Primates on the edge: Ecology and conservation of primate assemblages in the fragmented lowland rainforests of the Upper Brahmaputra valley, Northeastern India

Sharma, Narayan (2012) Primates on the edge: Ecology and conservation of primate assemblages in the fragmented lowland rainforests of the Upper Brahmaputra valley, Northeastern India. Doctoral thesis, NIAS.

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Thesis advisorSinha,
Thesis advisorMadhusudan, MD*
Abstract: The fragmentation of unbroken tracts of wildlife habitat mediated by human action is a critically important conservation problem, especially in the tropics. As tropical forests are increasingly being converted to other land-use forms, habitat fragments are becoming ubiquitous features of any tropical landscape. Most of these fragments, now located in intensely-modified production landscapes, are crucial in supporting regional biodiversity as considerable biota continue to persist in them. These fragments are, however, facing growing threats from various developmental activities as the marginal populace depends heavily on them to fulfill their daily resource needs. Understanding the process of habitat fragmentation and its various ecological consequences on species residing in such fragments is, therefore, essential in developing conservation strategies to mitigate the adverse impacts of habitat fragmentation. This study examines the causes and consequences of habitat fragmentation on the wild primates of the upper Brahmaputra valley of Assam, a rich landscape with seven primate species that has witnessed severe habitat fragmentation over the last century. The upper Brahmaputra valley of Assam, particularly the region south of the river, is extremely rich in biodiversity that includes seven primate species, comprising a loris, a langur, four macaques and an ape. It is, however, severely fragmented due to various historical and current socio-economic processes, and continuously sculpted by geological processes such as periodic earthquakes and seasonal floods. Our analysis of the historical socio-economic drivers during three watershed periods of upper Brahmaputra valley located these changes within the political economy and demographic milieu of each regime. The pre-colonial period (5th century AD–1826)—with its sparse population, agriculture-based economy and regional markets—appears to have had relatively little impact on the valley’s forest cover. During the colonial period (1826–1947), however, forest cover began to decline against the backdrop of unprecedented population increases and the emergence of new settlements in the valley. This followed colonial policies and institutions geared to extract and exploit the natural resources of the region, and linked the local economy to the demands of global markets. The post-colonial period (1947– present), considered by some as an extension of the policies of the colonial regime, continues to see an intensification of natural resource extraction, leading to further shrinkage and degradation of forest cover in the valley. By the end of the last century, most of the valley’s forest cover not only reduced to one fourth of its original extent but also became highly fragmented with several isolated habitat fragments, punctuated in a seemingly endless swathe of human settlements, agricultural fields and tea plantations, all crisscrossed by roads, railway tracks and electric power lines. Consequently, the once extensively distributed populations of several mammalian species, including primates, have become completely fragmented and a few of them already locally extinct; some of these splintered populations, however, continue to linger tenuously in a few of these rapidly shrinking fragments. The time has now come to ask whether it is worthwhile to invest scarce resources in conserving these habitat remnants situated within some of the most densely-populated production landscapes of the country. Are these fragments fated to lose their species anyway? If not, do other ecological, anthropogenic and species-related factors mitigate the effect of fragmentation and offer conservation opportunities for these habitats and their last primate populations? I answer these questions by evaluating the local- and landscapescale factors that influence the richness, abundance, distribution and local extinction of six primate species in 42 lowland tropical rainforest fragments in the upper Brahmaputra valley. These forest fragments appear to have lost, on average, at least one species in the last 30 years but still retain half their original species complement. Primate species richness has declined with the proportion of habitat lost by these fragments but seems not to be significantly affected by fragment size and isolation. The occurrence of western hoolock gibbon and capped langur in these fragments was inversely related to their isolation and habitat loss respectively. Fragment area determined stump-tailed and northern pig-tailed macaque occurrence, Assamese macaque distribution was influenced negatively by illegal tree felling while rhesus macaque abundance increased with increasing habitat heterogeneity. Primate extinction in a fragment was primarily governed by the extent of divergence in its food tree species richness from that in contiguous forests. These results underline the high conservation value of these last rainforest habitat remnants, which collectively retain the entire original species pool and individually retain significant fractions of it, even a century after fragmentation. Having examined the effects of different factors on primate species richness and abundance, I analysed how these primate communities vary spatially and have altered temporally within these fragments. I found a significantly greater variability in primate species composition and richness within fragments between 100 and 30 years ago than over the last three decades while across-fragment variation in these parameters was comparable to that 30 years ago. Turnover in primate species composition appeared to be related to geographical distance, dissimilarity in spatial features and to certain anthropogenic features of the fragments. I also observed that the primate communities in the study fragments were not competitively structured. The high variability in primate composition and richness within fragments from historical times to the recent past can possibly be attributed to local extinctions, the decline of this variability over the last 30 years to community inertia and the recent high levels of species turnover to dispersal limitations. Primate species composition has diverged between fragments with increasing geographic distance and differences in spatial characteristics. The original primate species pool being variably represented in subsets, I recommend that all these fragments be urgently protected, their connectivity enhanced and conservation interventions, such as reintroductions, attempted, wherever appropriate. These snapshot studies were, however, not sufficient to highlight the actual trends in primate population persistence and extinction in these fragments. I therefore, monitored the population of six diurnal primates in one large (2,098 ha) and three small (< 500 ha) fragments over a period of seven years and compare our observations with those from earlier studies. Our results suggest two different trends in population persistence and extinction in these fragments. There was a dramatic decline in the population of the six primate species in all the three small fragments, Borajan, Bherjan and Podumoni, over the observation period. Primate abundance has, however, increased significantly in the large fragment, the Hollongapar-Gibbon Wildlife Sanctuary, over the last decade. This fragment is, therefore, unusual in exhibiting a high diversity and abundance of primates; an understanding of how these primate species coexist here could thus be valuable in developing management strategies for the other fragments in the valley that continue to retain a healthy complement of its original primate assemblage. The final section of my thesis thus examines the ecological mechanisms that have enabled the co-existence of three closely related macaque species, the rhesus macaque Macaca mulatta, the northern pig-tailed macaque M. leonina and the stump-tailed macaque M. arctoides within this fragment. I specifically asked whether and how, if at all, the three sympatric congeneric macaques in such a fragmented, resource-limited habitat could partition themselves along two major niche dimensions—space and food. I found significant differences in both horizontal and vertical space use among the three species of macaques, which were able to segregate themselves in space and differentially use the specific food resources available in the sanctuary. Our results, therefore, support the classical niche theory, providing clear evidence of niche partitioning being able to promote the co-existence of congeneric macaques in this fragment. More proximally, at the fragment-level, such partitioning of resources may have allowed primates to persist in this fragment even after being isolated for over one hundred years. Our study has, thus, established the high conservation value of the last fragments of the upper Brahmaputra valley, which collectively retain the entire original primate species pool and individually retain significant fractions of it, even a century after fragmentation. It is important to point out also that as the original primate species pool is variably represented in the different fragments, all these fragments are in urgent need of conservation. Strict protection measures appear to have been effective in at least one of the fragments, Hollongapar, which has witnessed an increasing abundance of primates over the last decade. There, nevertheless, continues to be a number of uncertainties involved, particularly with regard to our comprehension of the responses displayed by species to increasing habitat fragmentation. The fragments of Upper Brahmaputra are undoubtedly critical for the conservation of regional biodiversity while many of these tracts may have to continue to support the livelihoods of the local human populations. It is, therefore, essential to introduce scientifically sound strategies that could aid in the management and conservation of the threatened, but unique, primate assemblages of the valley and, at the same time, establish socio-economically viable practices that will protect the livelihoods and aspirations of the people so as to make these fragments ecologically and socially sustainable in the future.
Item Type: Thesis (Doctoral)
Additional Information: Thesis was submitted to Manipal University, Manipal. [Year of Award 2013] [Thesis No. TH16]
Keywords: Primates, Brahmaputra valley, ecology, conservation
Subjects: School of Natural and Engineering Sciences > Conservation Biology
Doctoral Programme > Theses
Divisions: Schools > Natural Sciences and Engineering
Date Deposited: 02 Apr 2013 05:32
Last Modified: 19 May 2021 14:29
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