Many animals engage in aggression, but chimpanzees stand out in terms of fatal attacks against adults of their own species. Most lethal aggression occurs between groups, where coalitions of male chimpanzees occasionally kill members of neighboring communities that are strangers. However, the first observed cases of lethal violence in chimpanzees, which occurred at Gombe, Tanzania in the 1970s, involved chimpanzees that once knew each other. They followed the only observed case of a permanent community fission in chimpanzees. A second permanent fission recently transpired at Ngogo, Kibale National Park, Uganda. Members of a large western subgroup gradually ceased associating peacefully with the rest of the community and started behaving antagonistically toward them. Affiliation effectively ended by 2017. Here, we describe two subsequent lethal coalitionary attacks by chimpanzees of the new western community on males of the now separate central community, one in 2018 and the second in 2019. The first victim was a young adult male that never had strong social ties with his attackers. The second was a high-ranking male that had often associated with the western subgroup before 2017; he groomed regularly with males there and formed coalitions with several. Other central males present at the start of the second attack fled, and others nearby did not come to the scene. Several western females joined in the second attack; we suggest that female–female competition contributed to the fission. This event highlighted the limits on protection afforded by long-term familiarity and the constraints on costly cooperation among male chimpanzees.

中文翻译：

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乌干达基巴莱国家公园 Ngogo 与黑猩猩 (Pan troglodytes) 社区裂变相关的致命联盟侵略

许多动物都具有攻击性，但黑猩猩在对同类成年人的致命攻击方面脱颖而出。大多数致命的攻击发生在群体之间，雄性黑猩猩的联盟偶尔会杀死附近社区的陌生人。然而，在 1970 年代发生在坦桑尼亚贡贝的第一批观察到的黑猩猩致命暴力案件涉及曾经相互认识的黑猩猩。他们跟踪了唯一观察到的黑猩猩永久群落裂变的案例。最近在乌干达基巴莱国家公园的 Ngogo 发生了第二次永久性裂变。一个大型西方小组的成员逐渐停止与社区其他成员和平交往，并开始对他们采取敌对态度。隶属关系于 2017 年有效结束。在这里，我们描述了新西方社区的黑猩猩随后对现已独立的中央社区的男性发起的两次致命的联合攻击，一次是在 2018 年，第二次是在 2019 年。第一个受害者是一名年轻的成年男性，他从未与攻击者建立过牢固的社会联系。第二位是一位在 2017 年之前经常与西方亚组有联系的高级男性；他定期与那里的男性进行梳理，并与几个人结成联盟。在第二次袭击开始时在场的其他中央男性逃离，附近的其他人没有来到现场。几名西方女性加入了第二次攻击；我们认为女性与女性的竞争促成了裂变。这一事件突出了长期熟悉所提供的保护限制以及雄性黑猩猩之间昂贵的合作的限制。