Factors Influencing Grooming Social Networks: Insights from Comparisons of Colobines with Different Dispersal Patterns

Abstract

Many species in Hominidae and Atelidae form a male-philopatric/female-dispersal social system. Although female dispersal is not the typical pattern for Cercopithecidae, reports of male-philopatric/female-dispersal or both-sex-dispersal social systems have increased in Colobinae. Therefore, comparisons among colobine species with various dispersal patterns may provide insight on the influence of dispersal pattern differences on their social relationships. Here, we report the results of the first quantitative comparison of the proportion of time spent grooming by colobines and of the interindividual relationships within units among colobines based on grooming networks. We found that variations in the proportion of time spent grooming across colobine species were mostly explained by the classical group-cohesion model proposed by Dunbar (1991), i.e. group size is the most important factor with a positive effect. This indicates that colobines must spend a higher proportion of their time grooming to maintain cohesion of their larger social group. Although individual colobine dispersal patterns had no significant effect on the proportion of time spent grooming, the social network analysis indicated that the interindividual relationship differences across six species and the mechanisms underlying cohesion of units were affected by their dispersal patterns. Our findings provide insight into the colobine society, such as the effect of group size and individual dispersal patterns on grooming.