Certain species of plants and animals have been officially recognized as being in particular danger—the danger of imminent extinction. An "endangered species," as defined by the International Union for the Conservation of Nature (IUCN), is one that is in danger of extinction throughout all or part of its range (Hilton-Taylor, 2000). The list of endangered species includes plants and animals of diverse types. Some endangered species are well known, and their plight garners a great deal of concern from the public. Other endangered species are nearly anonymous, but as members of the fragile web of life their survival is as significant as that of the most celebrated species.
Endangered species in the United States are protected under one of the most powerful environmental protection mandates ever enacted. The 1973 U.S. Endangered Species Act (ESA) expanded the definition of "endangered species" to include subspecies, and it specifies criteria used to determine the degree of the threat. These criteria include current or threatened habitat destruction, overexploitation, excessive losses caused by disease or predation, inadequacy of existing laws to protect the species, or "other natural or manmade factors affecting its continued existence." Restricted ranges and fragmented populations frequently make endangered species more vulnerable to the effects of climate change and stochastic events because of reduced genetic variability within the populations. Being listed as endangered provides legal protection from harm for individuals of the species and prohibits federal agencies from authorizing, funding, or carrying out any action that is likely to jeopardize its continued existence—including habitat destruction. It also mandates that recovery plans be developed. The Endangered Species Act also carries protection a step further, by including as one of its stated purposes the conservation of ecosystems upon which endangered and threatened species depend (U.S.F.W.S., 1989).
The Endangered Species Act has had some notable successes, including the bald eagle (Hali-aeetus leucocephalus) and the peregrine falcon (Falco peregrinus anatum). These American bird species were listed as endangered in the late 1970s, when it became apparent that their populations had declined to perilously low levels. One of the key factors contributing to the decline of these raptor populations was the pesticide DDT, which caused the birds to lay eggs with weak shells and resulted in increased chick mortality. Pollutants like DDT accumulate within the food chain, and species at the top of the chain acquire the greatest burden. Habitat loss and persecution by humans were also significant factors in the decline of bird of prey populations. Bald eagles, forced to compete with humans for fish, were routinely shot by fishermen who were reluctant to share their catch. Peregrine falcons suffered from the encroachment of human populations on their habitats.
As a result of the ESA mandate, the use of DDT was abolished, vital habitat was protected, and heavy penalties were levied against those who harmed the birds. Also, intensive and successful breeding programs were established for peregrine falcons. As a result, bald eagle populations have made substantial recoveries, and the species has been down listed to "threatened" status; it has been proposed that it be delisted entirely. Eastern populations of peregrine falcons have rebounded from a low of a few hundred breeding pairs to 1,593 wild breeding pairs in 1998. Western populations have similarly increased. Peregrine falcons have taken up residence in urban areas, nesting on skyscrapers; they were formally removed from the endangered species list in 1999.
In contrast to the success of the protection efforts that made possible the recovery of the bald eagle and peregrine falcon, other endangered species have not fared well, despite a high degree of public awareness and concern. The tiger (Panthera tigris) is one example of an endangered species that has continued to decline despite all efforts at protection.
The tiger is the largest living representative of the cat family, and adult males can reach weights of more than 250 kg. These majestic animals once occupied a diverse array of habitats ranging across Asia and south to Iran and Indonesia. Several geographic subspecies were recognized, including three (Bali, Javan, and Caspian) that are now extinct. Although as
many as 100,000 tigers may have existed at the beginning of the twentieth century, it is estimated that today there may be fewer than 5,000 wild tigers left on earth.
The world's remaining wild tigers are threatened with extinction by the combined effects of human predation and habitat loss. Tigers are solitary predators, requiring large territories with ample prey. Forest destruction caused by logging and agriculture have isolated tiger populations and driven them into ever-smaller domains. As humans invade the tigers' habitat there is increasing human-tiger conflict over prey resources, and the fear of tiger attacks on humans prompts some to wish for their elimination. Efforts to protect tigers and their habitat are severely strained by a lack of alter native income sources for the local populations. Although captive breeding programs for tigers are very successful, without greater efforts to protect tiger habitat and to conserve the ecosystems that they depend upon, there will be no place for wild tigers in the future.
Illegal hunting has also been extremely detrimental to tiger populations. Since 1975 tigers have been protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which prohibits trafficking in endangered species and in products obtained from them. CITES protection has helped to curtail trophy and sport hunting, but it has failed to protect the species from poachers who sell tiger parts on the black market for use in tra ditional Asian medicines. Tiger protection will not become a reality until the local people are able to realize greater benefits as custodians of the species than they can as brokers of tiger carcasses.
For every species that has been recognized as endangered, there is likely to be an entire ecosystem of other plants and animals that is also vulnerable or is likely to suffer dire consequences if the endangered species becomes extinct. The recognition of endangered species such as the tiger and (formerly) the peregrine falcon is important not only for the survival of the species but also because they are sentinels for habitats and ecosystems at risk.
See also: Conservation Biology; Conservation, Definition and History; Ethics of Conservation; Preservation of Species
Dobson, Andrew P. 1998. Conservation and Biodiversity. New York: Scientific American Library; Hilton-Taylor, Craig. 2000. 2000 International Union for the Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species. Gland, Switzerland: IUCN Publications Service Unit; Macdonald, David, ed. 2001. The New Encyclopedia of Mammals. Abingdon, Oxfordshire, UK: Andromeda Oxford, Ltd; Meffe, Gary K., and C. Ronald Carroll. 1994. Principles of Conservation Biology. Sunderland, MA: Sin-auer.; U.S. Fish and Wildlife Service. 1989. Endangered Species: This Animal Is Protected under the Endangered Species Act of 1973: General Information. Washington, DC: U.S. Fish and Wildlife Service; U.S. Fish and Wildlife Service. 1991. Convention on International Trade in Endangered Species of Wild Fauna and Flora (1973): CITES, Appendices I, II, and III to the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Washington, DC: U.S. Fish and Wildlife Service; World Wildlife Fund. "Endangered Species: Tiger." http://www.world-wildlife.org (accessed January 13, 2002).
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