Endangered Species

An endangered species is any species of plant or animal that is threatened with extinction. Although extinction, or the situation in which no living member of a species exists any longer, can have natural causes, it is often being hastened by the activities of humans. International efforts to identify the most threatened species have begun, and various national and international laws have been passed to protect these endangered organisms.

Biologists estimate that about 500,000,000 species of plants and animals have existed since life began on Earth. Since there are only some 2,000,000 to 4,000,000 species in existence today, most of the species that ever lived on Earth are now extinct. This demonstrates that extinction is a natural phenomenon that occurs as the normal process in the course of evolution. Evolution has shown that species that cannot adapt to natural changes in their environment or to increased competition from other species will eventually become extinct. Besides climate or environment change and competition, disease and natural catastrophes can destroy an entire species. It is believed that such an occurrence took place more than 65,000,000 years ago when an asteroid struck the Earth and eliminated more than half of the planet's plant and animal life, including the dinosaurs.

ENDANGERMENT INCREASES DUE TO HUMANS

Although extinction may occur naturally, the growing problem in our modern world is that increased human activities have dramatically increased the natural rate of extinction. While people have always had an effect on their environment, the degree to which they have affected it has increased substantially since the Industrial Revolution of the eighteenth century. During the second half of the twentieth century in particular, technological advances combined with a rapidly expanding human population have changed the natural world as never before. As the twenty-first century begins, biologists estimate that the rate of extinction has increased to somewhere between 100 to 1,000 times nature's normal rate. Today, species are threatened and become endangered primarily because of a combination of three human factors: their habitat is either disturbed or eliminated; they are overhunted; or they are being eliminated by other nonnative "introduced" species.

CAUSES FOR ENDANGERMENT

Habitat destruction is the main reason for the increasing number of today's endangered species. The steadily increasing human population has in many ways taken over areas that formerly were habitats or homes for certain organisms. This "takeover" usually shows itself in the form of houses, highways, and industrial buildings in developed countries, and growing farms and farmland in less developed ones. Whenever a new airport or dam is built in a formerly natural landscape, the life forms that lived there must somehow either adapt, move, or die. Often a habitat is totally destroyed and changed into something that is totally unrecognizable from its former self. Other times however, habitat destruction is less obvious, such as when industrial runoff or city sewage degrades the quality of a habitat but leaves it apparently looking the same. As habitats are regularly chipped away and become smaller and smaller, the pressure on the organisms in the habitat becomes greater, and it becomes harder for them to survive.

The inhabitants in a given habitat are often also sought after by people for many different reasons. Whether people have killed animals for sport (such as the American bison was in the nineteenth century) or for profit (like the whale and the rhinoceros), overhunting has placed many of today's species close to extinction.

Finally, people have altered habitats dramatically by taking one species from its native habitat and transplanting it into a different habitat somewhere else. Sometimes this is done deliberately, as when rabbits were introduced to Victoria, Australia, by Thomas Austin in 1859. Austin release twenty-four of the animals from England to be used for sport hunting. However, within twenty years these twenty-four rabbits multiplied to millions. Not only did they became serious pests, but they set about actively destroying certain vegetative life.

Other times, introducing a new species is done accidentally, as when the gypsy moth was accidentally introduced into the United States from France in 1869. Sometimes newly introduced species cause little or no harm, but many times they upset the delicate balance that was established by the native organisms, and often out-compete these "natives" for scarce resources. Sometimes a new species can actually eliminate a species that was perfectly adapted to its habitat but had no natural defenses to use against the newcomer.

SAVING ENDANGERED SPECIES

Fortunately, something is being done for species that are so threatened that they may disappear altogether. On a global level, the International Union for Conservation of Nature and Natural Resources (IUCN) classifies such species as endangered, critically endangered, threatened, or rare. To the IUCN, an endangered species is in the greatest danger and faces immediate extinction, possibly even if action is taken in an effort to prevent it. A critically endangered species is one that will not survive without human help. Threatened species may still be abundant in their own habitat, but overall their population is rapidly declining. Rare species are considered at risk because of low overall population numbers. The Endangered Species Act of 1973, which became law in the United States that year, obligates the government to protect all animal and plant life threatened with extinction. It also provides for the drawing up of lists of such species and promotes the protection of critical habitats or places that are essential to the survival of a species. One of the first species placed on that list was the nation's own symbol, the bald eagle. In May 1998, the bird was taken off the list, along with several other species that have apparently been saved.

[See alsoExtinction; Habitat ]