A species (group of like organisms that can reproduce) is listed as endangered if it is in immediate danger of extinction throughout all or a significant part of its habitat. Fossils show that many plants and animals have become extinct over millions of years. As of 2004, there are about 400 animals and 600 plants that are native to the United States listed as endangered. Over 125 animals and nearly 150 plants are currently listed as threatened. A species is listed as threatened if that species is likely to become endangered in the foreseeable future.

Many species of plants and animals become endangered and extinct naturally, usually due to changes in climate or loss of food sources. However, over the last several centuries, humans have posed a new threat to plants and animals. Human activities have resulted in the extinction of thousands of species. Human activities, such as hunting...