Food Distribution, But Not Market Forces, Predict Behavioral Social Tolerance in Rhesus Macaques

Social inequality in primates is marked by dominance-based resource monopolization. Yet, high-ranking individuals sometimes yield to lower-ranking individuals to promote group stability, indicative of behavioral social tolerance. Social tolerance is dynamic and is shaped by resource availability, group structure, hierarchy steepness and kinship. Increasing social tolerance around resource access may promote group stability and improve individual wellbeing. The multifaceted nature of behavioral social tolerance means we still lack a full understanding of its temporal, individual, and social drivers and whether modifications in resource distribution promote or hinder tolerant behavior in unequal societies. We tested whether decentralizing food resources improved behavioral social tolerance via two measures: reduced aggression and increased co-feeding through the study of a large group of outdoor-housed rhesus macaques (Macaca mulatta), a macaque species typified by low social tolerance. We assessed whether reduced resource competition and time of day influenced co-feeding behavior, and whether investment in grooming afforded future social tolerance. We found that, relative to a baseline and follow-up period with centralized food resources, distributed resources promoted social tolerance, but this was modulated by dominance rank. High-ranking individuals may exhibit greater behavioral flexibility while low-ranking individuals are afforded increased access to resources through reduced competition. We found temporal variation in co-feeding behavior with more co-feeding occurring in the afternoon. Lastly, we found limited evidence to suggest individuals groomed to afford future co-feeding tolerance. Combined, these results suggest that increased resource distribution in captive populations could provide a social benefit and contribute positively to health and well-being.