Mate success affects sex ratio strategies in structured population

Abstract In this model, we considered the population density effect based on the evolutionary maintainable strategy (EMS) for optimal sex ratio strategy analysis, instead of the evolutionary stable strategy (ESS) under the population equilibrium. We used a cellular automaton model to simulate population dynamics using the birth-death process to monitor the effect of space structure on the optimal sex ratio in EMS.The simulation showed that when the whole population was a panmixia, the optimal sex ratio would be 1:1 (male/female), which conforms to the Fisher's theory prediction. However, in a structured population, the ratio favoured a female-bias sexratio, which conforms to the local mate competition theory prediction. With the decreased dispersal range, the sex ratio strategy tended towards a higher male proportion, which is similar to the local resource competition prediction.The predictions of our model partly conformed to classical theories and explained some gaps in the ESS model. However, the driving force differed from the classical sex ratio model.The sex ratio was selected by population fitness rather than mother's fitness. The optimal sex ratio strategy for a population is to guarantee mating success, indicating that population survival may provide a complementary explanation for the sex ratio evolution.