Characteristics of Populations

Several terms can be used to describe a population in nature.   Three important characteristics of a population are its geographic distribution, density, and growth rate. A fourth characteristic, the population's age structure, will be discussed later in this chapter. Geographic distribution, or range, is a term that describes the area inhabited by a population. The range can vary in size from a few cubic centimeters occupied by bacteria in a rotting apple to the millions of square kilometers occupied by migrating whales in the Pacific Ocean.

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Population density is the number of individuals per unit area. This number can vary tremendously depending on the species and its ecosystem. The population of saguaro cactus in the desert plant community, for example, has a low density, whereas other plants in that community have a relatively high density.