Abstract

It has long been shown that the social environment of individuals can have strong effects on health, well-being, and longevity in a wide range of species. Several recent studies found that an individual’s number of affiliative partners positively relates to its probability of survival. Here, we build on these previous results to test how both affiliation and aggression networks predict Barbary macaque (Macaca sylvanus) survival in a “natural experiment.” Thirty out of 47 wild Barbary macaques, living in 2 groups, died during an exceptionally cold winter in the Middle Atlas Mountains, Morocco. We analyzed the affiliation and aggression networks of both groups in the 6 months before the occurrences of these deaths, to assess which aspects of their social relationships enhanced individual survivorship. Using only the affiliation network, we found that network clustering was highly predictive of individual survival probability. Using
only the aggression network, we found that individual survival probability increased with a higher number of aggression partners and lower clustering coefficient. Interestingly, when both affiliation and aggression networks were considered together, only parameters from the aggression network were included into the best model predicting individual survival. Aggressive relationships might serve to stabilize affiliative social relationships, thereby positively impacting on individual survival during times of extreme weather conditions. Overall, our findings support the view that aggressive social interactions are extremely important for individual well-being and fitness.