CHAPTER OVERVIEW 23: Conservation Biology Learning Objectives Understand and explain the scientific process as related to conservation biology Be able to put the current biodiversity crisis in a historical perspective Identify and understand the main threats to biodiversity Show an understanding of the importance of biodiversity to human life Explain how biodiversity loss can be stopped, or slowed 23.1: The Science of Conservation Biology 23.2: Biodiversity Loss over time 23.3: Threats to Biodiversity 23.4: Scientist Spotlight - Scott Taylor 23.5: Importance of Biodiversity 23.6: Preserving Biodiversity Summary Biodiversity is declining rapidly at a global scale, leading to a human-caused sixth mass extinction. Conservation biology aims to document earth's biological diversity, to understand how humans impact this diversity, and to explore potential solutions to biodiversity decline. The major current threats to biodiversity include habitat loss, overexploitation, invasive species, pollution, and climate change - habitat loss is the most important, particularly in terrestrial habitats, and has lead to around 50% of all biodiversity loss. Preserving biodiversity has numerous benefits to humans through the protection of ecosystem services. 23: Conservation Biology is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
23.1: The Science of Conservation Biology
: East Africa's great migration is one of the most famous wildlife spectacles on Earth. Each year, tens of thousands of
tourists from around the world flock to the region to see the 1.7 million common wildebeest (Connochaetes taurinus, LC) and
hundreds of thousands of other plains mammals make their way from Tanzania's Ngorongoro Conservation Area, through the
Serengeti Plains, to Kenya's Maasai Mara National Reserve. "Wildebeest Migration in Serengeti National Park, Tanzania" by
Daniel Rosengren is licensed under CC BY 4.0.
Popular interest in protecting biological diversity--which describes the amazing range of species, genetic diversity within each species, and the multitude of Earth's complex biological communities with their associated ecosystem processes--has intensified during the past few decades. During this time, scientists and the public have recognized that biological diversity (often shortened to biodiversity) is being lost at increasing rates. Across the world, human activities are destroying ecological communities that have developed over millions of years. Over the next several decades, thousands of species and millions of populations will likely go extinct.
The fundamental driver of all the biodiversity losses we are currently witnessing is a rapidly expanding human population coupled
with increased consumptive needs. In 1850, after roughly 300,000 years of Homo sapiens on the planet, there were around 1 billion
people on Earth. By 1987, not even 140 years later, the world's human population had surpassed 5 billion. By 2017, there were 7.5
billion humans globally, of which over 1 billion lived in Sub-Saharan Africa (World Bank, 2019). With this many people, the
human population grows by tens of millions of people each year, even with modest population growth Figure
matters worse, Sub-Saharan Africa has the fastest population growth rate in the world, with a projected human population estimate
of over 4 billion people by the year 2100--a number that is well beyond the ecological capacity of the region to support.
: Sub-Saharan Africa's human population crossed the 1 billion mark in 2015. At the current annual population growth
rate of 2.7%, more than 28 million people will be added to the region in 2019. This number will escalate each subsequent year as
increases are compounded. Sources: Biraben, 2003; World Bank, 2019, CC BY 4.0.
To survive and prosper, people use natural resources. They harvest and use oil, water, and wildlife products, and convert natural ecosystems for agriculture, cities, roads, and industrial activities. This consumption, which reduces natural habitat and the associated wildlife populations, is intensifying because of the demands of a rapidly increasing human population. Consumption of resources also increases as countries develop and industrialize: the average citizen of the USA uses five times more resources than the average global citizen, 11 times more than the average Chinese citizen, and 32 times more than the average Kenyan citizen (Worldwatch Institute, 2015). This growth in the number of humans, together with their ever-more-intensive use of natural resources, is the fundamental driver behind most current species extinctions.
For conservation biologists and other nature lovers, the widespread extinction of species and destruction of natural ecosystems are incredibly discouraging.
Conservation Biology as a Discipline As a distinct scientific field, conservation biology is an integrated, multidisciplinary subject that developed in response to the challenge of preserving populations, species, ecosystems, and biological interactions. The main aim of conservation biology is to ensure the long-term preservation of biodiversity. To achieve its aim, conservation biology has set three goals: To document Earth's biological diversity. To investigate how humans influence species, evolution, and ecosystem processes. To investigate practical approaches to protect and restore biological communities, maintain genetic diversity, and prevent the extinction of species. The first two goals describe typical scientific research investigating objective facts. The third goal, however, is a part of what makes conservation biology a normative discipline; that is, conservation biology incorporates human values, not just facts, to understand and achieve its value-laden goals (Lindenmayer & Hunter, 2010). In this sense, conservation biology is related to environmentalism, in which people aim to protect the natural environment for its own sake. However, conservation biology is at its core a scientific discipline; it is founded on scientific principles. This is not to say you must be a scientist to practice conservation biology; there are many people who are not scientists who apply the principles of conservation biology in their professional and personal lives. The emergence of conservation biology as a distinct scientific field in the 1970s has given rise to the formation of various formal societies representing the field in a united voice. Most notable among these is the Society for Conservation Biology (SCB, Figure ), which is a non-profit international professional organization with a mission to advance "the science and practice of
conserving the Earth's biological diversity". To facilitate opportunities where like-minded people can share ideas locally, the SCB has regional branches, including an active Africa Section (http://conbio.org/groups/sections/africa) which hosts regular conferences. In addition to the SCB, a great number of other local, national, and regional conservation organizations also exist and act as mouthpieces for grassroots movements and as custodians of nature. Many of these groups focus on specific animals or local protected areas. Others organically adapt their missions and visions in response to a specific need or threat. For example, established in 1913 as an exchange forum between collectors of rare plants, the Botanical Society of South Africa now actively works toward protecting those rare plants in their natural habitats.
: The logo of the Society for Conservation Biology (SCB) has several layers of symbolism. Enclosed in the circle of
life are ocean waves, representing change. The bird symbolises beauty, and the leaves (the bird's wings) remind us of nature's
productivity. Image courtesy of SCB, all rights reserved.
In recent years, conservation practice has evolved from just a plan to save the environment to a vision that includes sustainable development and social justice.
Conservation biology also has a history of adapting to new challenges. The very first conservation activities, in Africa and beyond, were geared towards securing the rights to valuable natural resources for people in powerful positions, such as kings and tribal chiefs, enforced through a strictly adherence to cultural norms and customary laws. But as a growing human population expanded its influence on the environment, and wildlife started to decline, earliest conservation models gradually shifted towards fortress conservation approaches (Wilshusen et al., 2002) which aimed to shield wildlife from people by setting aside protected areas where human activities were strictly controlled.
Today, however, as human populations are exploding, and consumption is increasing, even protected areas are increasingly unable
to withstand the multitude of threats to biodiversity that ignore property boundaries and political borders. In response, fortress
conservation approaches are beginning to make way for large-scale integrated activities that highlight the social and economic
benefits of biodiversity conservation. To do this, new alliances are being formed and new agendas are being established, such as
those that directly link human health with environmental health (Box
). These integrated conservation philosophies that
pursue strategies that benefit both humans and biodiversity show much promise because they focus on fundamental extinction
drivers, and advocate for more inclusive sustainable development. In this way, the practice of conservation has evolved from just a
plan to save the environment to a vision that accomplishes its goals through sustainable development and social justice.
Yet, as we consider how to best invest limited conservation resources, some difficult questions arise. With seemingly more work to be done than can be accomplished, should we let some species go extinct (Bottrill et al., 2008)? Which species? Who decides? How can we even dare to think that we can play god? Such questions predictably bring about strongly opinionated and emotional debate (Soulé, 2013 vs. Marvier, 2014; Tallis & Lubchenco, 2014). Given the successful track record of fortress conservation initiatives in preventing extinctions despite limited budgets (Young et al., 2014), as well as the promising progress of more complex peoplecentred initiatives (Pooley et al., 2014), it seems clear that conservation relies on some balance between these two conservation philosophies (Sodhi et al., 2011). Conservation biologists of tomorrow will be able to fine-tune the balance between these strategies by closely inspecting the successes and failures of our actions today.
Conservation Through Public Health: A Case Study
Gladys Kalema-Zikusoka Conservation Through Public Health, Kampala, Uganda.
Conservation Through Public Health (CTPH) is a grassroots non-governmental organization (NGO) and non-profit that promotes biodiversity conservation by enabling people, wildlife, and livestock to coexist. The organization was founded in 2003 after fatal scabies skin disease outbreaks in mountain gorillas (Gorilla beringei beringei, EN) were traced to people living around Bwindi Impenetrable National Park, Uganda, who had limited access to basic health services (Kalema-Zikusoka et al., 2002). Since then, CTPH has contributed to conservation and sustainable development in Africa by improving human and animal health and welfare in and around protected areas.
One of the main goals of CTPH is to reduce disease transfer between humans and gorillas. We accomplish this through an
integrated population, health, and environment (PHE) program that was established in 2007 with funding from the US Agency
for International Development (USAID). As a first step, piloted around Bwindi, CTPH held consultative meetings with local
leaders, during which at least one Village Health and Conservation Team (VHCT) volunteer was selected from each village and
two from each parish (consisting of 11 villages) to oversee distribution of family planning supplies. This initiative rapidly
expanded into a sustainable social service delivery network that promotes family planning, hygiene, and sanitation. The
network resulted in a 20% to 60% (national average is 30%) increase in new users to modern family planning, and a 10% to
60% increase in adoption of hand washing facilities at homes visited by VHCTs. VHCT volunteers also refer people suffering
from infectious diseases and malnutrition to local health centres and promote more sustainable alternative livelihoods. Another
group of community volunteers, the "Human and Gorilla Conflict Resolution" (HUGO) team, in turn collect gorilla faecal
samples left on communal land to monitor their health Figure
, and visually monitor gorillas for clinical signs of disease
inside and outside protected areas (Gaffikin & Kalema-Zikusoka, 2010). In the process, we have seen reduced disease
incidences in the gorillas, reduced conflict between people and gorillas, and improved attitudes toward conservation. One
unintended outcome has been increased gender equality: men are now more involved in family planning, and women are more
: A park ranger from the Uganda Wildlife Authority teaching HUGO community volunteers how to collect
faecal samples from gorilla night nests during a CTPH training workshop. Photograph by CTPH, CC BY 4.0.
Our experience in initiating and managing PHE programs for the past 10 years has taught us several lessons. One of the most important lessons to ensure project sustainability is to regularly engage with local leaders and the government. The Uganda Wildlife Authority, Uganda's Ministry of Health, and local health centres all attend CTPH meetings with VHCTs. Attendance
by and representation of these groups not only informs them of our activities, but also provides a platform to inform or train the VHCTs in what they would like them to disseminate to the local communities. We have also learnt that PHE-implementing partners and projects need to be well-suited to each other and each site; this remains true even though health needs are often the same, regardless of the location. For example, at Mount Elgon National Park in Uganda, we found that training VHCTs in reducing conflict with park management played a key role in changing community attitudes toward conservation. In contrast, at Virunga National Park, Democratic Republic of the Congo (DRC), we found that VHCTs needed to work more closely with local health centres to prevent disease transmission between people and gorillas, and to promote family planning in a largely Catholic country. Lastly, we found that establishing income-generating projects for groups rather than individuals was key to sustaining VHCT networks and program goals beyond donor funding cycles where we have had no volunteer dropouts in the first 10 years of initiating the PHE program. These key components were accomplished by initiating livestock group enterprises and by encouraging VHCT volunteers to invest generated income into Village Saving and Loan Associations (see http://www.care.org/vsla). The Role of Conservation Biologists While there are a few extinctions that have only one cause, more generally, extinctions occur because several factors acted simultaneously and/or sequentially. Blaming a certain industry or specific group of people for an extinction (or other biodiversity loss) is thus simplistic, ineffective, and often counter-productive. Though challenging, a better approach would be to better understand how local, national, and international links led to those losses, and to find viable alternatives to prevent it from happening again. To succeed in this challenge, conservation biologists should strongly consider taking on one or more of several roles: Conservation biologists should be curious. The world around us is full of natural wonders waiting to be discovered. These discoveries underpin conservation action, by allowing us to define all the different components of biodiversity, enabling us to better understand the needs of different species, and providing us with opportunities to celebrate our conservation successes. Conservation biologists must be good listeners. Sometimes, the only difference between attracting a new ally and making an enemy, or between developing a landscape and saving a species from extinction, is the way we communicate. Conservationists must be careful and respectful listeners, especially to opposing perspectives. Careful listening is particularly important in rural areas, where villagers often have practical concerns related to their daily contact with wildlife, such as staying safe and preventing crop damage and livestock loss. Quite often, those villagers may also have unique insights into wildlife ecology that could prove valuable in local conservation measures. Conservation biologists must be law-abiding citizens. Activities that involve wildlife and ecosystems are regulated by laws and regulations. These laws are important because ethical boundaries differ from person to person--activities acceptable to one group of people may be considered harmful by another. As conservation biologists, abiding by environmental laws is especially important if we want others to take those laws seriously. Laws are important because ethical boundaries differ from person to person--activities acceptable to one person may be immensely harmful to another. Conservation biologists should become effective communicators. They should be able to discuss the problems facing biodiversity in depth, as well as the consequences of losing biodiversity, to as broad a range of people as possible. Groups like hunters, community leaders and organizers, and church leaders may be interested in participating in conservation efforts once they recognize that their activities, health, and emotional well-being depend on conservation action. Conservation biologists could become politically active leaders, so that they can influence public opinion and policy. As a starting point, those interested in this role can join a conservation organization to learn more about broader issues. They could also use their personal networks to form alliances with lawyers, citizen groups, and politicians. Conservation biologists could become pro-active land managers. Those taking on this task must be willing to walk on the land and go out on the water to find out what is really happening. They should also talk with local people to communicate their knowledge to others in ways that are clear and easily understood. Above all, a conservation biologist must be honest. To encourage effective action, both from the public and through policy, conservationists must present arguments backed by reliable evidence. To do otherwise, conservation biologists could lose
credibility, which would very likely delay or even compromise conservation efforts. It is worth taking a moment to distinguish between two important pillars of conservation action, namely conservation advocacy and conservation science. Conservation advocacy describes the roles that conservation biologists adopt to guide social, political, and economical systems towards a personally-preferred outcome--adopting environmentally-friendly practices; incorporating these activities makes conservation biology a normative discipline. Conservation science, in contrast, describes activities that conservation biologists undertake to generate knowledge, like objectively describing biodiversity and measuring biodiversity's response to stressors and safeguards. While conservation advocacy and conservation science often support and inform each other as to the next steps required for "doing conservation", it is important to distinguish between these two pillars to ensure that policymakers and other stakeholders in the environment understand when we advocate for personal preferences and when we offer objective findings (Rykiel, 2001; Lackey, 2007; Nelson & Vucetich, 2009). The next section will further expand on the importance of science in conservation biology.
The field of conservation biology applies scientific methods to achieve its goals. Like the medical sciences, which apply principles
from physiology, anatomy, and genetics to problems of human health, conservation biologists solve biodiversity problems using
principles from fields, such as mathematics, veterinary medicine, social sciences, and several natural sciences (Figure
Conservation biology differs from these and other component disciplines in that its primary goal is the long-term preservation of
biodiversity. Unlike many other scientific fields, conservation biology can also be described as a crisis discipline (Soulé, 1985;
Kareiva & Marvier, 2012). That is, conservation biologists are often required to take creative steps to respond to imminent threats,
typically without complete knowledge of the systems requiring attention. Conservation scientists must also articulate long-term
visions for conservation beyond solving immediate problems.
: Conservation biology draws from many other sciences to protect biodiversity. It is closely related to natural resource
management, which aims to manage biodiversity primarily for the benefit of humans. Integrated conservation and development
projects (ICDP) are projects that manage nature for the benefit of both humans and biodiversity. After Kareiva and Marvier, 2012;
To be effective, conservation biologists must demonstrate the relevance of their findings to a range of stakeholders. To be successful in this task, the importance of sound scientific principles cannot be over-emphasized. Nature is a complex network of many interdependent connections and feedback loops. Science is underpinned by principles that provide conservationists the
necessary quantitative and qualitative tools to better measure and control for all these different aspects of biodiversity. Such measurements allow us to gain a better understanding of complex natural systems, and the consequences of human activities. Reliable, unbiased data obtained from sound and transparent scientific methods also facilitate policymaking that is too often based on value judgments by non-experts who must balance many needs and different sources of information (Ntshotsho et al., 2015). One of the cornerstones of modern science is to identify a hypothesis (a proposed explanation for a specific observation) to evaluate. The best hypotheses, often expressed as goals or objectives, are usually those that are SMART: Specific: not overly general Measurable: has both units and a method of measurement Attainable: realistic to achieve Relevant: related to what needs to be accomplished Time-bound: achievable within a specific timeframe Identifying SMART goals and objectives is an essential aspect of conservation biology. Without such benchmarks, practitioners cannot know whether their tasks were successful, or when management actions should be adjusted to achieve success. While this may seem obvious, many previous conservation projects have failed because biologists neglected to set SMART goals and objectives (Tear et al., 2005). While lofty, "We're going to save all species" is not a SMART conservation goal because it is overly general, hard to measure, unrealistic, and not time-bound. In contrast, "We want to protect 25% of our country's wetlands within the next 10 years" is a SMART goal because it sets a very clear and measurable objective. In general, it is wise to set smaller shortterm (e.g. quarterly), and medium-term (e.g. annual) goals as one works towards long-term (e.g. 5-10 years) objectives; this allows one to constantly assess progress, which in turn provides opportunities for celebrations and strategic adjustments as and when needed. Conservation biology's ethical principles Conservation biology rests on a set of underlying ethical principles that is generally agreed upon (Soulé, 1985) and can be summarized as follows: The diversity of species and biological communities should be preserved: Most people appreciate biodiversity. Hundreds of millions of people visit national parks, game reserves, zoos, botanical gardens, and aquaria each year. They spend money and take actions to protect these places and species. People also recognize that biodiversity has economic value, whether through tourism, consumption, or other services. The untimely extinction of populations and species should be prevented: Throughout history, species have occasionally died off as a result of natural, non-human causes. The loss of a local population was generally temporary until a new population established itself through dispersal. However, human activities have increased the rate at which species are going extinct by more than a hundredfold. Meanwhile, there is no similar increase in the rate at which new populations and species are being created. Ecological complexity should be maintained: In complex natural environments, biodiversity expresses many of its most valuable features and interactions. Although the biodiversity of species may be partially preserved in captivity, maintaining ecological complexity requires that natural areas be preserved. Evolution should continue: Evolution creates new species, increases biodiversity over time, and facilitates adaptation to changing environmental conditions. People can help preserve these evolutionary processes by maintaining genetic diversity in wild populations and allowing populations to exchange genetic material. In captivity, many natural evolutionary processes do not occur, which can hamper survival when species are reintroduced in the wild. Biodiversity has intrinsic value: The value of species, communities, and ecosystems does not depend on their utility to people. They are intrinsically valuable on their own, with unique evolutionary histories and ecological roles. There are certain iconic
species that people simply want to have around, but other, lesser-known species or species seen as problematic to people are not less valuable. These principles are not absolute, nor are conservation biologists required to agree with them--they are actively discussed and debated. But many individuals and organizations agree with two, three, or all the principles, and support conservation efforts.
Nkengifor Nkeshia Valery, Regina International Cameroon, Member of Union Farms of Africa, Yaoundé, Cameroon.
What happened over the past 200 years that we have arrived where we are? How did we get to this modern paradox? A society where we cherish comfort at the cost of the ever-increasing destruction of our planet. Never in the history of humanity has the environment been degraded to the point that even the air we breathe has become cancerous. Animals are exploited by industries at an alarming rate and those remaining are killed to enrich a privileged few. And all this evil happens with our complicity as indirect consumers. Our inheritance from God, the source of all our nourishment, does not belong to us. Yet it has been bought and exploited by multinational corporations and financial markets that hinder us from cultivating sustainably. We are pushed to feed ourselves and our crops with chemical products that are dangerous to our long-term health. We are also experiencing the start of the sixth mass extinction episode of biodiversity (Ceballos et al., 2017). As a result, the natural world has declared World War III against humanity. This is a war fought not by nation against nation, but that the environment has declared against the whole human race. This war condemns us to live in an illusion of freedom; we are, in fact, destroyed at an increasing rate by different dangerous diseases and rendered slaves of the polluted environments that we blindly accept. The question we need to ask is not whether we should act to save our planet, but what future and meaning we are going to give the word "HUMANITY". We are all actors in a civilization that we are constructing; to quote the Indian leader Mahatma Gandhi: "If we could change ourselves, the tendencies in the world would also change. As a man changes his own nature, so does the attitude of the world change towards him. [...] We need not wait to see what others do". Let us pause and ask ourselves what we want the future to say of us. Are we a destructive generation, or a generation that is ready to sustainably preserve its biodiversity? It is a question every reader needs to ponder. The future is judging no one and blaming no one, but it needs us to change our habits towards protecting the world's biodiversity.
To change our attitude and make the world a better place, I drafted the following poem with passion to see my words become action for every lover of biodiversity
WORLD CHANGERS We are a people of peace called forth out of humanity into restoring life to our natural habitat. We are governed and guided by a sense of sustainability. Conservation and protection is our priority in all things at all times we are led and driven by the spirit of an environment free of pollution we are called to effect and affect every life that we come in contact with towards the sustainable development of the environment. We are called by humanity to be world changers we refuse to conform with the thinking pattern of the world system because we are world changers.
Contributors and Attributions Written and curated by A. Wilson and N. Gownaris (Gettysburg College) with material from the following open-access sources: © 2019 J.W. Wilson and R.B. Primack, CC BY 4.0 https://doi.org/10.11647/OBP.0177.01 13.1: What is Conservation Biology? by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.1: Conservation Biology is Still Evolving by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.2: The Role of Conservation Biologists by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177.
1.3: The Value of Scientific Methods by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.4: Environmental Ethics by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 23.1: The Science of Conservation Biology is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts. 13.1: What is Conservation Biology? by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.1: Conservation Biology is Still Evolving by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.2: The Role of Conservation Biologists by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.3: The Value of Scientific Methods by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177. 1.4: Environmental Ethics by John W. Wilson & Richard B. Primack is licensed CC BY 4.0. Original source: https://doi.org/10.11647/OBP.0177.
23.2: Biodiversity Loss over time Human activity is the driving force behind the current biodiversity crisis, which is causing great species loss in a short time period. Learning Objectives Explain the biodiversity crisis Describe how biodiversity has changed through geological time as a result of mass extinctions Describe the biodiversity loss associated with the Pleistocene extinction Describe the biodiversity loss during the Holocene extinction
The Biodiversity Crisis Traditionally, ecologists have measured biodiversity, a general term for the variety of species present in the biosphere, by taking into account both the number of species and their commonness. Biodiversity can be estimated at a number of levels of the organization of living things. These estimation indexes, which came from information theory, are most useful as a first step in quantifying biodiversity between and within ecosystems, yet they are less useful when the main concern among conservation biologists is simply the loss of biodiversity. However, biologists recognize that measures of biodiversity, in terms of species diversity, may help focus efforts to preserve the biologically or technologically important elements of biodiversity. Predictions of species loss within the next century, a tiny amount of time on geological timescales, range from 10 percent to 50 percent. The five previous extinctions on this scale were caused by cataclysmic events that changed the course of the history of life in each instance. Earth is now in one of those times.
The Lake Victoria cichlids provide an example through which we can begin to understand biodiversity. The biologists studying cichlids in the 1980s discovered hundreds of cichlid species representing a variety of specializations to particular habitat types and specific feeding strategies: eating plankton floating in the water, scraping and then eating algae from rocks, eating insect larvae from the bottom, and eating the eggs of other species of cichlid. The cichlids of Lake Victoria are the product of an adaptive radiation. An adaptive radiation is a rapid (less than three million years in the case of the Lake Victoria cichlids) branching through speciation of a phylogenetic tree into many closely-related species; typically, the species "radiate" into different habitats and niches. The Galápagos finches are an example of modest adaptive radiation with 15 species. The cichlids of Lake Victoria are an example of spectacular adaptive radiation that includes about 500 species.
At the time biologists were making this discovery, some species began to quickly disappear. A culprit in these declines was a species of large fish that was introduced to Lake Victoria by fisheries to feed the people living around the lake. The Nile perch was introduced in 1963, but was not a problem until the 1980s when its population began to surge by consuming cichlids, driving species after species to the point of extinction (the disappearance of a species). In fact, there were several factors that played a role in the extinction of perhaps 200 cichlid species in Lake Victoria. These factors included not only the Nile perch, but also the declining lake water quality due to agriculture and land clearing on the shores of Lake Victoria, and increased fishing pressure. Scientists had not even cataloged all of the species present, so many were lost that they were never named. The diversity is now a shadow of what it once was.
: Lake Victoria in Africa, shown in this satellite image, was the site of one of the most extraordinary evolutionary
findings on the planet, as well as a casualty of devastating biodiversity loss.
Biodiversity Change through Geological 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. Both are natural "birth" and "death" processes of macroevolution. When speciation rates begin to outstrip extinction rates, the number of species will increase; likewise, the number of species will decrease when extinction rates begin to overtake speciation rates. Throughout earth's history, these two processes have fluctuated, sometimes leading to dramatic changes in the number of species on earth.
: Extinction occurrences, as reflected in the fossil record, have fluctuated throughout earth's history. Sudden and
dramatic losses of biodiversity, called mass extinctions, have occurred five times.
Paleontologists have identified five strata in the fossil record that appear to show sudden and dramatic losses in biodiversity known as mass extinctions. There are many lesser, yet still dramatic, extinction events, but the five mass extinctions have attracted the most research. 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 Phanerozoic (since 542 million years ago). In most cases, the hypothesized causes are still controversial. The fossil record of the mass extinctions was the basis for defining periods of geological history, so they typically occur at the transition point between geological periods. The transition in fossils from one period to another reflects the dramatic loss of species and the gradual origin of new species.
: The transitions between the five main mass extinctions can be seen in the rock strata. The table shows the time that
The Ordovician-Silurian extinction event is the first-recorded mass extinction and the second largest. During this period, about 85 percent of marine species (few species lived outside the oceans) became extinct. The main hypothesis for its cause was a period of glaciation followed by warming. These two extinction events, cooling and warming, were separated by about 1 million years; the climate changes affected temperatures and sea levels. Some researchers have suggested that a gamma-ray burst caused by a nearby supernova is a possible cause of the Ordovician-Silurian extinction. The gamma-ray burst would have stripped away the earth's ozone layer, causing intense ultraviolet radiation from the sun. It may account for climate changes observed at the time. The late Devonian extinction may have occurred over a relatively long period of time. Its causes are poorly-understood and it appears to have have affected only marine species. The end-Permian extinction was the largest in the history of life. Estimates predict that 96 percent of all marine species and 70 percent of all terrestrial species were lost.The causes for this mass extinction are not clear, but the leading suspect is extended and widespread volcanic activity that led to a runaway global-warming event. The oceans became largely anoxic, suffocating marine life. Terrestrial tetrapod diversity took 30 million years to recover after the end-Permian extinction. The Permian extinction dramatically altered earth's biodiversity composition and the course of evolution. The causes of the Triassic-Jurassic extinction event are not clear. Hypotheses of climate change, asteroid impact, and volcanic eruptions have been argued. The extinction event occurred just before the breakup of the supercontinent Pangaea; although, recent scholarship suggests that the extinctions may have occurred more gradually throughout the Triassic. The causes of the end-Cretaceous extinction event are the ones that are best understood. It was during this extinction event, about 65 million years ago, that the dinosaurs, the dominant vertebrate group for millions of years, disappeared from the planet (with the exception of a theropod clade that gave rise to birds). Indeed, every land animal that weighed more then 25 kg became extinct. The cause of this extinction is now understood to be the result of a cataclysmic impact of a large meteorite or asteroid off the coast of what is now the Yucatán Peninsula. This hypothesis, proposed first in 1980, was a radical explanation based on a sharp spike in the levels of iridium (which rains down from space in meteors at a fairly constant rate, but is otherwise absent on earth's surface) at the rock stratum that marks the boundary between the Cretaceous and Paleogene periods. The Cretaceous-Paleogene (K-Pg) boundary marked the disappearance of the dinosaurs in fossils, as well as many other taxa. The researchers who discovered the iridium spike interpreted it as a rapid influx of iridium from space to the atmosphere (in the form of a large asteroid), rather than a slowing in the deposition of sediments during that period. It was a radical explanation, but the report of an appropriately aged and sized impact crater in 1991 made the hypothesis more credible. Now, an abundance of geological evidence supports the hypothesis. Recovery times for biodiversity after the end-Cretaceous extinction were shorter, in geological time, than for the end-Permian extinction: on the order of 10 million years.
: In 1980, Luis and Walter Alvarez, Frank Asaro, and Helen Michels discovered, across the world, a spike in the
concentration of iridium within the sedimentary layer at the K-Pg boundary. These researchers hypothesized that this iridium spike
was caused by an asteroid impact that resulted in the K-Pg mass extinction. In the photo, the iridium layer is the light band.
The Pleistocene Extinction The Pleistocene Extinction is one of the lesser extinctions and a relatively-recent one. It is well known that the North American, and to some degree Eurasian, megafauna disappeared toward the end of the last glaciation period. The extinction appears to have happened in a relatively-restricted time period between 10,000-12,000 years ago. In North America, the losses were quite dramatic and included the woolly mammoths (last dated about 4,000 years ago in an isolated population), mastodons, giant beavers, giant ground sloths, saber-toothed cats, and the North American camel, to name just a few. The possibility that the rapid extinction of these large animals was caused by over-hunting was first suggested in the 1900s; research into this hypothesis continues today. It seems probable that over-hunting was a factor in extinctions in many regions of the world.
: Giant ground sloths, relatives of the living South American tree sloths, lived across much of North America. The
giant sloths disappeared, along with the mammoths, mastodons, and many other large animals, at the end of the Pleistocene Epoch.
In general, the timing of the Pleistocene extinctions correlated with the arrival of humans and not with climate -change events, which is the main competing hypothesis for these extinctions. The extinctions began in Australia about 40,000 to 50,000 years ago, 10,000 to 20,000 years after the arrival of humans in the area. A marsupial lion, a giant one-ton wombat, and several giant kangaroo
species disappeared. In North America, the extinctions of almost all of the large mammals occurred 10,000 to 12,000 years ago, several thousand years after the first evidence of humans in North America. All that are left are the smaller mammals such as bears, elk, moose, and cougars. Finally, on many remote oceanic islands, the extinctions of many species occurred with the coincidence of human arrivals. Not all of the islands had large animals, but when there were large animals, they were lost. Madagascar was colonized about 2,000 years ago; the large mammals (prosimians) that lived there became extinct. Eurasia and Africa do not show this pattern, but they also did not experience a recent arrival of humans. Humans arrived in Eurasia hundreds of thousands to over one million years ago, after the origin of the species in Africa. This topic remains an area of active research and hypothesizing. It seems clear that even if climate played a role, human hunting was an additional factor in the extinctions. Present-Time Extinctions The sixth, or Holocene, mass extinction appears to have begun earlier than previously believed and is mostly due to the activities of Homo sapiens. Since the beginning of the Holocene period, there have been numerous recent extinctions of individual species that are recorded in human writings. Most of these coincide with the expansion of the European colonies in the 1500s. One of the earlier and popularly-known examples of extinction in this period is the dodo bird. The dodo bird lived in the forests of Mauritius, an island in the Indian Ocean, but became extinct around 1662. It was hunted for its meat by sailors as it 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. Another example, Steller's sea cows, became extinct in 1768.The sea cow, first discovered by Europeans in 1741, was hunted for meat and oil. The last of the species was killed in 1768, which amounts to 27 years between the species' first contact with Europeans and its extinction. In addition, the last living passenger pigeon died in a zoo in Cincinnati, Ohio in 1914. This species was hunted and suffered from habitat loss through the clearing of forests for farmland. Furthermore, in 1918, the last living Carolina parakeet died in captivity. This species, once common in the eastern United States, was a victim of habitat loss and hunting as well. Adding to the extinction list, the Japanese sea lion, which inhabited a broad area around Japan and the coast of Korea, became extinct in the 1950s due to overfishing. The Caribbean monk seal, found in the Caribbean Sea, was driven to extinction through hunting by 1952. 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 extinct species of vertebrates after 1500 AD, 86 of which were made extinct by over-hunting or overfishing. Estimates of Present-Time Extinction Rates Estimates of extinction rates are hampered by the fact that most extinctions are probably happening without observation since there are many organisms that are of less interest to humans and many that are undescribed. The background extinction rate is estimated to be about one per million species per year (E/MSY). For example, assuming there are about ten million species in existence, the expectation is that ten species would become extinct each year. 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. However, this value may be underestimated for three reasons. First, many species would not have been described until much later in the time period, so their loss would have gone unnoticed. Secondly, the number of recently-extinct species is increasing because extinct species now are being described from skeletal remains. Lastly, 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 closer to 100 E/MSY. The predicted rate by the end of the century is 1500 E/MSY. A second approach to estimating present-day extinction rates is to correlate species loss with habitat loss by 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. Studies have shown that the number of species present increases as the size of the island increases. This phenomenon has also been shown to hold true in other habitats as well. Turning this relationship around, if the habitat area is reduced, the number of species living there will also decline. Estimates of extinction rates based on habitat loss and species-area relationships have suggested that with about 90 percent habitat loss an expected 50 percent of species would become extinct. Species-area estimates have led to species extinction rate calculations of about 1000 E/MSY and higher. In general, actual observations do not show this amount of loss, suggesting that there is a delay in extinction. Recent work has also called into
question the applicability of the species-area relationship when estimating the loss of species. This work argues that the speciesarea relationship leads to an overestimate of extinction rates. A better relationship to use may be the endemics-area relationship. Using this method would bring estimates down to around 500 E/MSY in the coming century. Note that this value is still 500 times the background rate. Contributors and Attributions Written and curated by A. Wilson and N. Gownaris (Gettysburg College) with material from the following open-access sources: 47.1A: Loss of Biodiversity by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.1C: Biodiversity Change through Geological Time by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.1D: The Pleistocene Extinction by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.1E: Present-Time Extinctions by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 23.2: Biodiversity Loss over time is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts. 47.1A: Loss of Biodiversity by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.1C: Biodiversity Change through Geological Time by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.1D: The Pleistocene Extinction by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.1E: Present-Time Extinctions by Boundless (now LumenLearning) is licensed CC BY-SA 4.0.
23.3: Threats to Biodiversity Learning Objectives Describe the effects of habitat loss to biodiversity and concept of sustainability Explain why overharvesting is a threat to biodiversity Describe the impact of exotic and invasive species on native species Summarize the impact of pollution on species diversity Evaluate climate change and its impact on biodiversity
According to the 2020 Living Planet Report (https://livingplanet.panda.org/en-us/), there are five key drivers of biodiversity loss:
1. Habitat Loss (Changes in land and sea use, including habitat loss and degradation) 2. Species Overexploitation 3. Invasive species and disease 4. Pollution 5. Climate change
Of these, habitat loss is the most important, accounting for around half of all biodiversity loss (but see Box
to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource
exploitation. The human population requires resources to survive and grow, and 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 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. Environmental issues, such as toxic pollution, have specific targeted
effects on species, but they are not generally seen as threats at the magnitude of the others.
It should be noted that biodiversity doesn't just mean the loss of species, it also means a loss of the number of individuals of each species. In an analysis of the abundance of almost 21,000 populations, across 4,392 species of mammals, birds, fish, reptiles and amphibians, the Living Planet Index shows an average 68% decline in monitored populations between 1970 and 2016. Or put another way, on average less than one-third of the populations of these species found in 1970 remain. Further, many of these species were probably already present in much-depleted numbers in 1970, because human-driven biodiversity loss has been happening for thousands of years.
The IUCN Red List tracks the extinction status of thousands of species across the world, and assesses the threats to each. In a study published in Nature, Sean Maxwell and colleagues documented the threats to 8,688 near-threatened and threatened species that have been fully-assessed. This means this study will capture the threats of some taxonomic groups better than others. We know much more about the world's mammals, birds, reptiles and amphibians, than we do about its fungi and insects. All bird and mammal species have been assessed but only 0.1% of fungi species have. But most of the key drivers of extinction risk for these studied groups are similar to the lesser-studied ones: for example, insects are highly threatened by agriculture and habitat loss.
The headline message is that the largest threats to wildlife is overexploitation (Figure
meat, products such as horns and medicines, logging, and fishing - and agriculture. These have been the largest threats to
biodiversity for millennia, and this still holds true today.
In the chart we see the number of species that are threatened by each group of threats. You will notice that these sum to much greater than the 8,688 threatened species that the authors studied. This is because more than 80% of the species were affected by more than one major threat. Species that are under threat from human poaching might also be under threat from deforestation and loss of their habitats.
Overexploitation is the biggest threat. Nearly three-quarters (72%) of the studied species - that's 6,241 of them - were under pressure from hunting, fishing or logging of forests. Agriculture - which includes arable farming, livestock, timber plantations and aquaculture - was also a massive threat. Nearly two-thirds (62%) of species were affected. In this analysis, Habitat Loss is included in several categories, for example as part of Overexploitation (logging), Agriculture (conversion of land to crop farming or livestock farming), Urban Development (e.g housing), and Landscape Modification. These threats are not only the biggest pressures on all species that are near-threatened or threatened, we also see that they dominate for the species closest to extinction - the endangered and critically endangered ones.
: The numbers of species threatened with extinction by specific driver of biodiversity loss.
Habitat Loss Humans rely on technology to modify their environment and replace certain functions that were once performed by the natural ecosystem. Other species cannot do this. Elimination of their ecosystem--whether it is a forest, a desert, a grassland, a freshwater estuarine, or a marine environment--will kill the individuals in the species. Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct. Human destruction of habitats 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 products including food products, cosmetics, and biodiesel in Europe.
: (a) One species of orangutan, Pongo pygmaeus, is found only in the rainforests of Borneo, and the other species of
orangutan (Pongo abelii) is found only in the rainforests of Sumatra. These animals are examples of the exceptional biodiversity of
(c) the islands of Sumatra and Borneo. Other species include the (b) Sumatran tiger (Panthera tigris sumatrae) and the (d)
Sumatran elephant (Elephas maximus sumatranus), both critically endangered species. Rainforest habitat is being removed to make
way for (e) oil palm plantations such as this one in Borneo's Sabah Province. (credit a: modification of work by Thorsten Bachner;
credit b: modification of work by Dick Mudde; credit c: modification of work by U.S. CIA World Factbook; credit d: modification
of work by "Nonprofit Organizations"/Flickr; credit e: modification of work by Dr. Lian Pin Koh)
According to Global Forest Watch, 9.7% of tree cover was lost globally from 2002 to 2019, and 9% of that occurred in Indonesia
and Malaysia (where Sumatra and Borneo are located). Figure
shows the average annual change in forest area around the
world from 1990 to 2015. In the tropics, these losses certainly also represent the extinction of species because of high levels of
endemism (species unique to those areas).
: Average annual change in forest area globally from 2005 to 2015. China is dark green, indicating that have gained
more than 500 "kilohectares" (kha) of forest. Medium green indicates countries that have gained 250-500 kha, including the the
United States, India, Ghutan, and Bangladesh. Light green indicates countries that have gained 50-250 khA, including Chile, Spain,
France, Italy, Turkey, Iran, Russia, Vietnam, and Thailand. Indonesia and Brazil lost more than 500 kha of forest (marked with dark
red). Countries that lost 500-250 kha are marked with medium red, including Bolivia, Argentina, Nigeria, Democratic Republic of
the Congo, Tanzania, Zimbabwe, and Myanmar. Countries that lost 250-50 kha are marked with light red and an asterisk (*). These
include Mexico, Honduras, Nicaragua, Venezuela, Colombia, Ecuador, Peru, Paraguay, Mali, Burkina Faso, Benin, Cameroon,
Chad, Sudan, Ethiopia, Somalia, Uganda, Angola, Namibia, Botswana, Zimbabwe, Mozambique, Cambodia, North Korea, and
Australia. No data has been collected for Antarctica. All other regions have had lost or gained less than 50 kha in forest area. Image
by FAO, 2015. Global Forest Resources Assessment. FAO. Rome (Open Access Policy).
Everyday Connection: 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 stream in the United States, which is the world's largest consumer of wood products, is illegally logged. A 2012 United Nations and Interpol report estimated that the illegal timber trade is worth $30-100 billion each year. Most of the illegal products are imported from countries that act as intermediaries and are not the originators of the wood.
: The sawmill in Uaxactun, Guatamala is Forest Stewardship Council (FSC) certified and provides good income
from a sustainable resource for not only the saw operators but also many others who help keep the operation running. Image by
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; therefore, 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 (Figure ). Certification applies to specific products, not to a producer; some producers' products may not have certification while other products are certified. There are certifications other than the FSC, but these are run by timber companies 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. Worldwide, for example, the conversion of land to agriculture and cultivation have led to significant losses in grassland ecosystems. In North America, nearly 70% of the tallgrass prairie ecosystem (which once covered 142 million acres) has been converted to agriculture, and losses from other causes, such as urban development, have brought the total to about 90%. Current estimates indicate that agricultural activity and cultivation systems now cover nearly 25% of the Earth's surface.
Rivers and streams are important ecosystems and are frequently the target of habitat modification through building and from damming or water removal. Damming of rivers affects flows and access to all parts of a river. Altering a flow regime can reduce or eliminate populations that are adapted to seasonal changes in flow. For example, an estimated 91 percent of river lengths in the United States have been have modifications like dams, to create energy or store water; levees, to prevent flooding; or dredging or rerouting, to create land that is more suitable for human development. 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. The category "wetlands" includes many types of ecosystems, but current estimates indicate that about 50% of the world's wetland habitat has been lost. The former extent of wetland habitats worldwide (fresh, brackish and salt) is difficult to determine but certainly exceeded a billion acres.
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.
Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States. To begin, select "Visit the online mapper."
Habitat fragmentation occurs when the living space of a species is divided into discontinuous patches. For example, a mountain
highway could divide a forest habitat into separate patches. This is especially problematic for consumers at the top of the food
chain, which require large ranges to find adequate prey. Additionally, habitat fragmentation separates individuals from potential
mates. Wildlife corridors mitigate the damage of habitat fragmentation by connecting patches with suitable habitat. For example,
the bridge over a highway could allow animals to move between habitat patches (Figure
adjacent to bodies of water, such as streams, can serve as natural wildlife corridors when left intact.
: This overpass on the Trans-Canada Highway between Banff and Lake Louise, Alberta, serves as a wildlife corridor.
"Wildlife overpass Trans-Canada Hwy between Banff and Lake Louise Alberta" by WikiPedant is licensed under CC BY-SA 4.0.
Sustainability is a concept that describes how biological systems remain diverse and productive over time. Long-lived and healthy wetlands and forests are examples of sustainable biological systems. For humans, sustainability is the potential for long-term maintenance of well-being, which has ecological, economic, political, and cultural dimensions. Sustainability requires the reconciliation of environmental, social, and economic demands, which are also referred to as the "three pillars" of sustainability. Healthy ecosystems and environments are necessary for the survival and flourishing of humans and other organisms, and there are a number of ways to reduce humans' negative impact on the environment. One approach is environmental management, which is based largely on information gained from earth science, environmental science, and conservation biology. A second approach is management of human consumption of resources, which is based largely on information gained from economics. A third, more recent, approach adds cultural and political concerns into the sustainability matrix. Loss of biodiversity stems largely from the habitat loss and fragmentation produced by human appropriation of land for development, forestry and agriculture as natural capital is progressively converted to human-made capital. At the local human
scale, sustainability benefits accrue from the creation of green cities and sustainable parks and gardens. Similarly, environmental problems associated with industrial agriculture and agribusiness are now being addressed through such movements as sustainable agriculture, organic farming, and more-sustainable business practices.
: Since the Neolithic Revolution, nearly half of the world's forests have been destroyed for human use.
Sustainable practices, which preserve environments for long-term maintenance and well-being, can help preserve habitats and
Species Overexploitation Overharvesting, also called overexploitation, refers to harvesting a renewable resource to the point of diminishing returns. Ecologists use the term to describe populations that are harvested at a rate that is unsustainable, given their natural rates of mortality and capacities for reproduction. The term applies to natural resources such as wild medicinal plants, grazing pastures, game animals, fish stocks, forests, and water aquifers. Sustained overharvesting can lead to the destruction of the resource, and is one of the five main activities - along with pollution, introduced species, habitat fragmentation, and habitat destruction - that threaten global biodiversity today. All living organisms require resources to survive. Overharvesting these resources for extended periods of time can deplete natural resources to the point where they are unable to recover within a short time frame. Humans have always harvested food and other resources they have needed to survive; however, human populations, historically, were small and methods of collection limited to small quantities. Exponential increase in human population, expanding markets, and increasing demand, combined with improved access and techniques for capture, are causing the exploitation of many species beyond sustainable levels. As mentioned above, sustained overharvesting is one of the primary threats to biodiversity. Overharvesting can lead to resource destruction, including extinction at the population level and even extinction of whole species. Depleting the numbers or amount of certain resources can also change their quality; for example, the overharvesting of footstool palm (a wild palm tree found in Southeast Asia, the leaves of which are used for thatching and food wrapping) has resulted in its leaf size becoming smaller. Overharvesting not only threatens the resource being harvested, but can directly impact humans as well--for example by decreasing the biodiversity necessary for medicinal resources. A significant proportion of drugs and medicines are natural products which are derived, directly or indirectly, from biological sources. However, unregulated and inappropriate harvesting could potentially lead to overexploitation, ecosystem degradation, and loss of biodiversity; further, it can negatively impact the rights of the communities and states from which the resources are taken. Overexploitation of species can also result in cascade effects, particularly if a habitat loses its apex predator. Because of the loss of the top predator, a dramatic increase in their prey species can occur. In turn, the unchecked prey can then overexploit their own food resources until population numbers dwindle, possibly to the point of extinction. 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. Bluefin tuna are in danger of extinction. The once-abundant
Mediterranean swordfish fishery have been depleted to commercial and biological exhaustion. Figure
overfishing in the U.S. Despite considerable effort, few fisheries are managed sustainability.
: Map of overfishing and overfished stocks in the U.S. by region. Stocks on the overfishing list are being harvested
too quickly, and those on the overfished list have population sizes that are too low. For example, stocks of Chinook salmon, Coho
salmon, and Pacific sardines are overfished in the Pacific. Some species, including stocks of Pacific bluefin tuna and Atlantic cod,
are on both the overfishing and overfished lists. Image by NOAA (public domain).
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.
Overharvesting is a serious threat to many species, especially aquatic ones. Common resources - or resources that are shared, such as fisheries - are subject to an economic pressure known as "the tragedy of the commons," in which essentially no harvester has a motivation to exercise restraint in harvesting from a certain area, because that area is not owned by that harvester. The natural outcome of harvesting common resources is their overexploitation. For example, most fisheries are managed as a common resource even when the fishing territory lies within a country's territorial waters; because of this, fishers have very little motivation to limit their harvesting, and in fact 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 (for example, whales) economic forces will always drive toward fishing the population to extinction.
: Overharvesting fisheries is an especially salient problem because of a situation termed the
tragedy of the commons. In this situation, fishers have no real incentive to practice restraint when
harvesting fish because they do not own the fisheries.
Early efforts to control overfishing used several kinds of regulations on quotas, fishing effort, and gear. Some forms of fishery management limit the number of fish that can be caught in an entire fishery. Under a total allowable catch (TAC) system, fishers can fish when and how they want, but once the quota for the fishery has been met, fishing must stop until the next season. Unfortunately, TAC policies do not solve the underlying problem that fishermen compete for the fish, and often yield perverse incentives and undesirable outcomes such as overcapitalization of the industry (Beddington, Agnew, & Clark, 2007) and races between fishing boat crews to catch fish before the quota is reached. In the well-known case of the Alaskan halibut fishery, the race became so extreme that the fishing season was reduced to a single 24-hour mad dash; given that fish are perishable, this temporal clumping of the catch is not a desirable outcome. Resource economists developed the idea of a tradable permit scheme to help manage fisheries. Individual tradable quota (ITQ) schemes are cap-and-trade policies for fish, where total catch is limited but fishers in the fishery are given permits that guarantee them a right to a share of that catch. Players in the fishery can sell their quota
shares to each other (helping the catch to flow voluntarily to the most efficient boats in the industry) and there is no incentive for captains to buy excessively large boats or fish too rapidly to beat the other boats to the catch. ITQ policies have rationalized the Alaskan halibut fishery completely: the fish stock is thriving, overcapitalization is gone, and the fish catch is spread out over time (Levy, 2010). ITQs have also been implemented in the fisheries of New Zealand, yielding large improvements in the biological status of the stocks (Annala, 1996).
For the most part, fishery extinction is not equivalent to biological extinction--the last fish of a species is rarely fished out of the ocean. But there are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. Also, there are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing.
A related consequence of fishing practices is "bycatch," animals that fishers sometimes catch and discard because they do not want them, cannot sell them, or are not allowed to keep them. Bycatch can be fish, but also includes other animals such as dolphins, whales, sea turtles, and seabirds that become hooked or entangled in fishing gear. Fishing boats are forbidden in some places from using conventional longlines because that gear yields high levels of bycatch and kills endangered leatherback turtles.
Overfishing can result in a radical restructuring of the marine ecosystem in which a dominant species is so overexploited that it no longer serves its ecological function. For example, overfishing a tertiary consumer could causes populations of secondary consumers to increase. Secondary consumers would then feed on primary consumes (like zooplankton), decreasing their population size. With fewer zooplankton, populations of primary producers (phytoplankton, or photosynthetic microorganisms) would be unregulated.
Sustainable seafood is a movement that has gained momentum as more people become aware of overfishing and environmentallydestructive fishing methods. Sustainable seafood is seafood from either fished or farmed sources that can maintain or increase production in the future without jeopardizing the ecosystems from which it was acquired. In general, slow-growing fish that reproduce late in life, such as orange roughy, are vulnerable to overfishing and are considered unsustainable seafood. Seafood species that grow quickly and breed young, such as anchovies and sardines, are much more resistant to overfishing and are therefore labeled "sustainable" and promoted as good alternatives. You can find more information about sustainable seafood from Seafood Watch, the WWF Seafood Guide, or the EDF Seafood Selector.
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 4,000 species--despite making up only 1 percent of marine habitat. Most home marine aquaria are stocked with wild-caught organisms, not cultured organisms. Although no species is known to have been driven extinct by the pet trade in marine species, 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.
Terrestrial animals may be overexploited as sources of food, garments, jewelry, medicine, or pets. For example, the poaching of
elephants for their valuable ivory and rhinos for their horns, which are used in traditional medicine, is a major threat to these
species. 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. Harvesting of pangolins for their scales and meat, and as curiosities, has led to a drastic decline in
: Pangolins are threatened by overexploitation. "Manis temminckii" by David Brossard is licensed under CC-BY 2.0.
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.
Some plant and fungal species are also overexploited, particularly if they are slow-growing. For example, stocks of wild ginseng,
which is valued for its health benefits, are dwindling. Peyote cactus, which causes hallucinations and is used in sacred ceremonies,
is also declining. Yarsagumba, dead moth larvae that were infected by fungal parasites (caterpillar fungus, Ophiocordyceps
sinensis), is overexploited because it is highly valued in traditional medicine and used as an aphrodisiac (Figure
: Yarsagumba is a combination of moth larvae and the fungus that infected and killed it. "Yarsagumba" by Punya is licensed under CC BY-SA 4.0.
Exotic Species Non-native (exotic) refers to species occurring outside of their historic distribution. Exotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems, 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. I Invasive species can cause ecological and economic damage. They threaten other species through competition for resources, predation, or disease. For example, Kudzu (Pueraria lobata), which is native to Japan, was introduced in the United States in 1876. It was later planted for soil conservation. Problematically, it grows too well in the southeastern United States--up to a foot a day. It is now a pest species and covers over 7 million acres in the southeastern United States. 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; Figure
). Whether enjoying a forest hike, taking a summer boat trip, or simply walking
down an urban street, you have likely encountered an invasive species.
: In the United States, invasive species like (a) purple loosestrife (Lythrum salicaria) and the (b) zebra mussel
(Dreissena polymorpha) threaten certain aquatic ecosystems. Some forests are threatened by the spread of (c) common buckthorn
(Rhamnus cathartica), (d) garlic mustard (Alliaria petiolata), and (e) the emerald ash borer (Agrilus planipennis). The (f) European
starling (Sturnus vulgaris) may compete with native bird species for nest holes. (credit a: modification of work by Liz West; credit
b: modification of work by M. McCormick, NOAA; credit c: modification of work by E. Dronkert; credit d: modification of work
by Dan Davison; credit e: modification of work by USDA; credit f: modification of work by Don DeBold)
Explore an interactive global database of exotic or invasive species.
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
) 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.
: The brown tree snake, Boiga irregularis, is an exotic species that has caused numerous extinctions on the island of
Guam since its accidental introduction in 1950 (credit: NPS).
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 ship ballast. The zebra mussels in the Great Lakes have cost the industry 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 of native crabs. 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 (those that historically occurred in the area and are adapted to the local ecosystem) for these resources and alters 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. 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
). 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 toad (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 Batrachochytrium dendrobatidis and
: This Limosa Harlequin Frog (Atelopus limosus), an endangered species from Panama, died from a fungal disease
called chytridiomycosis. The red lesions are symptomatic of the disease (credit: Brian Gratwicke).
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
). 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 unclear, but one logical presumption would be that recreational cavers unintentionally brought the fungus on
: This little brown bat in Greeley Mine, Vermont, March 26, 2009, was found to have white-nose syndrome (credit:
Biological Control of Invasive Species One reason why invasive species proliferate dramatically outside of their native range is due to release from predators. This means that parasites, predators, or herbivores that usually regulate their populations are not present, allowing them to outcompete or overpredate native species, which are still regulated. Based on this principle, organisms that regulate the invasive species populations have been introduced to the newly colonized areas in some cases. The release of organisms (or viruses) to limit population size is called biological control. As described in the examples below, biological control of invasive species has had varying success, exacerbating the problem in some cases and solving it in others.
Introduced into Australia, this Prickly-pear Cactus (Opuntia) soon spread over millions of hectares of range land driving out forage plants. In 1924, the cactus moth, Cactoblastis cactorum, was introduced (from Argentina) into Australia. The caterpillars of the moth are voracious feeders on prickly-pear cactus, and within a few years, the caterpillars had reclaimed the range land without harming a single native species. However, its introduction into the Caribbean in 1957 did not produce such happy results. By 1989, the cactus moth had reached Florida, and now threatens five species of native cacti there.
The leaf beetle (Galerucella calmariensis) has been introduced to suppress purple loosestrife, a noxious weed (Figure
combination of four biological controls, including the leaf beetle were released in Minnesota since 1992. While it has not
eradicated populations of this invasive species, biological control largely removed leaves from 20% of the purple loosestrive
populations where it was released, which could reduce competition for native species. The biological controls established
populations in most locations where they were released and even spread to new patches of purple loosestrife.
: Young larvae of the leaf-beetle feed in and on the developing buds of plants, often destroying them. This may stunt
plant growth and delay or prevent flowering. Adults (shown) and older larvae feed on leaves and cause severe defoliation. Leaf-
beetles can be used to as a biocontrol for invasive plants such as purple loosestrife.
In 1946 two species of Chrysolina beetles were introduced into California to control the Klamath weed (St. Johnswort) that was ruining millions of acres of range land in California and the Pacific Northwest. Before their release, the beetles were carefully tested to make certain that they would not turn to valuable plants once they had eaten all the Klamath weed they could find. The beetles succeeded beautifully, restoring about 99% of the endangered range land and earning them a commemorative plaque at the Agricultural Center Building in Eureka, California.
In 1859, the European rabbit was introduced into Australia for sport. With no important predator there, it multiplied explosively
). The raising of sheep (another imported species) suffered badly as the rabbits competed with them for forage. In
1950, the myxoma virus was brought from Brazil and released. The epidemic that followed killed off millions of rabbits (more
than 99% of the population). Green grass returned, and sheep raising once again became profitable. Rabbit populations gradually
increased, however, because the rabbits evolved to be more resistant to the virus, and the myxoma virus evolved to cause less
damage. (Parasites, like viruses, benefit from multiplying inside the host and spreading to other individuals. If they kill their hosts
too soon, they typically limit opportunities to multiply and spread.) More recently, the rabbit hemorrhagic disease virus has been
: These rabbits in Australia removed all forage plants, which ordinarily supply them with water as well as food. They thus had to drink from a pool. Image by National Archives of Australia (public domain).
To summarize the lessons learned from biological control successes and failures, only candidates that have a very narrow target preference (eat only a sharply-limited range of hosts) should be chosen. Each candidate should be carefully tested to be sure that
once it has cleaned up the intended target, it does not turn to desirable species. Biological controls must not be used against native species. Finally, introduction of non-native species into the environment should be avoided because they could themselves be invasive.
Climate Change Climate change, and specifically the anthropogenic (meaning, caused by humans) 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 hypothesized to continue 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. These gases decrease the degree to which Earth is able to radiate heat energy created by the sunlight that enters the atmosphere. The changes in climate and energy balance caused by increasing greenhouse gases are complex and our understanding of them depends on predictions generated from detailed computer models. Scientists generally 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.
However, there is still a lack of understanding about outcomes for specific species related to climate change. Scientists disagree about the likely magnitude of the effects, with extinction rate estimates ranging from 15 percent to 40 percent of species committed to extinction by 2050. Scientists do agree, however, 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 with their adapted climate norms while facing habitat gaps along the way. Range shifts are already being observed: for example, on average, European bird species ranges have moved 91 km (56.5 mi) northward. 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.
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 (Figure
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.
: Since 2008, grizzly bears (Ursus arctos horribilis) have been spotted farther north than their historic range, a
possible consequence of climate change. As a result, grizzly bear habitat now overlaps polar bear (Ursus maritimus) habitat. The
two kinds of bears, which are capable of mating and producing viable offspring, are considered separate species as historically they
lived in different habitats and never met. However, in 2006 a hunter shot a wild grizzly-polar bear hybrid known as a grolar bear,
Changing climates also throw off species' delicate timing adaptations to seasonal food resources and breeding times. Many contemporary mismatches to shifts in resource availability and timing have already been documented.
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 the only source of protein available to polar bears. A trend to decreasing sea ice and glacier coverage has occurred
since observations began in the mid-twentieth century. The rate of decline observed in recent years is far greater than previously
: The effect of global warming can be seen in the continuing retreat of Grinnell Glacier. The mean annual
temperature in Glacier National Park has increased 1.33°C since 1900. The loss of a glacier results in the loss of summer
meltwaters, sharply reducing seasonal water supplies and severely affecting local ecosystems (credit: USGS, GNP Archives).
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.
: This photograph shows an example of a polluted sky, partially created by this smokestack's emissions. "Air Pollution" by Janak Bhatta is licensed under CC BY-SA 4.0.
Pollution is the introduction of contaminants into the natural environment that cause adverse change (Merriam-Webster, 2010). The United Nations considers pollution to be the "presence of substances and heat in environmental media (air, water, land) whose nature, location, or quantity produces undesirable environmental effects," (UNdata, n.d.). Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the components of pollution, can be either foreign substances/energies or naturally occurring contaminants. Although environmental pollution can be caused by natural events, the word pollution generally implies that the contaminants have an anthropogenic source - that is, a source created by human activities, such as manufacturing, extractive industries, poor waste management, transportation or agriculture. Pollution is often classed as point source (coming from a highly concentrated specific site, such as a factory or mine) or nonpoint source pollution (coming from a widespread distributed sources, such as microplastics or agricultural runoff). Many sources of pollution were unregulated parts of industrialization during the 19th and 20th centuries until the emergence of environmental regulation and pollution policy in the later half of the 20th century. Sites where historically polluting industries released persistent pollutants may
have legacy pollution long after the source of the pollution is stopped. Major forms of pollution include air pollution, light pollution, litter, noise pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, visual pollution, and water pollution. Pollution has been found to be present widely in the environment and has widespread negative impacts on the environment and human society. A pollutant may cause long- or short-term damage by changing the growth rate of plant or animal species, or by interfering with resources used by humans, human health or wellbeing, or property values. Some pollutants are biodegradable and therefore will not persist in the environment in the long term. However, the degradation products of some pollutants are themselves polluting such as the products DDE and DDD produced from the degradation of DDT. A 2022 study published in Environmental Science & Technology found that levels of anthropogenic chemical pollution have exceeded planetary boundaries and now threaten entire ecosystems around the world (Persson et al., 2022; Carrington, 2022). Pollution can directly affect a species by making the environment unsuitable for its survival (this is what happens, for example, in the case of an oil spill). Sometimes pollution does not directly cause the death of an organism, but can make it more susceptible to disease or predation. It can also affect a species indirectly, by affecting food availability or reproductive performance, thus reducing population numbers over time. There are a number of effects of pollution that can impact biodiversity: Biomagnification describes situations where toxins (such as heavy metals) may pass through trophic levels, becoming exponentially more concentrated in the process. So organisms from higher trophic levels are most likely to be impacted by pollutants. Carbon dioxide emissions cause ocean acidification, the ongoing decrease in the pH of the Earth's oceans as CO2 becomes dissolved. Ocean acidification alters the balance of dissolution and precipitation of calcium carbonate which impacts organisms that use calcium carbonate for shells or skeletons. The emission of greenhouse gases leads to climate change which affects ecosystems in many ways including changes in temperature, precipitation, and environmental variability. Invasive plants can contribute debris and biomolecules (allelopathy) that can alter soil and chemical compositions of an environment, often reducing native species competitiveness. Nitrogen oxides are removed from the air by rain and fertilize land which can change the species composition of ecosystems. Smog and haze can reduce the amount of sunlight received by plants to carry out photosynthesis and leads to the production of tropospheric ozone which damages plants. Soil can become infertile and unsuitable for plants due to the accumulation of toxins. This will affect other organisms in the food web. Sulfur dioxide and nitrogen oxides can cause acid rain which lowers the pH value of soil and lakes and can lead to increases in aluminum concentration and the loss of some plant nutrients (such as calcium and magnesium) from soils. Organic pollution of watercourses can deplete oxygen levels by stimulating decomposition and therefore reduce species diversity. Noise and light generated by traffic, ships, vehicles, buildings and aircraft can affect the survivability of wildlife species and can reach undisturbed habitats. Noise and light pollution can interrupt communication among organisms of the same species or make it difficult for species to navigate and/or detect predators or prey. Disrupted communication can lead to both higher mortality from predation and decreased reproductive success. Noise, light, water, and air pollution can also increase stress in organisms, leading to lower fitness. References Acheson, J. M. (1988). The lobster gangs of Maine. University Press of New England. Annala, J. H. (1996). New Zealand's ITQ system: Have the first eight years been a success or a failure? Reviews in Fish Biology and Fisheries, 6(1), 43-62. https://doi.org/10.1007/BF00058519
Beddington, J. R., Agnew, D. J., & Clark, C. W. (2007). Current problems in the management of marine fisheries. Science, 316(5832), 1713-1716. https://doi.org/10.1126/science.1137362
Carrington, D. (2022, January 18). Chemical pollution has passed safe limit for humanity, say scientists. The Guardian. https://www.theguardian.com/environment/2022/jan/18/chemical-pollution-has-passed-safe-limit-for-humanity-say-scientists
Costello, C., Gaines, S. D., & Lynham, J. (2008). Can catch shares prevent fisheries collapse? Science, 321(5896), 1678-1681. https://doi.org/10.1126/science.1159478
Global Forest Watch. (2020). World Resources Institute. https://www.globalforestwatch.org (Accessed July 29, 2020)
Illegal logging nets organized crime up to 100 billion dollars a year, INTERPOL-UNEP report reveals. (2012). Interpol. https://www.interpol.int/en/News-and...report-reveals (Accessed July 29, 2020)
Levy, S. (2010). Catch shares management. BioScience, 60(10), 780-785. https://doi.org/10.1525/bio.2010.60.10.3
Merriam-Webster. (2010, August 13). Pollution - Definition from the Merriam-Webster online dictionary. Merriam-Webster. https://www.merriam-webster.com/dictionary/pollution (Accessed August 26, 2010)
Montaigne, F. (2007). Still waters: The global fish crisis. http://ngm.nationalgeographic.com/print/2007/04/global-fisheries-crisis/montaigne-text
Persson, L., et al. (2022). Outside the safe operating space of the planetary boundary for novel entities. Environmental Science & Technology, 56(3), 1510-1521. https://doi.org/10.1021/acs.est.1c04158
UNdata. (n.d.). Pollution. In Glossary. https://data.un.org/Glossary.aspx?d=Glossary (Accessed May 1, 2022)
Worm, B., Barbier, E. B., Beaumont, N., Duffy, J. E., Folke, C., Halpern, B. S., Hackson, J. B. C., Lotze, H. K., Micheli, F., Palumbi, S. R., Sala, E., Selkoe, K. A., Stachowicz, J. J., & Watson, R. (2006). Impacts of biodiversity loss on ocean ecosystem services. Science, 314(5800), 787-790. https://doi.org/10.1126/science.1132294
Contributors and Attributions Written and curated by A. Wilson (Gettysburg College), N. Gownaris (Gettysburg College), Kyle Whittinghill (University of Vermont), and Melissa Ha with material from the following open-access sources: Threats to Biodiversity, Importance of Biodiversity, Community Ecology, and Sustainable Agriculture from Environmental Biology by Matthew R. Fisher (licensed under CC-BY) Threats to Biodiversity from General Biology by OpenStax (licensed under CC-BY) by Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at http://cnx.org/contents/185cbf87-c72...f21b5eabd@9.87). Case Study: Marine Fisheries, and Biodiversity, Species Loss, and Ecosystem Function from Sustainability: A Comprehensive Foundation by Tom Theis and Jonathan Tomkin, Editors. Download for free at CNX. (licensed under CC-BY) Understanding Bycatch. NOAA Fisheries. Accessed 28 March 2021 (public domain) Biological Control and Symbiosis from Biology by John W. Kimball (licensed under CC-BY) Environmental Science by Kamala Dorsner Provided by: National Geographic. Located at: images.nationalgeographic.com...33_600x450.jpg. License: CC BY: Attribution Chilean purse seine. Provided by: Wikimedia. Located at: http://commons.wikimedia.org/wiki/File:Chilean_purse_seine.jpg. License: CC BY: Attribution https://en.wikipedia.org/wiki/Pollution https://en.wikipedia.org/wiki/Biodiversity_loss
This page titled 23.3: Threats to Biodiversity is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by OpenStax. 47.1A: Loss of Biodiversity by Boundless (now LumenLearning) is licensed CC BY-SA 4.0.
47.3A: Habitat Loss and Sustainability by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.3: Threats to Biodiversity by OpenStax is licensed CC BY 4.0. 21.2: Threats to Biodiversity by OpenStax is licensed CC BY 4.0. 47.3B: Overharvesting by Boundless (now LumenLearning) is licensed CC BY-SA 4.0. 47.3C: Exotic Species by Boundless (now LumenLearning) is licensed CC BY-SA 4.0.
23.4: Scientist Spotlight - Scott Taylor Boasting the characteristics of small, round, and fluffy, the chickadee is an endearingly cute bird. Or should we say- are cute birds. The word "chickadee" refers to a group of birds in the Paridae family. Of the 59 species in this family, there are 7 species of chickadee. Deferring to the name "chickadee" rather than each species' specific (and/or scientific) name is understandable. To the untrained eye, these birds are almost indistinguishable from one another. For example, Poecile atricapillus has a black cap and bib surrounding its white cheeks, hence the name black-capped chickadee. Unlike P. atricapillus, Poecile hudsonicus has a brown cap. Why do we care about such minute differences? Politics (and climate change). In 1927, the Maine legislature designated the "chickadee" as the state bird. However, both black-capped and boreal chickadees reside in Maine. Aware of the two resident chickadee species, Nick Lund from Maine Audubon alerted local press. Representative Betty Austin then proposed a bill to specify Maine's official state bird (Pindell, 2019). In the end, the Maine Legislature decided to do nothing, but perhaps a warming climate will make the decision for them. At the University of Colorado Boulder, evolutionary biologist Dr. Scott Taylor is studying bird hybrid zones, areas where two species' ranges overlap, allowing interbreeding to occur. Because birds are sensitive to temperature, climate change is leading to shifts in species distributions, with many species moving northward. Different species shift at different rates, however, so climate change also alters species overlap and hybrid zones. One example of this is the climate-mediated northward shift of the chickadee hybrid zone in southeastern Pennsylvania. The importance of accurately identifying hybridization among species will only increase as climate change causes further shifts in species distribution (Taylor et al., 2014). Dr. Scott Taylor says that none of his "mentors in high school, college, or as a graduate student or postdoc were visible members of the LGBTQIA+ community," and it is crucial that this problem be solved for others. By being a visible member of the community, Dr. Taylor hopes to inspire students who may be struggling to see themselves as scientists because of their under-represented identity in STEM.
"Boreal Chickadee" by Daniel Arndt is licensed under CC BY-NC-SA 2.0.
"Black-capped Chickadee" by Colin Durfee is licensed under CC BY 2.0. References Scientist Spotlight Inspiration from Project Biodiversity American Ornithological Society. (2019). Researchers identify previously unknown hybrid zone between hummingbird species. <https://americanornithology.org/researchers-identify-previously-unknown-hybrid-zone-between-hummingbird-species/>. Accessed November 11, 2021.
Taylor, S.A., Larson, E.L., & Harrison, R.G. (2014). Hybrid zones: Windows on climate change. Trends in Ecology & Evolution, 30(7), pp. 398-406. Taylor, S.A., White, T.A., Honchahka, W.M., Ferretti, V., Curry, R.L., & Lovette, I. (2014). Climate-mediated movement of an avian hybrid zone. Current Biology, 24(6), pp. 1-6. Pindell, J. (2019). Maine's state-bird debate is ruffling some feathers. <https://www.bostonglobe.com/metro/2019/03/03/mainestate-bird-debate-ruffling-some-feathers/GpdBUYGIeY27IeMdhfBQgN/story.html> Accessed November 11, 2021. 23.4: Scientist Spotlight - Scott Taylor is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
23.5: Importance of Biodiversity Healthy ecosystems contain a diversity of species, and each species plays a role in ecosystem function; therefore, species diversity as well as ecosystem diversity are essential to maintaining ecosystem services. Loss of biodiversity eventually threatens other species we do not impact directly because of their interconnectedness; as species disappear from an ecosystem other species are threatened by the changes in available resources. 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: the ecosystem in which they existed. 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 extremes 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 our food. This includes living plants that grow in soil ecosystems and the animals that eat these plants (or other animals) as well as photosynthetic organisms in the oceans and the other organisms that eat them. Our ecosystems have provided and will provide many of the medications that maintain our health, which are commonly made from compounds found in living organisms. Ecosystems provide our clean water, which is held in lake and river ecosystems or passes through terrestrial ecosystems on its way into groundwater.
: This tropical lowland rainforest in Madagascar is an example of a high biodiversity habitat. This particular location
is protected within a national forest, yet only 10 percent of the original coastal lowland forest remains, and research suggests half
the original biodiversity has been lost (credit: Frank Vassen).
Often called ecological services or ecosystem services, the products and processes associated with biological systems are of immense value to the well being of people. An incomplete list of these services and products includes the formation of soil and cycling of nutrients; provisioning of food, fresh water, fuel, fiber, and recreation opportunities; the regulation of climate, flooding, and disease. The value of these services is often overlooked or simply taken for granted, but one global estimate puts it somewhere between
Many medications are derived from natural chemicals made by a diverse group of organisms. For example, many plants produce secondary plant compounds which are toxins used 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
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.
: Catharanthus roseus, the Madagascar periwinkle, has various medicinal properties. Among other uses, it is a source
of vincristine, a drug used in the treatment of lymphomas (credit: Forest and Kim Starr).
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 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.
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 (Figure
: A photo of the Mercado Modelo de Huancayo Peru showing many potato varieties on sale. Image by Thayne Tuason is licensed under CC BY 4.0.
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
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.
: The Svalbard Global Seed Vault is a storage facility for seeds of Earth's diverse crops (credit: Mari Tefre,
The Svalbard seed vault is located on Spitsbergen island in Norway, which has an arctic climate. Why might an arctic climate be good for seed storage?
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
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. Psychological and Moral Value Finally, it has been clearly shown that humans benefit psychologically from living in a biodiverse world. A chief proponent of this idea is Harvard entomologist E. O. Wilson. He argues that human evolutionary history has adapted us to live in a natural environment and that city environments generate psychological stressors that affect human health and well-being. There is considerable research into the psychological regenerative benefits of natural landscapes that suggests the hypothesis may hold some truth. In addition, there is a moral argument that humans have a responsibility to inflict as little harm as possible on other species. References Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G. O. U., Swartz, B., Quental, T. B., et al. (2011). Has the Earth's sixth mass extinction already arrived? Nature, 471, 51-57. https://doi.org/10.1038/nature09678 International Institute for Species Exploration. (2011). 2011 State of Observed Species (SOS). Tempe, AZ: International Institute for Species Exploration. https://species.asu.edu/SOS (Accessed May 20, 2012) Vié, J.-C., Hilton-Taylor, C., & Stuart, S. N. (Eds.). (2009). Wildlife in a changing world: An analysis of the 2008 IUCN Red List of threatened speciesTM. Gland, Switzerland: IUCN. http://data.iucn.org/dbtw-wpd/edocs/RL-2009-001.pdf Contributors and Attributions Modified by Kyle Whittinghill and Melissa Ha from the following sources: Community Ecology and Importance of Biodiversity from Environmental Biology by Matthew R. Fisher (licensed under CCBY) Environmental Science by Kamala Dorsner Biodiversity, Species Loss, and Ecosystem Function from Sustainability: A Comprehensive Foundation by Tom Theis and Jonathan Tomkin, Editors. Download for free at CNX. (licensed under CC-BY) Preserving Biodiversity, 21.1: Importance of Biodiversity, 47.2 The Importance of Biodiversity to Human Life, and 47.1: The Biodiversity Crisis by OpenStax, is licensed CC BY by Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at http://cnx.org/contents/185cbf87-c72...f21b5eabd@9.87). Access for free at https://openstax.org/books/biology-2e/pages/1-introduction This page titled 23.5: Importance of Biodiversity is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by OpenStax. 21.1: Importance of Biodiversity by OpenStax is licensed CC BY 4.0.
23.6: Preserving Biodiversity 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. Today, the main efforts to preserve biodiversity involve legislative approaches to regulate human and corporate behavior, setting aside protected areas, and habitat restoration.
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
approximately 35,000 "listed" species from being transported across nations' borders, thus protecting them from being caught or
killed when the purpose involves international trade. Species can be listed in one of three CITES appendices (Figure
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. Illegal wildlife trade is monitored by another non-profit: Trade
Records Analysis of Flora and Fauna in Commerce (TRAFFIC).
: Big-leaf mahogany (Swietenia macrophylla) timber is used to make furniture, musical instruments, boats, and other
products. It listed in CITES Appendix II, meaning that it is regulated. Specifically, a permit is required to ship big-leaf mahogany
timber. Image by Forest and Kim Starr (CC-BY).
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 Act,
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 ESA does not automatically protect species categorized as
threatened on the IUCN Red List. Instead, the U.S. Fish and Wildlife Service (FWS), which enforces the ESA, assesses candidates
for protected status as threatened or endangered (Figure
). Consideration of candidate species can be initiated by the FWS
itself or at the request of the public. Through the Species Status Assessment Framework, the FWS compiles biological data, such as
habitat and population information and current threats to the species. This biological data is used to inform decisions. Additionally,
species may be controversially taken off the list without necessarily having had a change in their situation. More fundamentally, the approach to protecting individual species rather than entire ecosystems is both inefficient and focuses efforts on a few highly visible and often charismatic species, perhaps at the expense of other species that go unprotected. At the same time, the ESA has a critical habitat provision outlined in the recovery mechanism that may benefit species other than the one targeted for management.
: Public Affairs Specialist for the U.S. Fish and Wildlife Service, Joanna Gilkeson, takes photos of federally
endangered San Diego fairy shrimp in a vernal pool in Otay Mesa, California. Vernal pools are shallow seasonal ponds, and vernal
pool species are uniquely adapted to changes in water availability. Image by Maideline Sanchez/USFWS (public domain).
The 1972 Marine Mammals Protection Act prohibits the "take" of marine mammals--including harassment, hunting, capturing, collecting, or killing--in U.S. waters and by U.S. citizens on the high seas. The act also makes it illegal to import marine mammals and marine mammal products into the United States without a permit. State laws can also aid in conservation. Through California Endangered Species Act (CESA), originally passed in 1970 and subsequently amended, the California Fish and Game Commission assesses species to be listed as threatened or endangered by the state. A listed species, or any part or product of the plant or animal, may not be imported into the state, exported out of the state, "taken" (killed), possessed, purchased, or sold without proper authorization. Note that endangered is a subcategory of threatened on the Red List, but for ESA and CESA, threatened and endangered are separate categories, with the latter representing at the greater risk of extinction.
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.
Climate change 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. The United States rejected it as a result of a powerful fossil fuel industry, while China did so because of a concern that it would stifle the nation's growth. 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. The intended replacement for the Kyoto Protocol has not materialized because governments cannot agree on timelines and benchmarks. Meanwhile, climate scientists predict the resulting costs to human societies and biodiversity will be high. 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.
Conservation in Preserves As already mentioned, the private non-profit sector plays a large role in the conservation effort both in North America and around the world. The approaches range from species-specific organizations to the broadly focused IUCN and TRAFFIC. The Nature Conservancy takes a novel approach. It purchases land and protects it in an attempt to set up preserves for ecosystems. Ultimately, human behavior will change when human values change. At present, the growing urbanization of the human population is a force that poses challenges to the valuing of biodiversity.
Establishment of wildlife and ecosystem preserves is one of the key tools in conservation efforts (Figure
area of land set aside with varying degrees of protection for the organisms that exist within the boundaries of the preserve.
Governments or private organizations establish nature preserves. Preserves can be effective in the short term for protecting both
species and ecosystems, but they face challenges that scientists are still exploring to strengthen their viability as long-term
Due to the way protected lands are allocated (they tend to contain less economically valuable resources rather than being set aside specifically for the species or ecosystems at risk) and the way biodiversity is distributed, determining a target percentage of land or marine habitat that should be protected to maintain biodiversity levels is challenging. The IUCN World Parks Congress estimated that 11.5 percent of Earth's land surface was covered by preserves of various kinds in 2003. This area is greater than previous goals; however, it only represents 9 out of 14 recognized major biomes. Research has shown that 12 percent of all species live only outside preserves; these percentages are much higher when only threatened species and high quality preserves are considered. For example, high quality preserves include only about 50 percent of threatened amphibian species. The conclusion must be that either the percentage of area protected must increase, or the percentage of high quality preserves must increase, or preserves must be targeted with greater attention to biodiversity protection. Researchers argue that more attention to the latter solution is required.
It is important to protect natural areas for several reasons. Some people feel a cultural or spiritual connection to the wilderness. Every year, millions of people visit recreational lands such as parks and wilderness areas to experience attractions of the great outdoors: hiking among the giant sequoias in California, traveling on a photo safari in Kenya or just picnicking at a local county park. Besides providing people with obvious health benefits and aesthetic pleasures, recreational lands also generate considerable tourist money for government and local economies. Outdoor recreation activities such as hiking and camping benefit tourist industries and manufacturers of outdoor clothes and equipment.
: Mequon Nature Preserve in Wisconsin. Image by Jennifer Tomaloff (CC BY-NC-SA 2.0).
Preserve Design There has been extensive research into optimal preserve designs for maintaining biodiversity. The fundamental principle behind much of the research has been the seminal theoretical work of Robert H. MacArthur and Edward O. Wilson published in 1967 on island biogeography.1 This work sought to understand the factors affecting biodiversity on islands. The fundamental conclusion was that biodiversity on an island was a function of the origin of species through migration, speciation, and extinction on that island. Islands farther from a mainland are harder to get to, so migration is lower and the equilibrium number of species is lower. Within island populations, evidence suggests that the number of species gradually increases to a level similar to the numbers on the mainland from which the species is suspected to have migrated. In addition, smaller islands are harder to find, so their immigration rates for new species are lower. Smaller islands are also less geographically diverse so there are fewer niches to promote speciation. And finally, smaller islands support smaller populations, so the probability of extinction is higher. As islands get larger, the number of species accelerates, although the effect of island area on species numbers is not a direct correlation. 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. For a species to persist in a preserve, the preserve must be large enough. The critical size depends, in part, on the home range that is characteristic of the species. A preserve for wolves, which range hundreds of kilometers, must be much larger than a preserve for butterflies, which might range within ten kilometers during its lifetime. But larger preserves 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. Preserves perform better when there are buffer zones around them of suboptimal habitat. The buffer allows organisms to exit the boundaries of the preserve without immediate negative consequences from predation or lack of resources. One large preserve is better than the same area of several smaller preserves because there is more core habitat unaffected by edges. 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 between them so that individuals and their genes can move between the preserves, for example along rivers and streams, will make the smaller preserves behave more like a large one. 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, biological, and ecological specifications of a preserve, there are a variety of policy, legislative, and enforcement specifications related to uses of the preserve for functions other than protection of species. These can include anything from timber extraction, mineral extraction, regulated hunting, human habitation, and nondestructive human recreation. Many of these policy decisions are made based on political pressures rather than conservation considerations. 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 areas of the tropics. Limitations on Preserves Some of the limitations on preserves as conservation tools are evident from the discussion of preserve design. Political and economic pressures typically make preserves smaller, never larger, so setting aside areas that are large enough is difficult. If the area set aside is sufficiently large, there may not be sufficient area to create a buffer around the preserve. In this case, an area on the outer edges of the preserve inevitably becomes a riskier suboptimal habitat for the species in the preserve. Enforcement of protections is also a significant issue in countries without the resources or political will to prevent poaching and illegal resource extraction.
Climate change will create inevitable problems with the location of preserves. The species within them will migrate to higher latitudes as the habitat of the preserve becomes less favorable. Scientists are planning for the effects of global warming on future preserves and striving to predict the need for new preserves to accommodate anticipated changes to habitats; however, the end effectiveness is tenuous since these efforts are prediction based. 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. Link to Learning
An interactive global data system of protected areas can be found at website. Review data about individual protected areas by location or study statistics on protected areas by country or region.
On an international level, important wilderness lands have been designated by the United Nations through its "Man and the Biosphere Program." This program was established in 1973 to protect examples of major natural regions throughout the world, and provide opportunities for ecological research and education. Biosphere reserves are organized into three interrelated zones: the core area, the buffer zone and the transition area. The core area contains the landscape and ecosystems to be preserved. The buffer zone is an area where activities are controlled to protect the core area. The outer transition area contains a variety of agricultural activities, human settlements and other uses. Local communities, conservation agencies, scientists and private enterprises that have a stake in the management of the region work together to make the reserves work. Mt Kenya in Africa and the Galapagos Islands are examples of wilderness areas protected under this provision.
Types of Protected Areas in the United States
The public lands described below differ in their level of protection. For example, national parks and forests allow camping whereas wildlife refuges place more limitations on human activities. National parks and forests and wildlife refuges can contain wilderness areas.
Wilderness areas, comprise ecosystems in which human activity has not significantly affected the plant and animal populations or
their environment. Natural processes predominate. According to the "Wilderness Act of 1964," wilderness areas are defined as
being those areas where the nearest road is at least five miles away and where no permanent buildings stand. Activities that could
disrupt native species, such as the use of motorized vehicles is prohibited. More than 100 million acres of land are now preserved
as wilderness under this act. Sparsely populated Alaska contains the largest chunk of wilderness areas, over half of it. Although
wilderness areas are scattered among most of the lower 48 states, the largest percentage is found in the western states. Few
undesignated areas in the contiguous states remain that would qualify as wilderness. California contains significant wilderness
areas, with over 4 million acres of National Forest Wilderness areas, and 1.5 million acres of mostly desert wilderness in the
). Wilderness areas provide an essential habitat for a wide array of fish, wildlife,
and plants, and are particularly important in protecting endangered species. For scientists, wilderness areas serve as natural
laboratories, where studies can be performed that would not be possible in developed areas.
: A variety of unique plant life grows at Mojave Desert National Preserve. Image by John Fowler (CC-BY 2.0).
The United States has set aside more land for public recreational use than any other country. The National Park System manages
more than 380 parks, recreation areas, seashores, trails, monuments, memorials, battlefields, and other historic sites. It consists of
more than 80 million acres nationwide (Figure
). The largest national park is Wrangell-St. Elias National Park and Preserve in
Alaska with over 13 million acres. California has eight national parks: Channel Islands, Death Valley, Joshua Tree, Lassen,
Redwood, Sequoia, Kings Canyon, and Yosemite. Many national parks such as Yosemite, Yellowstone and the Grand Canyon are
such popular recreation destinations that the ecosystems of those parks are being severely tested by human activities.
: National parks, such as Grand Teton National Park in Wyoming, help conserve biodiversity (credit: Don DeBold).
Every state has also set aside significant amounts of land for recreational use. The California State Park System manages more than one million acres of parklands including: coastal wetlands, estuaries, scenic coastlines, lakes, mountains and desert areas. California's largest state park is Anza-Borrego Desert State Park, which is the largest state park in the United States with 600,000 acres. The stated mission of the California State Park System is "to provide for the health, inspiration and education of the people of California by helping to preserve the state's extraordinary biological diversity, protecting its most valued natural and cultural resources and creating opportunities for high-quality outdoor recreation". This is the basic goal of all recreational lands: to manage and conserve natural ecosystems, while supporting a sustainable and balanced level of human use of those areas. Unfortunately, it is a goal which is sometimes difficult to achieve due to the increasing popularity and use of recreational lands.
The National Forest System, managed by the U.S. Forest Service (part of the United States Department of Agriculture), consists of more than 170 forestlands and grasslands, which are available for activities such as camping, fishing, hiking and hunting. These are managed as multiple use lands, which balance the needs for recreation, grazing, timber, watershed protection, wildlife and fish, and wilderness. Some examples of national forests are the Sierra National Forest in California and the White Mountain National Forest in New Hampshire. The Coronado National Forest in Arizona is famous for "sky islands", or steep mountain ranges surrounded by low-lying areas. The dramatic increase in elevation is associated with changes in the flora and fauna (Figure ). Explore national forests using this interactive map.
: The Santa Teresa Mountains of the Coronado National Forest form "sky islands." Image by Jstuby (public domain).
The U.S. Fish and Wildlife Service manage more than 500 national wildlife refuges (Figure
habitats and breeding areas but also provide recreational facilities. Find a Refuge is an interactive map for locating wildlife refuges.
: Bobcat at Sonny Bono National Wildlife Refuge in southern California. Image by Mark Stewart/USFWS (public domain).
Several other types of public lands complement the designated wilderness land system. These include: national forest roadless areas, national trails system, natural research areas and state and private wilderness lands. The national forest roadless areas consist of millions of acres of wild, undeveloped land without roads that exist on National Forest land outside of designated wilderness lands. The "National Trail System," established by Congress in 1968, includes trails in wilderness areas and other public lands. Research Natural Areas located throughout the country on public lands serve as outdoor laboratories to study natural systems. They are intended in part to serve as gene pools for rare and endangered species and as examples of significant natural ecosystems. Some wilderness lands are maintained by states or private organizations. For example, the state of New York has long preserved a region of the Adirondacks as wilderness.
Habitat Restoration, Remediation, and Reclamation
Habitat restoration holds considerable promise as a mechanism for restoring and maintaining biodiversity. Of course once a species
has become extinct, its restoration is impossible. However, restoration can improve the biodiversity of degraded ecosystems.
Reintroducing wolves, a top predator, to Yellowstone National Park in 1995 led to dramatic changes in the ecosystem that increased
) function to suppress elk and coyote populations and provide more abundant resources to
the guild of carrion eaters. Reducing elk populations has allowed revegetation of riparian areas, which has increased the diversity
of species in that habitat. Decreasing the coyote population has increased the populations of species that were previously suppressed by this predator. The number of species of carrion eaters has increased because of the predatory activities of the wolves. In this habitat, the wolf is a keystone species, meaning a species that is instrumental in maintaining diversity in an ecosystem. Removing a keystone species from an ecological community may cause a collapse in diversity. The results from the Yellowstone experiment suggest that restoring a keystone species 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 those species; likewise, it also makes sense to attempt to return them to their ecosystem if they have been removed.
: (a) The Gibbon wolf pack in Yellowstone National Park, March 1, 2007, represents a keystone species. The
reintroduction of wolves into Yellowstone National Park in 1995 led to a change in the grazing behavior of (b) elk. To avoid
predation, the elk no longer grazed exposed stream and riverbeds, such as (c) the Lamar Riverbed in Yellowstone. This allowed
willow and cottonwood seedlings to grow. The seedlings decreased erosion and provided shading to the creek, which improved fish
habitat. A new colony of (d) beaver may also have benefited from the habitat change. (credit a: modification of work by Doug
Smith, NPS; credit c: modification of work by Jim Peaco, NPS; credit d: modification of work by "Shiny Things"/Flickr).
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 freeflowing rivers and because many dams no longer provide the benefit and functions that they did when they were first built. The measured benefits of dam removal include restoration of naturally fluctuating water levels (the purpose of dams is frequently to reduce variation in river flows), which leads to increased fish diversity and improved water quality. In the Pacific Northwest, dam removal projects are expected to increase populations of salmon, which is considered a keystone species because it transports key nutrients to inland ecosystems during its annual spawning migrations. In other regions such as the Atlantic coast, dam removal has allowed the return of 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. The large-scale ecological experiments that these removal projects constitute will provide valuable data for other dam projects slated either for removal or construction. Besides physical processes, socioeconomic factors must also be considered in a restoration project. Actions of humans have historically been important in shaping ecosystems, and are important in determining the success of restoration efforts. Because the cost to restore an individual site can involve millions of dollars, government support is a necessity.
Danger to human health from both historic and modern pollution requires that cleanup measures be implemented. Remediation is aimed at neutralization, containment, and/or removal of the polluting chemicals. The goal is to prevent the spread of the pollution, or to reduce it to levels that will not appreciably risk human health. Many times, it is physically impossible or financially unfeasible to completely clear all contamination. Often, experts and the public disagree on how clean is clean enough.
Many communities are struggling to find the funds and technological expertise needed to clean up polluted areas. Some settings, such as brownfields, can be remediated fairly easily. Brownfields are abandoned industrial or commercial facilities or blighted urban areas that need to be cleansed of contamination before they can be redeveloped. Other areas, because of their size or the extreme toxicity of their contaminants, require very expensive, complex, and long-term remediation. Many of these have been designated as Superfund sites.
Superfund sites are areas with the most toxic contamination in the United States. The contamination may not only make the site
itself too dangerous to inhabit, but often leaks toxic levels of pollutants into the surrounding soil, water, or air. An example of a
Superfund site is Love Canal in Niagara Falls, New York (Figure
). The canal was a chemical waste dump for many years,
then in the 1950's was covered with soil and sold to the city. Over time, many homes and a school were built over the former dump.
In the 1970's, heavy rains raised the water table and carried contaminants back to the surface. Residents noticed foul smells, and
gardens and trees turned black and died. Soon after, rates of birth defects, cancer, and other illnesses began to rise sharply. In 1977,
the State of New York and the federal government began remediation work. Buildings were removed, and all residents were bought
out and relocated, contaminated deposits and soils were excavated, and remaining soils and groundwater were treated and sealed
off to prevent further spread of the contamination. Remediation activities have now been completed at this site.
: Love Canal. Source: US Environmental Protection Agency.
The type of pollution and the medium affected (air, water, or soil) determine remediation methods. Methods include incineration, absorption onto carbon, chemical methods, or bioremediation. Bioremediation is the use of plants, bacteria, or fungus to "digest" the contaminant to a non-toxic or less toxic form. All of these methods tend to be expensive and time-consuming.
Reclamation involves salvaging some features of a degraded habitat, but it may not restore the ecosystem fully (Figure
For example, instead of abandoning a mined area once resources have been collected, it can be reclaimed by planting vegetation,
reshaping the landscape, and redirecting water flow. However the reclaimed land still lacks many features of the original
ecosystem, such as complex topography, vegetation that took tens or hundreds of years to grow, soil quality, and an intricate
: The Seneca Yoast coal once land has been cleared in preparation for mining (left) and after reclamation (right). Image by Peabody Energy, Inc. (CC-BY).
Sometimes, actions can be taken to avoid, reduce or compensate for the effects of environmental damage. Such mitigation efforts have been taken by the Army Corps of Engineers during construction projects. The native plants are removed from a site before construction begins and transplanted at a special holding site. After the construction project is completed, the native plants are replanted using those from the holding site. Another example of mitigation might involve the creation or enhancement of wetlands in one area, in order to compensate for permitted wetland losses in another area. Mitigation often goes hand-in-hand with restoration. Texaco, in conjunction with environmental groups and the United States Fish and Wildlife Service, restored 500 acres of agricultural lands in the lower Mississippi Delta to bottomland hardwoods. Texaco received environmental credits for the mitigating effects of the new woodlands on air quality.
Zoos have sought to play a role in conservation efforts both through captive breeding programs and education (Figure
transformation of the missions of zoos from collection and exhibition facilities to organizations that are dedicated to conservation is
ongoing and gaining strength. 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. However,
captive breeding programs have yielded some success stories, such as the California condor reintroduction to the Grand Canyon
and the reestablishment of the Whooping Crane along the Midwest flyway. Unfortunately, zoo facilities are far too limited to
contemplate captive breeding programs for the numbers of species that are now at risk. Education is another 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; at present, the results tend to be mixed.
: Zoos and captive breeding programs help preserve many endangered species, such as this golden lion
Economic Influences on Conservation Economics greatly impacts conservation success. Short-term profits can incentivize individuals, companies, or governments to harvesting resources at an unsustainable rate and at the expense of ecosystem health. In impoverished regions, compromising habitat to grow high-value crops, such as coffee or oil palms, or poaching endangered species may seem like the only source of income. One solution is debt-for-nature swaps through which one country forgives the debt of another if the latter agrees to protect natural areas. These conservation efforts can provide a new source of income for residents near the protected areas. For example, the United States forgave