NATURAL SELECTION AND DENSITY-DEPENDENT POPULATION GROWTH

R. A. Desharnais ¹ and R. F. Costantino ²

¹ Department of Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada
² Department of Zoology, University of Rhode Island, Kingston, Rhode Island 02881

Natural selection was studied in the context of density-dependent population growth using a single locus, continuous time model for the rates of change of population size and allele frequency. The maximization principle of density-dependent selection was applied to a class of fitness expressions with explicit recruitment and mortality terms. Three general results were obtained: First, at low population densities, the genetic basis of selection is the difference between the mean recruitment rate and the mean mortality rate. Second, at densities much higher than the equilibrium population size, selection is expected to act to minimize the mean mortality rate. Third, as the population approaches its equilibrium density, selection is predicted to maximize the ratio of the mean recruitment rate to the mean mortality rate.