ESS EMERGENCE PATTERN OF MALE BUTTERFLIES IN STOCHASTIC ENVIRONMENTS

The evolutionarily stable (or ESS) emergence schedule for males of uni voltine butterflies is analysed in an environment in which the female emergence schedule fluctuates stochastically between years. The ESS em ergence curve, computed using the mutant invadability criterion, is sh own to be the one that maximizes mean logarithmic lifetime mating succ ess in the population in which it dominates. If males have accurate in formation about the female emergence schedule within each year, their emergence curve would evolve to the one predicted by a deterministic g ame model. The male emergence curve would then shift between years, cl osely following year to year changes in the female emergence pattern. If, instead, males have uncertainty about the female emergence schedul e, the ESS male emergence curve becomes broader than the one predicted by the deterministic game model and will not track the between-year f luctuation of female emergence well. In a special case, we show how th e between-year variation of mean emergence date, the variance of emerg ence date, the sexual difference in mean emergence dates (protandry) a nd the between-year correlation of mean emergence dates of both sexes should change with the degree of accuracy of information available to males.