Two-sex age structured dynamics in a fixed sex-ratio population

An age structured model is considered in order to analyze the growth of a two sex population with a fixed age-specific sex ratio. The model is intended to give an insight into the dynamics of a population where the mating process takes place at random and the proportion between females and males is not influenced by environmental or social factors, but only depends on a differential mortality or on a possible transition from one sex to the other (e.g. in sequential hermaphrodite species).First a basic model, asymptotically linear, is considered and its ergodicity is studied. Survival thresholds and their dependence on the sex ratio are then analyzed, in connection with the optimal sex ratio to guarantee survival.A further model including logistic effect is also considered and discussed in connection with existence and stability of steady states.