Abstract

Two mechanisms have been proposed to explain why scramble competition can increase the travel requirements of individuals within larger groups. Firstly, individuals in larger groups may be more likely to encounter food sites where other group members have already eaten, leading to greater asynchronous “individual” travel to find fresh sites. Secondly, when food sites are aggregated into patches, larger groups may need to visit more patches to obtain the same amount of food per capita, leading to greater synchronous “group” travel between patches. If the first mechanism can be mitigated by increasing group spread, then we expect the second mechanism to be more sensitive to group size. Here, we examine the individual travel and group travel of the Virunga mountain gorillas, along with potential implications for the two mechanisms of scramble competition. Asynchronous individual travel accounted for 67% of the total travel time, and the remainder arose from group travel. Group spread increased significantly for larger groups, but not enough to prevent an increase in individual travel. Contrary to expectations, group travel decreased with size among most groups, and we found only limited evidence of patch depletion that would cause the second mechanism of scramble competition. Collectively, our results illustrate how the influence of group size can differ for individual travel versus group travel, just as it differs among species for overall travel. Studies that distinguish between the two mechanisms of scramble competition may enhance our understanding of ecological constraints upon group size, including potential differences between frugivores and folivores.

Significance statement

Feeding competition provides insight into how group size can influence the foraging patterns of social animals, but two key mechanisms are not typically compared. Firstly, larger groups may visit more patches to access the same amount of food per capita (group travel). Secondly, their individuals may also need to move past more spots where another member has already eaten (individual travel). Contrary to expectations, we found that group travel decreased with size for most groups of mountain gorillas, which may reflect extra travel by smaller groups to avoid larger groups. Individual travel increased with size in most groups, even though gorillas in larger groups compensated by spreading out over a broader area. The two mechanisms revealed patterns that were not apparent in our previous study of overall travel. Our approach may help to explain potential differences between folivores and frugivores.

中文翻译：

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剖析维龙加山地大猩猩争抢的两种机制

摘要

已经提出了两种机制来解释为什么争夺竞争会增加更大群体中个人的旅行需求。首先，较大群体中的个人可能更有可能遇到其他群体成员已经吃过的食物地点，从而导致更多的异步“个人”旅行以寻找新鲜地点。其次，当食物地点聚集成块时，更大的群体可能需要访问更多的块以获得相同的人均食物量，从而导致块之间更大的同步“组”旅行。如果第一种机制可以通过增加群体分布来缓解，那么我们预计第二种机制对群体规模更敏感。在这里，我们考察维龙加山地大猩猩的个人旅行和团体旅行，以及对两种争夺竞争机制的潜在影响。非同步个人旅行占总旅行时间的67%，其余来自团体旅行。对于较大的团体，团体传播显着增加，但不足以阻止个人旅行的增加。与预期相反，大多数团体的团体旅行随着规模的扩大而减少，我们只发现了有限的补丁耗尽证据，这会导致争夺竞争的第二种机制。总的来说，我们的结果说明了团体规模对个人旅行和团体旅行的影响是如何不同的，正如它对整体旅行的物种之间的不同一样。区分争夺竞争的两种机制的研究可能会增强我们对生态限制对群体规模的理解，

意义陈述

喂食竞争让我们深入了解群体规模如何影响社会动物的觅食模式，但通常不会比较两个关键机制。首先，较大的团体可能会访问更多的补丁以获取相同数量的人均食物（团体旅行）。其次，他们的个人可能还需要经过更多其他成员已经吃过饭的地方（个人旅行）。与预期相反，我们发现大多数山地大猩猩群体的群体旅行随着规模的大小而减少，这可能反映了较小群体为避免较大群体而进行的额外旅行。大多数群体的个人旅行随着规模的扩大而增加，尽管较大群体中的大猩猩通过分布在更广泛的区域来弥补。这两种机制揭示了我们之前对整体旅行的研究中不明显的模式。