Social preference influences female community structure in a population of wild eastern grey kangaroos

Abstract

Communities, clusters of individuals who interact socially primarily with each other, are fundamental elements of social structure in many species. Community membership can be influenced by spatial factors and by social preferences resulting from genetic or phenotypic assortment or shared behavioural strategies. Very little is known about community social structure in herbivorous mammals with higher fission–fusion dynamics, which are societies in which group membership frequently changes. Using network analysis on data from 171 wild female eastern grey kangaroos, Macropus giganteus, a species exhibiting these foraging and social attributes, we quantified the presence of significant, strong community structure. Lagged association rates confirmed the temporal stability of this intermediate-level social tier. Communities' home ranges overlapped considerably, but their core home ranges were more dispersed, suggesting some influence of spatial factors on community membership. However, community-level social assortment was maintained in areas in which core home ranges overlapped, even though communities used these areas simultaneously, implying that social preferences also influence the presence of communities in female kangaroos. Within-community pairwise relatedness levels based on microsatellite markers were somewhat higher than those across the population, probably because of philopatry, but mitochondrial DNA revealed that communities did not reflect matrilines. This study contributes to the growing literature attempting to understand the factors driving fission–fusion social dynamics by showing that extensive home range overlap among communities can occur in the absence of behaviours usually associated with the maintenance of social preferences.