Seasonal incidence: Adaptive variation in the timing of life history stages

Abstract

We present a model for the entry of individuals into a seasonal population. The result can be a mixed evolutionarily stable strategy (ESS) which prescribes a characteristic probability distribution i( t) of “input times” for population. An input time is a data on which an individual enters the stage in which there is intense competition for limited resources. At the ESS, fitnesses are equal for all competitors irrespective of their input times. The model indicates that where the rate of mortality of competitors is high, i( t) should track quite closely the seasonal distribution of resource abundance; when the rate of mortality of competitors is low, the peak of input times should occur well before the peak of resource availability, and i( t) should be a much tighter distribution than that of the resources. A good fit is obtained between data on emergence times i( t) of male Orange Tip butterflies, Anthocharis cardamines (L.) and the predictions of the model. If we extend the model by having two sets of competitors, A and B, in which A is dependent upon (but not damaging to) B as a resource, and B is dependent on a seasonal resource C, then the peaks of the three distributions will be ordered temporally as A → B → C.