Density‐Dependent Natural Selection

Abstract

Density—dependent selective values illustrate the evolutionary effect of population—regulating processes that diminish an individual's probability of survival with increased crowding. The selective values, assumed to decrease as a linear function of density, lead in a mild environment to the evolution of phenotypes having a high carrying capacity, K, at the expense of a low intrinsic rate of increase, r. A graphical technique shows that selection causes evolution of phenotypes having a high r at the expense of a low K in harsh seasonal environments. A mathematical technique developed for analyzing evolution in coarse—grained seasonal environments reveals genetic mechanisms, including ones with full dominance, with which a moderately harsh seasonal environment causes stable polymorphism between high—r and high—K genes. The energy balance equation demonstrates the role of high—r and high—K phenotypes in the population's energy flow. A high—r phenotype makes a large expected contribution to the population's productivity under conditions of negligible crowding, and a high—K phenotype has, for a given contribution to the population's productivity under uncrowded conditions, a low sensitivity to having that contribution diminished by crowding.