Conflict management in wild spider monkeys (Ateles geoffroyi yucatanensis)

Animals living in groups are frequently exposed to conflicts of interest which can escalate into aggression. Aggressive interactions may be a means to resolve incompatibility among objectives. Nevertheless, aggression may undermine the benefits of group living by disrupting the relationships between opponents. Thus, conflict management mechanisms have evolved to cope with the potential damage brought about by aggressive interactions. The aim of my thesis was to investigate the mechanisms to prevent aggressive escalation and to mitigate its negative consequences in 2 communities of wild spider monkeys (Ateles geoffroyi yucanensis). I also examined the factors, such as relationship characteristics, affecting the occurrence of these mechanisms. Spider monkeys live in communities with a high degree of fission fusion dynamics in which individuals frequently split and merge into subgroups of variable composition. The implications of this social system for conflict management were also explored. To characterise spider monkeys’ social relationships, two components were identified and labelled compatibility and risk. These components were further related to relationship characteristics, such as kinship, sex combinations, and tenure in the community. Kin had more compatible relationships than non kin, but there was no difference for risk. Male-male dyads were characterised as being significantly more compatible and riskier than either female-female dyads or malefemale dyads. Furthermore, individuals with longer tenure had riskier relationships than individuals with shorter tenure. Among the post-conflict management mechanisms spider monkeys did not engage in reconciliation, redirected aggression, or bystander affiliation. However, an option afforded by their high degree of fission fusion dynamics was used in the aftermath of aggression. Fission from former aggressors was more likely to occur within one hour of the aggressive conflicts than in control periods. Furthermore, individuals sharing riskier and less compatible relationships had significantly shorter latencies to fission compared to those with less risky and more compatible relationships. These patterns suggest that fission may function to reduce the possibility of renewed aggression and cope with increased post-conflict anxiety. Indeed, anxiety levels were higher in the recipients of aggression during the first 5 post-conflict minutes compared to baseline levels. Whereas fission may be a mechanism to cope with the negative consequences of aggressive escalation, fusion of subgroups could lead to uncertainty and hostility. Indeed, aggression increased in the first five post-fusion minutes compared to baseline levels. There was also an increase in post-fusion friendly behaviours, which may function as signals of good intentions. This view was confirmed as post-fusion aggression was reduced when friendly behaviours took place. In addition, shorter latencies of post-fusion aggression and friendly behaviours were found between individuals with riskier relationships compared to those with less risky relationships. Prevention of aggressive conflicts may also be achieved by adjusting subgroup size to the availability of feeding resources thereby reducing competition. The effectiveness of this flexible adjustment was demonstrated during a period of drastic reduction in food sources caused by two consecutive hurricanes at the field site. Mean subgroup size and fusion rates were significantly reduced in the post-hurricane compared to pre-hurricane periods. Hence, my thesis adds to the study of social relationships and conflict management in non-human animals by making several contributions. I provided the first evidence of relationship components in new world monkeys. I then examined the potential of fission-fusion dynamics as a means to manage conflicts among community members. I was the first demonstrating that fission is a postconflict mechanism. Fission from the former aggressor was especially used by individuals with riskier and less compatible relationships. Subgroup fusion increased aggressive conflicts, especially between individuals with riskier relationships, but post-fusion friendly behaviours reduced them. The effectiveness of fission-fusion dynamics in conflict management was further demonstrated by how the spider monkeys coped with the potential increase in conflict among community members due to a dramatic reduction in food supplies due to two hurricanes. Overall, spider monkeys appear to deal with conflicts using the full range of the flexible social options afforded by their social system.