Birth sex ratio and social rank: consistency and variability within and between primate groups

Abstract

Variations in birth sex ratios in primates are notoriously inconsistent and have been repeatedly suggested to be mainly owing to stochastic processes. An examination of temporal consistency within primate populations revealed that the effect of dominance rank on birth sex ratio tends to remains stable over time. Furthermore, a meta-analysis of published data on sex ratio variations in primates shows that although no overall effect was detectable, the relation between birth sex ratio and dominance rank was affected by level of resource availability and degree of sexual dimorphism. These results suggest that purely stochastic processes are unlikely to explain observed variations in primate birth sex ratios, and may explain why adaptive sex ratio variations in primates have been so difficult to demonstrate. Key words: maternal investment; meta-analysis; population growth; sexual dimorphism. [Behav Ecol]