Population Biology

Population Biology, the study of populations of animals and plants, a population being a group of interbreeding organisms in a specific region—for example, the members of a fish species in a lake. A given population is usually isolated to some degree from others of its species, whether geographically or in terms of behavioral or anatomical differences, but its boundaries may be vague; for example, the fish in a lake may also interbreed with the fish of interconnecting waterways. Nevertheless, a population is a useful, if occasionally artificial, unit for study.

Populations are analyzed in terms of their variability, density, and stability, and of the environmental and other processes and circumstances that affect these characteristics. Among such determinants of a given population are birth and death rates; the distribution of ages and sexes; behavioral patterns of competition and cooperation; predator-prey, host-parasite, and other relationships with different species; food supplies and other environmental considerations; and migration patterns. In conducting analyses, population biologists use computers to develop mathematical models of the group under study that incorporate as many of these determinants and variables as possible. Such models enable scientists to predict what effect a change in any one determinant may have on a population as a whole.

Although all populations are unique in some way, some general characteristics can be described. Thus isolation, by whatever means, tends to cause a population to develop locally useful traits through natural selection. If the isolation persists, selection and random genetic drift—the introduction of mutations—may lead to the appearance of a new species, members of which are no longer likely or even able to interbreed with the species from which they originally derived.

Another characteristic of a population is its so-called environmental carrying capacity—that is, the maximum average number of individuals that the population can reach in its given setting. The degree to which this number affects and is affected by other changes in the population or its environment—that is, the population's dynamics—is yet another distinguishing characteristic. Long-term changes may result in the extinction of a population, its replacement by a better-adapted one, or a move by the population to a new environment. Finally, populations are characterized by a tendency to disperse from a region where the density of their numbers is high to a region of lower density. This is advantageous to those members that remain in the older region, but it may also be advantageous to those that explore new territories where there are greater food resources.

The study of population dynamics and of population genetics—the effects of heredity and evolution on populations—is important for all human interventions in the environment, from the growing of crops to attempts at pest and predator control. It also involves human populations themselves, in terms of population rates of growth and the availability of food supplies (see Population).