GENETIC ANALYSIS OF A POPULATION OF TRIBOLIUM: VII. STABILITY: RESPONSE TO GENETIC AND DEMOGRAPHIC PERTURBATIONS

Abstract

A biological counterpart to mathematical stability analysis was demonstrated using the Tribolium model. The responses to deliberate demographic and genetic perturbations of T. castaneum populations, initially homozygous for the corn oil sensitive (cos) allele and near demographic equilibrium, were examined experimentally. An equilibrium was said to be ecologically stable if it was locally stable to perturbations in population numbers alone and genetically stable if it was locally stable to changes in allele frequencies alone. A qualitative stability analysis of the within population age-class interactions indentified several conditions for stability, such as, the product of the rate of egg cannibalism by larvae times the rate of pupal cannibalism by adults must be greater than the product of the "net" fecundity of adults times the overall larval viability. The populations which were subjected to the addition or removal of genetically similar adults or immature life stages were ecologically stable. The cultures altered by the introduction of the + allele were genetically unstable to this perturbation and converged to an average polymorphic cos equilibrium allele frequency of 0.42. The incorporation of the + allele into populations initially homozygous for the cos allele was examined in terms of natural selection in a density-regulated population. The experimental data supported the theoretical prediction that selection is expected to move an ecologically stable system toward an evolutionarily stable strategy resulting in the maximization of adult numbers.