Demographic Factors Are Associated with Intergroup Variation in the Grooming Networks of Female Colobus (Colobus vellerosus)

Abstract

Intergroup variation in social networks can have important implications for inferring the evolution of primate social relationships, but the underpinnings of this variation remain poorly understood. To further our understanding of this topic, we investigated whether intergroup variation in colobus grooming networks was associated with group size, the proportion of female kin and infants, and stability in female group composition. Between 2008 and 2009, we collected behavioral data via focal sampling of 61 females in 8 groups at Boabeng-Fiema, Ghana, which we used to calculate grooming network metrics. We collected demographic data during the same time period to determine group sizes and group compositions, while we used longitudinal data (2000-2009) to estimate stability in group composition. We determined kinship via partial pedigrees and genetic data from 17 short tandem repeat loci. Females in larger groups had more grooming partners but did not form weaker networks than females in smaller groups. This finding suggests that time constraints linked to large group sizes do not limit sociality in this population, which is similar to findings in other folivorous black-and-white colobus but contrasts with those in many frugivorous primates. Groups with a larger proportion of infants spent more time grooming, similar to some other mammals. Group stability correlated positively with centralization, i.e., inequity, for incoming ties. Networks were not affected by kin compositions of groups, in contrast to those in some female resident-nepotistic cercopithecines. We suggest that the relative importance of demographic factors in shaping social networks may vary between populations depending on diet and social structure.