No abstract

Seasonal variations in the activity budget of Japanese macaques in the coniferous forest of Yakushima were studied over the course of 1 year. On an annual basis, they spent 38% of the daytime feeding, 16% traveling, 14% in social interactions, and 32% engaged in resting. The effects of temperature and food-related factors (i.e., food distribution, feeding speed, and food abundance) on the seasonal variations of activity budget were examined by stepwise multiple regression analysis. When the temperature was low, the macaques decreased traveling and feeding time, in accordance with the prediction that endothermal animals save energy under severe thermoregulatory cost. When the feeding speed of available foods was slow, they spent more time feeding. When high-quality foods were abundant, they decreased feeding time. These macaques did not respond to fluctuations in food distribution. The present results indicate the importance of temperature, in addition to food-related factors, as a determinant of activity budgets.

We analyzed regional variation in the diets of two primate clades, Asian macaques and colobines, whose distributions include temperate-alpine forests. We addressed feeding strategies that enabled them to adapt to harsh environments characterized by relatively low mean temperatures and strong seasonality in both temperature and food availability. Macaques in tropical-lowland forests feed mainly on fruit and animal matter whereas populations in temperate-alpine forests feed more on foliage and on such items as bark and fungi. In comparison, colobines in tropical-lowland forests feed more on fruit and foliage whereas populations in temperate-alpine forests feed less on flowers and more on lichens. Annual precipitation and mean temperature, both of which reflect primary production, had the most significant effects on the feeding behavior of the macaques, whereas only mean temperature had a significant effect on that of colobines. We found two behavioral strategies used by both clades to cope with severe environmental conditions in temperate-alpine forests--shifting to other food items and adjusting feeding plasticity for fruit and foliage. Macaques responded to latitudinal changes by use of both strategies whereas the colobines adapted by using the latter only. By contrast, changes in altitude resulted in the macaques' using the latter strategy and colobines' using both. The different current distributions of Asian macaques and colobines could be attributed to differences in their feeding strategies originating in their digestive systems.

The orangutan is the world's largest arboreal mammal, and images of the red ape moving through the tropical forest canopy symbolise its typical arboreal behaviour. Records of terrestrial behaviour are scarce and often associated with habitat disturbance. We conducted a large-scale species-level analysis of ground-based camera-trapping data to evaluate the extent to which Bornean orangutans Pongo pygmaeus come down from the trees to travel terrestrially, and whether they are indeed forced to the ground primarily by anthropogenic forest disturbances. Although the degree of forest disturbance and canopy gap size influenced terrestriality, orangutans were recorded on the ground as frequently in heavily degraded habitats as in primary forests. Furthermore, all age-sex classes were recorded on the ground (flanged males more often). This suggests that terrestrial locomotion is part of the Bornean orangutan's natural behavioural repertoire to a much greater extent than previously thought, and is only modified by habitat disturbance. The capacity of orangutans to come down from the trees may increase their ability to cope with at least smaller-scale forest fragmentation, and to cross moderately open spaces in mosaic landscapes, although the extent of this versatility remains to be investigated.

We examined the basal area of two life forms (conifers vs. broadleaf trees) along elevational gradients on Yakushima Island, Japan and on two series of geological substrate on Mount Kinabalu, Borneo. On Yakushima, total stand basal area abruptly increased from 700 to 1,050 m in accordance with the high dominance of conifers, indicating the presence of additive basal area of conifers in conifer-broadleaf mixed forests at higher elevations (1,050-1,300 m). Along two substrate series on Kinabalu, some forests at higher elevations (1,860-3,080 m) showed relatively high dominance of conifers, but conifer basal area did not appear to be additive. Conifers were emergents above the canopy of broadleaf trees in mixed forests on Yakushima, but two life forms usually coexisted in the single-story canopy in mixed forests on Kinabalu. Litterfall rate as a surrogate of productivity decreased with decreasing temperature along elevation on both the sites, but the rate of decrease was slower on Yakushima, where mixed forests at higher elevations showed relatively high rates. Thus, we suggest that additive basal area of conifers was linked to their emergent status, and that it enhanced productivity by complementary use of light by two life forms that occupy different stories. On Yakushima, typhoons are a major disturbance, but do not severely limit the height growth of conifers, allowing the development of twostory mixed forests. On Kinabalu, a major disturbance is El Nin˜o-driven drought, and hydraulic limitation to tree height may explain the non-additive and non-emergent nature of conifers.