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Endangered Species


ENDANGERED SPECIES. The environmental movement reached its peak with the enactment of the Endangered Species Act of 1973. As public concern over environmental degradation heightened, Congress passed the most sweeping piece of environmental legislation in American history. When President Richard M. Nixon signed the law on 28 December 1973, he enthusiastically proclaimed that nothing is more priceless and more worthy of preservation than the wildlife with which the country had been blessed. Intent on fulfilling Nixon's mandate, the authors of the Endangered Species Act (ESA) made an unmistakably strong statement on national species protection policy. The ESA provided for the protection of ecosystems, the conservation of endangered and threatened species, and the enforcement of all treaties related to wildlife preservation.

Pre-ESA Protection Efforts

Endangered species existed long before 1973, of course. The protection of individual species was an incremental process. Rooted in the tradition of colonial law, U.S. Supreme Court decisions through the nineteenth century ensured state jurisdictional control over that of landowners. By the 1870s, the federal government made it clear that it had an interest in wildlife issues. The establishment of the U.S. Fish Commission in 1871 and Yellowstone National Park in 1872 increased the role of the federal government substantially. The tension between federal and state authority resulted in the Yellowstone Game Protection Act of 1894, which established Yellowstone as a de facto national wildlife refuge in order to protect bison.

In the first half of the twentieth century, the federal government increased its direct, national jurisdiction with such legislation as the Lacey Act (1900), the creation of the first official national wildlife refuge at Pelican Island (1903), the ratification of the Migratory Bird Treaty Act with Canada (1918), and the passage of the Bald Eagle Protection Act (1940). Yet, a comprehensive national policy on species preservation was not enacted until the 1960s. The professionalization of ecology and the dawning of the American environmental movement created the needed atmosphere for reform. Building on the political response to Rachel Carson's Silent Spring (1962), the Bureau of Sport Fisheries and Wildlife established the Committee on Rare and Endangered Wildlife Species in 1964. The committee of nine biologists published a prototypical list of wildlife in danger of extinction, entitled the "Redbook," listing sixty-three endangered species. Congress passed a more comprehensive Endangered Species Preservation Act in 1966, requiring all federal agencies to prohibit the taking of endangered species on national wildlife refuges and authorizing additional refuges for conservation. The follow-up Endangered Species Conservation Act of 1969 extended protection to invertebrates. It also expanded prohibitions on interstate commerce provided by the Lacey Act and called for the development of a list of globally endangered species by the secretary of the Interior. The directive to facilitate an international conservation effort resulted in the Convention on International Trade in Endangered Species of Wild Fauna and Flora in early 1973. This set the stage for the Endangered Species Act later that year.

Passage of ESA and Early Challenges

Despite a surge of environmental regulatory lawmaking in the early 1970s, including the Clean Air Act, Federal Water Pollution Control Act Amendments (Clean Water Act), Federal Environmental Pesticide Control Act, and Coastal Zone Management Act, debate continued regarding

federal and state regulatory authority and the types of species warranting protection. Representative John Dingell, who introduced the bill that became the Endangered Species Act, insisted that all flora and fauna be included. Section 29a of the ESA makes this clear by stating that all "species of fish, wildlife, and plants are of aesthetic, ecological, educational, historical, recreational, and scientific value to the Nation and its people." The issue of regulation resulted in greater compromise. Section 6, which directs the secretary of the Interior to foster cooperative agreements with states while allowing them substantial involvement in species management, also provides funds for state programs. In an effort to address these issues and others, including the geographical extent of prohibitions and the location of governmental responsibility, the House worked on fourteen different versions while the Senate worked on three. The bill ultimately passed both houses of Congress almost unanimously, setting a clear mandate (with only twelve dissenting votes in the House and one in the Senate). The subsequent history of ESA was much more highly contested.

One of the first major challenges to the ESA came with the TVA v. Hill battle over the Tellico Dam. From its inception, the Tellico Dam project of the Tennessee Valley Authority (TVA) faced major challenges. In the early 1970s, a lawsuit charging the violation of the 1969 National Environmental Policy Act (NEPA) and an inadequate environmental impact statement delayed construction. Resuming construction in 1973, the project halted again in 1977 when a lawsuit charged Tellico with violating the Endangered Species Act. The discovery of a small fish, the snail darter, in the portion of the Little Tennessee River yet to be swallowed up by the dam, created what later became a textbook case in environmental ethics. U.S. Attorney General Griffin Bell, who argued the TVA case himself, compared the three-inch fish to the social and economic welfare of countless people. The Supreme Court response was unequivocal. With the law upheld, the project stopped in its tracks. When the ESA subsequently came up for reauthorization in 1978, a plan to provide a mechanism for dispute resolution, in cases like Tellico, resulted in the creation of the first major change in ESA. The Endangered Species Committee, dubbed the "God Squad," was given the power to decide when economic and societal interests outweighed the biological consequences. Ironically, after the committee rejected the exemption for Tellico, populations of snail darters were found in neighboring Tennessee creeks. This discovery came after the authorization for Tellico's completion squeaked through in an amendment to the 1979 Energy and Water Development Appropriations Act.

While the "God Squad" had refused the exemption for Tellico, the committee opened the door for mitigation plans by considering "alternative habitats" for endangered species. An exemption granted in 1979 to the Grayrocks Dam and Reservoir in Wyoming, which threatened whooping crane habitat downstream, became the precursor to the Habitat Conservation Plan (HCP). A 1982 amendment to ESA created HCPs as an effort to resolve alleged unequal treatment in federal and private sectors. HCPs allowed for the incidental taking of endangered species by private property owners in exchange for the creation of a plan to offset losses through separate conservation efforts. By 1990, the U.S. Fish and Wildlife Service (FWS) had formally approved seven HCPs, with twenty more under way.

Struggles between Competing Interests in the 1990s

The final extended reauthorization of ESA in 1988 allotted appropriations for five years. Amendments provided funding for state cooperative programs, encouraged the use of emergency powers to list backlogged species candidates, and strengthened the protection of endangered plants. Since 1993, however, Congress has authorized funds only in one-year increments, while bills to weaken ESA have been regularly introduced. The apparent ambivalence with respect to reauthorization reflected divisions between protagonists and antagonists for a strengthened ESA. Conservation organizations such as the World Wildlife Fund and the Nature Conservancy, along with activist oriented organizations such as the Sierra Club and the National Wildlife Federation, grew in strength and numbers during the 1990s, while demanding an expanded ESA. Meanwhile, private property advocates represented by the loose-knit but widespread "wise use" movement led efforts to stop ESA intrusion into the lives of private landowners. The National Endangered Species Act Reform Coalition was particularly effective at getting legislation introduced to modify ESA.

The widely publicized controversy over the northern spotted owl epitomized the struggle of competing interests. The U.S. Forest Service and the Bureau of Land Management advocated protection of this Pacific Northwest subspecies as early as 1977. Yet, the FWS listed the owl as threatened thirteen years later, in 1990, after years of recommendations for habitat preservation by scientific and environmental coalitions. The "God Squad" met for the third time in fourteen years, in 1993, to discuss the northern spotted owl. Amidst emotional media coverage of the plight of loggers and their families, thirteen out of forty-four tracts of land were opened up, as environmental regulations like ESA took the blame for contributing to economic hardship. While environmentalists used the spotted owl as a surrogate for old growth forests, the timber industry criticized the use of the owl to protect old growth trees. A resolution ultimately took the intervention of President Bill Clinton. The president organized a "Forest Summit" in 1993 to develop the Pacific Northwest Plan, which included a substantial reduction in timber harvesting, an ecosystem-based management plan for 25 million acres of federal land, and an economic plan for displaced loggers and their families.

The Pacific Northwest Plan signaled a shift in federal endangered species policy. In 1995 the National Research Council report on the ESA argued that an ecosystem-based approach to managing natural resources must maintain biological diversity before individual species are in dire trouble. The Clinton administration's Interagency Ecosystem Management Task Force echoed this proactive approach in their 1995 report, which called for a collaboratively developed vision of desired future conditions that integrated ecological, economic, and social factors.

The shift toward an ecosystem approach follows historical changes in the primary cause of species endangerment from overharvesting to habitat destruction to ecosystem-wide degradation. The history of ESA demonstrates that competing economic goals, political priorities, and ethical arguments have also made solutions more elusive.


Burgess, Bonnie B. Fate of the Wild: The Endangered Species Act and the Future of Biodiversity. Athens: University of Georgia Press, 2001.

Clark, Tim W. Averting Extinction: Reconstructing Endangered Species Recovery. New Haven, Conn.: Yale University Press, 1997.

Czech, Brian, and Paul R. Krausman. The Endangered Species Act: History, Conservation Biology, and Public Policy. Baltimore: Johns Hopkins University Press, 2001.

Kohm, Kathryn A., ed. Balancing on the Brink: The Endangered Species Act and Lessons for the Future. Washington, D.C.: Island Press, 1991.

Eric WilliamBoyle

See alsoEnvironmental Protection Agency .

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Endangered Species

Endangered Species

An endangered species is one that is likely to become extinct throughout all or part of its geographic range unless steps are taken to prevent its loss. Many of the species currently disappearing are tropical plants and insects that have not even been described by science but whose small ranges are being destroyed by deforestation. These species may contain valuable pharmaceuticals which could lead to cures for diseases, but they are also the irreplaceable products of millions of years of evolution.

The U.S. Endangered Species Act (ESA) protects any endangered species as well as the critical habitat on which it relies. Critical habitat does not necessarily include the entire ecosystem across the species' range. The ESA is the strongest ecological law in the world today because it has the power to restrict or eliminate human impact across an entire species range. Because the economic stakes can be high, officially designating a species as endangered can be a controversial process.

Given the costs of protecting endangered species, it is crucial to be certain that species are in fact endangered. The first step is to document a decline in population number. Doing so requires at least two population samples, using the same sampling methods, at different times. Even if a particular population shows no sign of decline, the species as a whole may decline as a result of range contraction and local population extinction; for example, deforestation eliminates whole populations while others remain intact.

Causes of Decline

Once a decline is established, the cause must be identified. First, natural history must be investigated in order to construct a list of possible agents. These may include prey extinction, pollutants, habitat change, habitat fragmentation, overharvesting, introduced species, disease, or inbreeding depression. Diagnosis requires the elimination of alternative hypotheses by observation and experiment.

A classic case of population decline was the decline and extinction of ten species of forest birds in Guam in the late 1960s. Pesticide use, hunting, competition from introduced bird species, habitat change, and disease were all measured and found to be uncorrelated with population densities of the forest birds. The only variable that was correlated with the decrease of the birds' range was the range of the brown tree snake, a species that was accidentally introduced to the island via an airplane wheel well in 1967. Subsequent live bait trapping indicated that brown tree snake predation on forest birds was higher where the birds were declining. An associated prediction that the snake would cause small mammal populations to decline was also supported.

Habitat change.

Habitat change is any change in the suite of resources and environmental conditions on which a species depends. It is not enough to know that habitat change or loss is causing species decline; the particular factors relevant to the species must be discovered. For example, the northern spotted owl nests in the tops of dead firs. These "snags" are commonly found in old-growth forests. Young forests provide marginal habitat. Nevertheless, understanding the owl's behavior, hunting habits, nesting habits, and other factors may allow some human activity in owl habitat without endangering the owl.

Habitat fragmentation.

This is a particularly harmful form of habitat change. Fragmentation is the loss of bits and pieces of habitat because of human activity, resulting in a patchwork habitat. Not only does this reduce the overall species range, it also changes the ratio of edge habitat to central habitat. For example, tropical forest fragmentation favors species that specialize in relatively open, sunny spaces such as treefalls, rather than the cooler, darker forest. This may cause forest specialists to decline as a result of competition as well as habitat loss. Demonstrating an effect of habitat fragmentation on population decline requires documenting fragment sizes and population densities.

Introduced species.

Introduced species, such as the brown tree snake, have been responsible for 40 percent of all extinctions. The Nile perch, introduced into Lake Victoria (located in east Africa) in the nineteenth century, caused the extinction of 200 species of cichlid by predation. To detect the impact of an introduced species, the timing of the introduction is compared to that of population decline. If there is a correlation, an experiment must demonstrate that the removal of the introduced species reverses the decline. Removal may involve surrounding the endangered species habitat with fencing or by poisoning the suspected introduced species. Unfortunately, it is difficult to remove a single species from a habitat without changing other variables. And introduced species, once established, are nearly impossible to eradicate.

Chains of extinction can make the diagnosis of species decline more complex. For example, Mauritanian kestrels declined because geckos, their food source, were eliminated by deforestation. Atlantic eelgrass limpets disappeared when a mold killed the eelgrass in which they lived. Black-footed ferrets declined along with their prey, the prairie dog. Saving one species may require saving several others as well.

Environmental contaminants.

These may also play a role in species decline. The mechanism by which organochlorides, such as DDT, can cause eggshell thinning in raptors was discovered in the 1960s, and DDT was soon banned in the United States and other countries. Blaming a chemical for the decline of a species, however, can result in banning a harmless substance while ignoring the actual problem. For example, eggshell thinning due to insufficient calcium deposition occurred in the Netherlands in the 1980s, well after DDT had been banned. Further investigation concluded that acid rain had leached calcium from the soil, reducing the amount found in the calcium carbonate shells of snails; the birds were unable to obtain sufficient calcium from feeding on snails.


This factor is thought to have contributed to the decline of many species. Infections can cross from one species to another (called transspecies infections); for example, an introduced species can carry novel pathogens with it into a community that has evolved no resistance to it. Often, disease is the result of stress on the species' immune system from another source, such as pollution. Although the disappearance of amphibians around the world remains a mystery, it is likely exacerbated by the effect of acid rain on immune function in aquatic species. Establishing such a connection requires investigating beyond the appearance of disease into underlying causes.


Overharvesting occurs when the number of individuals lost to hunting consistently exceeds the number gained from intrinsic population growth in the absence of harvesting. Overharvesting is a particularly difficult factor to measure because both annual harvests and population sizes vary in time and space. Furthermore, hunting yields are often underreported, especially if they are illegal.

Inbreeding depression.

This may be a factor in the decline of a population once the number of individuals is small. Inbreeding depression is the result of closely related individuals breeding, causing recessive harmful mutations to be passed on by both parents and therefore be expressed in subsequent generations. There is no evidence that inbreeding depression has ever caused extinction in the wild, though it can be a problem for captive-bred populations. It is likely that once a population is small enough for inbreeding depression to become relevant, extinction is inevitable for other reasons.

The Northern Spotted Owl

The case of the northern spotted owl in the Pacific Northwest region of the United States illustrates many of the issues surrounding the designation of an endangered species. The species is currently listed as threatened, meaning that it is at risk of becoming endangered in the foreseeable future. Its critical habitat is old-growth and late-successional forest with a dense canopy and open understory, which it requires for successful roosting. Such forests are extremely valuable to the timber industry. Since the spotted owl was listed as threatened in 1990, debate raged in the Pacific Northwest over the relative merits of a protection plan and the logging industry it would impact. At the beginning of the twenty-first century, there was no plan to protect the species, even though it was known that habitat destruction due to logging had caused the species' decline.

The current rate of extinction is greater than at any time in the last 65 million years. There have been only about five such mass extinctions in the history of the Earth, and they all occurred as a result of catastrophic changes in the environment. At no other time has the practices of a single species, humans, caused so many extinctions.

see also DDT; Extinction; Exotic Species; Habitat Loss; Habitat Restoration; Threatened Species.

Brian R. West


Caughley, Graeme. Conservation Biology in Theory and Practice. Cambridge, MA: Blackwell Science, 1996.

Sutherland, William J., ed. Conservation Science and Action. Malden, MA: Blackwell Science, 1998.

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Endangered Species

Endangered species

An endangered species is any animal or plant species whose very survival is threatened to the point of extinction. Once extinct, a species is no longer found anywhere on Earth. Once gone, it is gone forever.

Throughout Earth's geological history species have become extinct naturally. However, in modern times species and their natural habitats are mostly threatened by human activities. Humans have already caused the extinction of many species, and large numbers of many other species are currently endangered and may soon become extinct.

Causes of extinction and endangerment

Most of the species that have ever lived on Earth are now extinct. Extinction and endangerment can occur naturally. It can be the result of a catastrophic disturbance, such as the collision of an asteroid with Earth some 65 million years ago. The impact brought about the extinction of almost 50 percent of plant species and 75 percent of animals species then living on Earth, including the dinosaurs. Disease, a change in climate, and competition between species also can result in natural extinction.

However, since humans became Earth's dominant species, there has been a dramatic increase in the number of endangered or extinct species. The overhunting of wild animals (for their hides or meat or to protect livestock) and the destruction of natural habitats are the human activities most responsible. A wave of extinctions began in North America about 11,000 years ago, at about the time when people first migrated across a land bridge from Siberia to present-day Alaska. Probably within only a few centuries, species such as the mastodon, mammoth, and saber-toothed tiger had become extinct on the continent.

In modern times, overhunting has caused the extinction of such species as the dodo (1681), great auk (1844), and passenger pigeon (1914). In 2000, for the first time in about 300 years, a member of the primate order (the group of mammals that includes monkeys, apes, and humans) became extinct. The vanished primate was Miss Waldron's red colobus, a red-cheeked monkey. Scientists said its extinction was brought about by overhunting and the destruction of its habitat in the rain forest canopy in the African countries of Ghana and Ivory Coast.

How many endangered species are there?

Scientists readily agree that the rate at which species are becoming extinct around the world is increasing rapidly. At present, they believe extinctions caused by humans are taking place at 100 to 1,000 times nature's normal rate between great extinction episodes. It is hard, however, to put a figure on the actual number of endangered species. Researchers are able to document the endangerment of large and well-known animal and plant species. But it is impossible to measure the total number of species going extinct because scientists have described and named only a small percentage of the world's species. Only about 1.4 million speciesout of an estimated 10 million to 100 millionhave been described to date.

Words to Know

Biodiversity: The wide range of organismsplants and animalsthat exist within any given geographical region.

Endangered: When a species is vulnerable to extinction.

Extinct: When no members of a species are found anywhere on Earth.

Threatened: When a species is capable of becoming endangered in the near future.

There is an enormously large number of endangered species living in tropical rain forests, and most of these have not yet been "discovered" by scientists. Because rain forests are quickly being converted to farmland and human settlements, many of these species are becoming extinct before humans know anything about them.

Conservation organizations around the world have taken on the task of trying to catalog as many of the world's endangered species as possible. At the beginning of 2001, it was estimated that there were more than 1,200 endangered or threatened (those capable of becoming endangered) species in the United States and more than 1,800 worldwide. Because most of Earth's biodiversity (the number of species in a given habitat) is not yet discovered and cataloged, it is likely that there are perhaps several million endangered species on Earth.

Why are endangered species important?

It is critical that humans act to preserve endangered species and their natural habitats. These species are important and worthwhile for many reasons. First, and most important, all species have value simply because they are living organisms on Earth. Second, many species have a known value to humans. Food is provided by domestic plants and animals raised on farms, as well as certain animals, birds, and fish hunted in the wild. Humans also benefit from the role many species play in the environment. This includes cleansing the air and water, controlling erosion, providing atmospheric oxygen, and maintaining the food chain. Third, many species have a presently unknown value to humans, such as undiscovered medicinal plants.

Various actions have been taken to protect endangered species. In 1973, the U.S. Congress passed the Endangered Species Act. It established a list of endangered species and prohibited their trade (the list is updated periodically). The Convention on International Trade in Endangered Species (CITES, pronounced SIGH-tees) is a multinational agreement that took effect in 1975. Its aim is to prevent the international trade of endangered or threatened animal and plant species and the products made from them (by the end of 2000, 152 nations had signed the agreement). In 1992, the United Nations Conference

on Environment and Development (also known as the Earth Summit) was held in Rio de Janeiro, Brazil. One of the declarations adopted by the representatives at the conference called for an end to the loss of the world's species. The declaration was signed by more than 150 of the 172 nations that attended the conference.

Scientists took an even greater step toward preserving endangered species when, in early 2001, they announced the cloning of a gaur (pronounced GOW-er). The gaur is an ox native to Southeast Asia and India. While some 30,000 still exist in the wild, their numbers are declining because of hunting and habitat loss. To clone the gaur, the scientists removed the nucleus from a cow's egg cell and replaced it with the nucleus of a gaur skin cell. They then placed the fertilized egg cell in the womb of a domestic cow, which brought the gaur to term. Sadly, the baby gaur survived only two days after birth, dying of dysentery (a disease caused by an infection that is marked by severe diarrhea). While some scientists remain optimistic about the future of cloning endangered species, others believe that such cloning could hamper efforts to conserve biodiverse habitats by offering to rescue endangered species in a lab.

[See also Biodiversity; Environmental ethics; Rain forest ]

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endangered species

endangered species, any plant or animal species whose ability to survive and reproduce has been jeopardized by human activities. In 1999 the U.S. government, in accordance with the U.S. Endangered Species Act (1973), classified 935 native species as endangered or threatened, including animals such as the Florida panther, the Key deer, the San Joaquin kit fox, the northern spotted owl, the chinook salmon, the Karner blue butterfly, the snail darter, and the cave crayfish and plants such as the Hawaiian nehe and the clover lupine. Over 500 more species were so classified worldwide. The official list of endangered wildlife and plants in the United States is kept by the Fish and Wildlife Service; the National Marine Fisheries Service oversees marine species. In addition, many states keep their own lists. The International Union for the Conservation of Nature and Natural Resources maintains an international list, published as the Red Data Book.

Causes of Endangerment

Hunting, trapping, and poisoning to protect livestock have taken a great toll among predatory mammals and birds. Overharvesting is currently threatening species worldwide, especially food fish species such as the cod. A large number of species are threatened by introduced species, or "exotics," plants or animals that are introduced into a habitat and bring with them diseases or the ability to compete more effectively than native species. The now ubiquitous European starling, for example, purposely introduced into the United States in the 1890s, is displacing the native American bluebird and other species, and the brown tree snake, native to Australia and introduced to Guam during World War II, has preyed on native species of that island to the extent that nine bird species are now extinct. Another danger is hybridization with other species and subspecies.

Another important threat is destruction of habitat by chemical pollutants. For example, bird populations have suffered great losses because of insecticides. The chemicals they contain, such as DDT, accumulate in birds' bodies and interfere with calcium metabolism. As a result, the females lay eggs with extremely thin shells or no shells at all, so the embryos do not survive to hatching. Acid rain has destroyed the habitats of many North American fish and amphibians by lowering the pH of surface waters. It is also changing the soil chemistry and harming many tree species.

Most serious of all, the destruction of physical habitat—by the drainage and filling of swamps and marshes, by the damming of rivers, by the leveling of forests for residential and industrial development, by strip mining, and by oil spills and water pollution—has left many creatures with literally no room in which to live and breed. For example, only 5% of the original forests in the 48 coterminous states, i.e., those forests that were present at the time of the first European settlement, are still standing.

Efforts to Protect Species

Many local, national, and international organizations, such as Greenpeace, the Sierra Club, and the National Audubon Society, work to preserve habitats and heighten public awareness. Conservationists have pressed for habitat preservation through the establishment of new wildlife refuges and wilderness areas and for public and private land-use planning that would provide for development without habitat destruction. Some wildlife conservation organizations try to keep seriously endangered species viable with captive breeding programs, releasing new offspring into the species' native habitat when breeding is successful.

U.S. legislation affecting endangered species includes the various federal antipollution laws, the banning of DDT, the National Environmental Policy Act (NEPA) of 1969, and the Endangered Species Acts of 1966, 1969, 1973, 1978, 1982, and 1988. The landmark 1973 Endangered Species Act prohibits any trade in endangered species or their products and requires that federal agencies assess the impact on wildlife habitat of proposed projects—much as NEPA requires an environmental impact statement. These laws are often the only tool that conservationists have to prevent the development or other exploitation (e.g., logging or mining) of important habitats, but enforcement is also hampered by litigation and a lack of funds. Despite these problems, in the years since 1973 the status of a number of species, including the bald eagle, American alligator, and black-footed ferret, became stable or improved.

The protection of species in the United States has, however, become highly politicized. Asserting that the enforcement of environmental rules unfairly burdens business, the Republican 104th Congress prevented any further species from being added to the U.S. list of endangered and threatened wildlife and plants for 13 months from 1995 to 1996. Despite the perception that enforcement of the laws affects the economy and impedes progress, only 1% of the 50,000 projects that raised endangered-species questions between 1976 and 1986 required further investigation because of possible serious impact on a species; most of those moved forward after some modification.

On the international scene, efforts have been made to halt the trade in spotted cats and crocodiles and to curtail whaling and the taking of porpoises in tuna seines. A conference in Washington, D.C., in 1973, attended by 80 nations, drew up the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which protects more than 600 species of animals and plants. By the early 1990s some success had been achieved in banning the trade in rhinoceros horn, elephant ivory, South American parrots, bird eggs, and rare orchids, but poaching—for the high profits that can sometimes be gained from these items—continues to be a serious threat. In addition to CITES, the 1992 United Nations Conference on Environment and Development (the "Earth Summit" ) produced an agreement to stem the depletion of the world's diverse species (see biological diversity). See also conservation of natural resources.


See T. B. Allen, Vanishing Wildlife of North America (1974); L. Regenstein, The Politics of Extinction (1979); S. Boyd, Endangered Species (1989); E. O. Wilson, The Diversity of Life (1992); D. Ackerman, The Rarest of the Rare (1996); D. Quammen, The Song of the Dodo (1996); M. Walters, Bird Watch (2011); and the Red Data Books published by the International Union for the Conservation of Nature.

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Endangered Species

Endangered Species

Endangered species are species of plants or animals (or other life forms such as fungi) that are threatened with extinction. As well as being a biological term, "endangered" has a formal political meaning: nations, states, and other organizations evaluate the status of species and determine which are in the greatest danger of going extinct; these species are designated as endangered species. Other species that are declining rapidly in numbers, but are not yet believed to be on the brink of extinction, are designated as threatened species. In the United States, the Endangered Species Act protects such species.

Several factors can cause a species to become endangered. The most common cause is loss of habitat. Much of the world's forests, grasslands, and wetlands are being transformed into agricultural and urban areas, and many species that lived in those habitats are unable to adapt to the new environment. As a result, their numbers can drop greatly in a very short time. In some cases, human hunting or gathering of particular species can drive a species to the brink of extinction. This is the case of the rhinoceros, which has been killed in large numbers during the past century to meet market needs in certain areas of the world. The horn of the rhino is prized for dagger handles in the Middle East and for medicinal uses in parts of Asia. Tigers and sun bears in Asia have likewise been driven to the brink of extinction due to the huge market for animal parts that are believed by many to have potent medicinal powers.

Protection and Reestablishment

There are several ways that people can try to protect endangered species and to keep them from going extinct. One important way is to set up special protected areas around some of the last remaining populations of a species. China has created such reserves for the giant panda. However, for these reserves to be successful, they need to have the support of the resident people that live around the reserve. In some cases, the reserves provide the local people with jobs, and in other cases, some agricultural and even hunting activities are permitted within the reserve.

For some species, their habitat has essentially disappeared, or the species has declined to only a few individuals. In these instances, the only feasible way to try to preserve the species is to bring all the remaining individuals into captivity. One important function of zoos today is to house such endangered species. In some cases, captive breeding programs are initiated to increase the number of individuals of the endangered species. The ultimate goal of many of these captive breeding programs is to reintroduce the species back into the wild at some future date.

There are several ongoing reintroductions. In the 1980s, when the California condor had declined almost to the point of extinction, the few remaining individuals were captured and placed in captivity. A successful captive breeding program increased the numbers to several dozen individuals, and some have been released back into the wild. Reintroductions of endangered species are not always successful because the reintroduced animals usually have lived only in captivity. Thus, it is often necessary to prepare these animals for their new life in the wild by teaching them how to catch their food and to avoid predators.

Probably the greatest success story of the recovery of an endangered species involves the national bird of the United States, the bald eagle. The bald eagle, like many other birds of prey, fell victim to the heavy use of pesticides by farmers in the 1950s, including DDT. Much of the DDT that was sprayed onto agricultural fields ran off into streams and rivers and lakes when it rained. Small aquatic life consumed some of this DDT, and it remained in their body tissue. When a small fish ate these small aquatic organisms, DDT accumulated in their bodies too and was passed on when a larger fish ate the smaller fish. This process has been referred to as bioaccumulation, or biomagnification.

Thus, by the time the bald eagle ate the larger fish, it was eating contaminated food, and the eagles' own tissues accumulated high concentrations of DDT. One unfortunate consequence of these high concentrations of DDT was the severe weakening of the eggshell laid by the eagle. They were so weak they would often break during the normal parental brooding of the eggs. As a result, the birth rates of the eagles plummeted at the same time the death rates from DDT poisoning rose.

In response to environmentalists like Rachel Carson, who saw how the use of these sorts of chemicals was harming wildlife, the United States banned further use of DDT and provided the bald eagle with special protection under its endangered species status. The eagle populations responded slowly, but in the 1990s the populations began to increase at a rapid rate. In the early twenty-first century, the bald eagle is seen commonly in many parts of the United States and Canada, and its numbers have increased substantially enough that it is no longer considered an endangered species.

see also Biodiversity; Carson, Rachel; Extinction; Pollution and Bioremediation

Mark A. Davis


Primack, Richard B. Essentials of Conservation Biology. Sunderland, MA: Sinauer Associates, 1998.

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Endangered Species

Endangered Species

An endangered species is a species that is in immediate danger of becoming extinct. The designation of endangered to a species means that there is still time to save it but once it is extinct it is gone forever. Also of concern are threatened species, species whose numbers are low or declining but not in immediate danger of extinction. A threatened species is likely to become endangered if it is not protected.

Most species that are endangered are found in only limited geographic areas. Because these plants or animals are not widespread to begin with, they are more likely to be affected by major or catastrophic changes in their environment. Widespread common species, while sometimes significantly hurt by a regional catastrophe, are more likely to survive because many individuals will escape the damage elsewhere. In contrast, species found only in small and unusual habitats can suddenly become endangered or extinct if their limited habitat disappears.

Processes That Threaten Endangered Species

Extinction can be part of the natural order. Only about one in a thousand of all of the species that have ever lived on Earth is still living today. The vast majority became extinct because of naturally changing physical and biological conditions. Changing climate such as that experienced during the Ice Age (which eliminated many plant species from very large areas of North America and Europe) and other natural events such as volcanic activity have caused localized plant extinctions. The slow movement of the continents (most notably Antarctica and Australia) into unsuitable climate zones caused many organisms to become extinct. Far more widespread and devastating natural extinctions have been caused by the rare impacts of asteroids and comets on the Earth. Some impacts have caused the extinction of even common species on a global scale.

The danger to plants and animals today is most often a direct result of human activities and human population increase. These activities have taken the form of habitat alteration, economic exploitation, the intentional elimination of pests, the introduction of exotic (nonnative) organisms, the increase of invasive native grazers, and the effects of environmental pollution.

Habitat alteration is the main factor endangering species throughout the world, from the American Midwest where the prairies have been converted to cropland to the equator where the tropical rain forests are being cut and burned. Wetlands filling and draining, agricultural expansion, and residential housing development are all significant factors in habitat destruction.

Trade in live plants and animals and the products made from them is the second greatest factor endangering species. The cutting of forests for wood and fuel, the digging of rare plants for sale, and the harvesting of medicinal plants for commerce is as common as the illegal hunting and poaching of animals for sport, food, products, or pets. Plant examples include such species as ginseng, which has been harvested in several states to the point of near extinction.

The intentional elimination of species is a third human factor endangering species. Many plants and animals have become endangered or extinct simply because people decided they were pests. Killing for the sake of elim-inating an unwanted animal or plant has been common, as seen in the burning or clearing of forests for agriculture or other development, or in the killing of lions, wolves, sharks, or many snakes considered to be pests.

Invasions by exotic species (animal or plant species that have been introduced to an area where they did not naturally occur) threaten many endangered plants. When plants or animals are introduced into an area where they have no natural enemies, they may start to compete with the native plants and animals for food, water, shelter, and space and often replace them. Some plant examples include teasel and aggressive European pasture grasses that have invaded the few remaining tallgrass prairies or aquatic plants that have clogged streams and canals. The introduction of goats to tropical islands, for example, has caused the endangerment and extinction of many plant species that were not adapted to such grazing. A similar impact to plants can occur from locally overabundant or expanding native species such as beavers, rabbits, and deer that have altered many habitats because of the elimination of their former natural predators. For example, in many areas of the midwestern and eastern United States, heavy browsing by white-tailed deer is preventing the regeneration of the endangered components of native plant communities. Conservation biologists must be as effective in controlling invasive and destructive species as they are at saving endangered native species.

Environmental poisons and pollution are endangering numerous plants and animals worldwide as well. Examples of plants and animals today that are being poisoned by environmental toxins and solid wastes such as deadly chemicals, oils, and acids are numerous. Scientists learned long ago that groups of organisms in a limited environment can be killed by their own wastes.

Many Plants Are Endangered

One in ten, or a total of about three thousand plants native to the United States is endangered. Many of these endangered plants include some of the most showy, such as the large-flowered orchids. Increasingly, many plants around the world no longer reseed and therefore remain as lone survivors of their species. For example, the Presidio manzanita is so rare that only one plant survives in the wild, at San Francisco's Golden Gate Park. While cuttings have been propagated , they cannot self-fertilize. Another example of a lone survivor can be found on the Indian Ocean's Mascarene Islands where a palm tree, the Hyophorbe amaricaulis, survives as a single individual. One severe storm could cause its extinction. More than two hundred other plant species have also stopped reproducing. Worldwide, an impressive one in eight plants is endangered, according to the 1997 IUCN Red List of Threatened Plants.

Plant Extinctions Are Increasing

Although conservation efforts have begun in recent years, people are still exterminating entire species at an ever-increasing rate. Since the Pilgrims landed at Plymouth Rock, more than five hundred species, subspecies, and varieties of our nation's plants and animals have become lost forever. By contrast, during the three thousand years of the Pleistocene Ice Age, all of North America lost only about ninety species. The situation is even worse in many other parts of the world. Some scientists believe that if present trends continue, two-thirds of the world's three hundred thousand plant species will disappear by the end of the twenty-first century.

Extinction is a difficult concept to fully grasp. We are very aware that dinosaurs no longer exist and that other animals (such as the mammoth, dodo, Carolina parakeet, passenger pigeon, and the Atlantic grey whale) are gone forever due to human activity. The Sexton Mountain mariposa lily, a flower of southwestern Oregon, was unintentionally exterminated by a road crew when Interstate 5 was built in the 1960s. The maidenhair (ginkgo) tree was planted by the Chinese in gardens many centuries ago before it became extinct in the wild. A few plants that have become extinct in the wild in recent times have been saved in some form in cultivation . The Franklin tree (Franklinia, named after Ben Franklin) was last seen in the wild in 1803 in Georgia. However, a few individuals were planted in gardens at that time and have been propagated, saving the species from total extinction. In the mid-1990s the Graves's beach plum, a seashore tree found only in Connecticut, became extinct in the wild when the only known individual died. A few cuttings have been saved in botanical gardens. Although cloning results in plants that are genetically identical, those that have become extinct in the wild but that have been saved in cultivation cannot effectively reproduce.

Mechanisms of Environmental Protection for Endangered Species

Enacted in 1973, the Endangered Species Act (ESA) is the principal tool in the United States for slowing or stopping what has become the greatest rate of extinction worldwide since the disappearance of the dinosaurs sixty-five million years ago. In adopting the Endangered Species Act, Congress found that "various species have been rendered extinct as a consequence of economic growth and development untempered by adequate concern and conservation." In addition, Congress recognized that threatened and endangered species "are of aesthetic, ecological, educational, historical, recreational, and scientific value to the Nation and its people." Congress enacted the ESA in order "to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved" and to provide a program for the conservation of the species themselves. Under the ESA, species are listed as endangered or threatened. The Interior Secretary is generally required to designate critical habitats (areas essential to the survival and recovery of a species) for threatened and endangered species. In addition, recovery plans (blueprints for bringing species back to a point where they are no longer threatened or endangered) must be developed and implemented. About one-third of listed species are now stable or improving as a result of the ESA Protections for Listed Species. Effective protection is limited by the degree of funding and enforcement of the law.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), convened in Washington, D.C., in 1973, has been signed by more than 120 countries. CITES was established for the purposes of controlling and monitoring international trade in plants and animals considered to be threatened or likely to be threatened through commercial exploitation. It states that flora and fauna comprise an "irreplaceable part of natural systems which must be protected for generations to come" and "international cooperation is essential for the protection of certain species [endangered by] over-exploitation through international trade." This treaty was one of the first to take account of the need for conservation of both plants and animals and provided the legal framework within which those in trade can be protected from extinction.

Conservation practices provide the only solution for protecting endangered species. Propagation centers, such as botanical gardens, are actively attempting to save some endangered plant species. Protected collections of seeds and plants can help stop species loss, but protection in the wild is much more desirable because propagating endangered species can be considered to be meaningless if they do not have a home. Managing ecosystems or saving species collectively is the best known solution. Around the world more than thirty-five hundred protected areas (with a total of about 2 million square miles [5 million square kilometers], or 3 percent of Earth's land area) exist in the form of parks, wildlife refuges, and other reserves. Three percent of the planet's area, however, can only protect a relatively small number of species.

see also Biodiversity; Botanical Gardens; Ginkgo; Invasive Species; Rain Forests; Seed Preservation.

Steven R. Hill


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endangered species

endangered species Animals or plants threatened with extinction as a result of such activities as habitat destruction and overhunting. In 1948, the International Union for the Conservation of Nature and Natural Resources (IUCN) was founded to protect endangered species. The IUCN publishes the Red Data Book, which currently lists more than 1000 animals and 20,000 plants considered endangered. In the UK, the Wildlife and Countryside Act (1981) gives legal protection to a wide range of wild animals and plants. See also conservation; ecology; habitat; wetland;

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"endangered species." World Encyclopedia. . 10 Dec. 2017 <>.

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endangered species

endangered species A plant or animal species defined by the IUCN (International Union for the Conservation of Nature and Natural Resources) as being in immediate danger of extinction because its population numbers have reached a critical level or its habitats have been drastically reduced. If these causal factors continue the species is unlikely to survive. A list of endangered species is published by the IUCN, which also defines other categories of threatened species.

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"endangered species." A Dictionary of Biology. . 10 Dec. 2017 <>.

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endangered species

endangered species See rarity.

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