The Indian subcontinent has been exposed to radical geological and climatic variations over geological time. Contact with other major landmasses, and the dispersal events that resulted from them, have made India and the rest of South Asia a fascinating natural laboratory for biogeography.

Snakes constitute ideal model systems for biogeographic studies given their almost cosmopolitan distribution, the ecological influence they wield, and their evolutionary age. Snakes of the Family Homalopsidae are of special interest given their semi-aquatic habits, and the behavioural and morphological adaptations unique to this clade. Homalopsids exhibit stark differences in their distributions, abundances, and feeding ecologies. This makes them ideal for addressing questions pertaining to phylogeography, ecology, and subsequently biogeography.

I aim to study the ecological and evolutionary determinants of homalopsid distribution. First, I aim to unravel the location of origin of this family and the ancestral state (fossorial/terrestrial, or aquatic) of the crown group. This will serve as a precursor to addressing questions on how homalopsids dispersed and colonized the Indian subcontinent. I will then utilize comparative phylogeography of select species to estimate how population structure varies as a function of tolerances of these snakes to abiotic factors. This would provide insights into factors that have allowed this clade to colonize their range given the geology and paleoclimate of the Indian plate and South-East Asia. Finally, I propose to utilize species distribution models to elucidate how these and other semi-aquatic snakes respond to gradients of abiotic stressors as well as their response to other sympatric snakes.

Large herbivores can selectively feed on nutrient rich resources, resulting in regular deposition of high quality organic matter in the form of dung. In tropical forests such as in southern India it is estimated that large herbivores contribute to several hundred kilograms of dung on a daily basis. Decomposition of this dung and its implications on nutrient cycling in an ecosystem, has recently become a subject of interest to ecologists across the globe. However, most of our understanding on dung decomposition and its implication come from agroecosystem studies conducted on cattle dung. The identity of primary insect communities involved in dung comminution and feeding is well documented, but little is known of the processes and their impact on nutrient and carbon dynamics. We had set out with three primary objectives: 1) To identify the dung feeding insect communities, 2) Quantify the changes in dung composition during the decomposition and 3) Identify the impact of dung beetles on nutrient leachate and organic matter inclusion into the soil. To address these objectives, we carried out in-situ and ex-situ experiments in a tropical forest of southern India, the Mudumalai national park, for three large herbivores- elephant, gaur and cheetal, that constitute the major herbivore biomass of the region. We found two insect communities, termites and dung beetles, actively feeding on dung.However, their community composition, diversity and abundance varied with the age of the dung and the seasons. During the course of the experiments, we found that crude carbon is readily reduced but remains unaffected by seasons and across the three forest types (dry thorn, dry deciduous and moist deciduous) of the study area. We also analysed the recalcitrant component of carbon, lignin and easy to degrade, monosaccharides to understand what forms of carbon may be reduced in this process. Monosaccharides remained unaffected during the experiments, but lignin was reduced across habitats and seasons. The final experiment looking at the leachates from dung into the soil showed considerable difference between the herbivore dungs, but no effect of the dung beetle activity compared to the controls. To our knowledge, this study is among the first to use a comprehensive approach to study dung decomposition and its impact on nutrient and organic matter dynamics. It also helps in building a basic understanding of the direct role of large herbivores in cycling of nutrients.

Thesis Proposal Presentation

Thesis Proposal Presentation

Thesis Progress Presentation

Thesis Proposal Presentation

Thesis Progress Presentation

Marine systems appear to be more homogenous than terrestrial environments with few apparent barriers to dispersal. Despite this, population structuring and speciation are seen in organisms, even with high dispersal capabilities. For my thesis, I am studying a genus of tropical obligate near-shore dolphins and understand how speciation my have occurred in areas where no barriers are apparent and dispersal seems to have occurred across large distances in spite of conducive habitats. The study aims to resolve the taxonomic identity of the Sousa spp. complex in India, and examine population structure and connectivity for the Indian animals and understand how they place in the global phylogeny for the genus.

Discerning spatial patterns of biodiversity and understanding their proximate and ultimate causes is central to biogeography and macroecology. There has been substantial research on species richness along latitudinal and altitudinal gradients. Both ecological and evolutionary factors may drive diversity along these gradients but their effect on the distribution of species as mediated by species-specific traits has received far less attention.
In my first chapter, I focused on species functional trait variation along a latitudinal gradient. I found the effect of environmental filtering at higher latitudes, suggesting that environmental does play an important role in the distribution of species. Studies involving species environment relationships are important in identification and conservation of biodiverse areas. They are also important in the context of rapid climate change and in answering questions as to whether species will move to track their habitat or adapt to new environmental conditions.
To further understand this, in my second chapter, I modeled the potential distribution of 153 endemic woody species of the Western Ghats. Species distribution models (SDMs) are invaluable tools in mapping and conservation of endemic species, and also to understand the relationship between a species and its abiotic and biotic environment and which in turn can help us to generate a predictive map of where populations could potentially occur. For modeling the distribution of these species, I used MaxEnt and Ensemble methods. Species distribution models (SDMs) are used to understand the relationship between species and their environment which is then used to generate a predictive map of where populations could potentially occur. I compared these two methods and to show that Ensemble methods are better than single models. The most important environmental factor varied greatly from one species to another. However, it was observed that Precipitation of the Coldest Quarter, Slope and Forest Canopy Height contributed the most for a number of species.
For my third chapter, I used the results of species distribution modeling (binary maps) from the previous chapter to carry out preliminary assessments of conservation status of 151 endemic woody plants of Western Ghats, based on the categories and criteria proposed by the IUCN. I applied IUCN Criterion B for risk assessments and found that more than 50% of the endemic woody plants are threatened (1.9% Critically endangered, 23.84% Endangered, 30.46% Vulnerable). Of 151 endemic species, only 56 species have been assigned a conservation status by IUCN.

DCC/WWC Meeting