Food conditions, competitive regime, and female social relationships in Japanese macaques: within-population variation on Yakushima.

Feeding conditions, competitive regime, and female social relationships of Japanese macaques (Macaca fuscata) on Yakushima were compared between the two habitats at two different altitudes (coniferous forest, 1,000-1,200 m and coastal forest, 0-200 m). Fruit availability was higher in the coastal forest. There was no consistent difference in the frequency of agonistic interactions within a group during feeding between the two habitats. The coastal forest evoked stronger inter-group contest competition compared to the coniferous forest as evidenced by a higher inter-group encounter rate and a higher proportion of aggressive encounters to non-aggressive ones. Birth rate was higher in larger groups compared to smaller ones in the coastal forest, but did not differ in the coniferous forest. In spite of these differences in competitive regime, no variation in female social relationships was observed, such as direction and concentration on particular individuals in grooming, linearity in dominance rank, counter-attack, and support of juvenile kin during agonistic interactions. The present results indicate that the female social relationships of Japanese macaques are robust and do not change according to changes in the current environment.

Comparisons of food availability and group density of Japanese macaques in primary, naturally regenerated, and plantation forests.

We compared food availability and group density of Japanese macaques in Yakushima, southern Japan, among primary forest and two habitats that had been disturbed by logging and had different regeneration histories. The study was conducted in an undisturbed national park, forest that was logged 7-18 years ago and later naturally regenerated, and forest that was logged 19-27 years ago and later planted with Japanese cedar (Cryptomeria japonica) trees. The plantation forest was primarily composed of large Cryptomeria japonica trees at low stand density, while the naturally regenerated forest was composed of many small trees. The total basal area and number of trees in the primary forest were comparable to those in the plantation forest. Annual fruit production was greatest in the naturally regenerated forest, intermediate in the primary forest, and negligible in the plantation forest. Herb availability was high in the naturally regenerated forest, but low in the primary and plantation forests. The group density of Japanese macaques was high in the naturally regenerated forest, intermediate in the primary forest, and low in the plantation forest. Since group size in the naturally regenerated forest was small, individual density was almost the same as in the primary forest. These results suggest that the effects of regeneration on macaques vary between the two habitats. The plantation forest consisted mostly of Cryptomeria japonica, which supplies only flowers as food in a limited season, and had a lower density of macaques. On the other hand, in the naturally regenerated forest, fruit production and herb availability were high (probably because of the enhanced light conditions after logging), and the density of macaques was as high as in the primary forest.