Plants, animals, and other living things have developed, flourished, and vanished since the first flickerings of life. Sooner or later, every species, or kind, of living thing dies out because it cannot keep up with the natural changes in its environment. Yet, in recent times, many species have passed out of existence sooner than they would have naturally. Since the year 1600, more than 500 species of wild animals and plants have disappeared from the North American continent alone. At least 1,000 more are in trouble. Worldwide, scientists estimate that 20,000 species of plants are in danger of extinction, that is, dying out completely.
Scientists and conservationists have developed terms to pinpoint the species that are in danger of dying out. An endangered species is any species of animal, plant, or other living thing that will become extinct if nothing is done to stop the cause of its decline. Endangered species are in immediate danger of extinction. Species that are likely to become endangered in the near future are termed threatened. Other species that are not in immediate danger but that have small populations and so could move quickly toward extinction are called vulnerable or candidate species.
Some of the imperiled species are big and spectacular, like the black rhinoceros and elephant of Africa. Many more, however, are small and unfamiliar to most people. The little Moapa dace, a minnow about 3 inches (8 centimeters) long, lives only in about 2 miles (3 kilometers) of a Nevada river. It is endangered. So is the Madison Cave isopod, a tiny crustacean found only in one Virginia cave.
But no matter how small or unfamiliar, each species of living thing has its own special role in keeping the world of nature in balance. When one species becomes extinct, other species are affected. Just one plant may be food or shelter to more than 30 species of animals. Without that plant to feed or protect them, those animals may also die out.
At one time, living things were primarily endangered by natural events such as the cold climate of the Ice Age or the geological changes caused by an earthquake or volcano. Now the greatest problems facing plants and animals--and people, too--are the human activities that harm the environment on which plants, humans, and other animals depend. Although many different human activities can threaten or endanger a species, the greatest problems occur because of habitat destruction. Illegal hunting and trading and introduction of new species can also cause serious problems.
Plants and animals are adapted to their habitats. Some species can live in a variety of habitats, others can live in only a very specific type of habitat. Either way, if its habitat is destroyed, a species may not be able to find food or shelter, so it vanishes. This means that species such as the Moapa dace that inhabit only a very limited habitat are at great risk of extinction.
Habitat can be destroyed in many ways. As the human population increases, there is a greater need for food, places to live, fuel, and many other things. To meet these needs, tropical forests, wetlands, grasslands, and other natural areas are cleared, settled, and developed and their resources harvested for human use. In the process, habitats are destroyed.
Pollution can also harm habitats, sometimes killing species far from the source. Acid rain caused by pollution from factories in the United States falls on Canada, endangering the fish in northern lakes. Agricultural weed killers and insecticides have been washed by rain into many rivers, killing fish there. Predators that eat fish poisoned this way can also suffer.
The most dramatic effects of habitat destruction can be seen in tropical rain forests. These forests have the greatest diversity of plant and animal life. They are home to between 50 and 90 percent of the millions of species living on earth. Yet each hour, several thousand acres of tropical forest are destroyed. By conservative estimate, this destruction means that 50 to 150 species in the tropics become extinct each day!
Ever since the first people appeared on the earth, they have used nature's resources. People have killed or collected animals and gathered plants for a variety of uses. Animal and plant products have been used for food, medicine, clothing, and shelter, among other things. But many species have been used to death.
In the early 1800's, 2 billion passenger pigeons lived in the United States. Because they were slaughtered for sport and food, by 1914 the last one had died in a zoo. Cheetahs, ocelots, tigers, and other wild cats have been killed for their skins. Several species of whales have been hunted to near extinction for their oil and blubber.
Although most of these animals now are protected by law, many still are poached, or hunted illegally. Animals such as the black rhinoceros and elephant, which are valued for their horns and tusks, have been drastically diminished in number by poachers. Penalties for people who illegally kill and trade wildlife have become much more severe in recent years.
Some species have dwindled because people viewed them as threats to livestock. Wolves have been wiped out of most areas in which they lived because they sometimes prey on domestic animals. In Central Asia, people have killed the endangered snow leopard because of its attacks on sheep and goats.
Even if a living thing is not killed, taking it from the wild can endanger its species if it is rare. Many rare birds, including some parrots, have been caught for the pet trade. Some of these species are already menaced by the loss of their habitats. The combination of habitat loss and capture for commercial trade increases their risk of extinction.
Sometimes native animals are endangered when a new species is introduced into a habitat. In 1820, people released rabbits in Australia that multiplied and became pests. Foxes, which prey on rabbits, were then introduced to control the rabbits. Instead, the foxes killed off native Australian marsupials. Foxes, cats, and dogs introduced into Australia have exterminated nine types of marsupials and endangered more than a dozen others.
Among the greatest threats to plants and animals are parasites, which include tiny organisms, worms, and insects that feed off other species. Some fungi and bacteria can also endanger plants and animals. For example, the fungus that causes Dutch elm disease has destroyed many populations of elm trees throughout Europe and North America. Sometimes certain algae can cause "red tides" in coastal waters, producing chemicals that kill many birds and fish.
People have hurt plants and wildlife. But people are also helping them survive. All over the world, conservation organizations, such as the World Wildlife Fund, Rainforest Action Network, and Friends of the Earth, are helping to conserve species and habitats. Such groups raise money to fund projects, maintain and publish lists of endangered species, and bring the plight of endangered species and habitats to the attention of policymakers and the public. The International Union for the Conservation of Nature and Natural Resources, based in Switzerland, coordinates endangered species conservation on a global basis.
National laws and international agreements have been established to protect endangered species. One such agreement, the Convention on International Trade in Endangered Species (CITES), bans trade in many rare species. In the United States, the federal Endangered Species Act lists and protects hundreds of species and habitats from activities that might harm them. The act was first passed into law in 1973.
Saving habitat is the cornerstone of protecting species. However, even if their habitat is saved, some species have too few members in the wild to repopulate. Many of these have been taken to zoos or parks and bred there. Within these captive-breeding programs, species are bred with the hope that offspring can be raised and then returned to the wild. Programs such as this, combined with laws, awareness, and commitment, will help maintain the delicate balance of nature that is necessary for the survival of all living things.
Co-author, The Audubon Society Book of Wild Animals