On the meaning of density dependence.

Despite a long history, the term "density dependence" lacks a generally accepted definition. A definition is offered that seems consistent with most other definitions and general usage, that is, a density-dependent factor is any component of the environment whose intensity is correlated with population density and whose action affects survival and reproduction. This definition is used in evaluating the role of territorial behavior, the availability of nest sites, and competition in determining the size of a population. Because neither territory size nor the number of nest sites is correlated with either density or with changes in the birth and death rates of these populations, these cannot be considered density-dependent factors. Competition determines who does breed and who does not rather than the number of breeders, and thus it is not a density-dependent factor determining a population's size.