Feeding and behavioral ecology of Japanese macaques in the coniferous forest of Yakushima
Yakushima is a suitable place to study the effect of environment on animals because there are very different habitats over a close distance. When I was a doctoral course student, I conducted fieldwork for two years, based on the results of 'Yakushima Macaque Research Group'. I also conducted half-year fieldwork when I was a post doc.
This is the camp of my study site, although I just park my car and set a tent at the end of a logging road. I think I have spent more than 500 nights alone here.
1. Feeding ecology
I studied the diet of Japanese macaques by fecal analysis. I revealed that diet changes with altitude and fruit availability is the primary source of the altitudinal, seasonal and supra-annual variations.
I habituated and identified all the individuals of one macaque troop and conducted behavioral observation. Almost half of their annual feeding was occupied by fiber-rich foods (mostly leaves). At the same time, they strongly preferred fruits. The combination of high digestive ability of fiber-rich foods and preference for fruits is considered to be important in temperate regions, where fruit production is seasonally limited.
I studied mature leaf food selection by Japanese macaques in the coniferous and coastal forest of Yakushima. Among major food leaves, they selected the species of which the density is high. The present results suggest that the effect of traveling cost, which can be saved by selecting common trees, exceeds the benefits gained by selecting high-quality foods.
Analysis of activity revealed that the effect of temperature, namely the cost of thermoregulation, cannot be neglected even compared to food-related factors.
Ranging data of the same group supported the hypothesis that the macaques capitalize on habitat heterogeneity in a seasonally fluctuating habitat by shifting their home range and modifying their travel rate, in response to the food and thermal conditions in different seasons in different habitats.
Read the abstract of the paper on altitudinal variations in diet
Read the abstract of the paper on the diet in the coniferous forest
Read the abstract of the paper on the activity budget
Read the abstract of the paper on leaf selection
Read the abstract of the paper on ranging patterns
2. Socioecology: effects of food on feeding competition and social relationships
I tested a socioecological model, which assumes that ecological conditions determine primate social relationship, by the within-population comparisons of Japanese macaques between the coniferous and coastal forests. As the theory predicts, between-group contest was more intense in the coastal forest, in accordance to the higher fruit availability and higher population density there. However, there was no difference in female social relationships, such as grooming and aggressive interactions between the two habitats. Although the ecological plasticity of Japanese macaques is large, they may be socially not so flexible.
I also examined ecological factors affecting aggression during feeding. It was revealed that food type and number of feeding sites in the tree affected aggression.
Read the abstract of the paper on social relationships
Read the abstract of the paper on aggression
3. Behavioral thermoregulation
I studied behavioral thermoregulation, another important adaptations to survive in the temperate habitat. The frequency of behavioral thermoregulation, such as sunbathing and huddling, did not differ between the coastal and coniferous forests, where temperature differs more than 7 degree Celsius. It suggests that they acclimatize themselves to each thermal condition that requires behavioral thermoregulation only during the season when thermoregulation is most costly.
I also studied the activity pattern using camera trapping. The seasonal and daily fluctuations of the activity was consitent with the hypothesis that the macaques modify their activity in response to thermal conditions.
Read the abstract of the paper on behavioral thermoregulation
Read the abstract of the paper on activity patterns revealed by camera trapping