Behavioural ecology of primates in the Upper Brahmaputra Valley of Assam
Over the last two centuries, the forests of Upper Brahmaputra Valley has been cleared for agriculture, human settlements timber extractions leading to a landscape dotted with remnant lowland rain forests fragments of different sizes. We study how primates are coping to such heavy fragmentation of their habitats
How green was the Valley?
All landscapes has their own histories and in a noted historian’s words, “inquiry into their past can help us to learn how we came to this turn in the road and, what options lie ahead.” Historical deforestation had shaped the landscape of Upper Brahmaputra Valley. In this project we analysed the historical drivers of forest loss and habitat fragmentation in Upper Brahmaputra landscape over the last 15 centuries. The forest cover changes during the precolonial (before 1826), colonial (1826—1947) and the postcolonial (post 1947) periods were located within the political economy and demographic milieu of each regime. Our analysis showed that the Upper Assam landscape has shaped by the interplay of deforestation and natural reforestation which was strongly linked to the socio-political factors. In the current context of rising populations linked to immigration from neighbouring regions, dwindling share of agriculture in the state’s gross domestic product, and recent incentives to small tea growers in risk-prone agricultural landscapes, serious challenges remain to securing forests in this region
Coping with forest fragmentation
Having looking at the historical analysis of how various socio-economic factors led to forest loss and fragmentation in the Upper Brahmaputra Valley, we then examined how forest fragmentation, in turn, has affected primates in Upper Brahmaputra Valley (UBV). We investigated the distribution of primate species in 42 habitat fragments of UBV. We particularly examined the role of ecological and anthropogenic factors at the local and landscape scale in shaping patterns of primate species richness, individual primate species distribution and local extinctions across habitat fragments. We explored how patterns of primate species richness and composition vary across fragments temporally and spatially. We found a persistence of several primate species of primates in these fragments even after being isolated for over a century. Various ecological, landscape and anthropogenic factors were influenced the occurrence and extinction of species in these fragments.
Going, going, gone!
We analyse recent temporal trends in primate populations of four forest fragments of UBV using multi-year census data spanning 16 years. We report the recent history and current status of six diurnal primates in one large (2,098 ha) and three small (< 500 ha) fragments of the Upper Brahmaputra Valley. I censused primates in the small fragments during 2002, 2005, 2009, in the large fragment in 2008, and used other published census data to derive population trends. We used key informant surveys to obtain historical occurrence data for these populations. Our analyses reveal the recent extinction of some populations and the simultaneous long-term persistence of others in these fragments over 16 years. Most populations appeared to have declined in the small fragments but primate abundance has increased significantly in the largest fragment over the last decade. Addressing the biomass needs of the local human populations, which appears to drive habitat degradation, and better protection of these forests, will be crucial in ensuring the future survival of this diverse and unique primate assemblage in the last rainforest fragments of the human- dominated Upper Brahmaputra Valley.
Divide and thrive, unite and perish
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 design effective conservation strategies for these species. The project examined the niche partitioning and co-existence of three congeneric species, the rhesus macaque, pig-tailed macaque and stump-tailed macaque, in Hollongapar-Gibbon Wildlife 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 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.