Earth is a biosphere, a globe richly supplied with different types of living organisms, including animals, plants, fungi, and bacteria. Living organisms are named and categorized according to a taxonomy, a hierarchical system of order based on the natural relationships among all types of life. "Species" is a term assigned to a level of the taxonomy in which grouped organisms are considered capable of interbreeding with one another. Various living species coexist in their environments, forming complex, interrelated communities. Because all species depend on others for nutrients, shelter, or other resources, the removal of even one species in a community can set off a chain reaction affecting many others. In recent decades, large numbers of species have disappeared. The consequences of this loss of biological diversity, or biodiversity, are not only manifold but difficult to predict.

What Are Endangered Species?

A species...