Socioecological variables influence the rate and nature of encounters between conspecific primate groups. Both social (i.e., type of encounter) and ecological factors (i.e., fruit availability) affect rates and outcomes of intergroup encounters in eastern gorillas. However, the roles of individual factors underlying these events among western lowland gorillas (Gorilla gorilla gorilla) remain relatively understudied. We assessed whether group composition (the number of subordinate males and females in the group) and fruit availability influenced the rate of intergroup encounters in three groups of western lowland gorillas in the Republic of Congo. From April 2014 to October 2018, we monitored focal gorilla groups daily in the Goualougo and Djéké Triangles. To assess the ecological similarity between sites, we compared botanical surveys of trees and herbs across them and found overall herb densities were similar between sites. We observed 294 intergroup encounters over 2797 observation days, with a mean rate of 2.20 ± SD 0.93 encounters/month (range: 1.59–3.94) across groups, and these interactions ranged from tolerant to aggressive. The number of subordinate males in the group correlated negatively with the occurrence of intergroup encounters, and groups were more likely to avoid interaction or react aggressively when they encountered a solitary male than when they encountered another group. Some differences between the groups may be attributed to familiarity with extragroup members and the status of the dominant silverback. We found no relationship between the rate of encounters and fruit availability. Our findings indicate that defense of mates, rather than of food resources, may be the most important driver of between-group competition in western lowland gorillas. These findings, which are similar to those for mountain gorillas, suggest that primate social systems may be more variable than previously anticipated within taxa. Therefore, further longitudinal studies are needed to determine the generality of our findings and assess the direct impacts of intergroup encounters on fitness.

中文翻译：

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影响西部低地大猩猩群际相遇的社会生态因素（大猩猩大猩猩）

社会生态变量影响同种灵长类动物群体之间相遇的速度和性质。社会（即遭遇类型）和生态因素（即水果供应）都会影响东部大猩猩群际遭遇的比率和结果。然而，在西部低地大猩猩（Gorilla gorilla gorilla）中，这些事件背后的个体因素的作用仍然相对不足。我们评估了群体组成（群体中从属雄性和雌性的数量）和水果的可用性是否影响了刚果共和国三组西部低地大猩猩的群体间相遇率。从 2014 年 4 月到 2018 年 10 月，我们每天监测 Goualougo 和 Djéké 三角区的重点大猩猩群体。为了评估站点之间的生态相似性，我们比较了对树木和药草的植物调查，发现不同地点的整体药草密度相似。我们在 2797 个观察日内观察了 294 次组间相遇，平均发生率为 2.20 ± SD 0.93 次/月（范围：1.59-3.94），这些相互作用从宽容到攻击不等。群体中下属男性的数量与群体间遭遇的发生呈负相关，群体在遇到孤独的男性时比遇到另一个群体时更有可能避免互动或做出积极的反应。群体之间的一些差异可能归因于对群体外成员的熟悉程度以及占优势的银背鱼的地位。我们发现相遇率和水果供应之间没有关系。我们的研究结果表明，配偶的防御，而不是食物资源，可能是西部低地大猩猩群体间竞争的最重要驱动因素。这些发现与山地大猩猩的发现相似，表明灵长类动物的社会系统在分类​​群中可能比以前预期的更具可变性。因此，需要进一步的纵向研究来确定我们研究结果的普遍性，并评估群体间相遇对健康的直接影响。