Wins and Losses in Intergroup Conflicts Reflect Energy Balance in Red-Tailed Monkeys

The energetic costs and benefits of intergroup conflicts over feeding sites are widely hypothesized to be significant, but rarely quantified. In this study, we use short-term measures of energy gain and expenditure to test whether winning an intergroup encounter is associated with greater benefits, and losing with greater costs. We also test an alternative perspective, where groups fight for access to large food sources that are neither depletable nor consistently monopolizable: in this case, a group that has already fed on the resource and is willing to leave first (the loser) is supplanted by a newly arrived group (the winner). We evaluate energy balance and travel distance during and after encounters for six groups of red-tailed monkeys in Kibale National Park, Uganda. We find that winning groups experience substantial energetic benefits, but do so to recoup from earlier deficits. Losing groups, contrary to predictions, experience minimal energetic costs. Winners and losers are predictable based upon their use of the contested resource immediately before the encounter. The short-term payoffs associated with these stressful conflicts compensate for any associated costs and support the perception that between-group contests are an important feature of social life for species that engage in non-lethal conflicts.

学界普遍认为，围绕觅食场所的群体间冲突所涉及的能量成本与收益影响显著，但此类效应鲜少得到量化验证。本研究通过短期能量摄入与消耗的测量手段，验证群体间冲突的获胜方是否能获得更高收益，落败方是否需承担更高成本。同时，我们还检验了另一类假说场景：当群体争夺的是既无法被耗尽、也无法被持续垄断的大型食物资源时，率先享用过该资源且主动先行离开的群体（落败方）会被新抵达的群体（获胜方）取代。我们针对乌干达基巴莱国家公园中的6群红尾猴，评估了冲突发生期间及冲突结束后的能量平衡与移动距离。研究结果显示，获胜群体确实能获得可观的能量收益，但此类收益仅用于弥补此前的能量亏空。而落败群体的能量消耗却远低于预期，仅产生极少量的能量成本。通过冲突发生前双方对争议资源的使用情况，即可预判群体间交锋的胜负方。这类伴随压力的冲突所带来的短期收益，足以抵消相关成本，同时也佐证了一个观点：对于存在非致命性群体冲突的物种而言，群体间竞争是其社会生活的重要特征。