endangered species

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endangered species,

any plant or animal speciesspecies,
in biology, a category of classification, the original and still the basic unit in the demarcation of plant and animal types. The species marks the boundary between populations of organisms rather than between individuals.
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 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, trappingtrapping,
most broadly, the use of mechanical or deceptive devices to capture, kill, or injure animals. It may be applied to the practice of using birdlime to capture birds, lobster pots to trap lobsters, and seines to catch fish.
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, 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 codcod,
member of the large family Gadidae, comprising commercially important food fishes. The family, whose members are found in the N Atlantic and Pacific, includes the tomcods, the haddock, and the pollacks (or pollocks).
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. 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 insecticidesinsecticides,
chemical, biological, or other agents used to destroy insect pests; the term commonly refers to chemical agents only. Chemical Insecticides

The modern history of chemical insecticides in the United States dates from 1867, when Paris green proved
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. The chemicals they contain, such as DDTDDT
or 2,2-bis(p-chlorophenyl)-1,1,1,-trichloroethane, chlorinated hydrocarbon compound used as an insecticide. First introduced during the 1940s, it killed insects that spread disease and fed on crops, and Swiss scientist Paul Müller was awarded the 1948 Nobel Prize
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, 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 rainacid rain
or acid deposition,
form of precipitation (rain, snow, sleet, or hail) containing high levels of sulfuric or nitric acids (pH below 5.5–5.6).
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 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 GreenpeaceGreenpeace,
international organization that promotes environmental awareness and addresses environmental abuse through direct, nonviolent confrontations with governments and companies. Founded in 1971 to oppose U.S.
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, the Sierra ClubSierra Club,
national organization in the United States dedicated to the preservation and expansion of the world's parks, wildlife, and wilderness areas. Founded (1892) in California by a group led by the Scottish-American conservationist John Muir, the Sierra Club is made up of
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, and the National Audubon SocietyAudubon Society, National,
one of the oldest and best-known U.S. environmental organizations; founded 1886 by George Cird Grinnell and named for John James Audubon. The nonprofit organization, which has a membership of 550,000, operates 100 wildlife sanctuaries and nature
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, work to preserve habitats and heighten public awareness. Conservationists have pressed for habitat preservation through the establishment of new wildlife refugeswildlife refuge,
haven or sanctuary for animals; an area of land or of land and water set aside and maintained, usually by government or private organization, for the preservation and protection of one or more species of wildlife. Types of Refuges

The U.S.
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 and wildernesswilderness,
land retaining its primeval character with the imprint of humans minimal or unnoticeable. In the United States, the Wilderness Act of 1964 established the National Wilderness Preservation System with a nucleus of 9 million acres (3.
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 areas and for public and private land-useland use,
exploitation of land for agricultural, industrial, residential, recreational, or other purposes. Because the United States historically has a laissez-faire attitude toward land use, the land has been exploited at will for economic gain.
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 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 statementenvironmental impact statement,
analysis of the impact that a proposed development, usually industrial, will have on the natural and social environment. It includes assessment of long- and short-term effects on the physical environment, such as air, water, and noise pollution,
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. 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 whalingwhaling,
the hunting of whales for the oil that can be rendered from their flesh, for meat, and for baleen (whalebone). Historically, whale oil was economically the most important. Early Whaling

Whaling for subsistence dates to prehistoric times.
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 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 DevelopmentUnited Nations Conference on Environment and Development
(UNCED) or Earth Summit,
an 11-day meeting held in June, 1992, in Rio de Janeiro, Brazil, to discuss the global conflict between economic development and environmental protection.
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 (the "Earth Summit") produced an agreement to stem the depletion of the world's diverse species (see biological diversitybiological diversity
or biodiversity,
the number of species in a given habitat. Scientists have variously estimated that there are from 3 to 30 million extant species, of which 2.
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). See also conservation of natural resourcesconservation of natural resources,
the wise use of the earth's resources by humanity. The term conservation came into use in the late 19th cent. and referred to the management, mainly for economic reasons, of such valuable natural resources as timber, fish, game, topsoil,
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.

Bibliography

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.

Endangered species

A species that is in danger of extinction throughout all or a significant portion of its range. “Threatened species” is a related term, referring to a species likely to become endangered within the foreseeable future. The main factors that cause species to become endangered are habitat destruction, invasive species, pollution, and overexploitation.

Habitat destruction is the single greatest threat to species around the globe. Natural habitat includes the breeding sites, nutrients, physical features, and processes such as periodic flooding or periodic fires that species need to survive. Humans have altered, degraded, and destroyed habitat in many different ways. Logging around the world has destroyed forests that are habitat to many species. This has a great impact in tropical areas, where species diversity is highest. Although cut forests often regrow, many species depend upon old-growth forests that are over 200 years old; these forests are destroyed much faster than they can regenerate. Agriculture has also resulted in habitat destruction. In the United States, tallgrass prairies that once were home to a variety of unique species have been almost entirely converted to agriculture. Housing development and human settlement have cleared large areas of natural habitat. Mining has destroyed habitat because the landscape often must be altered in order to access the minerals. Finally, water development, especially in arid regions, has fundamentally altered habitat for many species. Dams change the flow and temperature of rivers and block the movements of species up and down the river. Also, the depletion of water for human use (usually agriculture) has dried up vegetation along rivers and left many aquatic species with insufficient water.

The invasion of nonnative species is another major threat to species worldwide. Invasive species establish themselves and take over space and nutrients from native species; they are especially problematic for island species, which often do not have defensive mechanisms for the new predators or competitors. Habitat destruction and invasion of nonnative species can be connected in a positive feedback loop: when habitat is degraded or changed, the altered conditions which are no longer suitable for native species can be advantageous for invasive species. In the United States, approximately half of all endangered species are adversely affected by invasive species.

Pollution directly and indirectly causes species to become endangered. In some cases, pesticides and other harmful chemicals are ingested by animals low on the food chain. When these animals are eaten by others, the pollutants become more and more concentrated, until the concentration reaches dangerous levels in predators and omnivores. These high levels cause reproductive problems and sometimes death. In addition, direct harm often occurs when pollutants make water uninhabitable. Agriculture and industrial production cause chemicals such as fertilizers and pesticides to reach waterways. Lakes have become too acidic from acid rain. Other human activities such as logging, grazing, agriculture, and housing development cause siltation in waterways. Largely because of this water pollution, two out of three fresh-water mussel species in the United States are at risk of extinction.

Many species have become endangered or extinct from killing by humans throughout their ranges. For example, the passenger pigeon, formerly one of the most abundant birds in the United States, became extinct largely because of overexploitation. This overexploitation is especially a threat for species that reproduce slowly, such as large mammals and some bird species. Overfishing by large commercial fisheries is a threat to numerous marine and fresh-water species. See Fisheries conservation

Efforts to save species focus on ending exploitation, halting habitat destruction, restoring habitats, and breeding populations in captivity. In the United States, the Endangered Species Act of 1973 protects endangered species and the ecosystems upon which they depend. Internationally, endangered species are protected from trade which depletes populations in the wild, through the Convention on International Trade in Endangered Species (CITES). Over 140 member countries act by banning commercial international trade of endangered species and by regulating and monitoring trade of other species that might become endangered. For example, the international ivory trade was halted in order to protect elephant populations from further depletion.

Typically, the first step is identifying which species are in danger of extinction throughout all or part of their range and adding them to an endangered species list. In the United States, species are placed on the endangered species list if one or more factors puts it at risk, including habitat destruction or degradation, overutilization, disease, and predation. Florida and California contain the most endangered species of all the contiguous 48 states. Hawaii has more endangered species than any other state. Hawaii, like other islands, has a diversity of unique species that occur nowhere else in the world. These species are also highly susceptible to endangerment because they tend to have small population sizes, and because they are particularly vulnerable to introduced competitors, predators, and disease.

For many endangered species, a significant captive population exists in zoos and other facilities around the world. By breeding individuals in captivity, genetic variation of a species can be more easily sustained, even when the species' natural habitat is being destroyed. Some species exist only in captivity because the wild population became extinct. For a few species, captive individuals have been reintroduced into natural habitat in order to establish a population where it is missing or to augment a small population. Depending on the species, reintroduction can be very difficult and costly, because individual animals may not forage well or protect themselves from predators. See Ecology