Endangered Species

I

Introduction

Endangered Species, plant and animal species that are in immediate danger of extinction. The following degrees of endangerment have been defined. Critically endangered species, such as the California condor, are those that probably cannot survive without direct human intervention. Threatened species are abundant but are declining in total numbers. Rare species exist in relatively low numbers over their ranges but are not necessarily in immediate danger of extinction.

Extinction is actually a normal process in the course of evolution. Throughout geological time, many more species have become extinct than exist today. These species slowly disappeared because of climatic changes and the inability to adapt to such conditions as competition and predation. Since the 1600s, however, the process of extinction has accelerated rapidly through the impact of both human population growth and technological advances on natural ecosystems. Today the majority of the world's environments are changing faster than the ability of most species to adapt to such changes through natural selection.

II

Causes

Species become extinct or endangered for a number of reasons, but the primary cause is the destruction of habitat. Drainage of wetlands, conversion of shrub lands to grazing lands, cutting and clearing of forests, desertification, urbanization and suburbanization, and highway and dam construction have seriously reduced available habitats. As the various habitats become fragmented into “islands”, the remaining animal populations crowd into smaller areas, causing further habitat destruction. Species in these small islands lose contact with other populations of their own kind, thereby reducing their genetic variation and making them less adaptable to environmental change. These small populations are highly vulnerable to extinction; for some species, the fragmented habitats become too small to support a viable population.

Since the 1600s, commercial exploitation of animals for food and other products has caused many species to become extinct or endangered. The slaughter of great whales for oil and meat, for example, has brought them to the brink of extinction; the African rhinoceros, killed for its horn, is also critically endangered. The great auk became extinct in the 19th century because of overhunting, and the Carolina parakeet perished as a species because of a combination of overhunting and habitat destruction. In 2000 cod was put on the endangered species list by the World Wide Fund for Nature (WWF). The number of cod in the United Kingdom’s waters has halved since the 1960s due to overfishing, which some claim is the result of excessively high quotas for catches set by the European Union. The decline in the cod population has also been influenced by a rise in sea temperatures, due to global warming, which has damaged the cod’s ability to spawn.

Introduced diseases, parasites, and predators against which native flora and fauna have no defenses have also exterminated or greatly reduced some species. The accidental introduction of a blight, for example, eliminated the chestnut tree from North American hardwood forests. Predator and pest control also have adverse effects. Excessive control of prairie dogs, for example, has nearly eliminated one of their natural predators, the black-footed ferret.

Pollution is another important cause of extinctions. Toxic chemicals—especially chlorinated hydrocarbons such as dichloro-diphenyl-trichloroethane (DDT) and polychlorinated biphenyls (PCBs)—have become concentrated in food webs, affecting most strongly those species at the end of the chain. Both DDT and the PCBs, for example, interfere with the calcium metabolism of birds, causing soft-shelled eggs and malformed young. PCBs also impair reproduction in some carnivorous animals. Even ordinarily non-toxic substances such as nitrogen-based fertilizers can be detrimental in excess. A 1999 UN report stated that worldwide fertilizer use has increased from 14 million tonnes in 1950 to 145 million tones in the late 1980s, resulting in a drastic increase in the amount of nitrogen in ground and water supplies. Excessive nitrogen has polluted drinking water supplies and has also contributed to “exuberant and unwanted” growth of algae and other plants in many freshwater habitats. The eutrophication and eventual decay of these plants produces harmful wastes and removes oxygen from the water, killing other organisms. Venting hot water or wastes from industrial plants, for example, can also encourage excessive vegetation and speed decay. Water pollution and increased water temperatures (see Global Warming) have wiped out endemic races of fish in several habitats. Terrestrial and aerial life also relies directly or indirectly on these water supplies. Additionally, the increasing scarcity of fresh water affects all species, including humans, as do other environmental concerns (see Environment: Environmental Problems).

A United Nations Environment Programme (UNEP) report on the global environment published in May 2002 concluded that over 11,000 species (including almost a quarter of all mammals) face extinction within 30 years. In total more than 5,000 plants, 1,000 mammals, and 5,000 other animals (including one in eight birds) are endangered, mostly due to habitat destruction and invasion by non-native species. The report states that factors that caused previous extinctions are operating with “ever-increasing intensity”, although it suggests that these problems could be eased if treaties and conventions such as the Kyoto Protocol and Convention on Biodiversity were implemented globally.

III

Preservation Efforts

Some private and governmental efforts have been directed at saving declining species. One immediate approach is to protect a species by legislation. Laws were enacted in the United States in the early 1900s, for example, to protect wildlife from commercial trade and overhunting. In 1973 the Endangered Species Act provided mechanisms for the conservation of ecosystems on which endangered species depend; it also discouraged the exploitation of endangered species in other countries by banning the importation and trade of any product made from such species. The United States also has various agreements with other nations—for example, with Canada and Mexico for the legal protection of migratory birds.

International efforts centre on the Convention on International Trade in Endangered Species of Wild Fauna and Flora, ratified by 51 nations. Its purpose is to restrict exploitation of wildlife and plants by regulating and restricting trade in species. The effectiveness of such laws in various countries, however, depends on enforcement and support by people and the courts. Because of a lack of law enforcement, the willingness of some segments of society to trade in endangered species, and the activities of poachers and dealers who supply the trade, the future of many species is in doubt in spite of legal protection.

Efforts to save endangered species also include the propagation of breeding stock for release in the wild, either to restore a breeding population (as in the case of the peregrine falcon) or to augment a natural population (as in the case of the whooping crane). Due to breeding in captivity, the number of known California condors had risen from 27 in 1987 to more than 240 by 2005. Another approach involves the determination of critical habitats that must be preserved for endangered species. These habitats may be protected by the establishment of reserves; the value of these may be limited, however, because of the island effect. The objections of special interest groups also make land preservation for the protection of endangered species difficult.