Spatial position-associated mating strategies employed by male Japanese macaques (Macaca fuscata yakui) in Yakushima.

In bisexual groups, dominant males occupy the central part of the group, which is advantageous because it is reproductively beneficial. However, high-ranking males do not necessarily monopolize reproductive success, which indicates that low-ranking males increase their reproductive success through alternative mating strategies. To reveal the effectiveness and cost of these strategies employed by group males, it is necessary to clarify the spatial configuration of males and their group, and show how males combine strategies in different situations. This study demonstrates the spatial configuration of male Japanese macaques (Macaca fuscata yakui) and their group when males adopt three mating strategies: mate guarding, sneak mating, and cross-boundary mating (mating with females of another group). High-ranking males tended to perform mate guarding, but they also mated with females in other groups when there were few sexually active females in their group. Low-ranking males performed sneak mating; they remained in the central part of the group to monitor sexually active females and moved toward the periphery for copulation but never completely left the group. In addition, males individually ventured outside the group's ranging area and succeeded in mating with females of other groups. The cross-boundary mating strategy has the advantage of increasing the number of potential mating partners, which is not present in the other two strategies. However, because of considerable costs and low contribution to mating frequency, this strategy is complementary and is employed when the expectation of mating success in their group is low.