Abstract
Groups of animals often compete over resources, such as territory, food, or mates, which are critical for survival. Successful groups tend to be those in which individuals cooperate effectively, and thus intergroup competition is thought to exert a selective pressure favouring the evolution of behavioural traits that promote intragroup affiliation. However, no cohesive pattern has emerged to describe the effect of intergroup conflict (IGC) on intragroup social behaviour. Furthermore, because most studies focus on intragroup behaviour during or immediately after conflict, we know relatively little about how groups perceive and respond to the risk of encountering rivals. Here, I investigate the function of intragroup behaviour in response to the threat and occurrence of IGC in three wild crested macaque (Macaca nigra) social groups. I use relative risk maps based on the timing and locations of intergroup encounters (IGEs) in conjunction with behavioural observations to test predictions that changes in intragroup behaviour function to increase social cohesion. Group spread, behavioural synchrony, and pre- and post-encounter focal observation data indicate that crested macaques remember the frequency, location, and outcome of previous IGEs: Also, that individuals in dominant and subordinate groups may perceive encounters differently. However, I found no evidence that intragroup behaviour functions to promote cohesion. Rather, my results indicate that both pre- and post-conflict behaviour functions primarily to minimise individual costs and reduce physiological anxiety. Rather than collective action being impeded by the lack of cohesion-enhancing behaviours, I suggest that this population may not need them in the context of IGC. These findings raise the possibility that (a) when food resources are abundant and mating access is easily monopolised, not all groups that engage in IGC have something worth fighting for, and (b) that we need to find ways of incorporating this into future models of intergroup hostility.
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