The term "stability" refers to the tendency of an individual organism, a community, a population, or an ecosystem to maintain a more or less constant structure over relatively long periods of time. Stability does not suggest that changes do not occur, but that the net result of those changes is nearly zero. A healthy human body is an example of a stable system. Changes are constantly taking place in a body. Cells die and are replaced by new ones. Chemical compounds are manufactured in one part of the body and degraded in another part. But, in spite of these changes, the body tends to look very much the same from day to day, week to week, and month to month.

The same is true with groups of individuals. A prairie grassland may look the same from year to year, even though the individual plants that make up the...