Female demographic changes contribute to the maintenance of social stability within a primate multilevel society

Abstract

Various primate species, including golden snub-nosed monkeys, Rhinopithecus roxellana , form highly complex multilevel social systems. Breeding bands of snub-nosed monkeys maintain stability even though multiple one-male units (OMUs) within a band do not appear to engage in affiliative behaviours among units. As such, female dispersal within breeding bands may be a key factor related to social stability in these complex social systems. However, how individual and group behaviours influence both the formation of this complex social system and the maintenance of social stability within it remain to be fully elucidated. In the current study, based on 16 years of accumulated data, we investigated female dispersal in a wild population of golden snub-nosed monkeys in the Qinling Mountains of China. Using social network analysis and dynamic social modelling, we found that male take-over had no influence on the dominance rank of an OMU, whereas the number of breeding females within an OMU had a significant positive effect on rank. Both the number of breeding females and the number of females entering an OMU had significant positive effects on eigenvector centrality of an OMU. Female dispersal between OMUs decreased the clustering coefficient and reduced the risk of subgroup formation. In addition, female kinship matrices between units were not significantly correlated with association behaviour patterns. Thus, this study sheds light on the internal mechanisms that drive social stability in a complex primate social system. • One-male units in a golden snub-nosed monkey band showed few affiliative behaviours. • Multiple females dispersed among units during the 16-year study period. • Social network analysis showed that female dispersal can maintain social stability. • Female dispersal, not male take-over, affected unit hierarchical rank. • Female kinship did not influence association patterns among one-male units.