The ecology and population dynamics of the lion-tailed macaque (Macaca silenus) in South India
The lion-tailed macaque is dispersed in patches of rain forest along the Western Ghat mountains in India. Its endangered status is the cumulative result of the geoclimatic history of the region, the evolutionary history of the species, and recent human activity. In this light, the objective of this project was to examine the variation in the demographic parameters of the species, and their ecological and behaviour correlates. Demographic data collected over a period of six years from a wild population in the Anamalai Wildlife Sanctuary (Tamil Nadu, India) showed that the lion-tailed macaques have a high age at first birth, a low birth rate and a high survival rate. The growth rate of a group and birth rate were decreasing functions of the group size. In the main study group there were significant differences in the activity, feeding and ranging patterns with a change in the group size. As the group became larger, it spent more time searching for food, but there was a decrease in feeding on animal matter, and no difference in time spent on plant foods. There was also an expansion of dietary range, and probably a reduction in dietary quality. Less time was spent on resting, but more time was spent on agonistic interactions. As the group became larger, the distance travelled, and the area covered each day, month and year increased. Spatial variation in the use of the habitat decreased, along with the overlap of areas used on successive days. This variation represented the differential regulation of ranging required by different group sizes. Such a regulation of ranging operates within the constraints placed by the availability of major food trees. The reproductive behaviour of the lion-tailed macaque is characterised by a relatively high adult female/male ratio, a high synchrony of female sexual cycles, and sexual harassment which increases in proportion to the number of adult females with sexual swellings. These factors might cause a suppression of conception by some ovulating females, and thus result in a decrease in birth rate, in a medium-sized one-male group. It is unlikely that the same effect would be evident across all the range of group sizes. The relevance of the differences between individuals to the above findings is examined briefly in the concluding chapter. The demographic processes expressed at the group level, and their ecological and behavioural correlates, could form a part of a model of the dynamics of a population composed of a number of such groups.