![]() rodents: Parmigiani & Palanza 1991 Wersinger et al. This idea contrasts with the finding that distinct mechanisms underlie predation and intraspecific aggression in other taxa (e.g. Specifically, predation by chimpanzees may have evolved as a by-product of selection for intraspecific territorial aggression ( Kortlandt 1972 Eibl-Eibesfeldt 1975 Wrangham 1999). 1979 van Hooff 1990 Wrangham & Peterson 1996 Wrangham 1999 Watts & Mitani 2001). The intense arousal and excitement shown during attacks on both chimpanzees and monkeys has prompted the suggestion that similar physiological and psychological mechanisms may be involved in predation and intergroup aggression ( Goodall et al. (reviewed by Gilby 2012), which involve many of the same behavioural elements as aggression against conspecifics. Male chimpanzees also engage in group hunts of monkeys, particularly red colobus monkeys, Procolobus spp. Male chimpanzees, Pan troglodytes, collectively defend group territories by conducting boundary patrols, advertising territory ownership with vocalizations and aggressively repelling members of other groups, sometimes injuring or killing them ( Wrangham 1999 Wilson & Wrangham 2003 Watts et al. Therefore, we conclude that ecological, rather than psychological, factors promote the co-occurrence of hunting and territorial aggression in this species. Additionally, parties that travelled to the periphery were more likely to encounter colobus in woodland, where hunts are more likely to occur and to succeed. Instead, the data suggest that the correlation arose because patrols typically involved males travelling long distances, which increased the probability of encountering prey. While this discovery has important implications for our understanding of the proximate causes of cooperation, it does not explain the temporal correlation between patrolling and hunting, since no males had such an impact in both contexts. Similarly, there were also three ‘impact patrollers’, who increased the likelihood that a visit to the periphery of the community range resulted in a patrol. We identified two ‘impact hunters’ whose presence increased hunting probability. We also reject the hypothesis that hunting and patrolling reflect an individual-level behavioural syndrome. However, hunting was equally likely to occur after a patrol and/or an intergroup interaction as it was before, and the occurrence of an intergroup interaction in which the chimpanzees approached strangers did not increase subsequent hunting probability. We test the hypothesis that this correlation arises because hunting and patrolling are components of a specieslevel aggressive behavioural syndrome specifically that predation arose as a by-product of territorial aggression in this species. Over 32 years, chimpanzees at Gombe National Park, Tanzania were significantly more likely to engage in a territorial border patrol on days when they hunted red colobus monkeys ( Procolobus spp.), and vice versa, even after statistically controlling for male chimpanzee party size. Specifically, it has been proposed that hunting behaviour in chimpanzees evolved from intraspecies aggression. The intense arousal and excitement shown by adult male chimpanzees, Pan troglodytes, during territorial attacks on other chimpanzees and predation upon monkeys suggest that similar psychological mechanisms may be involved.
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