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，围绕觅食场地展开的群体间冲突所涉及的能量成本与收益极为可观，但此类假设鲜少得到量化验证。本研究通过短期能量摄入与消耗的量化测量，验证群体间冲突遭遇的获胜方是否能获得更高收益，而落败方是否需承担更高成本。我们同时检验了另一类假说场景：当群体争夺的大型食物源既不可被耗尽，也无法被持续独占时，率先进食并主动撤离的群体（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内的6群红尾猴，评估了冲突遭遇期间及遭遇后的能量平衡与移动距离。研究结果显示，获胜群体确实获得了可观的能量收益，但该收益仅用于弥补此前的能量亏空。而落败群体的能量消耗则远低于预期，仅承担了极小的能量成本。获胜方与落败方的身份可通过冲突发生前二者对被争夺资源的使用情况进行预判。这类紧张冲突带来的短期收益足以抵消相关成本，同时也印证了一个观点：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。