Density-Dependent Natural Selection

• Published in: Ecology (Durham) Vol. 52; no. 3; pp. 453 - 468
• Main Author: Roughgarden, Jonathan
• Format: Journal Article
• Language: English
• Published: Brooklyn, N.Y., etc The Ecological Society of America 01-05-1971; Ecological Society of America; Brooklyn Botanic Garden, etc
• Subjects: Alleles; Ecological competition; Growing seasons; Heterozygotes; Homozygotes; Natural selection; Phenotypes; Population growth; Population size; Trajectories
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1937628

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.