Induction of matrilineal rank instability by the alpha male in a group of Japanese macaques.

Abstract

Destabilizing alliances and ensuing rank changes occur infrequently in matrilineal dominance systems, and consequently very little is known about their dynamics. In one such type of alliance, called bridging, dominant individuals are ultimately responsible for subordinate monkeys out-ranking intermediate-ranking animals. Previously reported bridging alliances were based on sexual attraction, kinship ties, or special affinitive bonds between partners. In this paper we describe bridging alliances involving the alpha male in a group of Japanese macaques (Macaca fuscata) housed at the University of Montreal Laboratory of Behavioral Primatology. The comparison of rank relations in the presence and absence of the alpha male indicates that the latter was responsible for the destabilization of more than half of rank relations between members of the first and second matrilines. Another experiment revealed that the alpha male also induced extensive intermatriline reversals in priority of access to concentrated and highly prized food. These effects could be attributed to the male's consistent pattern of agonistic interventions in favor of the second matriline. However, the alpha male was not engaged in preferential affinitive relationships or reciprocally supportive interactions with the members of the second matriline. On the other hand, various lines of evidence indicate that the alpha male competed for dominance with the matriarch of the first matriline, suggesting that he might have consistently joined other individuals against that female and her kin in this context. The present data constitute further evidence for the nonaltruistic nature of aggressive interventions and the effectiveness of bridging alliances. © 1995 Wiley-Liss, Inc.