Demography and despotism: making sense of inter-community differences in the behaviour of wild male chimpanzees (Pan troglodytes)

Comparative approaches are fundamental to behavioral ecology, yet differences in methodology and approach limit opportunities for this when studying chimpanzees. We studied two communities, the Sonso community of the Budongo Forest, Uganda, and M-group of the Mahale Mountains National Park, Tanzania using a common set of definitions and protocols focusing on male social interactions. We found striking differences between the two communities. Sonso males were similar to those in other East African communities, showing evidence of effective aggressive coercion of females, the provision of agonistic support and the trading of grooming for rank-restricted commodities. By contrast M-group males were ineffective in their use of aggression to coerce females, and neither seemed to provide nor trade for commodities such as agonistic support or social tolerance. Placing our data in a comparative context, we identified variation in structural despotism and in both membership and age profiles of adult male cliques. In our samples, Sonso males showed a high level of structural despotism while the M-group male fell at the opposite end of the cross-community distribution, being more structurally egalitarian. We discuss how demography, through aggressive interactions and structural despotism, impacts male social behavior (including both grooming & mating strategies). Our findings also highlight how the degree of structural despotism in a community is labile and not a species-specific characteristic.