Niche partitioning and coexistence of sympatric macaques in a fragmented habitat of the Upper Brahmaputra Valley, northeastern India

How closely related species co-exist, especially under conditions of resource limitation remains an intriguing problem in ecology. Having to share space and resources, such species are expected to have evolved a variety of behavioural mechanisms to reduce competition. Understanding such adaptation could also provide clues to designing effective conservation strategies for these species. In this chapter, I examine the niche partitioning and co-existence of three congeneric species, the rhesus macaque Macaca mulatta, northern pig-tailed macaque Macaca leonina and stump-tailed macaque Macaca arctoides, in a fragment of less than 20 km2, the Hollongapar Gibbon Sanctuary, which still harbours a significant proportion of original species pool. An intensive observational study was conducted on two troops each of the three species over a period of 23 months from March 2008 to January 2010. We examined niche partitioning among the macaques along two major axes—space and food. Our results found significant interspecific differences among macaques in their utilisation of both horizontal and vertical space, as well as in their utilisation of food resources. The differential utilisation of space and food has enabled the continued co-existence of the three macaque species in this fragment. At the fragment level and over proximate time scales, our results explain why primates, particularly the three species of macaques, are able to thrive even after being isolated for over one hundred years. Ecological and behavioural insights gleaned from this fragment will help us understand and promote the co-existence of primates in other habitat fragments of the Upper Brahmaputra Valley.