Intra-specific Variation in the Social Behavior of Barbary macaques (Macaca sylvanus)

Abstract

Non-human primates show an impressive behavioral diversity, both across and within species. However, the factors explaining intra-specific behavioral variation across groups and individuals are yet understudied. Here, we aimed to assess how group size and living conditions (i.e., captive, semi-free-ranging, wild) are linked to behavioral variation in 5 groups of Barbary macaques (N=137 individuals). In each group, we collected observational data on the time individuals spent in social interactions and on the group dominance style, along with experimental data on social tolerance over food and neophobia. Our results showed that differences in group size predicted differences in the time spent in social interactions, with smaller groups spending a higher proportion of time in close spatial proximity, but a lower proportion of time grooming. Moreover, group size predicted variation in dominance style, with smaller groups being more despotic. Social tolerance was affected by both group size and living conditions, being higher in smaller groups and in groups living in less natural conditions. Finally, individual characteristics also explained variation in social tolerance and neophobia, with socially integrated individuals having higher access to food sources, and higher-ranking ones being more neophobic. Overall, our results support the view that intra-specific variation is a crucial aspect in primate social behavior and call for more comparative studies to better understand the sources of within-species variation.

Keywords: Barbary macaques; access to food; intra-specific variation; neophobia; social behavior; social integration.

Figure 1

For each study group, (A) the mean (+SE) proportion of time spent in close spatial proximity and in grooming interactions, and (B) the mean (+SE) proportion of individuals retrieving food in each session of the social tolerance task. Please note that the figure is based on raw data.

Figure 2

(A) Proportion of food retrieved, as a function of individual social integration (measured as eigenvector centrality), and (B) probability of selecting familiar food (as a measure of neophobia), as a function of individual rank. Circles and crosses represent individual average response in the social tolerance (A) and neophobia (B) tasks and are depicted with different symbols depending on the study group they belonged to. The dashed line represents the fitted model, which is like Models 4 (A) and 5 (B), but unconditional on all the other predictors that were standardized.