable energies such as wind and solar have experienced strong growth in recent years, they still make up a small fraction of the world’s total energy needs. The largest share comes from traditional biomass, mostly fuel wood gathered in traditional societies for household cooking and heating, often without regard for sustainable replacement. Hydropower is the next largest contributor, an established technology that experienced significant growth in the 20th Century. The other contributors are more recent and smaller in contribution: water and space heating by biomass combustion or harvesting solar and geothermal heat, biofuels derived from corn or sugar cane, and electricity generated from wind, solar and geothermal energy. Wind and solar electricity, despite their large capacity and significant recent growth, still contributed less than 1% of total energy in 2008.
The potential of renewable energy resources varies dramatically. Solar energy is by far the most plentiful, delivered to the surface of the earth at a rate of 120,000 Terawatts (TW), compared to the global human use of 15 TW. To put this in perspective, covering 100×100 km2 of desert with 10% efficient solar cells would produce 0.29 TW of power, about 12% of the global human demand for electricity. To supply all of the earth’s electricity needs (2.4 TW in 2007) would require 7.5 such squares, an area about the size of Panama (0.05% of the earth’s total land area). The world’s conventional oil reserves are estimated at three trillion barrels, including all the oil that has already been recovered and that remain for future recovery. The solar energy equivalent of these oil reserves is delivered to the earth by the sun in 1.5 days.
The geographical distribution of useable renewable energy is quite uneven. Sunlight, often thought to be relatively evenly distributed, is concentrated in deserts where cloud cover is rare. Winds are up to 50% stronger and steadier offshore than on land. Hydroelectric potential is concentrated in mountainous regions with high rainfall and snowmelt. Biomass requires available land that does not compete with food production, and adequate sun and rain to support growth. | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/11%3A_Conventional__Sustainable_Energy/11.03%3A_Renewable_Energy_Sources.txt |
Summary
We derive our energy from a multitude of resources that have varying environmental challenges related to air and water pollution, land use, carbon dioxide emissions, resource extraction and supply, as well as related safety and health issues. Each resource needs to be evaluated within the sustainability paradigm. Coal (45 percent) and gas (23 percent) are the two primary fossil fuels for electricity production in the United States. Coal combustion produces nearly twice the carbon emissions of gas combustion. Increasing public opinion and regulatory pressure to lower carbon emissions are shifting electricity generation toward gas and away from coal. Oil for transportation and electricity generation are the two biggest users of primary energy and producers of carbon emissions in the United States. Transportation is almost completely dependent on oil and internal combustion engines for its energy. The concentration of oil in a few regions of the world creates a transportation energy security issue. Nuclear electricity offers the sustainable benefit of low carbon electricity at the cost of storing spent fuel out of the environment for up to hundreds of thousands of years. Reprocessing spent fuel offers the advantages of higher energy efficiency and reduced spent fuel storage requirements with the disadvantage of higher risk of weapons proliferation through diversion of the reprocessed fuel stream.
Strong interest in renewable energy arose in the 1970s as a response to the shortage and high price of imported oil, which disrupted the orderly operation of the economies and societies of many developed countries. Today there are new motivations, including the realization that growing greenhouse gas emission accelerates global warming and threatens climate change, the growing dependence of many countries on foreign oil, and the economic drain of foreign oil payments that slow economic growth and job creation. There are three ultimate sources of all renewable and fossil energies: sunlight, the heat in the earth’s core and crust, and the gravitational pull of the moon and sun on the oceans. Renewable energies are relatively recently developed and typically operate at lower efficiencies than mature fossil technologies. Like early fossil technologies, however, renewables can be expected to improve their efficiency and lower their cost over time, promoting their economic competitiveness and widespread deployment. The future deployment of renewable energies depends on many factors, including the availability of suitable land, the technological cost of conversion to electricity or other uses, the costs of competing energy technologies, and the future need for energy.
Review Questions
1. Which one of the following is not a renewable source of energy?
1. Nuclear
2. Wind
3. Solar
4. Hydropower
5. Geothermal
2. Coal, oil, and natural gas are created _______ and contain the remains of__________.
1. over millions of years; algae and plants
2. over millions of years; dinosaurs and other animals
3. over hundreds of years; algae and plants
4. over hundreds of years; dinosaurs and other animals
5. instantaneously; comet fragments
3. Which one of the following is a consortium of oil-producing countries that hold a significant portion of the world’s oil reserves (and thus influence global oil prices)?
1. UAE
2. OPEC
3. UN
4. CITES
5. UNESCO
4. About 44% of the electricity in the US is produced from _________. It produces about twice as much CO2 as an equivalent amount of _______.
1. Burning natural gas; coal
2. Hydropower; solar
3. Natural gas; Geothermal
4. Hydropower; geothermal
5. Burning coal; natural gas
5. Which one of the following is not true regarding nuclear power?
1. Energy is captured from the radioactive decay of elements
2. Nuclear power is considered an alternative fuel
3. Radioactive wastes must be stored 2-5 years before disposal
4. No CO2 is directly produced in nuclear power plants
5. Nuclear power is used to produce electricity
6. Which one of the following directly produces CO2 but is considered carbon neutral?
1. Wind
2. Biodiesel
3. Oil
4. Coal
5. Hydropower
7. The original source of energy that powers both wind energy and hydropower is…
1. Precipitation
2. Rotation of the Earth
3. The sun
4. Gravity
5. Radioactive decay within the Earth’s mantle
8. Burning sawdust that is leftover from lumber production and using it to generate electricity would be an example of which one of the following?
1. Municipal solid waste
2. Biofuel
3. Biogas
4. Bioethanol
5. Biofission
9. In the process of fracking, how is gas and oil extracted?
1. Layers of earth are stripped away from the surface, exposing the fossil fuels
2. Mining tunnels are created and the fossil fuels are extracted by teams working below ground
3. Ocean sediments are mined and the fossil fuels are chemically extracted
4. High-pressure fluids are injected underground to force out the fossil fuels
5. Offshore drilling pads tap into pre-existing cracks in the Earth’s crust
10. What fundamental similarity is shared between the following energy sources: biogas and municipal solid waste?
1. Both burn waste to generate CO2, which itself is burned to create electricity
2. Both chemically transform waste into oil
3. Both trap the heat generated from decaying waste and use it to generate energy
4. Both rely on the generation and combustion of methane
5. Both produce no CO2
See Appendix for answers
Attributions
EEA. (2013). Combined heat and power. Retrieved from www.eea.europa.eu/data-and-maps/indic ators/combined-heat-and-power-chp-1. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from original.
Theis, T. & Tomkin, J. (Eds.). (2015). Sustainability: A comprehensive foundation. Retrieved from http://cnx.org/contents/[email protected]. Available under Creative Commons Attribution 4.0 International License. (CC BY 4.0). Modified from original.
Page attribution: Essentials of Environmental Science by Kamala Doršner is licensed under CC BY 4.0. Modified from the original by Matthew R. Fisher. “Review Questions” is licensed under CC BY 4.0 by Matthew R. Fisher.
12: Appendix
Answer Key for End-of-Chapter Review Questions
Chapter 1
#1. A #2. D #3. E #4. B #5. A #6. C #7. C #8. A #9. B #10. B
Chapter 2
#1. B #2. B #3. C #4. B #5. C #6. D #7. A #8. D #9. A #10. B
Chapter 3
#1. C #2. A #3. A #4. D #5. C #6. A #7. D #8. A #9. E #10. A
Chapter 4
#1. D #2. B #3. A #4. A #5. B #6. A #7. B #8. B #9. C #10. A
Chapter 5
#1. E #2. D #3. C #4. D #5. E #6. B #7. B #8. C #9. B #10. A
Chapter 6
#1. C #2. C #3. B #4. B #5. D #6. A #7. A #8. E #9. C #10. D
Chapter 7
#1. A #2. E #3. A #4. A #5. E #6. A #7. B #8. C #9. A #10. D
Chapter 8
#1. D #2. C #3. A #4. D #5. A
Chapter 9
#1. D #2. B #3. A #4. B #5. A #6. C #7. E #8. E #9. D #10. E
Chapter 10
#1. C #2. B #3. A #4. B #5. B #6. C #7. A #8. E #9. A #10. E
Chapter 11
#1. A #2. A #3. B #4. E #5. C #6. B #7. C #8. B #9. D #10. D
Attribution
This work is licensed under CC BY 4.0 by Matthew R. Fisher.
Thumbnail image - This work is in the Public Domain, CC0 | textbooks/bio/Ecology/Environmental_Biology_(Fisher)/11%3A_Conventional__Sustainable_Energy/11.04%3A_Chapter_Resources.txt |
The objective of this unit is to not only get you acquainted with what this book will cover but to also introduce the rigors and structure of science and how mathematics plays a crucial role in helping scientists interpret results in the most unbiased way possible. Science and mathematics are not just for scientists. A base understanding of these subjects is crucial in our very complex modern world. Without a solid understanding of how science and mathematics play a role in our everyday lives, we cannot respond appropriately in everyday situations, know how to vote on scientific laws, or hold public representatives responsible for their decisions on scientific policy.
Attributions
Rachel Schleiger (CC-BY-NC)
• 1: Environmental Science Preface
What is environmental science and what will this book cover? This preface will give you an idea of what is to come.
• 2: What Is Science, and How Does It Work?
The scientific method is the process of objectively gathering information about the natural world. Science is more than just a body of knowledge, science provides a means to evaluate and create new knowledge without bias. Scientists use objective evidence over subjective evidence, to reach sound and logical conclusions. An objective observation is without personal bias and the same by all individuals.
• 3: Math Blast- An Overview of Essential Mathematics Used in Science
This section introduces essential terms used in mathematics/statistics as a part of the scientific method.
Thumbnail image - "Scientific method" by Thebiologyprimer is in the Public Domain, CC0
01: Introduction
What is Environmental Science?
Environmental science is the dynamic, interdisciplinary study of the interaction of living and non-living parts of the environment, with special focus on the impact of humans on the environment. The study of environmental science includes circumstances, objects, or conditions by which an organism or community is surrounded and the complex ways in which they interact.
Environmental Science is Interdisciplinary
Environmental science includes disciplines in the physical sciences (like geology, soil science, physical geography, chemistry, and atmospheric sciences), life sciences (like ecology, conservation biology, restoration biology, and population biology), social sciences (like human geography, economics, law, political science, and anthropology), and humanities (philosophy, ethics). As such, environmental scientists are a diverse bunch. However, they all come together for the focus of studying and identifying past, current, and future environmental issues while also exploring solutions to the environmental issues and also considering practical needs.
Why Study Environmental Science?
The need for equitable, ethical, and sustainable use of Earth’s resources by a global population that nears the carrying capacity of the planet requires us not only to understand how human behaviors affect the environment, but also the scientific principles that govern interactions between the living and non-living. Our future depends on our ability to understand and evaluate evidence-based arguments about the environmental consequences of human actions and technologies, and to make informed decisions based on those arguments.
From global climate change to habitat loss driven by human population growth and development, Earth is becoming a different planet—right before our eyes. The global scale and rate of environmental change are beyond anything in recorded human history. Our challenge is to acquire an improved understanding of Earth’s complex environmental systems; systems characterized by interactions within and among their natural and human components that link local to global and short-term to long-term phenomena, and individual behavior to collective action. The complexity of environmental challenges demands that we all participate in finding and implementing solutions leading to long-term environmental sustainability.
The Tragedy of the Commons
In his essay, The Tragedy of the Commons, Garrett Hardin (1968) looked at what happens when humans do not limit their actions by including the land as part of their ethic. The tragedy of the commons develops in the following way: Imagine a pasture open to all (the ‘commons’). It is to be expected that each herdsman will try to keep as many cattle as possible on the commons. As rational beings, each herdsman seeks to maximize their gain. Adding more cattle increases their profit, and they do not suffer any immediate negative consequence because the commons are shared by all. The rational herdsman concludes that the only sensible course is to add another animal to their herd, and then another, and so forth. However, this same conclusion is reached by each and every rational herdsman sharing the commons. Therein lies the tragedy: each person is locked into a system that compels them to increase their herd, without limit, in a world that is limited. Eventually this leads to the ruination of the commons. In a society that believes in the freedom of the commons, freedom brings ruin to all because each person acts selfishly.
Hardin went on to apply the situation to modern commons: overgrazing of public lands, overuse of public forests and parks, depletion of fish populations in the ocean, use of rivers as a common dumping ground for sewage, and fouling the air with pollution.
The “Tragedy of the Commons” is applicable to what is arguably the most consequential environmental problem: global climate change. The atmosphere is a commons into which countries are dumping carbon dioxide from the burning of fossil fuels. Although we know that the generation of greenhouse gases will have damaging effects upon the entire globe, we continue to burn fossil fuels. As a country, the immediate benefit from the continued use of fossil fuels is seen as a positive component (because of economic growth). All countries, however, will share the negative long-term effects.
Some Indicators of Global Environmental Stress
• Forests Deforestation remains a main issue. 1 million hectares of forest were lost every year in the decade 1980-1990. The largest losses of forest area are taking place in the tropical moist deciduous forests, the zone best suited to human settlement and agriculture. Recent estimates suggest that nearly two-thirds of tropical deforestation is due to farmers clearing land for agriculture. There is increasing concern about the decline in forest quality associated with intensive use of forests and unregulated access.
• Soil — As much as 10% of the earth’s vegetated surface is now at least moderately degraded. Trends in soil quality and management of irrigated land raise serious questions about longer-term sustainability. It is estimated that about 20% of the world’s 250 million hectares of irrigated land are already degraded to the point where crop production is seriously reduced.
• Fresh water — Some 20% of the world’s population lacks access to safe water and 50% lacks access to safe sanitation. If current trends in water use persist, two-thirds of the world’s population could be living in countries experiencing moderate or high water stress by 2025.
• Marine fisheries — 25% of the world’s marine fisheries are being fished at their maximum level of productivity and 35% are overfished (yields are declining). In order to maintain current per capita consumption of fish, global fish harvests must be increased; much of the increase might come through aquaculture which is a known source of water pollution, wetland loss and mangrove swamp destruction.
• Biodiversity — Biodiversity is increasingly coming under threat from development, which destroys or degrades natural habitats, and from pollution from a variety of sources. The first comprehensive global assessment of biodiversity put the total number of species at close to 14 million and found that between 1% and 11% of the world’s species may be threatened by extinction every decade. Coastal ecosystems, which host a very large proportion of marine species, are at great risk with perhaps one-third of the world’s coasts at high potential risk of degradation and another 17% at moderate risk.
• Atmosphere — The Intergovernmental Panel on Climate Change has established that human activities are having a discernible influence on global climate. CO2 emissions in most industrialized countries have risen during the past few years and countries generally failed to stabilize their greenhouse gas emissions at 1990 levels by 2000 as required by the Climate Change convention.
• Toxic chemicals — About 100,000 chemicals are now in commercial use and their potential impacts on human health and ecological function represent largely unknown risks. Persistent organic pollutants are now so widely distributed by air and ocean currents that they are found in the tissues of people and wildlife everywhere; they are of particular concern because of their high levels of toxicity and persistence in the environment.
• Hazardous wastes — Pollution from heavy metals, especially from their use in industry and mining, is also creating serious health consequences in many parts of the world. Incidents and accidents involving uncontrolled radioactive sources continue to increase, and particular risks are posed by the legacy of contaminated areas left from military activities involving nuclear materials.
• Waste — Domestic and industrial waste production continues to increase in both absolute and per capita terms, worldwide. In the developed world, per capita waste generation has increased threefold over the past 20 years; in developing countries, it is highly likely that waste generation will double during the next decade. The level of awareness regarding the health and environmental impacts of inadequate waste disposal remains rather poor; poor sanitation and waste management infrastructure is still one of the principal causes of death and disability for the urban poor.
Attributions
Modified by Melissa Ha and Rachel Schleiger from The Earth, Humans, & the EnvironmentEnvironment and Sustainability, and Environmental Ethics from Environmental Biology by Matthew R. Fisher (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.01%3A_Environmental_Science_Preface.txt |
Chapter Hook
It’s 1935, and you have another sore throat, the second time this month. After a doctor appointment you are referred to an otolaryngologist (ear, nose, and throat doctor). After a short appointment you are scheduled for a tonsillectomy the next day. The majority of children during this time period had their tonsils removed. In fact, the history of tonsillectomies goes back 2000 years! Medical professionals knew that taking out tonsils had benefits for their patients, mainly decreased throat infections and improved sleep due to obstructive sleep apnea. However, there was not extensive research performed on long term risks in addition to the surgical risks. By the 1970s tonsillectomy recommendations significantly decreased after research confirmed long term side effects for some patients. This is one of many examples where procedures and policies were created without appropriate evidence utilizing the scientific method, the backbone of science.
Figure \(\PageIndex{a}\) Anatomy of normal versus abnormal tonsils and throat. Image by BruceBlaus (licensed under CC-BY-3.0)
Attribution
Chapter Hook by Rachel Schleiger (CC-BY-NC)
Page summary modified by Melissa Ha from What is Science? from An Introduction to Geology by Chris Johnson et al. (licensed under CC-BY-NC-SA)
• 2.1: What is Science?
The process of science allows us to learn about the natural world in an objective manner, which is based on fact rather than opinion. Both inductive and deductive reasoning are important in the scientific method. Inductive reasoning is used in descriptive science and in generating hypotheses while deductive reasoning is key to hypothesis testing. Hypotheses and the predictions that stem from them must be falsifiable.
• 2.2: The Scientific Method
This section reviews the scientific method and discusses why it is so important to the the process of science. The main steps of the scientific method are observation, question, hypothesis, prediction, experimental design, results, and conclusion.
• 2.3: Scientific Papers
This section discusses what peer review is and how scientific papers are structured.
• 2.4: Basic and Applied Science
This section discusses the differences between basic and applied sciences. The goal of basic science is simply to expand knowledge. Applied scientist more specifically focuses on solving modern problems.
• 2.5: Data Dive- Tonsillectomy Trends
• 2.6: Review
1.02: What Is Science and How Does It Work
Like other natural sciences, environmental science gathers knowledge about the natural world. Science is more than just a body of knowledge, science provides a means to evaluate and create new knowledge. The methods of science include careful observation, record keeping, logical and mathematical reasoning, experimentation, and submitting conclusions to the scrutiny of others. Science also requires considerable imagination and creativity; a well-designed experiment is commonly described as elegant or beautiful. Science has considerable practical implications and some science is dedicated to practical applications, such as the prevention of disease (figure \(\PageIndex{a}\)). Other science proceeds largely motivated by curiosity. Whatever its goal, there is no doubt that science has transformed human existence and will continue to do so.
There are areas of knowledge, however, to which the methods of science cannot be applied. These include such things as morality, aesthetics, or spirituality. Science cannot investigate these areas because they are outside the realm of material phenomena, the phenomena of matter and energy, and cannot be observed and measured.
Evidence, Measurements, and Observations
Scientists use objective evidence over subjective evidence, to reach sound and logical conclusions. An objective observation is without personal bias and the same by all individuals. Bias refers to favoring one thing over another, and it can lead to inaccurate results. Humans are biased by nature, so they cannot be completely objective; the goal is to be as unbiased as possible. A subjective observation is based on a person’s feelings and beliefs and is unique to that individual (figure \(\PageIndex{b}\)).
Another way scientists avoid bias is by using quantitative over qualitative measurements whenever possible. A quantitative measurement is expressed with a specific numerical value. Qualitative observations are general or relative descriptions. For example, describing a rock as red or heavy is a qualitative observation. Determining a rock’s color by measuring wavelengths of reflected light or its density by measuring the proportions of minerals it contains is quantitative. Numerical values are more precise than general descriptions, and they can be analyzed using statistical calculations. This is why quantitative measurements are much more useful to scientists than qualitative observations.
Inductive and Deductive Reasoning
One thing is common to all forms of science: an ultimate goal to know. Curiosity and inquiry are the driving forces for the development of science. Scientists seek to understand the world and the way it operates. Two methods of logical thinking are used: inductive reasoning and deductive reasoning.
Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. This type of reasoning is common in descriptive science. A life scientist such as a biologist makes observations and records them. The raw data can be supplemented with drawings, pictures, photos, or videos. From many observations, the scientist can infer conclusions (inductions) based on evidence. Inductive reasoning involves formulating generalizations inferred from careful observation and the analysis of a large amount of data. Surveying land use (which areas are forested, agricultural, urban, etc.) across the United States and then concluding that forested areas are concentrated in the West is an example of descriptive science.
In deductive reasoning, the pattern of thinking moves in the opposite direction as compared to inductive reasoning. Deductive reasoning is a form of logical thinking that uses a general principle or law to forecast specific results. From those general principles, a scientist can extrapolate and predict the specific results that would be valid as long as the general principles are valid. For example, a prediction would be that if the climate is becoming warmer in a region, the distribution of plants and animals should change. Comparisons have been made between distributions in the past and the present, and the many changes that have been found are consistent with a warming climate. Finding the change in distribution is evidence that the climate change conclusion is a valid one. Deductive reasoning, or deduction, is the type of logic used in hypothesis-based science (see below).
To summarize, inductive reasoning moves from the specific (an observation) to general (conclusion), and deductive reasoning moves from the general (a hypothesis or principle) to the specific (results).
Both types of logical thinking are related to the two main pathways of scientific study: descriptive science and hypothesis-based science. Descriptive (or discovery) science aims to observe, explore, and discover, while hypothesis-based science begins with a specific question or problem and a potential answer or solution that can be tested. The boundary between these two forms of study is often blurred, because most scientific endeavors combine both approaches. Observations lead to questions, questions lead to forming a hypothesis as a possible answer to those questions, and then the hypothesis is tested. Thus, descriptive science and hypothesis-based science are in continuous dialogue.
Science is also a Social Process
Scientists share their ideas with peers at conferences, seeking guidance and feedback (figure \(\PageIndex{c}\)). Research papers and data submitted for publication are rigorously reviewed by qualified peers, scientists who are experts in the same field. The scientific review process aims to weed out misinformation, invalid research results, and wild speculation. Thus, it is slow, cautious, and conservative. Scientists tend to wait until a hypothesis is supported by an overwhelming amount of evidence from many independent researchers before accepting it as a scientific theory.
Characteristics of Scientists
There is nothing mysterious or even particularly unusual about the things that scientists do. There are many ways to work on scientific problems. They all require common sense. Beyond that, they all display certain features that are especially - but not uniquely - characteristic of science.
• Skepticism — Good scientists use highly-critical standards in the judging of evidence. They approach data, claims, and theories (ideally, even their own!) with healthy doses of skepticism.
• Tolerance of uncertainty — Scientists often work for years - sometimes for an entire career - trying to understand one scientific problem. This often involves finding facts that, for a time, fail to fit into any coherent pattern and that even may support mutually contradictory explanations. Sometimes, as one listens to scientists vigorously defending their views, their confidence seems absolute. But deep in their hearts, they know that their views are based on probabilities and that a new piece of evidence may turn up at any time and force a major shift in their views.
• Although they certainly have no monopoly on hard work, their willingness to work long hours and years pursuing a problem is the mark of all good scientists. For science is hard work.
Attribution
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.02%3A_What_Is_Science_and_How_Does_It_Work/1.2.01%3A_What_is_Science.txt |
The scientific method is a process of research with defined steps that include data collection and careful observation.
Observation
Scientific advances begin with observations. This involves noticing a pattern, either directly or indirectly from the literature. An example of a direct observation is noticing that there have been a lot of toads in your yard ever since you turned on the sprinklers, where as an indirect observation would be reading a scientific study reporting high densities of toads in urban areas with watered lawns.
During the Vietnam War (figure \(\PageIndex{a}\)), press reports from North Vietnam documented an increasing rate of birth defects. While this credibility of this information was initially questioned by the U.S., it evoked questions about what could be causing these birth defects. Furthermore, increased incidence of certain cancers and other diseases later emerged in Vietnam veterans who had returned to the U.S. This leads us to the next step of the scientific method, the question.
Question
The question step of the scientific method is simply asking, what explains the observed pattern? Multiple questions can stem from a single observation. Scientists and the public began to ask, what is causing the birth defects in Vietnam and diseases in Vietnam veterans? Could it be associated with the widespread military use of the herbicide Agent Orange to clear the forests (figure \(\PageIndex{b-c}\)), which helped identify enemies more easily?
Hypothesis and Prediction
The hypothesis is the expected answer to the question. The best hypotheses state the proposed direction of the effect (increases, decreases, etc.) and explain why the hypothesis could be true.
• OK hypothesis: Agent Orange influences rates of birth defects and disease.
• Better hypothesis: Agent Orange increases the incidence of birth defects and disease.
• Best hypothesis: Agent Orange increases the incidence of birth defects and disease because these health problems have been frequently reported by individuals exposed to this herbicide.
If two or more hypotheses meet this standard, the simpler one is preferred.
Predictions stem from the hypothesis. The prediction explains what results would support hypothesis. The prediction is more specific than the hypothesis because it references the details of the experiment. For example, "If Agent Orange causes health problems, then mice experimentally exposed to TCDD, a contaminant of Agent Orange, during development will have more frequent birth defects than control mice" (figure \(\PageIndex{d}\)).
Hypotheses and predictions must be testable to ensure that it is valid. For example, a hypothesis that depends on what a bear thinks is not testable, because it can never be known what a bear thinks. It should also be falsifiable, meaning that they have the capacity to be tested and demonstrated to be untrue. An example of an unfalsifiable hypothesis is “Botticelli’s Birth of Venus is beautiful.” There is no experiment that might show this statement to be false. To test a hypothesis, a researcher will conduct one or more experiments designed to eliminate one or more of the hypotheses. This is important. A hypothesis can be disproven, or eliminated, but it can never be proven. Science does not deal in proofs like mathematics. If an experiment fails to disprove a hypothesis, then we find support for that explanation, but this is not to say that down the road a better explanation will not be found, or a more carefully designed experiment will be found to falsify the hypothesis.
Hypotheses are tentative explanations and are different from scientific theories. A scientific theory is a widely-accepted, thoroughly tested and confirmed explanation for a set of observations or phenomena. Scientific theory is the foundation of scientific knowledge. In addition, in many scientific disciplines (less so in biology) there are scientific laws, often expressed in mathematical formulas, which describe how elements of nature will behave under certain specific conditions, but they do not offer explanations for why they occur.
Design an Experiment
Next, a scientific study (experiment) is planned to test the hypothesis and determine whether the results match the predictions. Each experiment will have one or more variables. The independent variable is what scientists hypothesize might be causing something else. In a manipulative experiment (see below), the independent variable is manipulated by the scientist. The dependent variable is the response, the variable ultimately measured in the study. Controlled variables (confounding factors) might affect the dependent variable, but they are not the focus of the study. Scientist attempt to standardize the controlled variables so that they do not influence the results. In our previous example, exposure to Agent Orange is the independent variable. It is hypothesized to cause a change in health (likelihood of having children with birth defects or developing a disease), the dependent variable. Many other things could affect health, including diet, exercise, and family history. These are the controlled variables.
There are two main types of scientific studies: experimental studies (manipulative experiments) and observational studies.
In a manipulative experiment, the independent variable is altered by the scientists, who then observe the response. In other words, the scientists apply a treatment. An example would be exposing developing mice to TCDD and comparing the rate of birth defects to a control group. The control group is group of test subjects that are as similar as possible to all other test subjects, with the exception that they don’t receive the experimental treatment (those that do receive it are known as the experimental, treatment, or test group). The purpose of the control group is to establish what the dependent variable would be under normal conditions, in the absence of the experimental treatment. It serves as a baseline to which the test group can be compared. In this example, the control group would contain mice that were not exposed to TCDD but were otherwise handled the same way as the other mice (figure \(\PageIndex{e}\))
In an observational study, scientists examine multiple samples with and without the presumed cause. An example would be monitoring the health of veterans who had varying levels of exposure to Agent Orange.
Scientific studies contain many replicates. Multiple samples ensure that any observed pattern is due to the treatment rather than naturally occurring differences between individuals. A scientific study should also be repeatable, meaning that if it is conducted again, following the same procedure, it should reproduce the same general results. Additionally, multiple studies will ultimately test the same hypothesis.
Results
Finally, the data are collected and the results are analyzed. As described in the Math Blast chapter, statistics can be used to describe the data and summarize data. They also provide a criterion for deciding whether the pattern in the data is strong enough to support the hypothesis.
The manipulative experiment in our example found that mice exposed to high levels of 2,4,5-T (a component of Agent Orange) or TCDD (a contaminant found in Agent Orange) during development had a cleft palate birth defect more frequently than control mice (figure \(\PageIndex{f}\)). Mice embryos were also more likely to die when exposed to TCDD compared to controls.
An observational study found that self-reported exposure to Agent Orange was positively correlated with incidence of multiple diseases in Korean veterans of the Vietnam War, including various cancers, diseases of the cardiovascular and nervous systems, skin diseases, and psychological disorders. Note that a positive correlation simply means that the independent and dependent variables both increase or decrease together, but further data, such as the evidence provided by manipulative experiments is needed to document a cause-and-effect relationship. (A negative correlation occurs when one variable increases as the other decreases.)
Conclusion
Lastly, scientists make a conclusion regarding whether the data support the hypothesis. In the case of Agent Orange, the data, that mice exposed to TCDD and 2,4,5-T had higher frequencies of cleft palate, matches the prediction. Additionally, veterans exposed to Agent Orange had higher rates of certain diseases, further supporting the hypothesis. We can thus accept the hypothesis that Agent Orange increases the incidence of birth defects and disease.
In practice, the scientific method is not as rigid and structured as it might first appear. Sometimes an experiment leads to conclusions that favor a change in approach; often, an experiment brings entirely new scientific questions to the puzzle. Many times, science does not operate in a linear fashion; instead, scientists continually draw inferences and make generalizations, finding patterns as their research proceeds (figure \(\PageIndex{g}\)). Even if the hypothesis was supported, scientists may still continue to test it in different ways. For example, scientists explore the impacts of Agent Orange, examining long-term health impacts as Vietnam veterans age.
Scientific findings can influence decision making. In response to evidence regarding the effect of Agent Orange on human health, compensation is now available for Vietnam veterans who were exposed to Agent Orange and develop certain diseases. The use of Agent Orange is also banned in the U.S. Finally, the U.S. has began cleaning sites in Vietnam that are still contaminated with TCDD.
Building on the Work of Others
Only rarely does a scientific discovery spring full-blown on the scene. When it does, it is likely to create a revolution in the way scientists perceive the world around them and to open up new areas of scientific investigation. Darwin's theory of evolution and Mendel's rules of inheritance are examples of such revolutionary developments. Most science, however, consists of adding another brick to an edifice that has been slowly and painstakingly constructed by prior work.
The development of a new technique often lays the foundation for rapid advances along many different scientific avenues. Just consider the advances in biology that discovery of the light microscope and, later, the electron microscope have made possible. Throughout these pages, there are many examples of experimental procedures. Each was developed to solve a particular problem. However, each was then taken up by workers in other laboratories and applied to their problems.
In a similar way, the creation of a new explanation (hypothesis) in a scientific field often stimulates workers in related fields to reexamine their own field in the light of the new ideas. Darwin's theory of evolution, for example, has had an enormous impact on virtually every subspecialty in biology as well as environmental science. To this very day, scientists in specialties as different as biochemistry and conservation biology are guided in their work by evolutionary theory (figure \(\PageIndex{g}\)).
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.02%3A_What_Is_Science_and_How_Does_It_Work/1.2.02%3A_The_Scientific_Method.txt |
This section discusses what peer review is and how scientific papers are structured.
Peer Review
Scientists must share their findings for other researchers to expand and build upon their discoveries. For this reason, an important aspect of a scientist’s work is disseminating results and communicating with peers. Scientists can share results by presenting them at a scientific meeting or conference, but this approach can reach only the limited few who are present. Instead, most scientists present their results in peer-reviewed articles that are published in scientific journals (figure \(\PageIndex{a}\)). Peer-reviewed articles are scientific papers that are reviewed, usually anonymously by a scientist’s colleagues, or peers. These colleagues are qualified individuals, often experts in the same research area, who judge whether or not the scientist’s work is suitable for publication. Peer reviewers assess experimental design, statistical analysis, presentation of data, and whether conclusions fit the results. The process of peer review helps to ensure that the research described in a scientific paper is original, significant, logical, ethical, and thorough. Scientists publish their work so other scientists can reproduce their experiments under similar or different conditions to expand on the findings. The experimental results must be consistent with the findings of other scientists.
As you review scientific information, whether in an academic setting or as part of your day-to-day life, it is important to think about the credibility of that information. You might ask yourself: has this scientific information been through the rigorous process of peer review? Are the conclusions based on available data and accepted by the larger scientific community? Scientists are inherently skeptical, especially if conclusions are not supported by evidence (and you should be too).
Structure of Scientific Papers
Scientific papers are usually divided into several sections (not necessarily in this order).
Summary or Abstract
This section includes only the essence of the other sections. It should be as brief as possible, telling the reader what the goal of the experiment was, what was found, and the significance of the findings. The abstract is often placed at the beginning of the paper rather than at its end.
Introduction
This section of the paper describes the scientific question or problem that was the subject of the investigation. The introduction also includes references to earlier reports of these and other scientists that have served as the foundation for the present work. Finally, the introduction states the hypothesis.
Materials and Methods
Here are precisely described the materials used (e.g., strains of organism, source of the reagents) and all the methods followed. The goal of this section is to give all the details necessary for workers in other laboratories to be able to repeat the experiments exactly. When many complex procedures are involved, it is acceptable to refer to earlier papers describing these methods in greater detail.
Results
Here the authors report what happened in their experiments. This report is usually supplemented with graphs, tables, and photographs.
Discussion
Here the authors point out what they think is the significance of their findings. This is the place to show that the results are compatible with certain hypotheses and less compatible, or even incompatible, with others. If the results contradict the results of similar experiments in other laboratories, the discrepancies are noted here, and an attempt may be made to reconcile the differences.
Acknowledgments
In this brief but important section, the authors give credit to those who have assisted them in the work. These usually include technicians (who may have actually performed most of the experiments!) and other scientists who donated materials for the experiments and/or gave advice about them.
Attribution
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.02%3A_What_Is_Science_and_How_Does_It_Work/1.2.03%3A_Scientific_Papers.txt |
Is it valuable to pursue science for the sake of simply gaining knowledge, or does scientific knowledge only have worth if we can apply it to solving a specific problem or bettering our lives? This question focuses on the differences between two types of science: basic science and applied science.
Basic science or “pure” science seeks to expand knowledge regardless of the short-term application of that knowledge. It is not focused on developing a product or a service of immediate public or commercial value. The immediate goal of basic science is knowledge for knowledge’s sake, though this does not mean that in the end it may not result in an application. Questions such as, "How have plants evolved to attract pollinators?" and "What factors determine which species will co-occur with each other?" fall under the scope of basic science (figure \(\PageIndex{a}\)).
In contrast, applied science aims to use science to solve real-world problems, such as improving crop yield, find a cure for a particular disease, or save animals threatened by a natural disaster. In applied science, the problem is usually defined for the researcher.
A layperson (nonscientist) may perceive applied science as “useful” and basic science as “useless”, posing the question, "What for?" to a scientist advocating knowledge acquisition. A careful look at the history of science, however, reveals that basic knowledge has resulted in many remarkable applications of great value. Many scientists think that a basic understanding of science is necessary before an application is developed; therefore, applied science relies on the results generated through basic science. Other scientists think that it is time to move on from basic science and instead to find solutions to actual problems. Both approaches are valid. It is true that there are problems that demand immediate attention; however, few solutions would be found without the help of the knowledge generated through basic science.
One example of how basic and applied science can work together to solve practical problems occurred after the discovery of DNA structure led to an understanding of the molecular mechanisms governing DNA replication. Strands of DNA, unique in every human, are found in our cells, where they provide the instructions necessary for life. During DNA replication, new copies of DNA are made, shortly before a cell divides to form new cells. Understanding the mechanisms of DNA replication (through basic science) enabled scientists to develop laboratory techniques that are now used to identify genetic diseases, pinpoint individuals who were at a crime scene, and determine paternity (all examples of applied science). Without basic science, it is unlikely that applied science would exist.
Another example of the link between basic and applied research is the Human Genome Project, a study in which each human chromosome was analyzed and mapped to determine the precise sequence of the DNA code and the exact location of each gene. (The gene is the basic unit of heredity; an individual’s complete collection of genes is his or her genome.) Other organisms have also been studied as part of this project to gain a better understanding of human chromosomes. The Human Genome Project (figure \(\PageIndex{b}\)) relied on basic research carried out with non-human organisms and, later, with the human genome. An important end goal eventually became using the data for applied research seeking cures for genetic diseases.
The discovery of penicillin, the first antibiotic, also originated in basic science. The mold Penicillium (figure \(\PageIndex{c}\)) contaminated petri dishes of bacteria and unexpectedly inhibited their growth. Read more about The Real Story behind Penicillin.
Ecological modeling, which is closely intertwined with the field of environmental science, is another example in which applied science closely relies on basic science. Ecological models are complex equations through which computers can predict the outcome of different decisions or scenarios based on existing data. For example, a forest manager might use a model to determine which pattern of tree removal will promote forest health and produce a steady, sustainable supply of timber. The data used to create the ecological model are collected through a combination of basic and applied studies.
Attribution
Modified by Melissa Ha from The Process of Science from Environmental Biology by Matthew R. Fisher (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.02%3A_What_Is_Science_and_How_Does_It_Work/1.2.04%3A_Basic_and_Applied_Science.txt |
Overview:
Tonsils (specifically the palatine tonsils) are a pair of soft tissue masses that vary in size from person to person, located adjacent to the throat (pharynx). Tonsils are part of the lymphatic organ system, which aids in fighting infections alongside the immune system. Like lymph nodes, tonsils can swell in response to infection. In the height of its popularity in the 1930's, tonsillectomies were viewed essential by the medical community because swelling was viewed as a result of disease rather than a physiological response to infection. Between the 1940's and 1970's evidence began accumulating that there was a correlation between tonsillectomies and contracting bulbar poliomyelitis (aka polio). In the 1970's, evidence then started accumulating that tonsillectomies didn’t significantly decrease contracting sore throats and other throat infections as originally thought. As such, tonsillectomy rates have declined as scientific method based research guided the medical community to enforce stricter policies on when the procedure is appropriate. Figure 1.2.5.a below is indicates tonsillectomy rates in Scotland for 20+ years:
Questions:
1. What kind of graph is this?
2. What is the independent (explanatory) variable and the dependent (response) variable?
3. What question(s) are the authors trying to answer with this graph?
4. Describe the trend you see for tonsillectomies and tonsillitis from 1993 to 2016.
5. In 1998 new policies were put in place restricting when a tonsillectomy could take place. How did this affect the trends after 1998?
6. What does the results of this graph make you curious about?
Raw Data For Above Graph(s)
Table \(\PageIndex{a}\) Raw data for Scotland tonsillectomy and tonsillitis trends from 1993 to 2016. Graph created by Rachel Schleiger (CC-BY-NC) modified from data in Douglas CM, Altmyer U, Cottom L, Young D, Redding P, and Clark LJ. 2019.
Years Tonsillectomy Count Tonsillitis Count
1993/1994 185 63
1994/1995 175 65
1995/1996 170 80
1996/1997 168 100
1997/1998 165 125
1998/1999 155 125
1999/2000 120 115
2000/2001 90 100
2001/2002 70 88
2002/2003 100 120
2003/2004 85 110
2004/2005 90 115
2005/2006 98 135
2006/2007 90 135
2007/2008 93 148
2008/2009 90 135
2009/2010 90 130
2010/2011 90 128
2011/2012 85 128
2012/2013 95 135
2013/2014 93 135
2014/2015 87 150
2015/2016 86 153
Attribution:
Rachel Schleiger (CC-BY-NC)
1.2.06: Review
Summary
After completing this chapter you should be able to...
• Describe the purpose of science.
• Distinguish between objective and subjective observations.
• Distinguish between quantitative measurements and qualitative observations.
• Distinguish between inductive and deductive reasoning and relate them to descriptive and hypothesis-based science.
• Outline the steps of the scientific method and explain its cyclical nature.
• Distinguish between manipulative experiments and observational studies.
• Identify the types of variables, control group, and replicates in a scientific study.
• Discuss the importance of peer review.
• Distinguish between basic and applied science and provide examples of the value of basic science.
Science is a means of systematically gathering information about the natural world. Science is based on objective observations, and following the scientific method helps scientists limit bias. Both induction and deduction are important to the scientific method. Observations lead to a question and hypothesis, an example of inductive reasoning. Making falsifiable predictions based on the hypothesis and testing them through manipulative experiments or observational studies requires deductive reasoning. Finally the results are collected and scientists conclude whether the data support the hypothesis. The scientific method is a cyclical process, in which the latter steps of the process can lead back to earlier steps.
Scientists publish their findings in scientific journals, which require peer review.
Applied science focuses on solving modern problems, but basic science simply focuses on expanding knowledge. However, the findings of basic science can later have useful applications.
Attribution
Melissa Ha (CC-BY-NC) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.02%3A_What_Is_Science_and_How_Does_It_Work/1.2.05%3A_Data_Dive-_Tonsillectomy_Trends.txt |
Chapter Hook
Are wildfires getting more destructive and deadly than ever? It is difficult to know for sure without diving into recent and historical fire data. Currently, available data supports that wildfires are worse on both counts. As such, policy makers can utilize this knowledge to create measures to better protect lives and property. Mathematics, especially statistics, is the keystone to successful application and inquiry of the scientific method. In some cases, it also provides a high level of confidence that actions taken will not likely be a waste of time or money.
Figure \(\PageIndex{a}\) A wildfire in a California forest. Image by Noah Berger (Public domain)
What is mathematics and statistics?
Mathematics is the abstract science of numbers, quantity and space. Mathematics may be studied in its own right (pure mathematics), or as it is applied to scientific disciplines such as (applied mathematics).
Statistics is a mathematical body of science that pertains to the collection, analysis, interpretation or explanation, and presentation of data, or as a branch of mathematics.
How does mathematics and statistics integrate into the scientific method?
Mathematics and statistics are vital for scientific inquiry. It is an especially imperative tool for disciplines that are inherently variable and require extensive collection of data. Ideally scientists would like to collect data from every individual in the population of interest, but this is rarely possible. As a result, scientists often must use data collected from a representative sample of individuals to draw inferences about basic biological phenomena for a population. This is where mathematics and statistics steps into the party.
What are the most important functions of statistics?
Some of the most important functions of statistics include:
• Description and summary of basic findings (Descriptive statistics).
• Testing hypotheses regarding relationships between variables so the cause and effect can begin to be understood (Inferential statistics).
• Presenting findings in an easily understood manner – misunderstandings keep science from moving forward!
Attribution
Rachel Schleiger (CC-BY-NC)
1.03: Math Blast- An Overview of Essential Mathematics Used in Science
General terms:
• Data – Systematically recorded information.
• Value – Each measurement or observation
• Variable – The object being controlled, manipulated, measured or observed. There are two main types:
• Independent (explanatory) – The variable that you think will affect what is being measured/observed.
• Dependent (response) – The variable that is being measured.
• Population – Entire set of objects to be studied.
• Parameter – Numerical characteristic of population.
• Sample – Sub-collection of objects from population.
• Statistic – Numerical characteristic of sample from population.
Example
You are a biologist who studies how monarch butterfly (Danaus plexippus) populations are affected by habitat destruction. You set up a long-term study to monitor populations in degraded, intact, and restored habitats where monarchs historically have been recorded/observed.
• Population: All monarch butterflies.
• Parameter: Not possible to collect a population worth of data for monarchs. Thus, no parameters can be calculated.
• Sample: Total monarchs observed at each field site during each year of the study.
• Statistic: Any calculations/manipulations from the field site data.
Types of statistics:
• Descriptive statistics – Are calculations to summarize trends in the data. Minimally, measures of center (averages) and spread (standard deviations) from data recorded.
• Inferential statistics – The point of inferential statistics is to take data from the sample to make inferences about the population. Calculations here test hypotheses and try to find/infer cause and effect relationships and/or correlations.
It is important to note that statistics can only be helpful if the data from the sample is representative of the population and the interpretation of the data is unbiased!
Types of data:
• Qualitative (categorical) data – Data expressed not in terms of numbers, but rather by means of a natural language description. There are two main types of qualitative data:
• Ordinal – When categories are in a particular order (ex: large, medium, small)
• Nominal – When categories have no natural ordering (ex: dog breed, color)
Graphs types used: Pie, bar
• Quantitative (numerical) data – Data expressed not by means of a natural language description, but rather in terms of numbers. There are two main types of quantitative data:
• Continuous – Numbers where any integer or fraction can be observed (ex: time, height, or weight)
• Discrete – A fixed number of outcomes is possible such that there are only whole integers possible (ex: counts)
Graphs types used: Histograms, line-graphs, scatterplots
Attribution
Rachel Schleiger (CC-BY-NC) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.03%3A_Math_Blast-_An_Overview_of_Essential_Mathematics_Used_in_Science/1.3.01%3A_Getting_down_the_basics-_What_are_the_essential_mathematical_and_statist.txt |
How do you summarize data?
Data is summarized in two main ways: summary calculations and summary visualizations
Calculations: What types of measures are used?
To be able to interpret patterns in the data, raw data must first be manipulated and summarized into two categories of measurements: Measures of central tendency and Measures of variability. These two categories of measurements encapsulate the first step of scientific inquiry, descriptive statistics.
Measures of central tendency (center) – Provides information of how data cluster around some single middle value. There are two measures of center used most often in biological inquiry:
• Mean (average) – Sum of all individual values divided by total number of values in sample/population. This is the most commonly used measure of center under symmetrical distribution and is sensitive to outliers.
• Median – The middle value when the data set is ordered in sequential rank (highest to lowest). This is commonly used when data is skewed and is resistant to outliers.
Measures of variability (spread) – Describes how spread out or dispersed the data are. There are two main measures of spread used in biological inquiry:
• Range – Quantifies the distance between the largest and smallest data values.
• Standard deviation – Quantifies the variation or dispersion from the average of a dataset. A low standard deviation indicates that the data tends to be very close to the mean; a high standard deviation indicates that the data points are spread out over a large range of values. This calculation is sensitive to outliers.
• Standard error – Quantifies the variation in the means from multiple datasets or a sample distribution of your original dataset.
Visualizing the data: How are tables and graphs used?
After all desired descriptive statistics are calculated, they are typically visually summarized into either a table or graph.
Tables:
A table is a set of data values arranged into columns and rows. Typically the columns encompass a broad data category, and the rows encompass another. Within each broad category there are subcategories that determine how many columns and rows the table consists of. Tables are used to both collect and summarize data. However, most of the time when tables are presented, they consist summarized data, not raw data. Although tables allow summarized data to be presented in an orderly manner, most people prefer to translate tables into the more powerful data visualization tool, a graph.
Graphs:
A graph is a a diagram showing the relation between variable quantities, typically of two variables, each measured along one of a pair of axes at right angles. Graphs can look like a chart or drawing. Most graphs use bars, lines, or parts of a circle to display data. However, there are sometimes when graphs are overlaid on top of maps to also display geographical location, or are even animated to be interactive.
Major graph type categories:
• Circle/Pie – A circular chart divided into slices to illustrate numerical proportion. In a pie chart, the arc length of each slice (and consequently its central angle and area), is proportional to the quantity it represents. While it is named for its resemblance to a pie which has been sliced, there are variations on the way it can be presented.
• Line – A type of chart which displays information as a series of data points called 'markers' connected by straight line segments. It is a basic type of chart common in many fields. It is similar to a scatter plot except that the measurement points are ordered (typically by their x-axis value) and joined with straight line segments. A line chart is often used to visualize a trend in data over intervals of time – a time series – thus the line is often drawn chronologically.
• Scatter plot – Is a graph in which the values of two variables are plotted along the horizontal and vertical axes, the pattern of the resulting points revealing any correlation preset. The data are displayed as a collection of points, each having the value of one variable determining the position on the horizontal axis and the value of the other variable determining the position on the vertical axis.
• Bar – A chart or graph that presents categorical data with rectangular bars with heights or lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally.
• Histogram – Is an approximate representation of the distribution of numerical data. To construct a histogram, the first step is to "bin" (or "bucket") the range of values—that is, divide the entire range of values into a series of intervals—and then count how many values fall into each interval. The bins are usually specified as consecutive, non-overlapping intervals of a variable. The bins (intervals) must be adjacent (meaning there are not spaces between them like there are in bar graphs), and are often (but not required to be) of equal size. If the bins are of equal size, a rectangle is erected over the bin with height proportional to the frequency—the number of cases in each bin.
Attribution
Rachel Schleiger (CC-BY-NC) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.03%3A_Math_Blast-_An_Overview_of_Essential_Mathematics_Used_in_Science/1.3.02%3A_Summarizing_the_data-_Descriptive_statistics.txt |
What is a hypothesis and are there different kinds?
Biological (Scientific) hypothesis: An idea that proposes a tentative explanation about a phenomenon or a narrow set of phenomena observed in the natural world. This is the backbone of all scientific inquiry! As such it is important to have a solid biological hypothesis before moving forward in the scientific method (i.e. procedures, results, discussion). After the creation of a solid biological hypothesis, it can then be simplified into a statistical hypothesis (as defined below) that will become the basis for how the data will be analyzed and interpreted.
Statistical hypotheses: After defining a strong biological hypothesis, a statistical hypothesis can be created based on what you will predict will be the measured outcome(s) (dependent variable(s)). If a study has multiple measured outcomes there can be multiple statistical hypotheses. Each statistical hypothesis will have two components (Null and Alternative).
• Null hypothesis (Ho) –This hypothesis states that there is no relationship (or no pattern) between the independent and dependent variables.
• Alternative hypothesis (H1) – This hypothesis states that there is a relationship (or is a pattern) between the independent and dependent variables.
Independent versus dependent variables: For both biological and statistical hypotheses there should be two basic variables defined:
• Independent (explanatory) variable – It is usually what phenomena you think will affect the measure you are interested in (dependent variable).
• Dependent (response) variable – A dependent variable is what you measure in the experiment and what is affected during the experiment. The dependent variable responds to (depends on) the independent variable. In a scientific experiment, you cannot have a dependent variable without an independent variable.
Example
Yellow-billed Cuckoo nests were counted during breeding season in degraded, restored, and intact riparian habitats to see overall habitat preference for nesting sites increased with habitat health.
• Scientific hypothesis: Yellow-billed Cuckoo will have habitat preferences because of habitat health/status.
• Statistical hypotheses: (Ho) There will be no differences in number of nests between habitats with different health/status. (H1) There will be more nests in restored and intact habitats compared to degraded.
• Independent variable = Habitat health/status
• Dependent variable = Number of nests counted
How do you make conclusions?
Finally, after defining the biological hypothesis, statistical hypothesis, and collecting all your data, a researcher can begin statistical analysis. A statistical test will mathematically “test” your data against the statistical hypothesis. The type of statistical test that is used depends on the type and quantity of variables in the study, as well as the question the researcher wants to ask. After computing the statistical test, the outcome will indicate which statistical hypothesis is more likely. This, in turn indicates to scientists what level of inference can be gained from the data compared to the biological hypothesis (the focus point of the study). Then a conclusion can be made based on the sample about the entire population. It is important to note that the process does not stop here. Scientists will want to continue to test this conclusion until a clear pattern emerges (or not) or to investigate similar but different questions.
Attribution
Rachel Schleiger (CC-BY-NC) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.03%3A_Math_Blast-_An_Overview_of_Essential_Mathematics_Used_in_Science/1.3.03%3A_Putting_it_all_together-_Inferential_statistics_and_hypothesis_testing.txt |
Overview
When the United States Forest Service was established in 1905 it was declared that, “Today we understand that forest fires are wholly within the control of men.” Humanity assumes time and time again that nature can be controlled, and the National Forest Service were shown how wrong their assumption was 5 years later… The Great Fire of 1910 burned about 3 million acres and killed 86 people. As a consequence of this fire, serious fire suppression policies were put in place and Smokey The Bear was slapped onto posters to represent the cause. At that point, Smokey the Bear told us, "only you can prevent forest fire," indicating that all fire is bad. It has only been in the last couple decades have these policies been questioned and the repercussions of fire suppression of them realized. Now Smokey has updated the saying to, "only you can prevent wildfire," indicating that only some types of fire are bad. The figure below illustrates the number of acres burned in California between 1987 and 2020:
Figure \(\PageIndex{a}\): Total acres burned through the years in California. Graph created by Rachel Schleiger (CC-BY-NC) modified from data collected by CalFire
Questions
1. What kind of graph is this?
2. What is the independent (explanatory) variable and the dependent (response) variable?
3. What question(s) are the authors trying to answer with this graph?
4. What trend(s) can be observed in this graph? Support your answer by referring to appropriate patterns in the graph.
5. How can we use the results of this graph to inform future fire policies/projects/etc?
6. What does the results of this graph make you curious about?
Raw Data For Above Graph(s)
Table \(\PageIndex{a}\): Raw data table of total acres burned through the years in California. Table by Rachel Schleiger (CC-BY-NC) modified from data collected by CalFire
Year Total Acres Burned
1987 873000
1988 345000
1989 173400
1990 365200
1991 44200
1992 282745
1993 309779
1994 526219
1995 209815
1996 752372
1997 283885
1998 215412
1999 1172850
2000 295026
2001 329126
2002 969890
2003 1020460
2004 264988
2005 222538
2006 736022
2007 1520362
2008 1593690
2009 422147
2010 109529
2011 168545
2012 869599
2013 601635
2014 625540
2015 893362
2016 669534
2017 1548429
2018 1975086
2019 259823
2020 4177856
Attributions
Rachel Schleiger (CC-BY-NC)
1.3.05: Review
Summary
After completing this chapter you should be able to...
• Know how mathematics and statistics fits into the scientific method
• Define the basic mathematical terms
• Know what data is what what types of data there are
• Understand the difference between descriptive and inferential statistics
• Have a general idea of what types of graphs there are to help visualize data
• Understand the difference between scientific and statistical hypotheses
• Know the process for how conclusions are made
Statistics are based on samples of data collected to be representative of a population of interest due to the impossibility of collecting a complete dataset. There are two types of statistics, descriptive (summary calculations) and inferential (hypothesis testing). Data can come from anywhere! There are two main types of data, qualitative (categorical) and quantitative (numerical).
For descriptive statistics, measures of center and spread are commonly calculated in addition to some sort of visualization of the data. The type of calculations and visualizations used depend on the study parameters and objectives.
For inferential statistics, hypotheses are clearly defined and analyses are run. There are two main types of hypotheses, scientific and statistical. The scientific proposes a potential explanation about a phenomenon while a statistical is used to predictions about measured outcomes and has two forms, null and alternative. Independent and dependent variables are used to structure the ideas outlined in the hypotheses. Once a study is performed to test the hypotheses then conclusions can be drawn based on evidence identified for each hypothesis.
Attribution
Rachel Schleiger (CC-BY-NC) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/01%3A_Introduction/1.03%3A_Math_Blast-_An_Overview_of_Essential_Mathematics_Used_in_Science/1.3.04%3A_Data_Dive-_California_Wildfires.txt |
Ecology is the study of the interactions of living organisms with their environment. One core goal of ecology is to understand the distribution and abundance of living things in the physical environment. Attainment of this goal requires the integration of scientific disciplines inside and outside of biology, such as biochemistry, physiology, evolution, biodiversity, molecular biology, geology, and climatology. Some ecological research also applies aspects of chemistry and physics, and it frequently uses mathematical models.
Why study ecology? Perhaps you are interested in learning about the natural world and how living things have adapted to the physical conditions of their environment. Or, perhaps you’re a future physician seeking to understand the connection between human health and ecology.
Humans are a part of the ecological landscape, and human health is one important part of human interaction with our physical and living environment. Lyme disease, for instance, serves as one modern-day example of the connection between our health and the natural world. More formally known as Lyme borreliosis, Lyme disease is a bacterial infection that can be transmitted to humans when they are bitten by the deer tick (Ixodes scapularis), which is the primary vector for this disease (figure \(\PageIndex{a}\)). However, not all deer ticks carry the bacteria that will cause Lyme disease in humans, and I. scapularis can have other hosts besides deer. In fact, it turns out that the probability of infection depends on the type of host upon which the tick develops: a higher proportion of ticks that live on white-footed mice carry the bacterium than do ticks that live on deer. Knowledge about the environments and population densities in which the host species is abundant would help a physician or an epidemiologist better understand how Lyme disease is transmitted and how its incidence could be reduced.
Ecologists ask questions across four levels of biological organization—organismal, population, community, and ecosystem. At the organismal level, ecologists study individual organisms and how they interact with their environments. At the population and community levels, ecologists explore, respectively, how a population of organisms changes over time and the ways in which that population interacts with other species in the community. Ecologists studying an ecosystem examine the living species (the biotic components) of the ecosystem as well as the nonliving portions (the abiotic components), such as air, water, and soil, of the environment. The objective of this unit will be to further explore these topics and how they connect to and overlap with environmental science.
Attribution
Modified by Melissa Ha and Rachel Schleiger from Ecology and the Biosphere by OpenStax (licensed under CC-BY)
• 4: Ecology Overview
Ecology can be studied at the organismal, population, community, and ecosystem levels.
• 5: Populations
Populations are interacting and interbreeding groups of individuals from the same species in a common area. The study of population ecology explores how individuals in a population are distributed over space, the factors that regulate population growth, and life history traits, which relate to lifespan and reproduction.
• 6: Communities
Communities consist of multiple interacting populations (of different species) in a common area. The study of communities focuses on how organisms interact with each other, trophic structure (food chains and food webs), and the stability of community structure.
• 7: Ecosystems
Ecosystems consist of biotic (living) and abiotic (non-living) components interacting together. Ecosystems may be freshwater, marine, or terrestrial. Biogeochemical cycles describe the movement of chemical elements through different ecosystem components. Soils are one of these components, and they are critical in determining plant distribution and abundance.
• 8: Biomes
Biomes are large geographical areas characterized by vegetation and climate, including temperature and precipitation. Temperature decreases with latitude and altitude. Precipitation is high at the equator and low at 30 degrees N and S. Terrestrial biomes are found on land, while aquatic biomes are found in water.
Thumbnail image - "Orchid mantis" is in the Public Domain
02: Ecology
Levels of Ecological Study
When a discipline such as biology is studied, it is often helpful to subdivide it into smaller, related areas. For instance, cell biologists interested in cell signaling need to understand the chemistry of the signal molecules (which are usually proteins) as well as the result of cell signaling. Ecologists interested in the factors that influence the survival of an endangered species might use mathematical models to predict how current conservation efforts affect endangered organisms. To produce a sound set of management options, a conservation biologist needs to collect accurate data, including current population size, factors affecting reproduction (like physiology and behavior), habitat requirements (such as plants and soils), and potential human influences on the endangered population and its habitat (which might be derived through studies in sociology and urban ecology). Within the discipline of ecology, researchers work at four specific levels, sometimes discretely and sometimes with overlap: organism, population, community, and ecosystem (figure \(\PageIndex{a}\)).
Organismal Ecology
Researchers studying ecology at the organismal level are interested in the adaptations that enable individuals to live in specific habitats. These adaptations can be morphological, physiological, and behavioral. For instance, the Karner blue butterfly (Lycaeides melissa samuelis) (figure \(\PageIndex{b}\)) is considered a specialist because the females preferentially oviposit (that is, lay eggs) on wild lupine. This preferential adaptation means that the Karner blue butterfly is highly dependent on the presence of wild lupine plants for its continued survival.
After hatching, the larval caterpillars emerge and spend four to six weeks feeding solely on wild lupine (figure \(\PageIndex{c}\)). The caterpillars pupate (undergo metamorphosis) and emerge as butterflies after about four weeks. The adult butterflies feed on the nectar of flowers of wild lupine and other plant species. A researcher interested in studying Karner blue butterflies at the organismal level might, in addition to asking questions about egg laying, ask questions about the butterflies’ preferred temperature (a physiological question) or the behavior of the caterpillars when they are at different larval stages (a behavioral question).
Population Ecology
A population is a group of interbreeding organisms that are members of the same species living in the same area at the same time. (Organisms that are all members of the same species are called conspecifics.) A population is identified, in part, by where it lives, and its area of population may have natural or artificial boundaries: natural boundaries might be rivers, mountains, or deserts, while examples of artificial boundaries include mowed grass, manmade structures, or roads. The study of population ecology focuses on the number of individuals in an area and how and why population size changes over time. Population ecologists are particularly interested in counting the Karner blue butterfly, for example, because it is classified as federally endangered. However, the distribution and density of this species is highly influenced by the distribution and abundance of wild lupine. Researchers might ask questions about the factors leading to the decline of wild lupine and how these affect Karner blue butterflies. For example, ecologists know that wild lupine thrives in open areas where trees and shrubs are largely absent. In natural settings, intermittent wildfires regularly remove trees and shrubs, helping to maintain the open areas that wild lupine requires. Mathematical models can be used to understand how wildfire suppression by humans has led to the decline of this important plant for the Karner blue butterfly.
Community Ecology
A biological community consists of the different species within an area, typically a three-dimensional space, and the interactions within and among these species. Community ecologists are interested in the processes driving these interactions and their consequences. Questions about conspecific interactions often focus on competition among members of the same species for a limited resource. Ecologists also study interactions among various species; members of different species are called heterospecifics. Examples of heterospecific interactions include predation, parasitism, herbivory, competition, and pollination. These interactions can have regulating effects on population sizes and can impact ecological and evolutionary processes affecting diversity.
For example, Karner blue butterfly larvae form mutualistic relationships with ants. Mutualism is a form of a long-term relationship that has coevolved between two species and from which each species benefits. For mutualism to exist between individual organisms, each species must receive some benefit from the other as a consequence of the relationship. Researchers have shown that there is an increase in the probability of survival when Karner blue butterfly larvae (caterpillars) are tended by ants. This might be because the larvae spend less time in each life stage when tended by ants, which provides an advantage for the larvae. Meanwhile, the Karner blue butterfly larvae secrete a carbohydrate-rich substance that is an important energy source for the ants. Both the Karner blue larvae and the ants benefit from their interaction.
Ecosystem Ecology
Ecosystem ecology is an extension of organismal, population, and community ecology. The ecosystem is composed of all the biotic components (living things) in an area along with the abiotic components (non-living things) of that area. Some of the abiotic components include air, water, and soil. Ecosystem biologists ask questions about how nutrients and energy are stored and how they move among organisms and the surrounding atmosphere, soil, and water.
The Karner blue butterflies and the wild lupine live in an oak-pine barren habitat. This habitat is characterized by natural disturbance and nutrient-poor soils that are low in nitrogen. The availability of nutrients is an important factor in the distribution of the plants that live in this habitat. Researchers interested in ecosystem ecology could ask questions about the importance of limited resources and the movement of resources, such as nutrients, though the biotic and abiotic portions of the ecosystem.
Career Connection: Ecologist
A career in ecology contributes to many facets of human society. Understanding ecological issues can help society meet the basic human needs of food, shelter, and health care. Ecologists can conduct their research in the laboratory and outside in natural environments (Figure \(\PageIndex{d}\)). These natural environments can be as close to home as the stream running through your campus or as far away as the hydrothermal vents at the bottom of the Pacific Ocean. Ecologists manage natural resources such as white-tailed deer populations (Odocoileus virginianus) for hunting or aspen (Populus spp.) timber stands for paper production. Ecologists also work as educators who teach children and adults at various institutions including universities, high schools, museums, and nature centers. Ecologists may also work in advisory positions assisting local, state, and federal policymakers to develop laws that are ecologically sound, or they may develop those policies and legislation themselves. To become an ecologist requires an undergraduate degree, usually in a natural science. The undergraduate degree is often followed by specialized training or an advanced degree, depending on the area of ecology selected. Ecologists should also have a broad background in the physical sciences, as well as a sound foundation in mathematics and statistics.
Attribution
Modified by Melissa Ha and Rachel Schleiger from Ecology and the Biosphere by OpenStax (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.01%3A_Ecology_Overview.txt |
Chapter Hook
Roadkill, we’ve all seen it on the roadside. It is just one very unfortunate outcomes of our extensive road networks. Roads, especially freeways and busy highways, also break apart habitats. When habitats are broken up into smaller pieces it weakens wildlife populations which need to move freely across landscapes for resources, refuge, and mates. Over long time scales, these fragmented habitats decrease species diversity, weaken species population gene pools, and can lead to extirpation (elimination of local population(s)) and extinction. As a result of numerous studies, ecologists have found one solution, wildlife crossings (aka green corridors or wildlife corridors). Wildlife crossings look like an underpass or overpass. However, they are filled with dirt and plants to look more natural. These crossings enable wildlife populations to move more freely, and safely, across landscapes all over the globe.
Populations are interacting and interbreeding groups of individuals from the same species in a common area. The study of population ecology focuses on population size and the factors that regulate population growth.
Attribution
Rachel Schleiger and Melissa Ha (CC-BY-NC)
• 5.1: Population Dispersion
Individuals in a population may be dispersed in a clumped, random, or uniform pattern.
• 5.2: Population Size
Population size is the number of individuals in a population, and population density is the number of individuals per unit area. Quadrat and mark and recapture techniques can estimate population size.
• 5.3: Population Growth and Regulation
Population ecologists make use of a variety of methods to model population dynamics. An accurate model should be able to describe the changes occurring in a population and predict future changes.
• 5.4: Life History
There are two main reproductive strategies, but most species fall somewhere in between them. K-selected species have long lifespans, high parental care, and few offspring. r-selected species have short lifespans, low parental care, and many offspring. Life tables organize life history information. Survivorship curves illustrate the relationship between mortality and age.
• 5.5: Data Dive- Wildlife Corridors
• 5.6: Review
2.02: Populations
The dispersion pattern (distribution pattern) of a population describes the arrangement of individuals within a habitat at a particular point in time, and broad categories of patterns are used to describe them. The three dispersion patterns are clumped, random, and uniform (figure \(\PageIndex{a}\)).
Individuals that are grouped into patches have a clumped distribution, or aggregated distribution. This can occur if resources are distributed unequally; for example, pipevine swallowtail caterpillars would be clumped in areas with their host plant, California pipevine. Clumped distribution may also reflect the locations of suitable microhabitats, such as an herbaceous (non-woody) plant species that only grows in the shade clustering under trees. Plants that drop their seeds straight to the ground, such as oak trees, may also have this distribution. Finally, social behavior in animals results in a clumped distribution, such as wolves hunting in a pack, a herd of elephants, or a school of fish traveling together for safety.
Populations that have a random distribution are not arranged in any particular pattern. Some individuals may be close together while others may be far apart. An example of random distribution occurs with dandelion and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in favorable environments.
Individuals that are equally spaced in the environment have a uniform distribution. Saguaro cacti are evenly spaced due to limited resources in the desert. (There is not sufficient water to support two large cacti side-by-side.) Uniform distributions can result from interference competition, when individuals take pre-emptive measures to avoid comeptition for resources. For example, some plants that secrete substances inhibiting the growth of nearby individuals (such as the release of toxic chemicals by sage plants), a phenomenon called allelopathy. Another example of interference competition occurs in territorial animal species, such as penguins that maintain a defined territory for nesting. The territorial defensive behaviors of each individual create a regular pattern of distribution of similar-sized territories and individuals within those territories. Thus, the distribution of the individuals within a population provides more information about how they interact with each other than does a simple density measurement (see Population Size and Density).
Attribution
Modified by Melissa Ha from Population Demographics and Dynamics from Environmental Biology by Matthew R. Fisher (CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.02%3A_Populations/2.2.01%3A_Population_Dispersion.txt |
Populations are dynamic entities. Their size and composition fluctuate in response to numerous factors, including seasonal and yearly changes in the environment, natural disasters such as forest fires and volcanic eruptions, and competition for resources between and within species. The study of populations is called demography.
Population Size and Density
Populations are characterized by their population size (total number of individuals) and their population density (number of individuals per unit area; figure $\PageIndex{a}$). A population may have a large number of individuals that are distributed densely, or sparsely. There are also populations with small numbers of individuals that may be dense or very sparsely distributed in a local area. Population size can affect potential for adaptation because it affects the amount of genetic variation present in the population. Density can have effects on interactions within a population such as competition for food, the ability of individuals to find a mate, and diseases spread. (Dispersion patterns can also affect these factors; for example, a solitary species with a random distribution might have difficulty finding a mate when compared to social species clumped together in groups.) Smaller organisms tend to be more densely distributed than larger organisms (figure $\PageIndex{b}$).
Estimating Population Size
The most accurate way to determine population size is to count all of the individuals within the area. However, this method is usually not logistically or economically feasible, especially when studying large areas. Thus, scientists usually study populations by sampling a representative portion of each habitat and using this sample to make inferences about the population as a whole. The methods used to sample populations to determine their size and density are typically tailored to the characteristics of the organism being studied. For immobile organisms such as plants, or for very small and slow-moving organisms, a quadrat may be used. A quadrat is a square structure that is randomly located on the ground and used to count the number of individuals that lie within its boundaries (Figure $\PageIndex{c}$). To obtain an accurate count using this method, the square must be placed at random locations within the habitat enough times to produce an accurate estimate.
For smaller mobile organisms, such as mammals, a technique called mark and recapture is often used. This method involves marking captured animals in and releasing them back into the environment to mix with the rest of the population. Later, a new sample is captured and scientists determine how many of the marked animals are in the new sample. This method assumes that the larger the population, the lower the percentage of marked organisms that will be recaptured since they will have mixed with more unmarked individuals. For example, if 80 field mice are captured, marked, and released into the forest, then a second trapping 100 field mice are captured and 20 of them are marked, the population size (N) can be determined using the following equation:
$N = \frac{(\text{number marked first catch} \times \text{total number of second catch})}{\text{number marked second catch}}$
Using our example, the equation would be:
$\frac{(80 \times 100)}{20} = 400$
These results give us an estimate of 400 total individuals in the original population. The true number usually will be a bit different from this because of chance errors and possible bias caused by the sampling methods.
The mathematical methods required to estimate population sizes can be influenced by dispersion pattern.
Attribution
Modified by Melissa Ha from Population Demographics and Dynamics from Environmental Biology by Matthew R. Fisher (CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.02%3A_Populations/2.2.02%3A_Population_Size.txt |
Population ecologists make use of a variety of methods to model population dynamics. An accurate model should be able to describe the changes occurring in a population and predict future changes. The two simplest models of population growth use deterministic equations (equations that do not account for random events) to describe the rate of change in the size of a population over time. The first of these models, exponential growth, describes populations that increase in numbers without any limits to their growth. The second model, logistic growth, introduces limits to reproductive growth that become more intense as the population size increases. Neither model adequately describes natural populations, but they provide points of comparison.
The Population Growth Rate (r )
The population growth rate (sometimes called the rate of increase or per capita growth rate, r) equals the birth rate (b) minus the death rate (d) divided by the initial population size (N0).
Another method of calculating the population growth rate involves final and initial population size (figure \(\PageIndex{a}\)). In this case, population growth rate (r) equals the final population size (N) minus the initial population size (N0) and divided by the initial population size (N0).
Doubling Time
The doubling time is how long it will take for a population to become twice its initial size. The doubling time (t) is equal to 0.69 divided by the population growth rate (r), written as a proportion.
Population ecologists sometimes round this equation and calculate doubling time using the "Rule of 70" (dividing 70 by the population growth rate, written as a percentage). To express population growth rate as a percentage, it is multiplied by 100%. Thus, the 0.69 in the original doubling time equation is also multiplied by 100. This value (69) is rounded to 70 for simplicity.
Exponential Growth
Charles Darwin, in developing his theory of natural selection, was influenced by the English clergyman Thomas Malthus. Malthus published his book in 1798 stating that populations with abundant natural resources grow very rapidly. However, they limit further growth by depleting their resources. The early pattern of accelerating population size is called exponential growth (figure \(\PageIndex{b}\)).
The best example of exponential growth in organisms is seen in bacteria. Bacteria are prokaryotes that reproduce quickly, about an hour for many species. If 1000 bacteria are placed in a large flask with an abundant supply of nutrients (so the nutrients will not become quickly depleted), the number of bacteria will have doubled from 1000 to 2000 after just an hour (figure \(\PageIndex{c}\)). In another hour, each of the 2000 bacteria will divide, producing 4000 bacteria. After the third hour, there should be 8000 bacteria in the flask. The important concept of exponential growth is that the growth rate—the number of organisms added in each reproductive generation—is itself increasing; that is, the population size is increasing at a greater and greater rate. After 24 of these cycles, the population would have increased from 1000 to more than 16 billion bacteria. When the population size, N, is plotted over time, a J-shaped growth curve is produced (figure \(\PageIndex{b}\)).
The bacteria-in-a-flask example is not truly representative of the real world where resources are usually limited. However, when a species is introduced into a new habitat that it finds suitable, it may show exponential growth for a while. In the case of the bacteria in the flask, some bacteria will die during the experiment and thus not reproduce; therefore, the growth rate is lowered from a maximal rate in which there is no mortality.
Logistic Growth
Extended exponential growth is possible only when infinite natural resources are available; this is not the case in the real world. Charles Darwin recognized this fact in his description of the “struggle for existence,” which states that individuals will compete, with members of their own or other species, for limited resources. The successful ones are more likely to survive and pass on the traits that made them successful to the next generation at a greater rate (natural selection). To model the reality of limited resources, population ecologists developed the logistic growth model.
In the real world, with its limited resources, exponential growth cannot continue indefinitely. Exponential growth may occur in environments where there are few individuals and plentiful resources, but when the number of individuals gets large enough, resources will be depleted and the growth rate will slow down. Eventually, the growth rate will plateau or level off (figure \(\PageIndex{b}\)). This population size, which is determined by the maximum population size that a particular environment can sustain, is called the carrying capacity, symbolized as K. In real populations, a growing population often overshoots its carrying capacity and the death rate increases beyond the birth rate causing the population size to decline back to the carrying capacity or below it. Most populations usually fluctuate around the carrying capacity in an undulating fashion rather than existing right at it.
A graph of logistic growth yields the S-shaped curve (figure \(\PageIndex{b}\)). It is a more realistic model of population growth than exponential growth. There are three different sections to an S-shaped curve. Initially, growth is exponential because there are few individuals and ample resources available. Then, as resources begin to become limited, the growth rate decreases. Finally, the growth rate levels off at the carrying capacity of the environment, with little change in population number over time.
While bacteria in a flask with abundant nutrients might initially exhibit exponential growth, bacteria grown with limited nutrients can exhibit logistic growth (figure \(\PageIndex{d}\)).
In some populations, there are variations to the S-shaped curve. Examples in wild populations include sheep and harbor seals (figure \(\PageIndex{e}\)). In both examples, the population size exceeds the carrying capacity for short periods of time and then falls below the carrying capacity afterwards. This fluctuation in population size continues to occur as the population oscillates around its carrying capacity. Still, even with this oscillation the logistic model is confirmed.
The logistic population growth model is not the only way that populations respond to limited resources. In some populations, growth is exponential until resources run low, wastes accumulate, or disease spreads (see limiting factors below), and the population then crashes. Thus, population growth rate (and size) may plummet rapidly instead of tapering as it approaches the carrying capacity.
Population Dynamics and Regulation
The logistic model of population growth, while valid in many natural populations and a useful model, is a simplification of real-world population dynamics. Implicit in the model is that the carrying capacity of the environment does not change, which is not the case. The carrying capacity varies annually. For example, some summers are hot and dry whereas others are cold and wet; in many areas, the carrying capacity during the winter is much lower than it is during the summer. Furthermore, some factors (growth factors) increase population growth rate while other factors (limiting factors) slow population growth. Examples of growth factors are resources like food, water, and space. Limiting factors can be classified as density-dependent or density-independent.
Density-dependent Regulation
Most density-dependent factors are biological in nature (biotic). Usually, the denser a population is, the greater its mortality rate. An example of density-dependent regulation is shown in figure \(\PageIndex{f}\) with results from a study focusing on the giant intestinal roundworm (Ascaris lumbricoides), a parasite of humans and other mammals. Denser populations of the parasite exhibited lower fecundity: they contained fewer eggs. One possible explanation for this is that females would be smaller in more dense populations (due to limited resources) and that smaller females would have fewer eggs. This hypothesis was tested and disproved in a 2009 study which showed that female weight had no influence. The actual cause of the density-dependence of fecundity in this organism is still unclear and awaiting further investigation.
Density-dependent factors include predation, parasitism, herbivory, competition, and accumulation of waste. As a population increases, its predators are able to harvest it more easily. Prey density also affects population growth rate of predators: low prey density increases the mortality of its predator because it has more difficulty locating its food sources.
Parasites are able to pass from host to host more easily as the population density of the host increases. For this reason, epidemics among humans are particularly severe in cities. In fact, for most of the period since humans began living in cities, city populations have been maintained only through continual immigration from the countryside. Not until the development of community sanitation, immunization, and other public health measures did cities avoid periodic sharp drops in population as a result of epidemics. The recurrent epidemics of the "black death" in Europe that began in the fourteenth century caused a sharp decline in population. In just three years (1348–1350), at least one-quarter of the population of Europe died from the disease (probably plague).
Similarly, herbivores can more easily spread between individual plants in a dense population. This is why strip cropping (see Sustainable Agriculture) helps control pests. An herbivore or plant pathogen may infect one row of plants, but it is less likely to spread to more distant rows of that species.
While interspecific competition occurs between different species, intraspecific competition occurs when members of the same species harm each other by using the same resources. For example, in the summer of 1980, much of southern New England was struck by an infestation of the gypsy moth (figure \(\PageIndex{g}\)). As the summer wore on, the larvae (caterpillars) pupated, the hatched adults mated, the females laid masses of eggs (each mass containing several hundred eggs) on virtually every tree in the region. In early May of 1981, the young caterpillars that hatched from these eggs began feeding and molting.
The results were dramatic: In 72 hours, a 50-ft beech tree or a 25-ft white pine tree would be completely defoliated. Large patches of forest began to take on a winter appearance with their skeletons of bare branches. In fact, the infestation was so heavy that many trees were completely defoliated before the caterpillars could complete their larval development. The result: a massive die-off of the animals; very few succeeded in completing metamorphosis. Here, then, was a dramatic example of how competition among members of one species for a finite resource - in this case, food - caused a sharp drop in population. The effect was clearly density-dependent. The lower population densities of the previous summer had permitted most of the animals to complete their life cycle.
Density-independent Regulation
Density-independent factors, typically physical or chemical in nature (abiotic), influence the mortality of a population regardless of its density, including weather (figure \(\PageIndex{h}\)), natural disasters (earthquakes, volcanoes, fires, etc.), and pollution. An individual deer may be killed in a forest fire regardless of how many deer happen to be in that area. Its chances of survival are the same whether the population density is high or low. The same holds true for cold winter weather.
In real-life situations, population regulation is very complicated and density-dependent and independent factors can interact. A dense population that is reduced in a density-independent manner by some environmental factor(s) will be able to recover differently than a sparse population. For example, a population of deer affected by a harsh winter will recover faster if there are more deer remaining to reproduce.
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.02%3A_Populations/2.2.03%3A_Population_Growth_and_Regulation.txt |
Life history characteristics, are those that relate to the survival, mortality, and reproduction of a species. Examples include birth rates, age at first reproduction, the number of offspring, and death rates. These characteristics evolve just like physical traits or behavior, leading to adaptations that affect population growth.
Reproductive Strategies
Population ecologists have hypothesized that suites of characteristics may evolve in species that lead to particular adaptations to their environments. These adaptations impact the kind of population growth their species experience. Population ecologists have described a continuum of life-history “strategies” with K-selected species on one end and r-selected species on the other (table \(\PageIndex{a}\)). K-selected species are adapted to stable, predictable environments. Populations of K-selected species tend to exist close to their carrying capacity (which is represented by the letter "K" in the equation for logistic population growth). These species tend to have larger, but fewer, offspring, contribute large amounts of resources to each offspring, and have long generation times. Elephants would be an example of a K-selected species (figure \(\PageIndex{a}\)). When a habitat becomes filled with a diverse collection of creatures competing with one another for the necessities of life, the advantage shifts to K-strategists. K-strategists have stable populations that are close to K. There is nothing to be gained from a high growth rate (r). The species will benefit most by a close adaptation to the conditions of its environment.
Table \(\PageIndex{a}\): Comparison of K- and r-selected species
Characteristics of K-selected species Characteristics of r-selected species
Mature late Mature early
Greater longevity Lower longevity
Increased parental care Decreased parental care
Strong competitors Weak competitors (strong colonizers)
Fewer offspring More offspring
Larger offspring Smaller offspring
r-selected species are adapted to unstable and unpredictable environments. They have large numbers of small offspring. Animals that are r-selected do not provide a lot of resources or parental care to offspring, and the offspring are relatively self-sufficient at birth. Examples of r-selected species are marine invertebrates such as jellyfish and plants such as the dandelion (figure \(\PageIndex{a}\)). r-strategists have short life spans and reproduce quickly, resulting in short generation times. For example, the housefly can produce 7 generations each year (each of about 120 young). Ragweed is well-adapted to exploiting its environment in a hurry - before competitors can become established. It grows rapidly and produces a huge number of seeds (after releasing its pollen, the bane of many hay fever sufferers). Because ragweed's approach to continued survival is through rapid reproduction (a high value of r) it is called an r-strategist. Other weeds, many insects, and many rodents are also r-strategists. If fact, if we consider an organism a pest, it is probably an r-strategist.
The two extreme strategies are at two ends of a continuum on which real species life histories will exist. In addition, life history strategies do not need to evolve as suites but can evolve independently of each other; therefore, each species may have some characteristics that trend toward one extreme or the other. Nevertheless, the r- and K-selection theory provides a foundation for a more accurate life history framework. New demographic-based models of life history evolution have been developed, which incorporate many ecological concepts included in r- and K-selection theory as well as population age structure and mortality factors.
Life Tables
Life tables provide important information about the life history of an organism and the life expectancy of individuals at each age. They are modeled after actuarial tables used by the insurance industry for estimating human life expectancy. Life tables may include the probability of each age group dying before their next birthday, the percentage of surviving individuals dying at a particular age interval (their mortality rate, and their life expectancy at each interval). An example of a life table is shown in Table \(\PageIndex{b}\) from a study of Dall mountain sheep, a species native to northwestern North America. Notice that the population is divided into age intervals (column A).
As can be seen from the mortality rate data (column D), a high death rate occurred when the sheep were between six months and a year old, and then increased even more from 8 to 12 years old, after which there were few survivors. The data indicate that if a sheep in this population were to survive to age one, it could be expected to live another 7.7 years on average, as shown by the life-expectancy numbers in column E. Life tables often include more information than shown in Table \(\PageIndex{b}\), such as fecundity (reproduction) rates for each age group.
Table \(\PageIndex{b}\): Life Table of Dall Mountain Sheep
Age interval (years) Number dying in age interval out of 1000 born Number surviving at beginning of age interval out of 1000 born Mortality rate per 1000 alive at beginning of age interval Life expectancy or mean lifetime remaining to those attaining age interval
0–0.5 54 1000 54.0 7.06
0.5–1 145 946 153.3
1–2 12 801 15.0 7.7
2–3 13 789 16.5 6.8
3–4 12 776 15.5 5.9
4–5 30 764 39.3 5.0
5–6 46 734 62.7 4.2
6–7 48 688 69.8 3.4
7–8 69 640 107.8 2.6
8–9 132 571 231.2 1.9
9–10 187 439 426.0 1.3
10–11 156 252 619.0 0.9
11–12 90 96 937.5 0.6
12–13 3 6 500.0 1.2
13–14 3 3 1000 0.7
Survivorship Curves
Another tool used by population ecologists is a survivorship curve, which is a graph of the number of individuals surviving at each age interval versus time. These curves allow us to compare the life histories of different populations (figure \(\PageIndex{c}\)). There are three types of survivorship curves. In a type I survivorship curve, mortality is low in the early and middle years and occurs mostly in older individuals. Organisms exhibiting a type I survivorship typically produce few offspring and provide good care to the offspring increasing the likelihood of their survival. Humans and most mammals exhibit a type I survivorship curve. In type II survivorship curves, mortality is relatively constant throughout the entire life span, and mortality is equally likely to occur at any point in the life span. Many bird populations provide examples of an intermediate or type II survivorship curve. In type III survivorship curves, early ages experience the highest mortality with much lower mortality rates for organisms that make it to advanced years. Type III organisms typically produce large numbers of offspring, but provide very little or no care for them. Trees and marine invertebrates exhibit a type III survivorship curve because very few of these organisms survive their younger years, but those that do make it to an old age are more likely to survive for a relatively long period of time.
While is no exact association between reproductive strategies (K- or r-selected) and survivorship curves (Type I, II, or III), K-selected species are more likely to have a Type III survivorship curve. r-selected species tend to have a Type I survivorship curve.
Attribution
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.02%3A_Populations/2.2.04%3A_Life_History.txt |
Overview
In 1999 the Sonoran Desert Conservation Plan was created to help wildlife populations and habitats. As a result of this plan, biologists were able to identify landscapes with wildlife barriers and get funding to install wildlife corridors. On State Route (SR) 77 two wildlife corridors were installed, one overpass and one underpass. These corridors were the first of their kind to be built in the Sonoran Desert so it was difficult to estimate what level of success they would have. As such, a monitoring plan was put in place to document which species used the corridors and how often they used it as time passed since their installation. The figure below illustrates the usage of the wildlife corridors 2+ years after their installation:
Questions
1. What is the independent (explanatory) variable and the dependent (response) variable?
2. What question(s) are the authors trying to answer with this graph?
3. Does this graph show a positive or negative relationship between the variables? Support your answer by referring to trends observed in the graph.
4. Do you think like the authors are satisfied with the results in the graph? Why?
5. How can we use the results of this graph to inform future wildlife corridor installations?
6. What information/patterns is not clear from this graph?
Raw Data For Above Graph(s)
Table \(\PageIndex{a}\): Raw data for total wildlife crossings after installation for overpass and underpass on SR 77. Graph by Rachel Schleiger (CC-BY-NC) modified from data in Santa Catalina - Tortolita Mountain Corridor Progress Report
Month Overpass Underpass
April 0 0
June 150 150
August 249 250
October 296 294
December 600 500
February 750 502
April 1000 600
June 1200 605
August 1800 750
October 1550 950
December 1700 1050
February 2000 1500
April 2400 1850
June 2500 2000
August 2700 2250
October 3000 2500
December 3200 2750
Attribution
Rachel Schleiger (CC-BY-NC)
2.2.06: Review
Summary
After completing this chapter you should be able to...
• Describe three different population dispersion patterns.
• Differentiate between population size and density.
• Explain how ecologists measure population size.
• Calculate population growth rate (r) and doubling time (t).
• Distinguish between exponential and logistic population growth models, explaining the role of the carrying capacity in logistic growth.
• Provide examples of density-dependent and density-independent factors that regulate populations.
• Compare K-selected and r-selected reproductive strategies.
• Interpret life tables.
• Compare type I, type II, and type III survivorship curves.
Populations are interacting, interbreeding groups of individuals from the same species. Ecologists measure characteristics of populations: dispersion pattern, population size, and population density. Populations with unlimited resources grow exponentially—with an accelerating growth rate. When resources become limiting, populations follow a logistic growth curve in which population size will level off at the carrying capacity. Density-dependent factors limit population growth as they reach their carrying capacity and include biotic factors such as predation, competition, and disease. Density-independent factors, such as storms and fires, are abiotic and decrease population size regardless of density.
Several frameworks explain how life history can influence population dynamics. K-selected species tend to have long life spans and produce few offspring with much parental care whereas r-selected species mature and reproduce rapidly, producing many offspring and offering little parental care. Life tables are useful to calculate life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time.
Attribution
Modified by Melissa Ha from Community and Population Ecology and Chapter Resources from Environmental Biology by Matthew R. Fisher (CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.02%3A_Populations/2.2.05%3A_Data_Dive-_Wildlife_Corridors.txt |
Chapter Hook
Until the late 1800s, Bison (Bison bison) numbered tens of millions in the Great Plains of the United States. By 1890, roughly 1000 Bison were left because the United States government campaign to eradicate the native people, their culture, and habitats they relied on. Slowly, a movement started to try and save Bison from extinction. It took until the early 2000’s for Bison numbers to reach a half a million. During this time, scientists were able to observe the Bison reintroduction back into the Great Plains. Bison were found to be the most critical species to restoring and maintaining the function and diversity in the Great Plains community. Both plants and animal populations in the community were strengthened from the return of the Bison. Understanding community dynamics is essential to conserving and restoring these systems and the species that define them. This is particularly critical for communities with one particular species that acts as a keystone to the health of the system.
Figure \(\PageIndex{a}\): American bison with starlings on its back. Image by NPS photos/Kim Acker (Public Domain)
Populations typically do not live in isolation from other species. Populations that interact within a given area form a community. The organisms that form a community are found in habitats, physical environments where organisms live; however, biotic (living) components are considered part of a community. Scientists study ecology at the community level to understand how species interact with each other and compete for the same resources.
Attribution
Modified by Rachel Schleiger and Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
• 6.1: Biotic Interactions
Biotic interactions describe the relationship between organisms. They may be intraspecific (within a species) or interspecific (between species). Antagonisms are interactions in which one or both organisms are harmed. In facilitation, at least one species benefits, and neither is harmed.
• 6.2: Community Structure and Dynamics
Community structure refers to the species and their relative abundances in a community, and community dynamics describe how community structure changes over time. Keystone species can facilitate species diversity in a community. Communities change over time through the process of succession.
• 6.3: Data Dive- Bison Impacts In Prairies
• 6.4: Review
2.03: Communities
Biotic interactions refer to the relationships among organisms. They can be intraspecific (between members of the same species) or interspecific (between members of different species). When at least one of the interactants is harmed, the relationship is called an antagonism. Trophic interactions, in which one species consumes another, are antagonisms. Competition is another antagonism in which species at the same trophic level (that eat the same things) interact through using the same resources. Interactions in which at least one species benefits and neither is harmed are called facilitation, which can be categorized as commensalism or mutualism.
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
2.3.01: Biotic Interactions
Trophic interactions occur when one organism feeds on another. The three main types of trophic interactions are predation (figure \(\PageIndex{a}\)), herbivory, or parasitism. During these interactions, one species benefits by gaining food at the expense of the other, which either dies or loses nutrients, tissues, or organs (such as leaves). Trophic interactions involve the flow of energy, and the trophic interactions in a community can be represented by food chains and food webs.
Attribution
Melissa Ha (CC-BY-NC)
2.3.1.01: Trophic Interactions
Perhaps the classical example of a biotic interaction is the predator-prey relationship. Predation occurs when one species (the predator) kills and eats multiple prey over its lifetime.
Predator-Prey Dynamics
Population sizes of predators and prey in a community are not constant over time, and they may vary in cycles that appear to be related. For example, 100 years of trapping data from North America shows how population dynamics of the lynx (predator) and the snowshoe hare (prey) cycle (figure \(\PageIndex{a}\)-b).
This cycling of predator and prey population sizes has a period of approximately ten years, with the predator population lagging one to two years behind the prey population (figure \(\PageIndex{a}\)-c). An apparent explanation for this pattern is that as the hare numbers increase, there is more food available for the lynx, allowing the lynx population to increase as well. When the lynx population grows to a threshold level, however, they kill so many hares that hare numbers begin to decline, followed by a decline in the lynx population because of scarcity of food. When the lynx population is low, the hare population size begins to increase due, in part, to low predation pressure, starting the cycle anew.
The dynamic of closely matched population cycling occurs because the snowshoe hare is the primary food source for the lynx. When predators have generalists, feeding on a variety of prey species, and prey are consumed by a variety of predators species, their population dynamics are less likely to cycle together.
Adaptations of Predators
Predators have a variety of adaptations to catch and consume prey, and the specific adaptations depend on the predator. For example, raptors, such as owls and hawks, have hooked beaks for tearing flesh and talons for grabbing prey. Mammal predators often have sharp teeth and claws. Some predators can run quickly to chase prey, and others "sit and wait", lunging forward when prey pass them. Some predators, like rattlesnakes and tarantulas, subdue their prey by injecting them with venom (figure \(\PageIndex{d}\)). Predators often have large eyes located forward (like a wolf) rather than eyes spaced far apart on the sides of the head (like a sheep). Forward-facing eyes allow for depth perception, which is key to tracking prey. In contrast, peripheral vision is expanded when eyes are located to the sides, and this helps prey identify threats.
Defensive Traits in Prey
Prey evolve mechanical, chemical, physical, or behavioral defenses against predators. Some prey have armor (such as a turtle shell or the bony plates protecting armadillos), a mechanical defense that reduces predation by discouraging physical contact. Many animals produce or obtain chemical defenses from plants and store them to prevent predation. Other species use their body shape and coloration as camouflage to avoid being detected by predators, an example of a physical defense. The tropical walking stick is an insect with the coloration and body shape of a twig, which makes it very hard to see when it is stationary against a background of real twigs (figure \(\PageIndex{e}\)-a). In another example, the chameleon can change its color to match its surroundings (figure \(\PageIndex{e}\)-b).
Some species use coloration as a way of warning predators that they are distasteful or poisonous. For example, the monarch butterfly caterpillar sequesters poisons from its food (plants and milkweeds) to make itself poisonous or distasteful to potential predators. The caterpillar is bright yellow and black to advertise its toxicity. The caterpillar is also able to pass the sequestered toxins on to the adult monarch, which is also dramatically colored black and red as a warning to potential predators. Fire-bellied toads produce toxins that make them distasteful to their potential predators (figure \(\PageIndex{f}\)). They have bright red or orange coloration on their bellies, which they display to a potential predator to advertise their poisonous nature and discourage an attack. Warning coloration only works if a predator uses eyesight to locate prey and can learn—a naïve predator must experience the negative consequences of eating one before it will avoid other similarly colored individuals.
While some predators learn to avoid eating certain potential prey because of their coloration, other species have evolved mechanisms to mimic this coloration to avoid being eaten, even though they themselves may not be unpleasant to eat or contain toxic chemicals. In some cases of mimicry, a harmless species imitates the warning coloration of a harmful species. Assuming they share the same predators, this coloration then protects the harmless ones. Many insect species mimic the coloration of wasps, which are stinging, venomous insects, thereby discouraging predation (figure \(\PageIndex{g}\)). In other cases of mimicry, multiple species share the same warning coloration, but all of them actually have defenses. The commonness of the signal improves the compliance of all the potential predators.
Running from predators, hiding, and playing dead are examples of behavioral defenses. Some prey also exhibit behaviors that threaten predators. For example, snapping turtles stretch their legs to appear larger and snap aggressively at predators.
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
2.3.1.1.02: Herbivory
When an animal feed on parts of another organism (usually a plant), herbivory occurs. For example, the koala eats the eucalyptus leaves (figure \(\PageIndex{a}\)) or a cicada feeds a plant's sap (figure \(\PageIndex{b}\)). Like predators, herbivores may feed on multiple individuals over their lives; however, herbivores do not necessarily kill the plants that they eat.
Plant species have evolved numerous defenses that reduce herbivory. Thorns are an example of a mechanical defense that discourages large herbivores from feeding on a plant (Figure \(\PageIndex{c}\)-a). Many plant species produce secondary plant compounds that serve no function for the plant except that they are toxic to animals and discourage consumption, acting as a chemical defense. For example, the foxglove produces several compounds, including digitalis, that are extremely toxic when eaten (Figure \(\PageIndex{c}\)-b). (Biomedical scientists have repurposed the chemical produced by foxglove as a heart medication, which has saved lives for many decades.)
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
2.3.1.1.03: Parasitism
Parasitism occurs when one organism (the parasite) takes nutrients from another (the host). The host is usually weakened by the parasite as it siphons resources the host would normally use to maintain itself. Parasites do not necessarily kill their hosts. When they do, it is often a slow process, allowing the parasite time to complete its reproductive cycle before it or its offspring are able to spread to another host. A parasite may remain attached to the same host for its full lifespan, but some parasites have complex life cycles involving multiple host species. For example, a tapeworm causes disease in humans when contaminated and under-cooked meat such as pork, fish, or beef is consumed. Figure \(\PageIndex{a}\) illustrates the life cycle of the pork tapeworm. The tapeworm can live inside the intestine of the host for several years, benefiting from the host’s food, and it may grow to be over 50 feet long by adding segments. The parasite moves from one host species to a second host species in order to complete its life cycle.
Parasites infect many types of organisms, including other animals and plants. For example, fleas and roundworms are common dog parasites. Plants can be infected by fungi, bacteria, and viruses; there are also plants that parasitize other plants (figure \(\PageIndex{b}\)). Even bacteria can be parasitized by viruses called bacteriophages.
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.03%3A_Communities/2.3.01%3A_Biotic_Interactions/2.3.1.01%3A_Trophic_Interactions/2.3.1.1.01%3A_Predation.txt |
Trophic interactions in a community can be represented by diagrams called food chains and food webs. Before discussing these representations in detail, we must first review the basics of energy. Energy flows through a community as a result of trophic interactions.
Energy
Virtually every task performed by living organisms requires energy. In general, energy is defined as the ability to do work, or to create some kind of change. Energy exists in different forms. Examples include light energy, kinetic energy, heat energy, potential energy, and chemical energy.
When an object is in motion, there is energy associated with that object. Think of a wrecking ball. Even a slow-moving wrecking ball can do a great deal of damage to other objects. Energy associated with objects in motion is called kinetic energy. Heat energy is the energy of motion in matter (anything that takes up space and has mass) and is considered a type of kinetic energy. The warmer the substance, the faster its molecules are moving. The rapid movement of molecules in the air, a speeding bullet, and a walking person all have kinetic energy. Now what if that same motionless wrecking ball is lifted two stories above ground with a crane? If the suspended wrecking ball is not moving, is there energy associated with it? The answer is yes. The energy that was required to lift the wrecking ball did not disappear, but is now stored in the wrecking ball by virtue of its position and the force of gravity acting on it. This type of energy is called potential energy. If the ball were to fall, the potential energy would be transformed into kinetic energy until all of the potential energy was exhausted when the ball rested on the ground. Wrecking balls also swing like a pendulum; through the swing, there is a constant change of potential energy (highest at the top of the swing) to kinetic energy (highest at the bottom of the swing). Other examples of potential energy include the energy of water held behind a dam or a person about to skydive out of an airplane (figure \(\PageIndex{a}\)).
Potential energy is not only associated with the location of matter, but also with the structure of matter. Chemical energy is an example of potential energy that is stored in molecules. When molecules that are higher energy and less stable react to form products that are lower energy and more stable, this stored energy is released. Chemical energy is responsible for providing living cells with energy from food.
To appreciate the way energy flows into and out of biological systems, it is important to understand two of the physical laws that govern energy. The first law of thermodynamics states that the total amount of energy in the universe is constant and conserved. In other words, there has always been, and always will be, exactly the same amount of energy in the universe. Energy exists in many different forms. According to the first law of thermodynamics, energy may be transferred from place to place or transformed into different forms, but it cannot be created or destroyed. The transfers and transformations of energy take place around us all the time. Light bulbs transform electrical energy into light and heat energy. Gas stoves transform chemical energy from natural gas into heat energy. Plants perform one of the most biologically useful energy transformations on earth: that of converting the energy of sunlight to chemical energy stored within biological molecules, such as sugars (figure \(\PageIndex{b}\)).
The challenge for all living organisms is to obtain energy from their surroundings in forms that are usable to perform cellular work. A living cell’s primary tasks of obtaining, transforming, and using energy to do work may seem simple. However, the second law of thermodynamics explains why these tasks are harder than they appear. All energy transfers and transformations are never completely efficient. In every energy transfer, some amount of energy is lost in a form that is unusable. In most cases, this form is heat energy. For example, when a light bulb is turned on, some of the energy being converted from electrical energy into light energy is lost as heat energy. Likewise, some energy is lost as heat energy during the metabolic reactions that occur in organisms.
The concept of order and disorder relates to the second law of thermodynamics. The more energy that is lost by a system to its surroundings, the less ordered and more random the system is. Scientists refer to the measure of randomness or disorder within a system as entropy. High entropy means high disorder and low energy. Living things are highly ordered, requiring constant energy input to be maintained in a state of low entropy.
Energy Flow
Cells run on the chemical energy found mainly in carbohydrate molecules, and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules (figure \(\PageIndex{c}\)). The energy that is harnessed from photosynthesis enters the communities continuously and is transferred from one organism to another. Therefore, directly or indirectly, the process of photosynthesis provides most of the energy required by living things on Earth. See the Carbon Cycle and Photosynthesis in OpenStax Concepts of Biology for more details about photosynthesis.
Organisms that conduct photosynthesis (such as plants, algae, and some bacteria), and organisms that synthesize sugars through other means are called producers. Without these organisms, energy would not be available to other living organisms, and life would not be possible. Consumers, like animals, fungi, and various microorganisms depend on producers, either directly or indirectly. For example, a deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer (figure \(\PageIndex{d}\)). Using this reasoning, all food eaten by humans can be traced back to producers that carry out photosynthesis (figure \(\PageIndex{e}\)).
Consumers can be classified based on whether they eat animal or plant material (figure \(\PageIndex{f}\)). Consumers that feed exclusively on animals are called carnivores. Lions, tigers, snakes, sharks, sea stars, spiders, and ladybugs are all carnivores. Herbivores are consumers that feed exclusively on plant material, and examples include deer, koalas, some bird species, crickets, and caterpillars. Herbivores can be further classified into frugivores (fruit-eaters), granivores (seed eaters), nectivores (nectar feeders), and folivores (leaf eaters). Consumers that eat both plant and animal material are considered omnivores. Humans, bears, chickens, cockroaches, and crayfish are examples of omnivores.
Dead producers and consumers are eaten by detritivores (which ingest dead tissues) and decomposers (which further break down these tissues into simple molecules by secreting digestive enzymes). Invertebrate animals, such as worms and millipedes, are examples of detritivores, whereas fungi and certain bacteria are examples decomposers.
Food Chains
A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. Each organism in a food chain occupies a specific trophic level (energy level), its position in the food chain. The first trophic level in the food chain is the producers. The primary consumers (the herbivores that eat producers) are the second trophic level. Next are higher-level consumers. Higher-level consumers include secondary consumers (third trophic level), which are usually carnivores that eat the primary consumers, and tertiary consumers (fourth trophic level), which are carnivores that eat other carnivores. In the Lake Ontario food chain, shown in figure \(\PageIndex{g}\), the Chinook salmon is the apex consumer at the top of this food chain. Some communities have additional trophic levels (quaternary consumers, fifth order consumers, etc.). Finally, detritivores and decomposers break down dead and decaying organisms from any trophic level. There is a single path through a food chain.
One major factor that limits the number of steps in a food chain is energy. Only about 10% of the energy in one trophic level is transferred to the next trophic level. This is because much energy is lost as heat during transfers between trophic levels or to decomposers due to the second law of thermodynamics. Thus, after four to six trophic energy transfers, the amount of energy remaining in the food chain may not be great enough to support viable populations at higher trophic levels (also see Community Productivity and Transfer Efficiency).
Certain environmental toxins can become more concentrated as they move up the food chain, with the highest concentrations occurring in the top consumers, a process called biomagnification. Essentially, a top consumer ingests all the toxins that had previously accumulated in the bodies of the organisms at the lower trophic levels. This explains why frequently eating certain fish, like tuna or swordfish, increases your exposure to mercury, a toxic heavy metal.
Food Webs
While food chains are simple and easy to analyze, there is a one problem when using food chains to describe most communities. Even when all organisms are grouped into appropriate trophic levels, some of these organisms can feed at more than one trophic level. In addition, species feed on and are eaten by more than one species. In other words, the linear model of trophic interactions, the food chain, is a hypothetical and overly simplistic representation of community structure. A holistic model—which includes all the interactions between different species and their complex interconnected relationships with each other and with the environment—is a more accurate and descriptive model. A food web is a concept that accounts for the multiple trophic interactions between each species (figure \(\PageIndex{h}\) and i).
The trophic level of each species in a food web is not necessarily a whole number. In figure \(\PageIndex{i}\), phytoplankton are the primary producers (trophic level 1). Zooplankton only feed on phytoplankton, making them primary consumers (trophic level 2). Determining the trophic level of the other species is more complex. For example, krill eat both phytoplankton and zooplankton. If krill only ate phytoplankton they would primary consumers (trophic level 2). If they ate only zooplankton, they would be secondary consumers (trophic level 3). Since, krill consume both, their trophic level is 2.5.
Community Productivity and Transfer Efficiency
The rate at which photosynthetic producers incorporate energy from the sun is called gross primary productivity. In a cattail marsh, plants only trap 2.2% of the energy from the sun that reaches them. Three percent of the energy is reflected, and another 94.8% is used to heat and evaporate water within and surrounding the plant. However, not all of the energy incorporated by producers is available to the other organisms in the food web because producers must also grow and reproduce, which consumes energy. At least half of the 2.2% trapped by cattail marsh plants is used to meet the plants own energy needs.
Net primary productivity is the energy that remains in the producers after accounting for the metabolic needs of the producers and heat loss. The net productivity is then available to the primary consumers at the next trophic level. One way to measure net primary productivity is to collect and weigh the plant material produced on a m2 (about 10.7 ft2) of land over a given interval. One gram of plant material (e.g., stems and leaves), which is largely the carbohydrate cellulose, yields about 4.25 kcal of energy when burned. Net primary productivity can range from 500 kcal/m2/yr in the desert to 15,000 kcal/m2/yr in a tropical rain forest.
In an aquatic community in Silver Springs, Florida, the gross primary productivity (total energy accumulated by the primary producers) was 20,810 kcal/m2/yr (figure \(\PageIndex{j}\)). The net primary productivity (energy available to consumers) was only 7,632 kcal/m2/yr after accounting for energy lost as heat and energy require to meet the producer's metabolic needs.
Only a fraction of the energy captured by one trophic level is assimilated into biomass, which makes it available to the next trophic level. Assimilation is the biomass of the present trophic level after accounting for the energy lost due to incomplete ingestion of food, energy used to conduct work by that trophic level, and energy lost as waste. Incomplete ingestion refers to the fact that some consumers eat only a part of their food. For example, when a lion kills an antelope, it will eat everything except the hide and bones. The lion is missing the energy-rich bone marrow inside the bone, so the lion does not make use of all the calories its prey could provide. In Silver Springs, only 1103 kcal/m2/yr from the 7618 kcal/m2/yr of energy available to primary consumers was assimilated into their biomass. (The trophic level transfer efficiency between the first two trophic levels was approximately 14.8 percent.)
An animal's source of heat influences its energy needs. Ectotherms, such as invertebrates, fish, amphibians, and reptiles, rely on external sources for body heat, and endotherms, such as birds and mammals, rely on internally generated heat. Generally, ectotherms require less of the energy to meet their metabolic needs and than endotherms do, and therefore, many endotherms have to eat more often than ectotherms.
The inefficiency of energy use by endotherms has broad implications for the world's food supply. It is widely accepted that the meat industry uses large amounts of crops to feed livestock, and because a low percentage of this is assimilated into biomass, much of the energy from animal feed is lost. For example, it costs about 1¢ to produce 1000 dietary calories (kcal) of corn or soybeans, but approximately \$0.19 to produce a similar number of calories growing cattle for beef consumption. The same energy content of milk from cattle is also costly, at approximately \$0.16 per 1000 kcal. Thus, there has been a growing movement worldwide to promote the consumption of non-meat and non-dairy foods so that less energy is wasted feeding animals for the meat industry.
Attribution
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.03%3A_Communities/2.3.01%3A_Biotic_Interactions/2.3.1.01%3A_Trophic_Interactions/2.3.1.1.04%3A_Food_Chains_and_Food_Webs.txt |
Resources are often limited within a habitat and multiple species may compete to obtain them. Competition occurs when organisms use the the same resources, and one or both organisms is harmed. Competing species are often occupy the same trophic level and compete for food, but species on different trophic levels could still compete for space, water, etc. Intraspecific competition occurs within a species. For example, most penguins defend territories from other individuals of the same species because they compete for suitable habitat and other resources (figure \(\PageIndex{a}\)). Interspecific competition occurs between different species. For example, the invasive vine, kudzu, competes with trees in the southeastern United States for light (figure \(\PageIndex{b}\)). Kudzu is considered invasive in this region because it occurs outside of its historical range (Asia and Australia) and causes ecological harm.
Ecologists have come to understand that all species have an ecological niche: the unique set of resources used by a species, which includes its interactions with other species. The competitive exclusion principle states that two species cannot occupy the exact same niche in a habitat. In other words, different species cannot coexist in a community if they are competing for all the same resources. Competition harms one or both competitors because it wastes energy. In an experimental test of competitive exclusion, two species of the freshwater microbe Paramecium were cultured separately and together. When cultured separately, both species reproduced, and the number of cells (individuals) increased. However, when the two species were grown together, one species (P. aurelia) grew, and the the other species (P. caudatum) was eliminated. Because both species occupied the same ecological niche, they could not coexist. Paramecium aurelia was the superior competitor in this case (figure \(\PageIndex{c}\)). Competitive exclusion may be avoided if a population evolves to make use of a different resource, a different area of the habitat, or feeds during a different time of day. This is called resource partitioning. The two species are then said to occupy different microniches. These species coexist by minimizing direct competition.
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
2.3.1.03: Facilitation
Interactions in which one or both species benefit and neither is harmed are called facilitation. There are two types of facilitation: commensalism and mutualism.
Commensalism
Commensalism is a type of facilitation that occurs when one species benefits from an interaction, while the other neither benefits or is harmed. Many potential commensal relationships are difficult to identify because it is difficult to demonstrate that one partner is unaffected by the presence of the other. Birds nesting in trees provide an example of a commensal relationship (figure \(\PageIndex{a}\)). The tree is not harmed by the presence of the nest among its branches. The nests are light and produce little strain on the structural integrity of the branch, and most of the leaves, which the tree uses to get energy by photosynthesis, are above the nest so they are unaffected. The bird, on the other hand, benefits greatly. If the bird had to nest in the open, its eggs and young would be vulnerable to predators.
Another example or a commensal relationship involves the Little Blue Heron and the White Ibis, which are both wading birds. The Little Blue Heron catches more fish in the presence of the White Ibis, but the White Ibis is unaffected. Interestingly, Little Blue Herons attempt to catch fish more often in the presence of the species, but the success rate of their attempts does not change. Nevertheless, more frequent attempts still increases the total number of fish caught. The White Ibis may make fish more visible to Little Blue Herons, causing changes in their behavior (figure \(\PageIndex{b}\)).
Mutualism
In a mutualism, both species benefit from their interaction. For example, pollinators, such as bees, butterflies, and hummingbirds, benefit because they eat the collect pollen and/or nectar that they collect from flowers. The plants also benefit because their pollen is dispersed to other plants, allowing them to reproduce. Both the pollinators and the plants benefit, demonstrating a mutualism (figure \(\PageIndex{c}\)). Clownfish and anemones are another example of mutualisms. Clownfish gain protection from living among anemones. In return, clownfish clean the anemones and scare away predators. In addition, their waste provides nutrients (figure \(\PageIndex{d}\)).
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher's (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.03%3A_Communities/2.3.01%3A_Biotic_Interactions/2.3.1.02%3A_Competition.txt |
Some biological interactions are brief, such as predation. In others, species are closely associated for long periods. Such associations are called symbiotic ("living together"). One species always benefits in a symbiosis, but the other may be harmed (parastitism), unaffected (commensalism), or benefited (mutualism). Some experts considered all parasitisms, commmensalisms, and mutualisms to be symbiotic, but others only consider interactions in which species are living together in a close association (such as when one species lives on or in the other) as symbiotic.
Termites have a symbiotic relationship with microorganisms called protozoa that live in the insect’s gut (figure \(\PageIndex{a}\)-a). The termite benefits from the ability of the protozoa to digest cellulose, a carbohydrate important in plant structure. However, the protozoa are able to digest cellulose only because of the presence of symbiotic bacteria within their cells that produce the cellulase enzyme. The termite itself cannot do this; without the protozoa, it would not be able to obtain energy from its food (cellulose from the wood it chews and eats). The protozoa benefit by having a protective environment and a constant supply of food from the wood chewing actions of the termite. In turn, the protists benefit from the enzymes provided by their bacterial endosymbionts, while the bacteria benefit from a doubly protective environment and a constant source of nutrients from two hosts.
Lichen are a symbiotic relationship between a fungus and algae (or a photosynthetic bacteria; Figure \(\PageIndex{a}\)-b). In lichen, the algal cells are fully surrounded by the fungus. The sugars produced by the algae through photosynthesis provide nourishment for both organisms. The physical structure of the fungus protects the algae from the elements and makes certain nutrients in the atmosphere more available to the algae. The algae of lichens can sometimes live independently given the right environment, but many of the fungal partners are unable to live on their own. Note that while both lichen and the example involving termites mutually benefit the species involved, symbioses are not always mutualisms.
The remora and the shark is a commensal symbiosis. The top fin of the remora is modified into a sucker with which it forms an attachment to the shark. When the shark feeds, the remora picks up scraps. Additionally, the remora gains transportation and protection. The shark makes no attempt to prey on the remora and is unaffected by it (figure \(\PageIndex{b}\)).
There are many additional examples of symbiosis. Coral are small animals that harbor photosynthetic microorganisms called dinoflagellates. (The corals group together and deposit hardened calcium carbonate skeletons.) Mycorrhizae are fungi that surround or live within plant root cells and help plants absorb nutrients from the soil in exchange for sugars. In fact truffles are often found in oak forests because the fungus that produce this spore-forming body establishes mycorrhizae on oak roots. Root nodules are structures on the roots of legume plants that house nitrogen-fixing bacteria (see The Nitrogen Cycle). Epiphytes are plants adapted to live on top of other plants and are common in the tropical rainforest (see Biomes). Humans have a diversity of microorganisms, called the normal flora, that live in and on our bodies. While we often think of bacteria as causing infection (a parasitism), the species of our normal floral exemplify commensalism and mutualism. For example, our gut microbiota aids with digestion and helps us synthesize certain vitamins.
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.03%3A_Communities/2.3.01%3A_Biotic_Interactions/2.3.1.04%3A_Symbiosis.txt |
Communities are complex systems that can be characterized by community structure (the number and size of populations and their interactions) and community dynamics (how the members and their interactions change over time). Understanding community structure and dynamics allows us to minimize impacts on ecosystems and manage ecological communities we benefit from.
Keystone Species
A keystone species is one whose presence has inordinate influence in maintaining the prevalence of various species, the ecological community’s structure, and sometimes its biodiversity. Pisaster ochraceus, the intertidal sea star, is a keystone species in the northwestern portion of the United States (figure \(\PageIndex{a}\)). Studies have shown that when this organism is removed from communities, mussel populations (their natural prey) increase, which completely alters the species composition and reduces biodiversity. Another keystone species is the banded tetra, a fish in tropical streams, which supplies nearly all of the phosphorus, a necessary inorganic nutrient, to the rest of the community. The banded tetra feeds largely on insects from the terrestrial ecosystem and then excretes phosphorus into the aquatic ecosystem. The relationships between populations in the community, and possibly the biodiversity, would change dramatically if these fish were to become extinct.
Community Dynamics
Community dynamics are the changes in community structure and composition over time, often following environmental disturbances such as volcanoes, earthquakes, storms, fires, and climate change. Communities with a relatively constant number of species are said to be at equilibrium. The equilibrium is dynamic with species identities and relationships changing over time, but maintaining relatively constant numbers. Following a disturbance, the community may or may not return to the equilibrium state.
Succession describes the sequential appearance and disappearance of species in a community over time after a severe disturbance. In primary succession, newly exposed or newly formed rock is colonized by living organisms. In secondary succession, a part of an ecosystem is disturbed and remnants of the previous community remain. In both cases, there is a sequential change in species until a more-or-less permanent community develops.
Primary Succession and Pioneer Species
Primary succession occurs when new land is formed, or when the soil and all life is removed from pre-existing land. An example of the former is the eruption of volcanoes on the Big Island of Hawaii, which results in lava that flows into the ocean and continually forms new land. From this process, approximately 32 acres of land are added to the Big Island each year. An example of pre-existing soil being removed is through the activity of glaciers. The massive weight of the glacier scours the landscape down to the bedrock as the glacier moves. This removes any original soil and leaves exposed rock once the glacier melts and retreats.
In both cases, the ecosystem starts with bare rock that is devoid of life. New soil is slowly formed as weathering and other natural forces break down the rock and lead to the establishment of hearty organisms, such as lichens and some plants, which are collectively known as pioneer species (figure \(\PageIndex{b}\)) because they are the first to appear. These species help to further break down the mineral-rich rock into soil where other, less hardy but more competitive species, such as grasses, shrubs, and trees, will grow and eventually replace the pioneer species. Over time the area will reach an equilibrium state, with a set of organisms quite different from the pioneer species.
The relationship between pioneer species and the more competitive (late-successional) species illustrates the complexity of biotic interactions. Pioneer species facilitate the growth of the late-successional species, and this initially appears to be a commensalism. However, the late-successional species later outcompete the pioneer species, shifting the interaction to competition.
Secondary Succession
A classic example of secondary succession occurs in forests cleared by wildfire, or by clearcut logging (figure \(\PageIndex{c}\)). Wildfires will burn most vegetation, and unless the animals can flee the area, they are killed. Their nutrients, however, are returned to the ground in the form of ash. Thus, although the community has been dramatically altered, there is a soil ecosystem present that provides a foundation for rapid recolonization.
Before the fire, the vegetation was dominated by tall trees with access to the major plant energy resource: sunlight. Their height gave them access to sunlight while also shading the ground and other low-lying species. After the fire, though, these trees are no longer dominant. Thus, the first plants to grow back are usually annual plants followed within a few years by quickly growing and spreading grasses and other pioneer species. Due, at least in part, to changes in the environment brought on by the growth of grasses and forbs, over many years, shrubs emerge along with small trees. These organisms are called intermediate species. Eventually, over 150 years or more, the forest will reach its equilibrium point and resemble the community before the fire. This equilibrium state is referred to as the climax community, which will remain until the next disturbance. The climax community is typically characteristic of a given climate and geology. Although the community in equilibrium looks the same once it is attained, the equilibrium is a dynamic one with constant changes in abundance and sometimes species identities.
Attribution
Modified by Melissa Ha from Community Ecology from Environmental Biology by Matthew R. Fisher's (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.03%3A_Communities/2.3.02%3A_Community_Structure_and_Dynamics.txt |
Overview
In many grassland ecosystems the activities of large grazers, like bison, play a key role in shaping grassland habitat structure and diversity. A 2017 study sought to investigate how bison in tall-grass prairies affect local plant competition. Specifically, they wanted to know if bison have a positive impact on herbaceous forbs (non-woody flower species). To investigate this, they observed plant communities in tall-grass prairies in the presence and absence of bison. The two graphs below display some of the results in this study:
Questions
1. What kind of graphs are these?
2. Does the presence of bison increase diversity? How do you know this? Which graph(s) support this?
3. How does the presence of bison affect the percent cover of bare ground, grasses, forbs, and shrubs?
4. Based on the authors objectives/predictions described above, do the results of these graphs support them? Why/why not?
5. How can we use the results of this graph to inform conservation projects for tallgrass prairies in the future?
6. What does the results of this graph make you curious about?
Raw Data From Above Graph(s)
Table \(\PageIndex{2a}\): Raw data for average percent covers (aka what percent of an area a species took up) for grasses, forbs, shrubs, and bare ground in tall-grass prairies with and without bison. Graph by Rachel Schleiger (CC-BY-NC) modified from data in Elson A and Hartnett D, 2017.
Status Average Percent Cover With Bison Average Percent Cover With No Bison
Bare Ground 27 3
Grass 80 98
Forb 81 63
Shrub 7 6
Table \(\PageIndex{b}\): Raw data for average diversity of non-grasses in tall-grass prairies with and without bison. Graph by Rachel Schleiger (CC-BY-NC) modified from data in Elson A and Hartnett D, 2017.
Average Diversity (Non-Grasses) With Bison Average Diversity (Non-Grasses) With No Bison
24 13
Attributions
Rachel Schleiger (CC-BY-NC)
2.3.04: Review
Summary
After completing this chapter you should be able to...
• Name and distinguish among the major types of biotic interactions, providing examples of each.
• Describe how prey have adapted to reduce predation and how plants have adapted to reduce herbivory.
• Define energy and distinguish among the different types of energy.
• Explain the first and second laws of thermodynamics as they relate to trophic interactions in a community.
• Distinguish between and interpret food webs and food chains, explaining the advantages of each representation and identifying the trophic levels in each.
• Explain what limits the number of trophic levels in a community.
• Define symbiosis and provide examples.
• Explain the role of keystone species in maintaining community structure.
• Summarize the process of succession.
Communities consists of populations of different species interacting in a common area. Biotic interactions describe the relationships among organisms, and trophic interactions, including predation, herbivory, and parasitism, are the biotic interactions that involve one organism eating another. Trophic interactions are diagrammed through food chains and food webs.
Some biotic interactions are not trophic. For example, competition is a biotic interaction in which one or both organisms that use the same resources are harmed, and it can occur between individuals of the same species (intraspecific) or between members of different species (interspecific). Facilitation refers to interactions in which one or both species benefit and neither is harmed. Examples include commensalism and mutualism. A symbiosis is a close association in which species are living together.
Communities are characterized by their structure (number and size of populations and their interactions) and dynamics (how the community structure changes). Keystone species have a great influence on community structure, which is disproportionately large relative to their abundance. Succession describes how community composition changes over time following a disturbance.
Attribution
Melissa Ha (CC-BY-NC) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.03%3A_Communities/2.3.03%3A_Data_Dive-_Bison_Impacts_In_Prairies.txt |
Chapter Hook
In semi-urban areas beavers (Castor canadensis) are considered a nuisance as their dams block drainage pipes and cause flooding. However, in wild areas beavers are one of the most important species. Beaver dams are known for altering the flow of water. However, these dams not only slow down the movement of water, but they spread and store water in a way that is much more efficient than human-made dams. In addition, they slow and spread sediment and nutrients as they move through watersheds. What this does is create a mosaic of habitats across a landscape, both aquatic and terrestrial. More habitats lead to more species, both for plants and animals. In this way, beavers create ecosystems, one stick at a time.
Figure \(\PageIndex{a}\) American beaver. Image by NeexPix (Public domain)
Attribution
Rachel Schleiger (CC-BY-NC)
• 7.1: Ecosystem Types and Dynamics
An ecosystem is a community of organisms and their nonliving environment. Ecosystems may be freshwater, marine, or terrestrial. Some ecosystems are more resistant to disturbances than others. Resilience refers to how quickly an ecosystem returns to equilibrium following a disturbance. Foundation species have great influence on community structure.
• 7.2: Matter
At its most fundamental level, life is made of matter. Matter is something that occupies space and has mass. All matter is composed of elements, substances that cannot be broken down or transformed chemically into other substances. Each element is made of atoms, which can bind together to form molecules. The four biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.
• 7.3: Biogeochemical Cycles
Biogeochemical cycles represent the movement of chemical elements through water, air, soil, rocks, and organisms. Carbon cycles slowly between the ocean and land, but it moves quickly from the atmosphere to organisms (through photosynthesis) and back to the atmosphere (through cellular respiration). The nitrogen cycle and phosphorus cycles are other key biogeochemical cycles. Excess nutrients can disrupt aquatic ecosystems through eutrophication.
• 7.4: Soils
Soil is the outer loose layer that covers the Earth's surface and is the foundation for agriculture and forestry. Soils consist of organic material, inorganic material, water and air, and they differ in proportions of clay, silt, and sand. A soil profile is characterized by horizontal layers called horizons. Climate, organisms, topography, parent material, and time influence soil composition and formation.
• 7.5: Soil Degradation
Erosion, compaction, salinization, and desertification are interacting processes that degrade soil (lower its quality).
• 7.6: Data Dive- Beaver Impacts on Wetlands
• 7.7: Review
Thumbnail image - This sage thrasher’s diet, like that of almost all organisms, depends on photosynthesis.
2.04: Ecosystems
An ecosystem is a community of organisms (biotic components) and their abiotic (non-living) environment. Ecosystems can be small, such as the tide pools found near the rocky shores of many oceans, or large, such as those found in the tropical rainforest of the Amazon in Brazil (figure \(\PageIndex{a}\)).
Ecosystem Categories
There are three broad categories of ecosystems based on their general environment: freshwater, marine, and terrestrial. Within these three categories are individual ecosystem types based on the environmental habitat and organisms present.
Freshwater ecosystems are the least common, occurring on only 1.8 percent of Earth’s surface. These systems comprise lakes, rivers, streams, and springs; they are quite diverse and support a variety of animals, plants, fungi, protists and prokaryotes.
Marine ecosystems are the most common, comprising 75 percent of Earth’s surface and consisting of three basic types: shallow ocean, deep ocean water, and deep ocean bottom. Shallow ocean ecosystems include extremely biodiverse coral reef ecosystems. Small photosynthetic organisms suspended in ocean waters, collectively known as phytoplankton, perform 40 percent of all photosynthesis on Earth. Deep ocean bottom ecosystems contain a wide variety of marine organisms. These ecosystems are so deep that light is unable to reach them. Freshwater and marine ecosystems are found in aquatic biomes, which are discussed in the Biomes chapter.
Terrestrial ecosystems, also known for their diversity, are grouped into large categories called biomes. A biome is a large-scale community of organisms, primarily defined on land by the dominant plant types that exist in geographic regions of the planet with similar climatic conditions. Examples of biomes include tropical rainforests, savannas, deserts, grasslands, temperate forests, and tundras. Grouping these ecosystems into just a few biome categories obscures the great diversity of the individual ecosystems within them. For example, the saguaro cacti (Carnegiea gigantean) and other plant life in the Sonoran Desert, in the United States, are relatively diverse compared with the desolate rocky desert of Boa Vista, an island off the coast of Western Africa (figure \(\PageIndex{b}\)).
Ecosystem Dynamics
Ecosystems are complex with many interacting parts. They are routinely exposed to various disturbances, or changes in the environment that affect their compositions: yearly variations in rainfall and temperature and the slower processes of plant growth, which may take several years. Many of these disturbances are a result of natural processes. For example, when lightning causes a forest fire and destroys part of a forest ecosystem, the ground is eventually populated by grasses, then by bushes and shrubs, and later by mature trees, restoring the forest to its former state. The impact of environmental disturbances caused by human activities is as important as the changes caused by natural processes. Human agricultural practices, air pollution, acid rain, global deforestation, overfishing, eutrophication, oil spills, and illegal dumping on land and into the ocean are all issues of concern to conservationists.
Equilibrium is the steady state of an ecosystem where all organisms are in balance with their environment and with each other. In ecology, two parameters are used to measure changes in ecosystems: resistance and resilience. The ability of an ecosystem to remain at equilibrium in spite of disturbances is called resistance. The speed at which an ecosystem recovers equilibrium after being disturbed, called its resilience. Ecosystem resistance and resilience are especially important when considering human impact. The nature of an ecosystem may change to such a degree that it can lose its resilience entirely. This process can lead to the complete destruction or irreversible altering of the ecosystem.
Foundation Species
Foundation species are considered the “base” or “bedrock” of an ecosystem, having the greatest influence on its overall structure. They are often primary producers, and they are typically an abundant organism. For example, kelp, a species of brown algae, is a foundation species that forms the basis of the kelp forests off the coast of California.
Foundation species may physically modify the environment to produce and maintain habitats that benefit the other organisms that use them. Examples include the kelp described above or tree species found in a forest. The photosynthetic corals of the coral reef also provide structure by physically modifying the environment (figure \(\PageIndex{c}\)). The calcium carbonate deposits of living and dead coral make up most of the reef structure, which protects many other species from waves and ocean currents.
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.04%3A_Ecosystems/2.4.01%3A_Ecosystem_Types_and_Dynamics.txt |
Matter is the "stuff" found in ecosystems. Technically, matter is defined as anything that occupies space or has mass. Mass is resistance to acceleration. Put more simply, mass is similar to weight, but weight accounts for acceleration due to gravity. Matter moves between biotic and abiotic ecosystem components through biogeochemical cycles. Fully understanding these cycles, requires a background in the particles that comprise matter, atoms.
Atoms and Molecules
Elements are substances that cannot be broken down or transformed chemically into other substances (figure \(\PageIndex{a}\)). A total of 118 elements have been defined; however, only 92 occur naturally and fewer than 30 are found in organisms. The remaining 26 elements are unstable and therefore do not exist for very long or are theoretical and have yet to be detected. Each element is designated by its chemical symbol (such as H, N, O, C, and Na), and possesses unique properties. These unique properties allow elements to combine and to bond with each other in specific ways.
An atom is the smallest component of an element that retains all of the chemical properties of that element. For example, one hydrogen atom has all of the properties of the element hydrogen, such as it exists as a gas at room temperature and it bonds with oxygen to create a water molecule. Hydrogen atoms cannot be broken down into anything smaller while still retaining the properties of hydrogen. If a hydrogen atom were broken down into smaller particles, it would no longer have the properties of hydrogen. At the most basic level, all organisms are made of a combination of elements. They contain atoms that combine together to form molecules. Molecules can interact to form cells, the structural and functional units of life. In multicellular organisms, such as animals, these cells combine to form tissues, which make up organs. These combinations continue until entire multicellular organisms are formed.
Atoms combine to form molecules. Molecules are chemicals made from two or more atoms bonded together. Some molecules are very simple, like O2, which is comprised of just two oxygen atoms. Some molecules used by organisms, such as DNA, are made of many millions of atoms. All atoms contain protons, electrons, and neutrons (figure \(\PageIndex{b}\)). The only exception is hydrogen (H), which is typically only made of one proton and one electron. A proton is a positively charged particle that resides in the nucleus (the core of the atom) of an atom and has a mass of 1 and a charge of +1. An electron is a negatively charged particle that travels in the space around the nucleus. In other words, it resides outside of the nucleus. It has a negligible mass and has a charge of –1. Neutrons, like protons, reside in the nucleus of an atom. They have a mass of 1 and no charge. The positive (protons) and negative (electrons) charges balance each other in a neutral atom, which has a net zero charge.
Each element contains a different number of protons and neutrons, giving it its own atomic number and mass number. The atomic number of an element is equal to the number of protons that element contains. The mass number is the number of protons plus the number of neutrons of that element. Therefore, it is possible to determine the number of neutrons by subtracting the atomic number from the mass number.
Chemical Bonds
How elements interact with one another depends on the number of electrons and how they are arranged. When an atom does not contain equal numbers of protons and electrons it is called an ion. Because the number of electrons does not equal the number of protons, each ion has a net charge. For example, if sodium loses an electron, it now has 11 protons and only 10 electrons, leaving it with an overall charge of +1. Positive ions are formed by losing electrons and are called cations. Negative ions are formed by gaining electrons and are called anions. Elemental anionic names are changed to end in -ide. As an example, when chlorine becomes an ion it is referred to as chloride.
Ionic and covalent bonds are strong bonds formed between two atoms. These bonds hold atoms together in a relatively stable state. Ionic bonds are formed between two oppositely charged ions (an anion and a cation). Because positive and negative charges attract, these ions are held together much like two oppositely charged magnets would stick together. Covalent bonds form when electrons are shared between two atoms. Each atom shares one of their electrons, which then orbits the nuclei of both atoms, holding the two atoms together. Covalent bonds are the strongest and most common form of chemical bond in organisms. Unlike most ionic bonds, covalent bonds do not dissociate in water. Hydrogen bonds form when molecules have an uneven distribution of electrons and thus have partially positive and partially negative ends. They are thus attracted to each other (figure \(\PageIndex{c}\)). Technically, hydrogen bonds only occur between hydrogen and either oxygen (O), nitrogen (N), or fluorine (F). Sometimes hydrogen bonds connect different parts or large molecules, as is the case in DNA and proteins. Hydrogen bonds are weaker than ionic and covalent bonds and can break easily. (Note that hydrogen bonds are among the strongest of intermolecular forces, those that occur between molecules, however.)
Biological Macromolecules
Organisms contain large, organic molecules called biological macromolecules. Organic molecules are those that contain carbon covalently bonded to hydrogen. (In contrast, inorganic molecules lack carbon bonded to hydrogen and are often simpler than organic molecules.) In addition, they may contain oxygen, nitrogen, phosphorus, sulfur, and additional elements.There are four major classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Each is an important component of the cell and performs a wide array of functions.
It is often said that life is “carbon-based”. This means that carbon atoms, bonded to other carbon atoms or other elements, form the fundamental components of many of the molecules found uniquely in living things. Other elements play important roles in biological molecules, but carbon certainly qualifies as the “foundation” element for molecules in living things. It is the bonding properties of carbon atoms that are responsible for its important role. Carbon can form four covalent bonds with other atoms or molecules. The simplest organic carbon molecule is methane (CH4), in which four hydrogen atoms bind to a carbon atom (figure \(\PageIndex{d}\)).
Carbohydrates include what are commonly referred to as simple sugars, like glucose, and complex carbohydrates such as starch. While many types of carbohydrates are used for energy, some are used for structure by most organisms, including plants and animals. For example, cellulose is a complex carbohydrate that adds rigidity and strength to the outer layer of plant cells (the cell walls).
Lipids include a diverse group of compounds that are united by a common feature: lipids are insoluble in water. Lipids perform many different functions in a cell. Cells store energy for long-term use in the form of lipids called fats. Lipids also provide insulation from the environment for plants and animals. For example, they help keep aquatic birds and mammals dry because of their water-repelling nature. Lipids are also the building blocks of many hormones and are an important constituent of the membranes that surround cells and form many of their internal structures.
Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. They are all polymers of amino acids. The functions of proteins are very diverse because there are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order. Proteins can function in facilitated chemical reactions in organisms, such as photosynthesis, transmitting messages as hormones, causing muscles to contract, and much more.
Nucleic acids are very large molecules that are important to the continuity of life. They carry the genetic blueprint of a cell and thus the instructions for its functionality. The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is the genetic material found in all organisms, ranging from single-celled bacteria to multicellular mammals. The other type of nucleic acid, RNA, is mostly involved in protein synthesis. DNA and RNA are made up of small building blocks known as nucleotides. DNA has a beautiful double-helical structure (Figure \(\PageIndex{e}\)).
Attribution
Modified by Melissa Ha from Matter from Environmental Biology by Matthew R. Fisher (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.04%3A_Ecosystems/2.4.02%3A_Matter.txt |
Biogeochemical cycles, also known as nutrient cycles, describe the movement of chemical elements through different media, such as the atmosphere, soil, rocks, bodies of water, and organisms. Biogeochemical cycles keep essential elements available to plants and other organisms.
Energy flows directionally through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during energy transformation between trophic levels. Rather than flowing through an ecosystem, the matter that makes up organisms is conserved and recycled. The law of conservation of mass states that matter is neither created nor destroyed. For example, after a chemical reaction, the mass of the products (ending molecules) will be the same as the mass of the reactants (starting molecules). The same is true in an ecosystem. Matter moves through different media, and atoms may react to form new molecules, but the amount of matter remains constant.
The biogeochemical cycles of four elements—carbon, nitrogen, phosphorus, and sulfur—are discussed below. The cycling of these elements is interconnected with the water cycle. For example, the movement of water is critical for the leaching of sulfur and phosphorus into rivers, lakes, and oceans. Today, anthropogenic (human) activities are altering all major ecosystems and the biogeochemical cycles they drive.
The Carbon Cycle
Carbon is the basic building block of all organic materials, and therefore, of living organisms. The carbon cycle is actually comprised of several interconnected cycles: one dealing with rapid carbon exchange among living organisms and the other dealing with the long-term cycling of carbon through geologic processes (figure \(\PageIndex{a}\)). The overall effect is that carbon is constantly recycled in the dynamic processes taking place in the atmosphere, at the surface and in the crust of the earth. The vast majority of carbon resides as inorganic minerals in crustal rocks. Other reservoirs of carbon, places where carbon accumulates, include the oceans and atmosphere. Some of the carbon atoms in your body today may long ago have resided in a dinosaur's body, or perhaps were once buried deep in the Earth's crust as carbonate rock minerals.
Carbon Cycles Slowly between Land and the Ocean
On land, carbon is stored in soil as organic carbon in the form of decomposing organisms or terrestrial rocks. Decomposed plants and algae are sometimes buried and compressed between layers of sediments. After millions of years fossil fuels such as coal, oil, and natural gas are formed. The weathering of terrestrial rock and minerals release carbon into the soil.
Carbon-containing compounds in the soil can be washed into bodies of water through leaching. This water eventually enters the ocean. Atmospheric carbon dioxide also dissolves in the ocean, reacting with water molecules to form carbonate ions (CO32-). Some of these ions combine with calcium ions in the seawater to form calcium carbonate (CaCO3), a major component of the shells of marine organisms. These organisms eventually die and their shells form sediments on the ocean floor. Over geologic time, the calcium carbonate forms limestone, which comprises the largest carbon reservoir on Earth.
Carbonate also precipitates in sediments, forming carbonate rocks, such as limestone. Carbon sediments from the ocean floor are taken deep within Earth by the process of subduction: the movement of one tectonic plate beneath another. The ocean sediments are subducted by the actions of plate tectonics, melted and then returned to the surface during volcanic activity. Plate tectonics can also cause uplifting, returning ocean sediments to land.
Carbon Cycles Quickly between Organisms and the Atmosphere
Carbon dioxide is converted into glucose, an energy-rich organic molecule through photosynthesis by plants, algae, and some bacteria (figure \(\PageIndex{b}\)). They can then produce other organic molecules like complex carbohydrates (such as starch), proteins and lipids, which animals can eat. Most terrestrial autotrophs obtain their carbon dioxide directly from the atmosphere, while marine autotrophs acquire it in the dissolved form (bicarbonate, HCO3).
Plants, animals, and other organisms break down these organic molecules during the process of aerobic cellular respiration, which consumes oxygen and releases energy, water and carbon dioxide. Carbon dioxide is returned to the atmosphere during gaseous exchange. Another process by which organic material is recycled is the decomposition of dead organisms. During this process, bacteria and fungi break down the complex organic compounds. Decomposers may do respiration, releasing carbon dioxide, or other processes that release methane (CH4).
Photosynthesis and respiration are actually reciprocal to one another with regard to the cycling of carbon: photosynthesis removes carbon dioxide from the atmosphere and respiration returns it (figure \(\PageIndex{c}\)). A significant disruption of one process can therefore affect the amount of carbon dioxide in the atmosphere.
Cellular respiration is only one process that releases carbon dioxide. Physical processes, such as the eruption of volcanoes and release from hydrothermal vents (openings in the ocean floor) add carbon dioxide to the atmosphere. Additionally, the combustion of wood and fossil fuels releases carbon dioxide. The level of carbon dioxide in the atmosphere is greatly influenced by the reservoir of carbon in the oceans. The exchange of carbon between the atmosphere and water reservoirs influences how much carbon is found in each.
Importance of the Carbon Cycle
The carbon cycle is crucially important to the biosphere. If not for the recycling processes, carbon might long ago have become completely sequestered in crustal rocks and sediments, and life would no longer exist (figure \(\PageIndex{e}\)). Photosynthesis not only makes energy and carbon available to higher trophic levels, but it also releases gaseous oxygen (O2). Gaseous oxygen is necessary for cellular respiration to occur. Photosynthetic bacteria were likely the first organisms to perform photosynthesis, dating back 2-3 billion years ago. Thanks to their activity, and a diversity of present-day photosynthesizing organisms, Earth’s atmosphere is currently about 21% O2. Also, this O2 is vital for the creation of the ozone layer, which protects life from harmful ultraviolet radiation emitted by the sun. Ozone (O3) is created from the breakdown and reassembly of O2.
The global carbon cycle contributes substantially to the provisioning ecosystem services upon which humans depend. We harvest approximately 25% of the total plant biomass that is produced each year on the land surface to supply food, fuel wood and fiber from croplands, pastures and forests. In addition, the global carbon cycle plays a key role in regulating ecosystem services because it significantly influences climate via its effects on atmospheric CO2 concentrations.
Human Alteration of the Carbon Cycle
Atmospheric CO2 concentration increased from 280 parts per million (ppm) to 413 ppm between the start of industrial revolution in the late eighteenth century and 2020. This reflected a new flux in the global carbon cycle—anthropogenic CO2 emissions—where humans release CO2 into the atmosphere by burning fossil fuels and changing land use. Fossil fuel burning takes carbon from coal, gas, and oil reserves, where it would be otherwise stored on very long time scales, and introduces it into the active carbon cycle. Land use change releases carbon from soil and plant biomass pools into the atmosphere, particularly through the process of deforestation for wood extraction or conversion of land to agriculture. In 2018, the additional flux of carbon into the atmosphere from anthropogenic sources was estimated to be 36.6 gigatons of carbon (GtC = 1 billion tons of carbon)—a significant disturbance to the natural carbon cycle that had been in balance for several thousand years previously. High levels of carbon dioxide in the atmosphere cause warming that results in climate change. (See Threats to Biodiversity and Climate Change for more details.)
The Nitrogen Cycle
All organisms require nitrogen because it is an important component of nucleic acids, proteins, and other organic molecules. Getting nitrogen into living organisms is difficult. Plants and algae are not equipped to incorporate nitrogen from the atmosphere (where it exists as tightly bonded, triple covalent N2) although this molecule comprises approximately 78 percent of the atmosphere. Because most of the nitrogen is stored in the atmosphere, the atmosphere is considered a reservoir of nitrogen.
The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy. Nitrogen fixation is the process of converting nitrogen gas into ammonia (NH3), which spontaneously becomes ammonium (NH4+). Ammonium is found in bodies of water and in the soil (figure \(\PageIndex{f}\)).
Three processes are responsible for most of the nitrogen fixation in the biosphere. The first is atmospheric fixation by lightning. The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates, that are carried to the earth. Atmospheric nitrogen fixation probably contributes some 5-8% of the total nitrogen fixed. The second process is industrial fixation. Under great pressure, at a temperature of 600°C (1112°F), and with the use of a catalyst (which facilitates chemical reactions), atmospheric nitrogen and hydrogen can be combined to form ammonia (NH3). Ammonia can be used directly as fertilizer, but most of it is further processed to urea and ammonium nitrate (NH4NO3).
The third process is biological fixation by certain free-living or symbiotic bacteria. Some form a symbiotic relationship with plants in the legume family, which includes beans, peas, soybeans, alfalfa, and clovers (figure \(\PageIndex{g}\)). Some nitrogen-fixing bacteria even establish symbiotic relationships with animals, e.g., termites and "shipworms" (wood-eating bivalves). Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of semi-aquatic environments like rice paddies. Although the first stable product of the process is ammonia, this is quickly incorporated into protein and other organic nitrogen compounds.
Ammonium is converted by bacteria and archaea into nitrites (NO2) and then nitrates (NO3) through the process of nitrification. Like ammonium, nitrites and nitrates are found in water and the soil. Some nitrates are converted back into nitrogen gas, which is released into the atmosphere. The process, called denitrification, is conducted by bacteria.
Plants and other producers directly use ammonium and nitrates to make organic molecules through the process of assimilation. This nitrogen is now available to consumers. Organic nitrogen is especially important to the study of ecosystem dynamics because many processes, such as primary production, are limited by the available supply of nitrogen.
Consumers excrete organic nitrogen compounds that return to the environment. Additionally dead organisms at each trophic level contain organic nitrogen. Microorganisms, such as bacteria and fungi, decompose these wastes and dead tissues, ultimately producing ammonium through the process of ammonification.
In marine ecosystems, nitrogen compounds created by bacteria, or through decomposition, collects in ocean floor sediments. It can then be moved to land in geologic time by uplift of Earth’s crust and thereby incorporated into terrestrial rock. Although the movement of nitrogen from rock directly into living systems has been traditionally seen as insignificant compared with nitrogen fixed from the atmosphere, a recent study showed that this process may indeed be significant and should be included in any study of the global nitrogen cycle.
Human activity can alter the nitrogen cycle by two primary means: the combustion of fossil fuels, which releases different nitrogen oxides into the atmosphere, and by the use of artificial fertilizers in agriculture. Atmospheric nitrogen (other than N2) is associated with several effects on Earth’s ecosystems. Nitrogen oxides (HNO3) can react in the atmosphere to form nitric acid, a form of acid deposition, also known as acid rain. Acid deposition damages healthy trees, destroys aquatic systems and erodes building materials such as marble and limestone. Like carbon dioxide, nitrous oxide (N2O) causes warming resulting in climate change.
Humans are primarily dependent on the nitrogen cycle as a supporting ecosystem service for crop and forest productivity. Nitrogen fertilizers are added to enhance the growth of many crops and plantations (figure \(\PageIndex{h}\)). The enhanced use of fertilizers in agriculture was a key feature of the green revolution that boosted global crop yields in the 1970s. The industrial production of nitrogen-rich fertilizers has increased substantially over time and now matches more than half of the input to the land from biological nitrogen fixation (90 megatons = 1 million tons of nitrogen each year). If the nitrogen fixation from legume crops is included, then the anthropogenic flux of nitrogen from the atmosphere to the land exceeds natural fluxes to the land. Fertilizers are washed into lakes, streams, and rivers by surface runoff, resulting in saltwater and freshwater eutrophication, a process whereby nutrient runoff causes the overgrowth of algae, the depletion of oxygen, and death of aquatic fauna.
The Phosphorus Cycle
Several forms of nitrogen (nitrogen gas, ammnoium, nitrates, etc.) were involved in the nitrogen cycle, but phosphorus remains primarily in the form of the phosphate ion (PO43-). Also in contrast to the nitrogen cycle, there is no form of phosphorus in the atmosphere. Phosphorus is used to make nucleic acids and the phospholipids that comprise biological membranes.
Rocks are a reservoir for phosphorus, and these rocks have their origins in the ocean. Phosphate-containing ocean sediments form primarily from the bodies of ocean organisms and from their excretions. However, volcanic ash, aerosols, and mineral dust may also be significant phosphate sources. This sediment then is moved to land over geologic time by the uplifting of Earth’s surface (figure \(\PageIndex{i}\)). The movement of phosphate from the ocean to the land and through the soil is extremely slow, with the average phosphate ion having an oceanic residence time between 20,000 and 100,000 years.
Marine birds play a unique role in the phosphorous cycle. These birds take up phosphorous from ocean fish. Their droppings on land (guano) contain high levels of phosphorous and are sometimes mined for commercial use. A 2020 study estimated that the ecosystem services (natural processes and products that benefit humans) provided by guano are worth \$470 million per year.
Weathering of rocks releases phosphates into the soil and bodies of water. Plants can assimilate phosphates in the soil and incorporate it into organic molecules, making phosphorus available to consumers in terrestrial food webs. Waste and dead organisms are decomposed by fungi and bacteria, releasing phosphates back into the soil. Some phosphate is leached from the soil, entering into rivers, lakes, and the ocean. Primary producers in aquatic food webs, such as algae and photosynthetic bacteria, assimilate phosphate, and organic phosphate is thus available to consumers in aquatic food webs. Similar to terrestrial food webs, phosphorus is reciprocally exchanged between phosphate dissolved in the ocean and organic phosphorus in marine organisms.
The movement of phosphorus from rock to living organisms is normally a very slow process, but some human activities speed up the process. Phosphate-bearing rock is often mined for use in the manufacture of fertilizers and detergents. This commercial production greatly accelerates the phosphorous cycle. In addition, runoff from agricultural land and the release of sewage into water systems can cause a local overload of phosphate. The increased availability of phosphate can cause overgrowth of algae. This reduces the oxygen level, causing eutrophication and the destruction of other aquatic species.
Eutrophication and Dead Zones
Eutrophication occurs when excess phosphorus and nitrogen from fertilizer runoff or sewage causes excessive growth of algae. Algal blooms that block light and therefore kill aquatic plants in rivers, lakes, and seas. The subsequent death and decay of these organisms depletes dissolved oxygen, which leads to the death of aquatic organisms such as shellfish and fish. This process is responsible for dead zones, large areas in lakes and oceans near the mouths of rivers that are periodically depleted of their normal flora and fauna, and for massive fish kills, which often occur during the summer months (figure \(\PageIndex{j}\)). There are more than 500 dead zones worldwide. One of the worst dead zones is off the coast of the United States in the Gulf of Mexico. Fertilizer runoff from the Mississippi River basin created a dead zone, which reached its peak size of 8,776 square miles in 2017. Phosphate and nitrate runoff from fertilizers also negatively affect several lake and bay ecosystems including the Chesapeake Bay in the eastern United States.
Everyday Connection: Chesapeake Bay
The Chesapeake Bay has long been valued as one of the most scenic areas on Earth; it is now in distress and is recognized as a declining ecosystem. In the 1970s, the Chesapeake Bay was one of the first ecosystems to have identified dead zones, which continue to kill many fish and bottom-dwelling species, such as clams, oysters, and worms (figure \(\PageIndex{k}\)). Several species have declined in the Chesapeake Bay due to surface water runoff containing excess nutrients from artificial fertilizer used on land. The source of the fertilizers (with high nitrogen and phosphate content) is not limited to agricultural practices. There are many nearby urban areas and more than 150 rivers and streams empty into the bay that are carrying fertilizer runoff from lawns and gardens. Thus, the decline of the Chesapeake Bay is a complex issue and requires the cooperation of industry, agriculture, and everyday homeowners.
Of particular interest to conservationists is the oyster population; it is estimated that more than 200,000 acres of oyster reefs existed in the bay in the 1700s, but that number has now declined to only 36,000 acres. Oyster harvesting was once a major industry for Chesapeake Bay, but it declined 88 percent between 1982 and 2007. This decline was due not only to fertilizer runoff and dead zones but also to overexploitation. Oysters require a certain minimum population density because they must be in close proximity to reproduce. Human activity has altered the oyster population and locations, greatly disrupting the ecosystem.
The restoration of the oyster population in the Chesapeake Bay has been ongoing for several years with mixed success. Not only do many people find oysters good to eat, but they also clean up the bay. Oysters are filter feeders, and as they eat, they clean the water around them. In the 1700s, it was estimated that it took only a few days for the oyster population to filter the entire volume of the bay. Today, with changed water conditions, it is estimated that the present population would take nearly a year to do the same job.
Restoration efforts have been ongoing for several years by non-profit organizations, such as the Chesapeake Bay Foundation. The restoration goal is to find a way to increase population density so the oysters can reproduce more efficiently. Many disease-resistant varieties (developed at the Virginia Institute of Marine Science for the College of William and Mary) are now available and have been used in the construction of experimental oyster reefs. Efforts to clean and restore the bay by Virginia and Delaware have been hampered because much of the pollution entering the bay comes from other states, which stresses the need for inter-state cooperation to gain successful restoration.
The new, hearty oyster strains have also spawned a new and economically viable industry—oyster aquaculture—which not only supplies oysters for food and profit, but also has the added benefit of cleaning the bay.
The Sulfur Cycle
Sulfur is an essential element for the molecules of living things. As part of the amino acid cysteine, it is critical to the three-dimensional shape of proteins. As shown in Figure \(\PageIndex{l}\), sulfur cycles among the oceans, land, and atmosphere. Atmospheric sulfur is found in the form of sulfur dioxide (SO2), which enters the atmosphere in three ways: first, from the decomposition of organic molecules; second, from volcanic activity and geothermal vents; and, third, from the burning of fossil fuels by humans.
On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and geothermal vents. Atmospheric sulfur is found in the form of sulfur dioxide (SO2), and as rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid (H2SO4). Sulfur can also fall directly from the atmosphere in a process called fallout. Also, as sulfur-containing rocks weather, sulfur is released into the soil. These rocks originate from ocean sediments that are moved to land by the geologic uplifting of ocean sediments. Terrestrial ecosystems can then make use of these soil sulfates (SO42-), which enter the food web by being taken up by plant roots. When these plants decompose and die, sulfur is released back into the atmosphere as hydrogen sulfide (H2S) gas.
Sulfur enters the ocean in runoff from land, from atmospheric fallout, and from hydrothermal vents. Some ecosystems rely on microorganisms using sulfur as a biological energy source (in contrast to ecosystems with photosynthetic producers). This sulfur then supports marine ecosystems in the form of sulfates.
Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases sulfur dioxide, which reacts with the atmosphere to form sulfuric acid. Like nitric acid, sulfuric acid contributes to acid deposition.
Suggested Supplementary Reading
Bruckner, M. 2018. The Gulf of Mexico Dead Zone. [Website]
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.04%3A_Ecosystems/2.4.03%3A_Biogeochemical_Cycles.txt |
Soil is the outer loose layer that covers the surface of Earth. Soil quality is a major determinant, along with climate, of plant distribution and growth. Soil quality depends not only on the chemical composition of the soil, but also climate, topography, and organisms living in the soil. In agriculture, the history of the soil, such as the cultivating practices and previous crops, modify the characteristics and fertility of that soil.
Importance of Soil
Soil is important to our society primarily because it provides the foundation of agriculture and forestry. Soil plays a key role in plant growth. Beneficial aspects to plants include providing physical support, water, heat, nutrients, and oxygen. Mineral nutrients from the soil can dissolve in water and then become available to plants. Through their roots, plants absorb water and minerals (e.g., nitrates, phosphates, potassium, copper, zinc). With these and carbon dioxide acquired during photosynthesis, plants produce carbohydrates, proteins, lipids, nucleic acids, and the vitamins, on which consumers depend.
Soil plays a role in nearly all biogeochemical cycles on the Earth’s surface. Global cycling of key elements such as carbon (C), nitrogen (N), phosphorous (P), and sulfur (S) all pass through soil. In the hydrologic (water) cycle, soil helps to mediate infiltration (percolating) from the surface into the groundwater. Microorganisms living in soil can also be important components of biogeochemical cycles through the action of decomposition and other processes such as nitrogen fixation.
Several elements are considered essential for plant growth. Carbon (C), hydrogen (H), and oxygen (O) are required in large quantities, but they are not absorbed as mineral nutrients from the soil. Plants obtain carbon from carbon dioxide in the atmosphere and hydrogen from the water absorbed by the roots. Oxygen atoms come from carbon dioxide acquired during and gaseous oxygen in the atmosphere (acquire through aerobic cellular respiration) as well as water. Of the mineral nutrients absorbed from the soil, macronutrients, including nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), sulfur (S), and silicon (Si) are needed by plants in significant quantities. Micronutrients are essential elements that are needed only in small quantities, but can still be limiting to plant growth since these nutrients are not so abundant in nature. Micronutrients include chlorine (Cl), iron (Fe), boron (B), manganese (Mn), sodium (Na), zinc (Zn), copper (Cu), nickel (Ni), and molybdenum (Mo). There are some other elements that tend to aid plant growth but are not absolutely essential.
Although many aspects of soil are beneficial to plants, excessively high levels of trace metals (either naturally occurring or added by humans) or applied herbicides can be toxic to some plants (figure \(\PageIndex{a}\)).
Micronutrients and macronutrients are desirable in particular concentrations and can be detrimental to plant growth when concentrations in soil solution are either too low (limiting) or too high (toxicity). Mineral nutrients are useful to plants only if they are in an extractable form in soil solutions, such as a dissolved ion rather than in solid mineral. Many nutrients move through the soil and into the root system as a result of concentration gradients, moving by diffusion from high to low concentrations. However, some nutrients are selectively absorbed by the root membranes, enabling concentrations to become higher inside the plant than in the soil.
An important factor affecting soil fertility is soil pH (the negative log of the hydrogen ion concentration). Soil pH is a measure of the acidity or alkalinity of the soil solution. On the pH scale (0 to 14) a value of seven represents a neutral solution; a value less than seven represents an acidic solution and a value greater than seven represents an alkaline solution (figure \(\PageIndex{b}\)). Soil pH affects the health of microorganisms in the soil and controls the availability of nutrients in the soil solution. Strongly acidic soils (less than 5.5) hinder the growth of bacteria that decompose organic matter in the soil. This results in a buildup of organic matter that has yet to be decomposed, which leaves important nutrients such as nitrogen in forms that are unusable by plants. Soil pH also affects the solubility of nutrient-bearing minerals. This is important because the nutrients must be dissolved in solution for plants to assimilate them through their roots. Most minerals are more soluble in slightly acidic soils than in neutral or slightly alkaline soils. Strongly acid soils (pH four to five), though, can result in high concentrations of aluminum, iron and manganese in the soil solution, which may inhibit the growth of some plants.
Several factors determine soil pH. Organic material in soil decreases pH to an extent, but it also acts as a buffer, limiting changes in pH. Climate is also important, with high amounts of rainfall increasing leaching and lowering pH. Some types of parent material, such as those high in silicon, decrease pH, while others, such as limestone increase pH.
Soil Composition
Soil consists of organic matter (about 5%), inorganic mineral matter (40-45% of soil volume), water (about 25%) and air (about 25%). The amount of each of the four major components of soil depends on the amount of vegetation, soil compaction, and water present in the soil.
The organic material consists of dead organisms in various stages of decomposition. It is dark-colored because it contains humus, partially decayed matter containing organic acids. Humus enriches the soil with nutrients, gives the soil a loose texture that holds water, and allows air to diffuse through it. Oxygen is important for plant roots and many inhabitants of the soil. The organic component of soil serves as a cementing agent, returns nutrients to the plant, allows soil to store moisture, makes soil tillable for farming, and provides energy for soil microorganisms. Most soil microorganisms—bacteria, algae, or fungi—are dormant in dry soil, but become active once moisture is available.
The inorganic material of soil consists of rock, slowly broken down into smaller particles that vary in size. Soil particles that are 100 μm to 2 mm in diameter are sand. (A micrometerμm, 10-6 m, or a millionth of a meter.) Soil particles between 2 and 100 μm are called silt, and even smaller particles, less than 2 μm in diameter, are called clay.
Soil should ideally contain 50 percent solid material and 50 percent pore space (figure \(\PageIndex{c}\)). Pore space refers to the gaps in between soil particles. The larger the soil particles, the larger the pore spaces. Water can quickly pass through large pore spaces, so soils high in sand drain easily. Smaller soil particles have more surface area relative to volume and produce narrow pore spaces. Water clings to these surfaces, and soils high in clay thus retain water. (Clay is also negatively charged, which attracts water.) About one-half of the pore space should contain water, and the other half should contain air.
Soil texture is based on percentages of sand, silt, and clay (figure \(\PageIndex{d}\)). Soils that have a high percentage of one particle size are named after that particle (a clay soil has a high percentage of clay). Other soils have a mixture of two particle sizes and very little of the third size. For example, silty clay has roughly 50% clay and 50% silt while sandy clay has 50-60% sand and 35-50% clay. Some soils have no dominant particle size and contain a mixture of sand, silt, and humus. These soils are called loams, and they are optimal for agriculture. A medium loam has roughly 40% sand, 40% silt, and 20% clay. Larger particles (sand) facilitate drainage, and small particles (clay) facilitate water retention, so loam soils both have good drainage and can remain moist. Soils that deviate slightly from a medium loam include loamy sand, sandy loam, sandy clay loam, clay loam, silty clay loam, and silty loam.
Organic Versus Mineral Soils
Soils can be divided into two groups based on how they form. Organic soils are those that are formed from sedimentation and often contain more than 30% organic matter. They form when organic matter, such as leaf litter, is deposited more quickly than it can be decomposed (figure \(\PageIndex{e}\)). Mineral soils are formed from the weathering of rocks, typically contain no more than 30% organic matter, and are primarily composed of inorganic material. Weathering occurs when biological, physical, and chemical processes, such as erosion, leaching, or high temperatures, break down rocks.
Soil Horizons
Soil distribution is not uniform because its formation results in the production of layers; together, the vertical section of a soil is called the soil profile. Within the soil profile, soil scientists define zones called horizons. A horizon is a soil layer with distinct physical and chemical properties that differ from those of other layers.
The soil profile has four distinct layers: 1) O horizon; 2) A horizon; 3) B horizon and 4) C horizon (figure \(\PageIndex{f}\)-g). Upper horizons (labeled as the A and O horizons) are richer in organic material and so are important in plant growth, while deeper layers (such as the B and C horizons) retain more of the original features of the bedrock below. Some soils may have additional layers (like the E horizon, figure \(\PageIndex{f}\)), or lack one of these layers. The thickness of the layers is also variable, and depends on the factors that influence soil formation. In general, immature soils may have O, A, and C horizons, whereas mature soils may display all of these, plus additional layers.
O horizon
The very top of the O horizon consists of partially decayed organic debris like leaves. This horizon is usually dark in color because of humus.
A horizon
The A horizon (topsoil) consists of a mixture of organic material with inorganic products of weathering, and it is therefore the beginning of true mineral soil. In this area, rainwater percolates through the soil and carries materials from the surface. The A horizon may be only 5 cm (2 in.), or it may over a meter. For instance, river deltas like the Mississippi River delta have deep layers of topsoil. Microbial processes occur in the top soil, and this horizon supports plant growth. Many organisms, such as earthworms and insects live among the plant roots in this horizon.
B horizon
The B horizon (subsoil) consists of small particles that have moved downward, resulting in a dense layer in the soil. In some soils, the B horizon contains nodules or a layer of calcium carbonate. The subsoil is usually lighter in color than topsoil and often contains an accumulation of minerals.
C horizon
The C horizon (soil base), includes the parent material, the organic and inorganic substances from which soils form. Weathering parent material represents the first steps in the chemical breakdown of rock into soil. Often the weathered parent material is underlain by the parent material itself, although in some places it has been carried from another location by wind, water, or glaciers. Beneath the C horizon lies bedrock. The chemical nature of the parent material, whether granite, limestone, or sandstone, for example, has a great influence on the fertility of the soil derived from it.
Factors Affecting Soil Formation and Composition
The fundamental factors that affect soil genesis can be categorized into five elements: climate, organisms, topography, parent material, and time. One could say that the relief, climate, and organisms dictate the local soil environment and act together to cause weathering and mixing of the soil parent material over time.
Climate
The role of climate in soil development includes aspects of temperature and precipitation. Soils in very cold areas with permafrost conditions (such as the arctic tundra) tend to be shallow and weakly developed due to the short growing season. In warm, tropical climates, soils tend to be thicker (but lacking in organic matter), with extensive leaching and mineral alteration. In such climates, organic matter decomposition and chemical weathering occur at an accelerated rate. The presence of moisture and nutrients from weathering will also promote biological activity: a key component of a quality soil. See the Biomes chapter for more details about the effect of climate on soils.
Ancient soils, sometimes buried and preserved in the subsurface, are referred to as paleosols (figure \(\PageIndex{h}\)) and reflect past climatic and environmental conditions.
Organisms
The presence of living organisms in the soil (soil biota) greatly affects soil formation and structure. A diversity of animals are found in the soil such as nematodes, spiders, insects, centipedes, millipedes, pillbugs, slugs, and earthworms (figure \(\PageIndex{i}\)). The soil also contains microorganisms like bacteria, archaea, fungi, and "protists". Animals and microorganisms can produce pores and crevices, and plant roots can penetrate into crevices to produce more fragmentation. Additionally, leaves and other material that fall from plants decompose and contribute to soil composition. Microorganisms not only decompose organic matter, but contribute to other processes in nutrient cycles, such as nitrogen fixation
Parent Material
Mineral soils form directly from the weathering of bedrock, the solid rock that lies beneath the soil, and therefore, they have a similar composition to the original rock. Other soils form in materials that came from elsewhere, such as sand and glacial drift. Materials located in the depth of the soil are relatively unchanged compared with the deposited material. Sediments in rivers may have different characteristics, depending on whether the stream moves quickly or slowly. A fast-moving river could have sediments of rocks and sand, whereas a slow-moving river could have fine-textured material, such as clay.
The type of parent material may also affect the rapidity of soil development. Parent materials that are highly weatherable (such as volcanic ash) will transform more quickly into highly developed soils, whereas parent materials that are quartz-rich, for example, will take longer to develop. Parent materials also provide nutrients to plants and can affect soil internal drainage.
Topography
Regional surface features (familiarly called “the lay of the land”) can have a major influence on the characteristics and fertility of a soil. Topography affects water runoff, which strips away parent material and affects plant growth. Soils on steep slopes are more prone to erosion and may be thinner than soils that are on relatively level ground. Infiltration, the percolating of water through the soil, is limited in steep soils.
The local topography can have important microclimatic effects. In the northern hemisphere, south-facing slopes are exposed to more direct sunlight angles and are thus warmer and drier than north-facing slopes. The cooler, moister north-facing slopes have a more dynamic plant community and thicker soils because extensive root systems stabilize the soil and reduce erosion (figure \(\PageIndex{j}\)).
Time
Time is an important factor in soil formation because soils develop over long periods. Soil formation is a dynamic process. Materials are deposited over time, decompose, and transform into other materials that can be used by living organisms or deposited onto the surface of the soil.
In general, soil profiles tend to become thicker (deeper), more developed, and more altered over time. However, the rate of change is greater for soils in youthful stages of development. The degree of soil alteration and deepening slows with time and at some point, after tens or hundreds of thousands of years, may approach an equilibrium condition where erosion and deepening (removals and additions) become balanced. Young soils (< 10,000 years old) are strongly influenced by parent material and typically develop horizons and character rapidly. Over time, as weathering processes deepen, mix, and alter the soil, the parent material becomes less recognizable as chemical, physical, and biological processes take effect. Moderate age soils (roughly 10,000 to 500,000 years old) are slowing in profile development and deepening, and may begin to approach equilibrium conditions. Old soils (>500,000 years old) have generally reached their limit as far as soil horizonation and physical structure, but may continue to alter chemically or mineralogically.
Soil development is not always continual. Geologic events such as landslides, glacier advance, or the rising of shorelines can rapidly bury soils. Erosion in rivers and shorelines can cause removal or truncation of soils, and wind or flooding slowly deposit sediment that adds to the soil. Animals can mix the soil and sometimes cause soil regression, a reversal or "bump in the road" for the normal path of development, and this increases development over time.
Soil Taxonomy
Soils are classified into one of 12 soil orders based on soil horizons, how they form, and their chemical compositions. For example, Mollisols (figure \(\PageIndex{f}\)), which are found in temperate grasslands, have a thick topsoil rich in organic content. Aridisols, on the other hand, are dry soils that contain calcium carbonate and are found in deserts. Each soil order is further divided into suborders. See USDA's The Twelve Orders of Soil Taxonomy and The Twelve Soil Orders from the University of Idaho for more details.
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.04%3A_Ecosystems/2.4.04%3A_Soils.txt |
Once fertile topsoil is lost, it is not easily replaced. Soil degradation refers to deterioration in the quality of the soil and the resultant reduction in its capacity to produce. Soils are degraded primarily by erosion, compaction, and salinization. Such processes often arise from poor soil management during agricultural activities. In extreme cases, soil degradation can lead to desertification (conversion of land to desert-like conditions) of croplands and rangelands in semi-arid regions. See the Sustainable Agriculture section for strategies to preserve soil quality (soil conservation).
Erosion
Erosion is the biggest cause of soil degradation. Soil productivity is reduced as a result of losses of nutrients, water holding capacity, and organic matter. Water holding capacity is a measure of of the soils ability to retain water. The two agents of erosion are wind and water, which act to remove the finer particles from the soil. Wind erosion occurs mostly in flat, dry areas and moist, sandy areas along bodies of water. Wind not only removes soil, but also dries and degrades the soil structure. Water erosion is the most prevalent type of erosion. It occurs when raindrops splash on the ground and when water moves down slope as a thin film, small streams, or a large stream.
Some amount of soil erosion is a natural process along sloping areas and/or in areas with soft or materials that do not stick together and are susceptible to movement by water, wind, or gravity. For instance, soil material can be mobilized in strong windstorms, along the banks of rivers, in landslides, or by wave action along coastlines. However, human activities such as construction, logging, and off-road vehicle use promote erosion by removing the natural vegetation cover protecting the soil. Agricultural practices such as overgrazing and leaving plowed fields bare for extended periods contribute to farmland erosion. Each year, an estimated two billion metric tons of soil are eroded from farmlands in the United States alone. The soil transported by the erosion processes can also create problems elsewhere (for example, by clogging waterways and filling ditches and low-lying land areas). The areas most vulnerable to soil erosion include locations with thin organic (A and O) horizons and hilly terrains (figure \(\PageIndex{a}\)).
Compaction
In modern agricultural practices, heavy machinery is used to prepare the seedbed, for planting, to control weeds, and to harvest the crop. The use of heavy equipment has many advantages in saving time and labor, but can cause compaction of soil and disruption of the natural soil biota. Much compaction is reversible and some is unavoidable with modern practices; however, serious compaction issues can occur when the equipment is used excessively during times when the soil has a high water content. The problem with soil compaction is that increased soil density limits root penetration depth and may inhibit proper plant growth.
Salinization
When considerable quantities of salt accumulate in the soil in a process known as salinization, many plants are unable to grow properly or even survive. This is especially a problem in irrigated farmland. Groundwater used for irrigation contains small amounts of dissolved salts. Irrigation water that is not absorbed into the soil evaporates, leaving the salts behind. This process repeats itself and eventually severe salinization of the soil occurs. A related problem is water logging of the soil. When cropland is irrigated with excessive amounts of water in order to leach salts that have accumulated in the soil, the excess water is sometimes unable to drain away properly. In this case it accumulates underground and causes a rise in the subsurface water table. If the saline water rises to the level of the plant roots, plant growth is inhibited.
Desertification
Land that was previously suited for growing crops may be turned into desert by climate change and the activities of humans, such as poor farming practices, livestock overgrazing, and overuse of available water. This process, called desertification, is a serious problem worldwide. Plants and soil types that are non-arid (not dry) specifically help water soak into the ground (infiltration) and water retention. When desertification begins, it leads to a reduction in vegetation and degraded soil quality, and this further increases the aridity and spreads the desert via a positive feedback loop (meaning that the processes feed on themselves promoting an increasing spiral).
Figure \(\PageIndex{b}\) shows areas of the world and their vulnerability to desertification. Note the red and orange areas in the western and midwestern United States. The Dust Bowl of the 1930s is a classic example of human-caused desertification (figure \(\PageIndex{c}\)). Poor cultivation and grazing practices -- coupled with severe drought conditions -- led to severe wind erosion of soil in a region of the Great Plains that became known as the "Dust Bowl". Wind stripped large areas of farmlands of topsoil, and formed clouds of dust that traveled as far as the eastern United States.
Sometimes there is a conflict between what is known to prevent desertification and what an individual farmer feels is needed to do to make a living. Mitigating the desertification process includes both societal steps and individual education on alternatives.
Attribution
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.04%3A_Ecosystems/2.4.05%3A_Soil_Degradation.txt |
Overview
An ecosystem engineer is any animal that creates, significantly modifies, maintains or destroys a habitat. These organisms impact both the abiotic and biotic components of a habitat and can thus completely change landscapes. One 2017 study sought to understand if beavers (classic ecosystem engineer) could even be used as a tool for habitat restoration of wetlands. Specifically, this study focused on quantifying if wetland biodiversity improved as a result of reintroducing beavers on a landscape degraded by agriculture. Figure 2.4.6a below displays some of the results in this study:
Questions
1. What is the independent (explanatory) variable and the dependent (response) variable?
2. What question(s) are the authors trying to answer with this graph?
3. What trend(s) can be observed in this graph between the 1-2 and 10-12 timetables? Support your answer by referring to appropriate patterns in the graph.
4. Do you think like the authors are satisfied with the results in the graph? Why?
5. How can the results of this graph to inform future reintroduction of beavers where wetland restoration is needed?
6. What information/patterns is not clear from this graph?
Raw Data From Above Graph(s)
Table \(\PageIndex{a}\): Raw data for average number of species observed in sample plots 1-2 years and 10-12 years after beavers were introduced. Graph by Rachel Schleiger (CC-BY-NC) modified from data in Law A, Graywood MJ, Jones KC, Ramsay P, and Willby NJ 2017.
Number Of Plots Average Number Of Species After 1-2 Years Average Number Of Species After 10-12 Years
0 3 3
20 10 28
40 11 35
60 12 38
80 13 39
100 13.5 40
130 14 41
Attribution
Rachel Schleiger (CC-BY-NC)
2.4.07: Review
Summary
After completing this chapter you should be able to...
• Differentiate between abiotic and biotic ecosystem components.
• Describe the three main categories of ecosystems.
• Explain the law of conservation of mass.
• Discuss the biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur.
• Explain how human activities have impacted these cycles and the potential consequences for Earth.
• Explain how soil characteristics influence plant growth.
• Identify and describe each component of soil.
• Distinguish among sand, silt, and clay and explain how particle size influences soil texture.
• Describe each horizon in a typical soil profile.
• Explain how soils are formed, describing each of the five major factors that affect soil formation and composition.
• Describe the major types and causes of soil degredation.
Ecosystems consist of living (biotic) and nonliving (abiotic) components. They can be classified as freshwater, marine, or terrestrial. Resistance and resilience are measures of ecosystem health.
Matter is anything that occupies space and has mass. Pure forms of matter are called elements and the smallest units of an element are atoms. Atoms form molecules through ionic, covalent, or hydrogen bonding. Molecules that contain carbon and hydrogen covalent bonds are called organic. There are four main type of large organic molecules (biological macromolecules) in organisms: carbohydrates, lipids, proteins, and nucleic acids.
The chemical elements that organisms need continuously cycle through ecosystems. Cycles of matter are called biogeochemical cycles, or nutrient cycles, because they include both biotic and abiotic components and processes. Examples of biogeochemical cycles include the carbon, nitrogen, phosphorus, and sulfur cycles, and each of these can be altered through human activities.
Soil consists of organic and inorganic material as well as water and air. The organic material of soil is made of humus, which improves soil structure and provides nutrients. Soil inorganic material consists of rock slowly broken down into smaller particles that vary in size, such as sand, silt, and loam. Soils form slowly as a result of biological, physical, and chemical processes. Soil is not homogenous because its formation results in the production of layers called a soil profile. Most soils have four distinct horizons, or layers: O, A, B, and C. Their composition is influenced by the climate, presence of living organisms, topography, parent material, and time. The processes of erosion, compaction, and desertification degrade soils. While these processes occur naturally to an extent, they are exacerbated by certain agricultural practices, deforestation, and other human activities.
Attribution
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.04%3A_Ecosystems/2.4.06%3A_Data_Dive-_Beaver_Impacts_on_Wetlands.txt |
Chapter Hook
At the North Pole there is nothing but ice and snow. The taiga (also known as the boreal forest) is the northernmost place that trees can grow. At first, trees are very sparse and stunted. Sometimes these trees can take upwards of 50 years to get bigger than a seedling. Eventually, the taiga turns into a sea of trees. There are as many trees here as in all rainforests combined, representing nearly a third of all trees on Earth. As such, the taiga is the largest carbon sink on land and contributes significantly to the contribution of oxygen in the atmosphere. The taiga is just one of Earths biomes, each is unique and extraordinary in their own ways.
Attribution
Rachel Schleiger (CC-BY-NC
• 8.1: Climate and Biomes
A biome is a large, distinctive complex of plant communities created and maintained by climate.
• 8.2: Terrestrial Biomes
There are eight major terrestrial biomes: tropical rainforests, savannas, deserts, chaparral, temperate grasslands, temperate forests, taiga (boreal forests), and Arctic tundra. Each has characteristics vegetation with adaptations suited to the climate of the biome. The vegetation is one factor determining which animals are found in a biome.
• 8.3: Aquatic Biomes
Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water still absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach.
• 8.4: Data Dive- Biome Carbon Storage
• 8.5: Review
2.05: Biomes
Biomes are large-scale environments that are distinguished by characteristic climate and vegetation (figure \(\PageIndex{a}\)). Biomes are also characterized by the animals and other organisms there, which are influenced by vegetation and climate patterns. The Earth’s biomes are categorized into two major groups: terrestrial and aquatic. Terrestrial biomes are based on land, while aquatic biomes include both ocean and freshwater biomes. Altitude and latitude, which affect temperature and precipitation determine the distribution of biomes.
Low latitudes (near the equator) have high temperatures, while high latitudes (near the poles) have low temperatures. This is because the sun hits the equator more directly. Sunlight hits the poles at an angle, reducing the intensity of light (and heat energy) per unit of area. Temperature also decreases with altitude. At high altitudes, the atmosphere is thinner and traps less heat energy from the sun. Because temperatures decline with altitude as well as latitude, similar biomes exist on mountains even when they are at low latitudes. As a rule of thumb, a climb of 1000 feet (about 300 m) is equivalent in changed flora and fauna to a trip northward of some 600 miles (966 km).
Where precipitation is moderately abundant — 40 inches (about 1 m) or more per year — and distributed fairly evenly throughout the year, the major determinant is temperature. It is not simply a matter of average temperature, but includes such limiting factors as whether it ever freezes or length of the growing season. Biomes are thus characterized not only by average temperature and precipitation but also their seasonality.
Not only does latitude influence temperature, but it also affects precipitation. For example, deserts tend to occur at latitudes of around 30° and at the poles, both north and south, driven by circulation and prevailing wind patterns in the atmosphere. The engine that drives circulation in the atmosphere and oceans is solar energy, which is determined by the average position of the sun over the Earth’s surface. Direct light provides uneven heating depending on latitude and angle of incidence, with high solar energy in the tropics, and little or no energy at the poles. Atmospheric circulation and geographic location are the primary causal agents of deserts. At approximately 30° north and south of the equator, sinking air produces trade wind deserts like the Sahara and the Outback of Australia (figure \(\PageIndex{b}\)).
The MinuteEarth video below discusses the global climate patterns which lead to deserts.
Rainshadow deserts are produced where prevailing winds with moist air dries as it is forced to rise over mountains. The prevailing winds in the western half of North America blow in from the Pacific laden with moisture. Each time this air rises up from the western slopes of, successively, the Coast Ranges, the Sierras and Cascades, and finally the Rockies, it cools and its capacity to hold moisture decreases. The excess moisture condenses to rain or snow, which drenches the mountain slopes beneath. When the air reaches the eastern slopes, it is relatively dry, and much less precipitation falls. This phenomenon is called the rainshadow effect (figure \(\PageIndex{c}\)). How much rain falls and when influences the type of biome. For example, the Great Basin Desert (figure \(\PageIndex{d}\)) is a rain shadow desert produced as moist air from the Pacific rises by lifting over the Sierra Nevada Mountain (and other) and loses moisture from previous condensation and precipitation on the rainy side of the range(s).
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.05%3A_Biomes/2.5.01%3A_Climate_and_Biomes.txt |
Because each biome is defined by climate, the same biome can occur in geographically distinct areas with similar climates (figure \(\PageIndex{a}\)). You can further explore the distribution of biomes using the HHMI Biome Viewer.
There are eight major terrestrial biomes: tropical rainforests, savannas, deserts, chaparral, temperate grasslands, temperate forests, taiga (boreal forests), and Arctic tundra.
Tropical Rainforests
Tropical rainforests, found in equatorial regions (figure \(\PageIndex{a}\)), are the most biodiverse terrestrial biome (figure \(\PageIndex{b}\)). In the Western Hemisphere, the tropical rain forest reaches its fullest development in the jungles of Central and South America. The trees are very tall and of a great variety of species. One rarely finds two trees of the same species growing close to one another. Most of the animals — mammals and reptiles, as well as birds and insects — live in the trees.
This biodiversity is under extraordinary threat primarily through logging and deforestation for agriculture. Tropical rainforests have also been described as nature’s pharmacy because of the potential for new drugs that is largely hidden in the chemicals produced by the huge diversity of plants, animals, and other organisms. The vegetation is characterized by plants with spreading roots and broad leaves. The broad-leafed trees are mostly evergreen, with leaves that persist throughout the year, but in tropical seasonal forests (see below), some are deciduous, with leaves falling off in the dry season.
The temperature and sunlight profiles of tropical rainforests are stable in comparison to other terrestrial biomes, with average temperatures ranging from 20oC to 34oC (68oF to 93oF). Month-to-month temperatures are relatively constant in tropical rainforests, in contrast to forests farther from the equator. This lack of temperature seasonality leads to year-round plant growth rather than just seasonal growth. In contrast to other ecosystems, a consistent daily amount of sunlight (11–12 hours per day year-round) provides more solar radiation and therefore more opportunity for net primary productivity (a measure of how carbon is stored by the photosynthesis that occurs in a community).
The annual rainfall in tropical rainforests ranges from 125 to 660 cm (50–200 in). Some tropical rainforests have relatively consistent rainfall whereas others (the tropical seasonal forests) have distinct wet months, in which there can be more than 30 cm (11–12 in) of precipitation, as well as dry months in which there are fewer than 10 cm (3.5 in) of rainfall. Nevertheless, the driest month of a tropical rainforest can still exceed the annual rainfall of some other biomes, such as deserts.
Tropical rainforests are characterized by vertical layering of vegetation and the formation of distinct habitats for animals within each layer. The vegetation is so dense that little light reaches the forest floor. On the forest floor is a sparse layer of plants and decaying plant matter. Above that is an understory of short, shrubby foliage. A layer of trees rises above this understory and is topped by a closed upper canopy—the uppermost overhead layer of branches and leaves. Some additional trees emerge through this closed upper canopy. These layers provide diverse and complex habitats for the variety of plants, animals, and other organisms. Many species of animals use the variety of plants and the complex structure of the tropical wet forests for food and shelter. Some organisms live several meters above ground, rarely descending to the forest floor.
Epiphytes
Epiphytes are plants that live perched on sturdier plants. They do not take nourishment from their host as parasitic plants do. Because their roots do not reach the ground, they depend on the air to bring them moisture and inorganic nutrients. Examples of epiphytes include many orchids, ferns (figure \(\PageIndex{c}\)), and bromeliads (members of the pineapple family like "Spanish moss").
Tropical Soils
While productivity is high in tropical rainforests, the soils themselves tend to be of very poor quality. Because of the high rainfall, nutrients are quickly washed out of the topsoil unless they are incorporated in the forest plants. As plant and animal debris falls to the ground, it is quickly decomposed because of the warmth and moisture there. Thus minerals are found mainly in the forest plants, not in the soil. When the plants are removed and cultivation attempted, the soils quickly lose fertility. The situation is made worse by the lack of humus. Additionally, the topsoil may be no thicker than 5 cm (~2 inches), and most of these soils have high iron and aluminum content. Once exposed to the sun, these soils quickly bake into a bricklike material that cannot be cultivated.
Savannas
Savannas have mostly perennial, herbaceous plants (non-woody plants that persist for more than one year) with scattered trees, and they are located in Africa, South America, and northern Australia. Savannas are usually hot, tropical areas with temperatures averaging from 24 °C to 29 °C (75 °F to 84 °F) and an annual rainfall of 10–40 cm (3.9–15.7 in). Savannas have an extensive dry season; for this reason, forest trees do not grow as well as they do in the tropical rainforest. As a result, grasses and forbs (herbaceous plants other than grasses) are dominant (figure \(\PageIndex{d-e}\)). Since fire is an important source of disturbance in this biome, plants have evolved well-developed root systems that allow them to quickly resprout after a fire. Depending on the region, large grazing animals like giraffes, zebras, and gazelles and their predators (cheetahs, lions, etc.) are found in savannas.
Deserts
Deserts exist between 15o and 30o north and south latitude. As discussed in the previous section (Climate and Biomes), deserts are frequently located on the downwind, or lee side, of mountain ranges due to the rain shadow effect. This is typical of the North American deserts, such as the Mohave and Sonoran deserts and the previously mentioned Great Basin Desert. Deserts in other regions (tradewind deserts), such as the Sahara and the Outback of Australia (both previously mentioned) as well as the Namib Desert in southwestern Africa and are dry because of the high-pressure, dry air descending at those latitudes.
Deserts are very dry; evaporation typically exceeds precipitation. Deserts are characterized by low annual precipitation of fewer than 30 cm (12 in) with little monthly variation and lack of predictability in rainfall. Some years may receive tiny amounts of rainfall, while others receive more. In some cases, the annual rainfall can be as low as 2 cm (0.8 in) in deserts located in central Australia (“the Outback”) and northern Africa.
Hot deserts (subtropical deserts) can have daytime soil surface temperatures above 60oC (140oF) and nighttime temperatures approaching 0oC (32oF). Cold deserts that experience freezing temperatures during the winter and any precipitation is in the form of snowfall. The largest of these deserts are the Gobi Desert in northern China and southern Mongolia, the Taklimakan Desert in western China, the Turkestan Desert, and the Great Basin Desert of the United States.
The low species diversity of this biome is closely related to its low and unpredictable precipitation. Despite the relatively low diversity, desert species exhibit fascinating adaptations to the harshness of their environment. Very dry deserts lack perennial vegetation that lives from one year to the next; instead, many plants are annuals that grow quickly and reproduce when rainfall does occur, then they die. Perennial plants in deserts are characterized by adaptations that conserve water: deep roots, reduced foliage, and water-storing stems (figure \(\PageIndex{f}\)). Seed plants in the desert produce seeds that can lie dormant for extended periods between rains. Most animal life in deserts has adapted to a nocturnal life, spending the hot daytime hours beneath the ground. The Namib Desert is the oldest on the planet, and has probably been dry for more than 55 million years. It supports a number of endemic species (species found only there) because of this great age. For example, the unusual gymnosperm Welwitschia mirabilisis the only extant species of an entire order of plants. There are also five species of reptiles considered endemic to the Namib.
Many of the animals in the desert (mammals, lizards and snakes, insects, and even some birds) are adapted for burrowing to escape the scorching heat of the desert sun. Many of them limit their forays for food to the night.
The net primary productivity of the desert is low. High productivity can sometimes be achieved with irrigation, but these gains are often only temporary because it leads to the buildup of salts and minerals. Large areas of formerly unproductive desert in the United States, Israel, and Egypt have been converted into fertile fields through irrigation. However, even the best irrigation water contains dissolved salts. Because the rainfall in deserts is so low, any water that does not immediately run off remains near the surface and is largely lost by evaporation. The salts it carries are left near the top of the soil. Their accumulation may make the soil so alkaline (basic) and so salty that it is prohibitive to agriculture (figure \(\PageIndex{g}\)). In the U. S., the situation is especially severe in the Great Basin because water flowing down from the mountains—bearing its load of dissolved salts—cannot flow on to the ocean but simply flows out onto the valley floors and evaporates.
Mediterranean Scrub (Chaparral)
The Mediterranean scrub, is also called chaparral or scrub forest and is found in California, along the Mediterranean Sea, and along the southern coast of Australia (figure \(\PageIndex{h}\)). The annual rainfall in this biome ranges from 65 cm to 75 cm (25.6–29.5 in) and the majority of the rain falls in the winter. Summers are very dry and many chaparral plants are dormant during the summertime.
The Mediterranean scrub vegetation is dominated by shrubs and is adapted to periodic fires, with some plants producing seeds that germinate only after a hot fire. The ashes left behind after a fire are rich in nutrients like nitrogen and fertilize the soil, promoting plant regrowth. Fire is a natural part of the maintenance of this biome. The trees in the chaparral are mostly oaks, both deciduous and evergreen. Scrub oaks and shrubs like manzanita and the California lilac (not a relative of the eastern lilac) form dense, evergreen thickets. All of these plants are adapted to drought by such mechanisms as waxy, waterproof coatings on their leaves. Many plants that thrive in one chaparral region are successfully cultivated in other chaparral regions. For example, vineyards, olives, and figs from their native Mediterranean and eucalyptus trees from Australia thrive in California. However, blue gum eucalyptus from Australia disrupts California ecosystems by changing the hydrology and outcompeting native plants.
Temperate Grasslands
Temperate grasslands are found throughout central North America, where they are also known as prairies (figure \(\PageIndex{i}\)), and in Eurasia, where they are known as steppes. Temperate grasslands have pronounced annual fluctuations in temperature with hot summers and cold winters. The annual temperature variation produces specific growing seasons for plants. Plant growth is possible when temperatures are warm enough to sustain plant growth, which occurs in the spring, summer, and fall.
Temperate grasslands have few trees except for those found growing along rivers or streams. The dominant vegetation tends to consist of grasses. The treeless condition is maintained by low precipitation, frequent fires, and grazing. Fires, which are a natural disturbance in temperate grasslands, can be ignited by lightning strikes. It also appears that the lightning-caused fire regime in North American grasslands was enhanced by intentional burning by humans. When fire is suppressed in temperate grasslands, the vegetation eventually converts to scrub and dense forests. Often, the restoration or management of temperate grasslands requires the use of controlled burns to suppress the growth of trees and maintain the grasses.
Annual precipitation ranges from 25.4 cm to 88.9 cm (10–35 in) and is concentrated in the summer and spring. In the plains of North America, the annual rainfall is sufficiently low (~50 cm, 20") that little or no rainfall percolates down to the water table. Calcium and other minerals are not carried below the reach of plant roots and so remain available for use. This keeps the pH and general fertility high. The grasses in undisturbed prairie are perennial. Their extensive root systems help prevent soil erosion, and the return of the season's above-ground growth to the topsoil returns minerals and provides humus to it. These advantages are diminished when annual grasses such as wheat and corn are grown instead and removed in the harvest.The self-restoring fertility of the soils of the plains states accounts for this region being the "breadbasket" of the nation (and other countries as well).
Temperate Forests
Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand (figure \(\PageIndex{i}\)). This biome is found throughout mid-latitude regions. Temperatures range between –30oC and 30oC (–22oF to 86oF) and drop to below freezing on an annual basis. These temperatures mean that temperate forests have defined growing seasons during the spring, summer, and early fall.
Temperate forests may be deciduous, mixed (with deciduous and evergreen trees), or coniferous (with evergreen conifers). Examples of temperate deciduous trees are beech, maple, oak, and hickory. The deciduous trees of temperate forests drop their leaves in the winter; thus, little photosynthesis occurs during the dormant winter period. (In other biomes, such as chaparral and tropical seasonal forests, trees or shrubs may drop their leaves during the summer or dry season.) Each spring, new leaves appear as temperature increases. Because of the dormant period, the net primary productivity of temperate forests is less than that of tropical rainforests. In addition, temperate forests show far less diversity of tree species than tropical rainforest biomes. Large stands dominated by a single species are common.
The deciduous trees of the temperate forests leaf out and shade much of the ground. However, more sunlight reaches the ground in this biome than in tropical rainforests because trees in temperate forests do not grow as tall as the trees in tropical rainforests. The soils of the temperate forests are rich in inorganic and organic nutrients compared to tropical rainforests. This is because of the thick layer of leaf litter on forest floors and reduced leaching of nutrients by rainfall. As this leaf litter decays, nutrients are returned to the soil. The leaf litter also protects soil from erosion, insulates the ground, and provides habitats for invertebrates and their predators. Deer, raccoons, and salamanders are characteristic inhabitants of temperate forests.
Precipitation is relatively constant throughout the year and ranges between 75 cm and 150 cm (29.5–59 in). Enough water falls on the soil so that much of it soaks deep into the ground and carries minerals with it. Such soils tend to be acidic and of low and (if unattended) diminishing fertility. Only by regular fertilization and liming (to restore calcium and raise pH) can productive agriculture be carried out in them. In the U.S., the soils east of the Appalachian Mountains tend to be of this sort.
Taiga
The taiga, also known as boreal forest in North America, is found roughly between 50° and 60° north latitude across most of Canada, Alaska, Russia, and northern Europe ((figure \(\PageIndex{i}\)). Boreal forests are also found above a certain elevation (and below high elevations where trees cannot grow) in mountain ranges throughout the Northern Hemisphere. This biome has cold, dry winters and short, cool, wet summers. The annual precipitation is from 40 cm to 100 cm (15.7–39 in) and usually takes the form of snow. Although precipitation is relatively low, the taiga is dotted with lakes, bogs, and marshes because the cold temperatures limit evaporation.
The long and cold winters in the boreal forest have led to the predominance of cold-tolerant cone-bearing plants. These are evergreen coniferous trees like pines, spruce, and fir, which retain their needle-shaped leaves year-round. Evergreen trees can photosynthesize earlier in the spring than deciduous trees because less energy from the sun is required to warm a needle-like leaf than a broad leaf. In the taiga, evergreen trees grow faster than deciduous trees. In addition, soils in boreal forest regions tend to be acidic with little available nitrogen. Leaves are a nitrogen-rich structure, and deciduous trees must produce a new set of these nitrogen-rich structures each year. Therefore, coniferous trees that retain nitrogen-rich needles in a nitrogen-limiting environment may have had a competitive advantage over the broad-leafed deciduous trees.
In North America, the moose is such a typical member that it has led to the name: "spruce-moose" biome. Deer, bears, and wolves are also found in the taiga. Before the long, snowy winter sets in, many of the mammals hibernate, and many of the birds migrate south.
The net primary productivity of taiga is lower than that of temperate forests and tropical rainforests. The aboveground biomass (mass of living organisms) of taiga is high because these slow-growing tree species are long-lived and accumulate standing biomass over time. Species diversity is less than that seen in temperate forests and tropical rainforests. Taiga lacks the layered forest structure seen in tropical rainforests or, to a lesser degree, temperate forests. The structure of the taiga is often only a layer of trees and the understory of low-lying plants and lichen. When conifer needles are dropped, they decompose more slowly than broad leaves; therefore, fewer nutrients are returned to the soil to fuel plant growth.
At the coldest parts of the taiga, the soil remains frozen year after year, forming a layer called permafrost. When the permafrost melts in unusually warm years, the trees are no longer supported by this hard surface and lean in different directions, forming a "drunken forest". At extreme latitudes, the trees of the taiga become stunted by the harshness of the subarctic climate. Where they finally disappear (above the "tree line"), the Arctic tundra begins.
Arctic Tundra
The Arctic tundra lies north of the subarctic boreal forests and is located throughout the Arctic regions of the Northern Hemisphere. Tundra also exists at elevations above the tree line on mountains. The average winter temperature is –34°C (–29.2°F), and the average summer temperature is 3°C–12°C (37°F –52°F). Plants in the Arctic tundra have a short growing season of approximately 50–60 days. However, during this time, there are almost 24 hours of daylight and plant growth is rapid. The annual precipitation of the Arctic tundra is low (15–25 cm or 6–10 in) with little annual variation in precipitation. And, as in the taiga, there is little evaporation because of the cold temperatures.
There is little species diversity, low net primary productivity, and low above-ground biomass. Like some of the taiga, the soils of the Arctic tundra may remain in a perennially frozen state, forming permafrost. The permafrost makes it impossible for roots to penetrate far into the soil and slows the decay of organic matter, which inhibits the release of nutrients from organic matter. The surface layer of soil above the permafrost melts in the brief summer, water is released and provides for a burst of productivity while temperatures and long days permit it. Because of these harsh growing conditions, the Arctic tundra is particularly sensitive to disturbances (disruptions that decrease biomass, such as heavy machinery passing through and squishing some of the plants).
Plants in the Arctic tundra are generally low to the ground and include low shrubs, sphagnum moss, grasses, lichens, and small flowering plants (figure \(\PageIndex{k}\)). Caribou feed on this growth as do vast numbers of insects. Swarms of migrating birds, especially waterfowl, invade the tundra in the summer to raise their young, feeding them on a large variety of aquatic invertebrates and vertebrates. As the brief arctic summer draws to a close, the birds fly south, and all but a few of the permanent residents, in one way or another, prepare themselves to spend the winter in a dormant state.
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.05%3A_Biomes/2.5.02%3A_Terrestrial_Biomes.txt |
Abiotic Factors Influencing Aquatic Biomes
Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water still absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach. While there are some abiotic and biotic factors in a terrestrial ecosystem that might obscure light (like fog, dust, or insect swarms), usually these are not permanent features of the environment. The importance of light in aquatic biomes is central to the communities of organisms found in both freshwater and marine ecosystems. In freshwater systems, temperature stratification due to differences in density is perhaps the most critical abiotic factor and is related to the energy aspects of light. The thermal properties of water (rates of heating and cooling) are significant to the function of marine systems and have major impacts on global climate and weather patterns. Marine systems are also influenced by large-scale physical water movements, such as currents; these are less important in most freshwater lakes.
Marine Biomes
The ocean is the largest marine biome. It is a continuous body of salt water that is relatively uniform in chemical composition; it is a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second kind of marine biome. Estuaries, coastal areas where salt water and fresh water mix, form a third unique marine biome.
Ocean
The physical diversity of the ocean is a significant influence on plants, animals, and other organisms. The ocean is categorized by several areas (Figure \(\PageIndex{a}\)). Each area has a distinct group of species adapted to the biotic and abiotic conditions particular to it. The intertidal zone, which is the zone between high and low tide, is the oceanic region that is closest to land. Generally, most people think of this portion of the ocean as a sandy beach. In some cases, the intertidal zone is indeed a sandy beach, but it can also be rocky or muddy. Organisms are exposed to air and sunlight at low tide and are underwater most of the time, especially during high tide. Therefore, living things that thrive in the intertidal zone are adapted to being dry for long periods of time. The shore of the intertidal zone is also repeatedly struck by waves, and the organisms found there are adapted to withstand damage from the pounding action of the waves (figure \(\PageIndex{b}\)). The exoskeletons of shoreline crustaceans (such as the shore crab, Carcinus maenas) are tough and protect them from desiccation (drying out) and wave damage. Another consequence of the pounding waves is that few algae and plants establish themselves in the constantly moving rocks, sand, or mud.
The neritic zone extends from the intertidal zone to depths of about 200 m (or 650 ft) at the edge of the continental shelf. Because light can penetrate this depth, photosynthesis can occur. The water here contains silt and is well-oxygenated, low in pressure, and stable in temperature. Phytoplankton and floating Sargassum (a type of free-floating marine seaweed) provide a habitat for some sea life found in the neritic zone. Zooplankton, protists, small fishes, and shrimp are found in the neritic zone and are the base of the food chain for most of the world’s fisheries.
Beyond the neritic zone is the open ocean area known as the oceanic zone. Within the oceanic zone there is thermal stratification where warm and cold waters mix because of ocean currents. Abundant plankton serve as the base of the food chain for larger animals such as whales and dolphins. Nutrients are scarce and this is a relatively less productive part of the marine biome. When photosynthetic organisms and the protists and animals that feed on them die, their bodies fall to the bottom of the ocean where they remain.
All of the ocean’s open water is referred to as the pelagic realm. The pelagic realm is divided into the photic, aphotic, and abyssal zones from top to bottom based on how far light reaches into the water. The photic zone, which is the portion of the ocean that light can penetrate (approximately 200 m or 650 ft). At depths greater than 200 m, light cannot penetrate; thus, this is referred to as the aphotic zone. The majority of organisms in the aphotic zone include sea cucumbers (phylum Echinodermata) and other organisms that survive on the nutrients contained in the dead bodies of organisms in the photic zone.
The deepest part of the ocean is the abyssal zone, which is at depths of 4000 m or greater. Both the aphotic and abyssal zones lack sufficient light for photosynthesis, and together, they constitute most of the ocean. The deepest part of the ocean, the Challenger Deep (in the Mariana Trench, located in the western Pacific Ocean), is about 11,000 m (about 6.8 mi) deep. To give some perspective on the depth of this trench, the ocean is, on average, 4267 m deep. These zones are relevant to freshwater lakes as well. The abyssal zone is very cold and has very high pressure, high oxygen content, and low nutrient content. There are a variety of invertebrates and fishes found in this zone, but the abyssal zone does not have plants because of the lack of light. Cracks in the Earth’s crust called hydrothermal vents are found primarily in the abyssal zone (figure \(\PageIndex{c}\)). Around these vents, bacteria that utilize the hydrogen sulfide and other minerals emitted as an energy source serve as the base of the food chain found in the abyssal zone.
The benthic realm, extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor. It is comprised of sand, silt, and dead organisms. This is a nutrient-rich portion of the ocean because of the dead organisms that fall from the upper layers of the ocean. Because of this high level of nutrients, a diversity of sponges, sea anemones, marine worms, sea stars, fishes, and bacteria exist.
Coral Reefs
Coral reefs are characterized by high biodiversity and the structures created by invertebrates that live in warm, shallow waters within the photic zone of the ocean. They are mostly found within 30 degrees north and south of the equator. The Great Barrier Reef is a well-known reef system located several miles off the northeastern coast of Australia. The coral organisms are colonies of saltwater polyps that secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, forming the underwater reef (figure \(\PageIndex{d}\)).
Corals found in shallower waters (at a depth of approximately 60 m or about 200 ft) have a mutualistic relationship with photosynthetic unicellular algae called dinoflagellates. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor, and, without this mutualism, it would not be possible for large corals to grow. Some corals living in deeper and colder water do not have a mutualistic relationship with algae; these corals attain energy and nutrients using stinging cells on their tentacles to capture prey. It is estimated that more than 4,000 fish species inhabit coral reefs. These fishes can feed on coral, other invertebrates, or the seaweed and algae that are associated with the coral.
Estuaries: Where the Ocean Meets Fresh Water
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity; mixing results in a diluted (brackish) saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives. Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies and is based on the rate of flow of its freshwater sources. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water.
The short-term and rapid variation in salinity due to the mixing of fresh water and salt water is a difficult physiological challenge for the plants and animals that inhabit estuaries. Many estuarine plant species are halophytes, plants that can tolerate salty conditions. Halophytic plants are adapted to deal with the salinity resulting from saltwater on their roots or from sea spray. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs. Other plants are able to pump oxygen into their roots. Animals, such as mussels and clams, have developed behavioral adaptations that expend a lot of energy to function in this rapidly changing environment. When these animals are exposed to low salinity, they stop feeding, close their shells, and stop using oxygen. When high tide returns to the estuary, the salinity and oxygen content of the water increases, and these animals open their shells, begin feeding, and return to using oxygen.
Freshwater Biomes
Freshwater biomes include lakes and ponds (standing water) as well as rivers and streams (flowing water). They also include wetlands, which will be discussed later. Humans rely on freshwater biomes to provide aquatic resources for drinking water, crop irrigation, sanitation, and industry. These various roles and human benefits are referred to as ecosystem services. Lakes and ponds are found in terrestrial landscapes and are, therefore, connected with abiotic and biotic factors influencing these terrestrial biomes.
Lakes and Ponds
Lakes and ponds can range in area from a few square meters to thousands of square kilometers. Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with deeper, cooler water. Like oceans, lakes and ponds have photoic zones through which light can penetrate and aphotic zones without light. Phytoplankton (small photosynthetic organisms such as algae and photosynthetic bacteria that float in the water) are found here and carry out photosynthesis, providing the base of the food web of lakes and ponds. Zooplankton (very small animals that float in the water), such as rotifers and small crustaceans, consume these phytoplankton (figure \(\PageIndex{e}\)). At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom.
Rivers and Streams
Rivers and streams are continuously moving bodies of water that carry large amounts of water from the source, or headwater, to a lake or ocean. The largest rivers include the Nile River in Africa, the Amazon River in South America (Figure \(\PageIndex{f}\)), and the Mississippi River in North America. Abiotic features of rivers and streams vary along the length of the river or stream. Streams begin at a point of origin referred to as source water. The source water is usually cold, low in nutrients, and clear. The channel (the width of the river or stream) is narrower than at any other place along the length of the river or stream. Because of this, the current is often faster here than at any other point of the river or stream.
The fast-moving water results in minimal silt accumulation at the bottom of the river or stream, therefore the water is clear. Photosynthesis here is mostly attributed to algae that are growing on rocks; the swift current inhibits the growth of phytoplankton. An additional input of energy can come from leaves or other organic material that falls into the river or stream from trees and other plants that border the water. When the leaves decompose, the organic material and nutrients in the leaves are returned to the water. Plants and animals have adapted to this fast-moving water. For instance, leeches have elongated bodies and suckers on both ends. These suckers attach to the substrate, keeping the leech anchored in place. Freshwater trout species are an important predator in these fast-moving rivers and streams.
As the river or stream flows away from the source, the width of the channel gradually widens and the current slows. This slow-moving water, caused by the gradient decrease and the volume increase as tributaries unite, has more sedimentation. Phytoplankton can also be suspended in slow-moving water. Therefore, the water will not be as clear as it is near the source. The water is also warmer. Worms and insects can be found burrowing into the mud. The higher order predator vertebrates include waterfowl, frogs, and fishes.
Wetlands
Wetlands are environments in which the soil is either permanently or periodically saturated with water. Wetlands are different from lakes because wetlands are shallow bodies of water that may periodically dry out. Emergent vegetation consists of wetland plants that are rooted in the soil but have portions of leaves, stems, and flowers extending above the water’s surface. There are several types of wetlands including marshes, swamps, bogs, mudflats, and salt marshes (figure \(\PageIndex{g}\)).
Attribution
Modified by Melissa Ha from Aquatic Biomes from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
2.5.04: Data Dive- Biome Carbon Storage
Overview
Carbon sequestration is the process by which atmospheric carbon dioxide is taken up by trees, grasses, and other plants through photosynthesis and stored as carbon in biomass (trunks, branches, foliage, and roots). Carbon storage can also occur in soil formed from organic matter found in decomposing litter. Terrestrial carbon sequestration has been a recent topic of interest because of its implications for use in climate change mitigation. The carbon storage in terrestrial biomes helps to offset sources of carbon dioxide to the atmosphere, such as deforestation, wildfires, and fossil fuel emissions. As such, carbon storage in each biome can be altered by both natural and human caused events. The figure below indicates the estimated storage above (plants) and below (soil) ground by terrestrial biomes:
Questions
1. What kind of graph is this?
2. What is the independent (explanatory) variable and the dependent (response) variable?
3. Which biome has the greatest storage in plants? What about soil?
4. What are the top three terrestrial biomes in terms of their carbon storage?
5. How can the results of this graph to inform future conservation efforts?
6. What do the results of this graph make you curious about?
Raw Data From Above Graph(s)
Table \(\PageIndex{a}\): Raw data of carbon storage (in metric tons of CO2 per hectare) above (plant) and below (soil) ground in various biomes. Graph by Rachel Schleiger (CC-BY-NC) modified from data in Islam KK, Sato N 2012.
Biome Plant Carbon Soil Carbon Total Carbon
Tropical Forests 442 450 892
Temperate Forests 208 352 561
Taiga Forests 236 1260 1496
Tundra 23 467 490
Tropical Savannas 108 430 538
Temperate Grasslands 26 865 892
Deserts/Semi-Desert Lands 6 154 160
Attribution
Rachel Schleiger (CC-BY-NC)
2.5.05: Review
Summary
After completing this chapter you should be able to...
• Describe how latitude and altitude affect temperature and precipitation, which in turn, determine the distribution of biomes.
• Compare the eight major terrestrial biomes.
• Describe how light, temperature, flow, and salinity influence aquatic biomes.
• Distinguish between marine and freshwater biomes and describe examples of each.
• Explain the different realms and zones of the ocean.
Earth has terrestrial biomes and aquatic biomes. Temperature and precipitation, and variations in both, are key abiotic factors that shape the composition of animal and plant communities in terrestrial biomes. There are eight major terrestrial biomes: tropical rainforests, savannas, deserts, chaparral, temperate grasslands, temperate forests, taiga, and Arctic tundra.
Like terrestrial biomes, aquatic biomes are influenced by abiotic factors. In the case of aquatic biomes, the abiotic factors include light, temperature, flow regime, and dissolved solids. Aquatic biomes include both marine biomes and freshwater biomes. Oceans, coral reefs, and estuaries are marine biomes while lakes, ponds, rivers, streams, and wetlands are freshwater biomes.
Attribution
Modifed by Melissa Ha from Ecosystems and the Biosphere- Chapter Resources from Environmental Biology by Matthew R. Fisher (licensed under CC-BY) | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/02%3A_Ecology/2.05%3A_Biomes/2.5.03%3A_Aquatic_Biomes.txt |
Conservation biology is the management of Earth's ecosystems with the aim of protecting species, their communities, and ecosystems from escalated extinction rates and the destruction and degradation of their habitats. This field focuses on both evaluating past, current, and future trends and creating conservation action plans to reverse trends leading to extinction and destroyed habitats. More specifically, procedures have been put in place to protect threatened species, design habitat preserves, creating breeding programs, and reconciling conservation concerns with practical human needs.
As conservation biology needs to pull from so many fields, it is an interdisciplinary subject drawing on physical, life, and social sciences, as well as natural resource management procedures. The field seeks to integrate social science policy with theories from the fields of ecology, demography, taxonomy, and genetics. The principles underlying each of these disciplines have direct implications for the management of species and ecosystems, captive breeding and reintroduction, genetic analyses, and habitat restoration. Social science disciplines not only help with putting policies in place to legally protect species and habitats but also help fund conservation actions. Conservation action plans help direct research, monitoring, and education programs that engage concerns at both local and global scales.
The goal of this unit is to overview the essential conservation biology topics as we head into an uncertain future.
Attributions
Rachel Schleiger (CC-BY-NC)
• 9: The Value of Biodiversity
Biodiversity is the variety of life on Earth. There are three main levels of biodiversity: ecosystem, species, and genetic diversity.
• 10: Threats to Biodiversity
In the history of life on Earth, five dramatic reductions in species richness (mass extinctions) have occurred. The sixth mass extinction is occurring now and is driven by human activity. Biodiversity loss can be measured by categorizing species based on extinction risk according to the Red List, but it can also be assessed at the ecosystem scale. The greatest threats to biodiversity are habitat loss, overexploitation, pollution, the spread of invasive species, and climate change.
• 11: Protecting Biodiveristy
Conservation biology involves applying ecological knowledge to protect biodiversity. Policies, non-profit organizations, approaches focused on a single species, protected areas, and individual behaviors all contribute to conservation efforts.
Thumbnail image - "Environmental protection" is in the Public Domain
03: Conservation
Chapter Hook
Most of the medicine we depend on today originated because of the diversity of plants across the globe. New medicines sometimes come from newly found species, but there is still much to learn from already discovered species as well. In 2019, research was published about a newly discovered quality on a well-known California plant called yerba santa (Eriodictyon californicum). Among native people of California, yerba santa was already well known to have medicinal qualities, but only recently did research scientists begin to test them. It was discovered that a compound in yerba santa decreases the onset of Alzheimer’s disease, a leading cause of death in the United States, by having protective and supportive qualities on the neurons in our nervous system. This research is not only vital from a medical perspective, but also exemplifies the importance of protecting diversity.
Figure \(\PageIndex{a}\) Yerba santa (Eriodictyon californicum) in bloom. Image by Breck22 (Public domain)
Biodiversity is a broad term for the variety of life on Earth. Traditionally, ecologists have measured biodiversity by taking into account both the number of species and the number of individuals of each species. However, biologists now measure biodiversity at a number of organizational levels, including ecosystem, species, and genetic diversity. This focuses efforts to preserve the biologically and technologically important elements of biodiversity. Biodiversity is important to the survival and welfare of human populations because it has impacts on our health and our ability to feed ourselves through agriculture and harvesting populations of wild animals.
Attribution
Modified by Rachel Schleiger and Melissa Ha from Importance of Biodiversity from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)
• 9.1: Ecosystem Diversity
Ecosystem diversity is the number and relative abundances of different types of ecosystems, such as coral reefs, prairies, and forests. This level of diversity is key to providing ecosystem services, natural products and processes that benefit humans, such as climate regulation, pollination, and food. The annual value of ecosystem services is estimated to be at least \$53 trillion.
• 9.2: Species Diversity
Species diversity consists of species richness, the number of species, and species evenness, the relative abundance of species. While only 1.5 million species have been described, there are estimated to be 8-11 million species on Earth. Species richness is a key source of new pharmaceuticals.
• 9.3: Genetic Diversity
Genetic diversity is variation within species and provides the raw material for evolutionary adaptation to occur. Without genetic diversity, a species or population risks susceptibility to new diseases. When all individuals are genetically similar, it is less likely that some will have disease-resistant genes.
• 9.4: Patterns of Biodiversity
Biogeography, the study of the past and present distribution of species around the world, reveals high species richness in the tropics. Most of the world's biodiversity hotspots, which have high species richness and risk of species loss, are concentrated in the tropics. These regions also have many endemic species, which are occur occur locally.
• 9.5: Data Dive- Biodiversity and Drugs
• 9.6: Review
3.01: The Value of Biodiversity
Measuring biodiversity on a large scale involves measuring ecosystem diversity, the number of different ecosystems on Earth or in a geographical area as well as their relative abundances (figure \(\PageIndex{a}\)). The loss of an ecosystem means the loss of the interactions between species and the loss of biological productivity that an ecosystem is able to create. An example of a largely extinct ecosystem in North America is the prairie ecosystem (figure \(\PageIndex{a}\)). Prairies once spanned central North America from the boreal forest in northern Canada down into Mexico. They are now all but gone, replaced by crop fields, pasture lands, and suburban sprawl. Many of the species survive, but the hugely productive ecosystem that was responsible for creating our most productive agricultural soils is now gone. As a consequence, their soils are now being depleted unless they are maintained artificially at great expense.
The soil productivity described above is an example of an ecosystem service. These are the products and processes associated with biological systems and are directly or indirectly of immense value to the well-being of people. Some ecosystem services are processes such as the regulation of climate, flooding, and disease. Nutrient cycling, pollination, and regulation of crop pests are ecosystem services important to food production (see the Food Production and Ecosystem Services box below). The water cycle provides fresh water, and photosynthesis adds oxygen to our air. Other ecosystem services are human provisions including food, fuel, and fiber (such as cotton for clothing or timber). Medicines are another important provision (see Importance of Species Diversity). Furthermore, healthy ecosystems allow for recreational activities, such as hiking, kayaking, and camping, and educational opportunities, such as field trips. Nature is also the basis for a significant part of aesthetic and spiritual values held by many cultures.
In 1997, Robert Costanza and his colleagues estimated to annual value of ecosystem services to be \$33 trillion dollars (\$53 trillion in 2019 dollars), and many consider this to be an underestimation. For comparison the gross domestic product of the United States in 2020 was \$21 trillion. Valuing ecosystem services can be difficult, particular for those services that are processes rather than provisions. One strategy is to calculate replacement cost. For example, how much would it cost to control a pest population if it was not regulated by natural processes? Figure \(\PageIndex{b}\) illustrates the value of a few ecosystem services.
Food Production and Ecosystem Services
Food production relies on several interacting ecosystem services. Most soils contain a huge diversity of organisms that maintain nutrient cycles, breaking down organic matter into nutrient compounds that crops need for growth. These organisms also maintain soil texture that affects water and oxygen dynamics in the soil that are necessary for plant growth. Replacing the work of these organisms in forming arable (farmable) soil is not practically possible. They occur within ecosystems, such as soil ecosystems, as a result of the diverse metabolic activities of the organisms living there, but they provide benefits to human food production, drinking water availability, and breathable air.
Other key ecosystem services related to food production are plant pollination and crop pest control. It is estimated that honeybee pollination within the United States brings in \$1.6 billion per year; other pollinators contribute up to \$6.7 billion. Over 150 crops in the United States require pollination to produce. Many honeybee populations are managed by beekeepers who rent out their hives’ services to farmers. Honeybee populations in North America have been suffering large losses caused by a syndrome known as colony collapse disorder, a phenomenon with complex and interacting causes.
Other pollinators include a diverse array of other bee species and various insects and birds. Loss of these species would make growing crops requiring pollination impossible, increasing dependence on other crops. A 2002 study by Claire Kremen and colleagues found that native pollinators in Central California (those that historically occurred there; figure \(\PageIndex{c}\) and d) provided full pollination to watermelon crops. This was only true on organic farms that were located near the natural habitat for these pollinators, highlighting the importance of sustainable farming practices and habitat conservation in preserving ecosystem services. Essentially, in a healthy ecosystem, native pollinators eliminated the need for rented honeybee hives. Note that while honeybees are valuable in an agricultural setting, they are not native to North America and can disrupt ecosystems by competing with native bees.
Finally, humans compete for their food with crop pests, most of which are insects. Pesticides control these competitors, but these are costly and lose their effectiveness over time as pest populations adapt. They also lead to collateral damage by killing non-pest species as well as beneficial insects like honeybees, and risking the health of agricultural workers and consumers. Moreover, these pesticides may migrate from the fields where they are applied and do damage to other ecosystems like streams, lakes, and even the ocean (see Industrial Agriculture and Environmental Toxicology). Ecologists believe that the bulk of the work in removing pests is actually done by predators and parasites of those pests, but the impact has not been well studied. A review found that in 74 percent of studies that looked for an effect of landscape complexity (forests and fallow fields near to crop fields) on natural enemies of pests, the greater the complexity, the greater the effect of pest-suppressing organisms. Another experimental study found that introducing multiple enemies of pea aphids (an important alfalfa pest) increased the yield of alfalfa significantly. This study shows that a diversity of pests is more effective at control than one single pest. Loss of diversity in pest enemies will inevitably make it more difficult and costly to grow food. The world’s growing human population faces significant challenges in the increasing costs and other difficulties associated with producing food.
Attributions
Modified by Melissa Ha from the following sources: | textbooks/bio/Ecology/Environmental_Science_(Ha_and_Schleiger)/03%3A_Conservation/3.01%3A_The_Value_of_Biodiversity/3.1.01%3A_Ecosystem_Diversity.txt |
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