Data from: Chimpanzee females queue but males compete for social status

Dominance hierarchies are widespread in animal social groups and often have measureable effects on individual health and reproductive success. Dominance ranks are not static individual attributes, however, but instead are influenced by two independent processes: 1) changes in hierarchy membership and 2) successful challenges of higher-ranking individuals. Understanding which of these processes dominates the dynamics of rank trajectories can provide insights into fitness benefits of within-sex competition. This question has yet to be examined systematically in a wide range of taxa due to the scarcity of long-term data and a lack of appropriate methodologies for distinguishing between alternative causes of rank changes over time. Here, we expand on recent work and develop a new likelihood-based Elo rating method that facilitates the systematic assessment of rank dynamics in animal social groups, even when interaction data are sparse. We apply this method to characterize long-term rank trajectories in wild eastern chimpanzees (Pan troglodytes schweinfurthii) and find remarkable sex differences in rank dynamics, indicating that females queue for social status while males actively challenge each other to rise in rank. Further, our results suggest that natal females obtain a head start in the rank queue if they avoid dispersal, with potential fitness benefits.

优势等级制度（dominance hierarchy）在动物社会群体中广泛存在，且通常会对个体健康与繁殖成功率产生可量化的影响。然而，优势等级位次并非个体的静态属性，而是受两类独立过程调控：其一为等级群体成员构成的变化，其二为对高阶个体的成功挑战。明晰这两类过程中何者主导等级位次的动态变化，有助于揭示性内竞争的适合度（fitness）收益。由于长期数据匮乏，且缺乏能够区分不同时期等级位次变化诱因的合适方法，这一问题迄今尚未在广泛的分类群中得到系统性研究。本研究拓展了近期相关研究成果，提出一种全新的基于似然的Elo评分法（likelihood-based Elo rating method），即便在互动数据稀缺的场景下，也可实现对动物社会群体等级动态的系统性评估。我们将该方法应用于野生东部黑猩猩（Pan troglodytes schweinfurthii）的长期等级位次动态特征刻画，发现等级动态存在显著的性别差异：雌性通过排队竞争获取社会地位，而雄性则通过主动相互挑战来提升自身等级。此外，研究结果显示，若雌性个体不发生扩散，其在等级排队竞争中可获得先发优势，并由此具备潜在的适合度收益。