Coalitions destabilize dyadic dominance relationships in male Barbary macaques (Macaca sylvanus)

Dyadic agonistic dominance relationships are thought to result from asymmetries in both intrinsic and extrinsic power. One form of extrinsic power is the ability to solicit agonistic support from other individuals. In extreme cases extrinsic power differences may override intrinsic power differences so that physically inferior individuals attain rank positions above stronger competitors. In other cases superior extrinsic power in physically inferior individuals may destabilize the otherwise clear dominance relationships. We tested this prediction with observational data on adult males in one of three free-ranging groups of Barbary macaques at Affenberg Salem, Germany. All prime males that were subjects of this study were at least 5-8 years (average 10 years) younger than the old post-prime males that were all subordinate to them. Assuming large age differences to reflect large intrinsic/physical power differences, interactions between these prime and the old males allowed investigation of the separate effects of intrinsic and extrinsic power asymmetries on dominance relationships. We estimated relationship instability using four different estimates (counter aggression, conflicts initiated by aggression from the subordinate, spontaneous submissions by dominants, and decided conflicts won by the subordinate). Relationship instability did not decrease with increasing asymmetry in intrinsic power. Instead, all four measures of relationship instability were positively related to the number of times the dominant in a dyad was target of destabilizing coalitions. Destabilizing coalitions targeted dominant males in old male-prime male dyads more often than in old male-old male dyads. Consequently, old males had less stable relationships with the much stronger prime males than with each other. We conclude that extrinsic power asymmetries predicted the instability of dyadic dominance relationships and may systematically override intrinsic power asymmetries.