Effects of Perturbations on Aggression and Affiliation Networks in Male Domestic Horses (Equus caballus)

Abstract

This study examines the effects of perturbations on aggression and affiliation patterns in a herd of male domestic horses. It consists of four two-day, one-horse removal experiments, in which removed group members are selected based either on their dominance or centrality. To create comparisons of the four experiments, either dominance or centrality was held constant between differing pairs of removed individuals. When the focal individual’s dominance was held static, removing a mid centrality individual caused more disruptions in affiliation and aggression than the removal of a low centrality group member. However, when centrality was held constant, taking out a highly dominant individual had more effect on the group’s social networks than the removal of a mid dominant, though the latter was more influential in affecting others within the same dominance category. When the two dimensions were crossed to compare the effects of removing an individual with low dominance and high centrality to an individual of high dominance and low centrality, it was determined that removing those with the former combination of social personality traits was more disruptive to the group’s affiliative and agonistic networks. With these three comparisons in mind, it was then concluded that the removed animal’s centrality is more crucial to social stability and group dynamics than his dominance. Therefore, stable managers and herd owners should be particularly careful when removing mid to high centrality individuals in order to avoid major disruptions in the herd’s affiliative and agonistic networks. Following this simple guideline will result in more effective herd management, as well as decrease rates of group aggression and stress by avoiding the removals of certain key individuals.