Lincoln S. Gifford, Jr., age 11, of Salt Lake City, Utah, for his question:

What is meant by an ecosystem?

Ecology is the study of how plants and animals share life in their environment. On a global scale, this includes the adaptation to basic items such as air and water, food chains and the interdependence of plant and animal species. But our total, planet is a world of wondrous variations. It has oceans, warm and shallow, torrid and temperate and frigid climate zones, mountains and valleys, wide plains and arid deserts. Each of these regions presents a different environment, suitable for a certain assortment of plants and animals.

An ecosystem includes the native plants and animals that share a certain environment. It may be a vast plain supporting its own variety of plant life and populated with its unique assortment of animals. It may be a temporary snowbank, supporting a variety of microscopic organisms, or a small desert pond including a few hundred unique pupfish. In any case, each plant and animal in the system is interdependent upon all the others. When one species is threatened with extinction, the entire system must either readjust to the change, or perish.