UC Irvine

The action of density-dependent population growth is modeled through the effects of limited food. Scramble competition for food affects viability and adult size, which are correlated with the fecundity of females. Adult effects on fecundity are also explicitly modeled. In the 2 submodels considered, changes in the minimum amount of food necessary for successful pupation lead to 1) changes in minimum size of an adult with no change in overall efficiency or 2) constant minimum size but changes in efficiency of food use. Resulting population dynamics of the 2 submodels are qualitatively different. For both submodels population stability requires some degree of adult effects on female fecundity for parameter values typical of Drosophila. When genetic variation is present for competitive ability and minimum food required, natural selection at equilibrium population size favors increasing competiitve ability and decreasing the minimum food requirement. Decreases in minimum food requirements typically increase the equilibrium adult population size but have variable effects on equilibrium egg numbers. Competitive ability and minimum food requirements may be positively correlated. Genetic models with this antagonistic pleiotropy can maintain allelic variation without overdominance in either character. -from Author