Department of Anthropology, California State University, Sacramento, California.
Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, Stony Brook, New York.
Am J Primatol. 2020 Feb;82(2):e23094. doi: 10.1002/ajp.23094. Epub 2020 Jan 21.
When competitors are able to assess the asymmetry in the resource holding potential before interacting, individuals or groups should avoid interacting with stronger opponents, thereby avoiding the energy costs and risk of injury associated with aggressive intergroup encounters. Thus, escalated aggression is expected only between closely matched competitors. Among Argentine tufted capuchin monkeys (Sapajus nigritus), intergroup dominance is decided by the asymmetry in male group size. Using playback experiments, I simulated intergroup encounters with neighboring groups, manipulating both the apparent numerical asymmetry and the resource context. During experimental trials, I recorded the approach behavior of the focal individual, as well as changes in neighbor density and individual travel speed following the presentation of the playback stimulus, to assess whether individual willingness to participate in resource defense was affected by the probability of winning the encounter. In spite of the competitive disadvantage, neither males nor females showed a decreased probability of approach when the numerical odds strongly favored the opposing group. Instead decisions regarding whether to participate appear to be driven primarily by the resource context. Nevertheless, changes in individual behavior during approaches suggest that tufted capuchin monkeys are sensitive to the relative odds. Individuals accelerated less when approaching a larger group, although no changes in neighbor density were apparent. The absence of an effect of the numerical asymmetry on willingness to approach the playback speaker suggests that subordinate groups benefit from engaging in intergroup aggression with larger neighbors, despite the high probability of losing. These encounters may serve to assess the current subjective resource valuation of the neighboring group or limit territorial expansion by large groups by decreasing the marginal value of home range exclusivity. Because these encounters are riskier, however, individuals appear to alter their approaches, becoming more tentative as the numerical odds increasingly favor the opposing group.
当竞争者能够在相互作用之前评估资源持有潜力的不对称性时，个人或群体应避免与更强的对手相互作用，从而避免与攻击性群体间遭遇相关的能量成本和风险。因此，只有在实力相当的竞争者之间才会出现升级的攻击性。在阿根廷卷尾猴（Sapajus nigritus）中，群体间的支配地位是由雄性群体大小的不对称性决定的。通过播放实验，我模拟了与邻近群体的群体间遭遇，操纵了明显的数量不对称性和资源背景。在实验过程中，我记录了焦点个体的接近行为，以及在播放刺激物呈现后邻居密度和个体旅行速度的变化，以评估个体参与资源防御的意愿是否受到赢得遭遇的可能性的影响。尽管处于竞争劣势，但无论雄性还是雌性，在数量优势明显偏向对方时，接近的可能性都没有降低。相反，参与决策似乎主要取决于资源背景。然而，接近过程中个体行为的变化表明，卷尾猴对相对优势是敏感的。个体在接近较大群体时的加速度降低，尽管邻居密度没有明显变化。数量不对称性对接近播放扬声器的意愿没有影响，这表明尽管失败的可能性很高，但从属群体从与较大邻居进行群体间攻击中受益。这些遭遇可能有助于评估邻近群体当前的主观资源价值，或者通过降低对领地排他性的边际价值来限制大群体的领土扩张。然而，由于这些遭遇风险更高，个体似乎会改变他们的接近方式，当数量优势越来越偏向对方时，变得更加犹豫。
