Social Tolerance in Chimpanzees Depends on Group Composition: A Longitudinal Study Across Four Communities

Abstract

Social tolerance in primates has commonly been treated as a stable, species-specific characteristic. Recent research, however, has questioned this position and emphasized the importance of considering intra-species variation in social tolerance. Here, we investigate the temporal stability of social tolerance in chimpanzees using the commonly employed measure of cofeeding tolerance; our results present the first multi-group, longitudinal, experimental assay of cofeeding tolerance in chimpanzees using quantitative methods. Cofeeding tolerance is measured in four groups of neighboring sanctuary-housed chimpanzees over the course of eight years. We pair these experimental data with accessory data on the demographic compositions of the groups to study factors that may influence cofeeding tolerance. We find appreciable levels of variation across both groups and years. We show that most of this variation can be explained by specific demographic variables, such as the number of young infants and the number of juvenile and adolescent females present within a group in a given year. These results imply that social tolerance is a ‘responding trait’ of chimpanzee sociality, reflecting individual- and group-level responses to social and demographic changes. To fully describe intra-species ranges of social tolerance, future research should consider the extent of variation both between groups as well as within groups over time.