Sex ratio dependent dispersal when sex ratios vary between patches

Abstract

Female biased sex ratios reduce competition between brothers when mating takes place within local patches. Male dispersal proir to mating is another strategy that reduces competition between brothers. One may thus expect these two traits to co-evolve and this is partially met in that sex ratios becomes less female baised as dispersal increases. However, the evolutionary stable degree of dispersal is unaffected by the sex ratio. The analytical models developed to reach these conslusions ignored variance in sex ratios, since this increases the structural complexity of models. For similar reasons finite clutch size are also routinely ignored. To overcome these shortfalls, we developed individual besed simulations that allowed us to incorporate ralistic clutch sizes and binomial variance in sex ratios between patches. We show that under variable sex ratios, males evolve to more readily disperse away from pathces with higher sex ratios that lower sex ratios. We show that, while the dispersal rate is insensitive tot the sex ratio when sex ratios are precise, it is affected by the number of males with dispersal decreasing as the number of males decreases.