Between-group competition in social animals appears to be a prominent selective pressure shaping the evolution of territoriality and cooperation [1-4]. Evidence for an effect of between-group competition on fitness in territorial species, however, is mostly lacking because of difficulty in measuring between-group competition and its long-term impact [5]. Between-group competition corresponds to a complex set of interactions between neighboring groups, and its intensity seems to depend on the competitive abilities of each interacting group [6, 7]. We tested whether the competitive ability of groups and the pressure exerted by neighboring groups affected the reproductive success of wild female chimpanzees (Pan troglodytes verus). Using long-term data on four neighboring groups in the Taï National Park, Côte d'Ivoire, collected over the course of 54 observation years, we measured the competitive ability of habituated groups using the number of mature males and the pressure exerted by non-habituated neighbors with an index of neighbor pressure that combined the frequency of neighboring encounters and related spatial information. Importantly, we found that experiencing low neighbor pressure provides fitness benefits through increased offspring survival and shorter inter-birth intervals. Also, many males in a group are associated with shorter inter-birth intervals. We conclude that high between-group competition hampers fast reproduction and offspring survival when exposure is during the prenatal period. Our findings suggest that having many males in a group results in fitness benefits and that between-group competition should be considered as a potential selective pressure that shaped key social adaptations in the hominoid lineage.

中文翻译：

---

群体间竞争影响野生黑猩猩的生殖成功。

社交动物的群体间竞争似乎是一个显着的选择压力，它决定着领土和合作的发展[1-4]。但是，由于缺乏衡量群体间竞争及其长期影响的证据，因此缺乏关于群体间竞争对领土物种适应性影响的证据[5]。组间竞争对应于相邻组之间的一组复杂的交互作用，其强度似乎取决于每个交互组的竞争能力[6，7]。我们测试了群体的竞争能力和邻近群体施加的压力是否影响了野生雌性黑猩猩（Pan troglodytes verus）的繁殖成功。利用有关科特迪瓦泰伊国家公园四个相邻小组的长期数据，在54个观察年的过程中，我们收集了成年男性的数量和非习惯性邻居施加的压力，并结合了邻居相遇的频率和相关的空间信息来衡量习惯性群体的竞争能力。重要的是，我们发现经历低邻居压力可通过增加后代存活率和缩短出生间隔来提供健身益处。同样，一组中的许多男性与较短的生育间隔相关。我们得出的结论是，当暴露在产前期间，较高的群体间竞争会阻碍快速繁殖和后代存活。