Life in social groups, while potentially providing social benefits, inevitably leads to conflict among group members. In many social mammals, such conflicts lead to the formation of dominance hierarchies, where high-ranking individuals consistently outcompete other group members. Given that competition is a fundamental tenet of the theory of natural selection, it is generally assumed that high-ranking individuals have higher reproductive success than lower-ranking individuals. Previous reviews have indicated large variation across populations on the potential effect of dominance rank on reproductive success in female mammals. Here, we perform a meta-analysis based on 444 effect sizes from 187 studies on 86 mammal species to investigate how life-history, ecology and sociality modulate the relationship between female dominance rank and fitness. We show that (1) dominance rank is generally positively associated with reproductive success, independent of the approach different studies have taken to answer this question; (2) life-history mechanisms mediate the relationship between rank and reproductive success, with higher effects of dominance rank on reproductive output than on survival, particularly in species with high reproductive investment; (3) the fitness benefits to high-ranking females appear consistent across ecological conditions, and (4) instead the social environment consistently mitigates rank differences on reproductive success by modulating female competition.
Dental microstructure records life history events: A histological study of mandrills (Mandrillus sphinx) from Gabon
