Detecting an effect of group size on individual responses to neighboring groups in grey-cheeked mangabeys (Lophocebus albigena)
Brown, Michelle (2019), Detecting an effect of group size on individual responses to neighboring groups in grey-cheeked mangabeys (Lophocebus albigena), UC Santa Barbara, Dataset, https://doi.org/10.25349/D91017
Evolutionary game theory posits that competitive ability affects the initiation, escalation, and resolution of conflicts. When these contests occur among groups, rather than individuals, competitive ability is generally measured as the size of the group. Oddly, there exist a number of examples in which individual participation during intergroup conflicts appears unaffected by competitive ability. To determine whether the absence of a group size effect might be due to an unduly strict definition of participation, I re-evaluate the responses of grey-cheeked mangabeys (Lophocebus albigena) to the calls of real and simulated neighboring groups. In contrast with previous analyses, I consider multiple measures of group size (both the focal group size and its size relative to the caller), treat movement responses as a continuous variable, and evaluate individual responses. Males made stronger approaches toward calling neighbors than females, though both sexes tended to retreat from nearby groups (<400m) and to approach more distant neighbors. After both naturally occurring and simulated calls, individuals in small(er) groups retreated while those in large(r) groups both approached and retreated. There was no evidence of a collective action problem: i.e., approaches were more likely within large groups than small groups, and approaches were stronger when at least one other individual within the focal group made a dramatic approach toward the caller. In sum, there is an effect of group size during the initiation phase of grey-cheeked mangabey intergroup contests, but this effect was previously obscured by coarse analytical methods.
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