Fission–fusion dynamics have evolved in a broad range of animal taxa and are thought to allow individuals to mitigate feeding competition. While this is the principal benefit of fission–fusion, few studies have evaluated its costs. We compared gregariousness, foraging budgets, and social budgets between lactating bonobos and chimpanzees from wild populations to evaluate potential costs. Both species exhibit fission–fusion dynamics, but chimpanzees, particularly in East African populations, appear to experience higher feeding competition than bonobos. We expected lactating chimpanzees to be less gregarious than lactating bonobos; reduced gregariousness should allow lactating chimpanzees to mitigate the costs of higher feeding competition without requiring more foraging effort. However, we expected the reduced gregariousness of lactating chimpanzees to limit their time available for affiliative interactions. Using long-term data from LuiKotale bonobos and Gombe chimpanzees, we found that lactating chimpanzees were indeed less gregarious than lactating bonobos, while feeding and travel time did not differ between species. Contrary to our predictions, lactating females did not differ in social interaction time, and lactating chimpanzees spent proportionately more time interacting with individuals other than their immature offspring. Our results indicate that lactating chimpanzees can maintain social budgets comparable to lactating bonobos despite reduced gregariousness and without incurring additional foraging costs. We discuss potential explanations for why lactating bonobos are more gregarious.

中文翻译：

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哺乳倭黑猩猩和黑猩猩的群居性、觅食努力和亲缘关系

裂变融合动力学已经在广泛的动物分类群中进化，并被认为可以让个体减轻进食竞争。虽然这是裂变聚变的主要好处，但很少有研究评估其成本。我们比较了来自野生种群的哺乳倭黑猩猩和黑猩猩之间的群居性、觅食预算和社会预算，以评估潜在成本。两种物种都表现出裂变融合动力学，但黑猩猩，尤其是东非种群，似乎比倭黑猩猩经历更高的进食竞争。我们预计哺乳期黑猩猩的合群性不如哺乳期倭黑猩猩；减少群居性应该允许哺乳期黑猩猩在不需要更多觅食努力的情况下减轻更高的进食竞争的成本。然而，我们预计哺乳期黑猩猩的群居性减少会限制它们可用于亲缘互动的时间。使用 LuiKotale 倭黑猩猩和 Gombe 黑猩猩的长期数据，我们发现哺乳期黑猩猩确实不如哺乳期倭黑猩猩群居，而不同物种的觅食和旅行时间没有差异。与我们的预测相反，哺乳期雌性在社交互动时间上没有差异，哺乳期黑猩猩与未成熟后代以外的个体互动的时间成比例地更多。我们的结果表明，哺乳期黑猩猩可以维持与哺乳期倭黑猩猩相当的社会预算，尽管它们的群居性降低，而且不会产生额外的觅食成本。我们讨论了为什么哺乳期倭黑猩猩更合群的潜在解释。