Beyond the group: how food, mates and group size influence inter-group encounters in wild bonobos

In social-living animals, interactions between groups are frequently agonistic, but they can also be tolerant and even cooperative. Inter-group tolerance and cooperation are regarded as a crucial step in the formation of highly-structured multilevel societies. Behavioral ecological theory suggests that inter-group tolerance and cooperation can emerge either when the costs of hostility outweigh the benefits of exclusive resource access, or when both groups gain fitness benefits through their interactions. However, the factors promoting inter-group tolerance are still unclear due to the paucity of data on inter-group interactions in tolerant species. Here, we examine how social and ecological factors affect the onset and termination of inter-community encounters in two neighboring communities of wild bonobos, a species exhibiting flexible patterns of inter-group interactions, at Kokolopori Bonobo Reserve, DRC. We recorded the timing and location of inter-community encounters and measured fruit abundance and distribution, groups' social characteristics, and space use dynamics over a 19-month period. We found that inter-community tolerance was facilitated by a decrease in feeding competition, with high fruit abundance increasing the likelihood of communities to encounter, and high clumpiness of fruit patches increasing the probability to terminate encounters, likely due to increased contest. In addition, the possibility for extra-community mating, as well as the potential benefits of more efficient foraging in less familiar areas, reduced the probability that the communities terminated encounters. By investigating the factors involved in shaping relationships across groups, this study contributes to our understanding of how animal sociality can extend beyond the group level