Despite extensive conservation efforts, wildlife populations continue to decline globally, largely driven by human activities such as habitat loss and illegal resource extraction. Timber poaching represents a relatively understudied but significant threat to forest ecosystems and arboreal wildlife. This study investigates the ecological and socio-economic dimensions of timber poaching in the Hoollongapar Gibbon Wildlife Sanctuary (HGWS), Assam, India, with a particular focus on its implications for the endangered western hoolock gibbon (Hoolock hoolock). The research adopts an interdisciplinary framework integrating remote sensing analysis, vegetation surveys, behavioural observations, and ethnographic investigation to examine conservation challenges across ecological and human systems.

Land Use and Land Cover (LULC) analysis using satellite imagery (2017–2023), supported by field validation in 2025, revealed that although HGWS remains largely forested, gradual landscape transformation is occurring. Tree cover declined modestly, while built infrastructure and other anthropogenic features increased, indicating expanding human influence within the sanctuary landscape. Vegetation surveys across 20 dominant plant species further revealed spatial heterogeneity in tree diversity and canopy structure across forest compartments, reflecting variation in habitat quality and resource distribution.

Field surveys documented 31 timber poaching sites, with the southern region of HGWS exhibiting particularly high extraction pressure. Poachers often exploit a legal loophole in the Wildlife (Protection) Act of 1972, which criminalises tree cutting but not the collection of fallen wood. By cutting V-shaped notches into tree trunks, they weaken trees and cause them to collapse under natural stress, allowing the timber to be collected as “fallen wood.” This covert practice complicates enforcement, as forest guards often struggle to distinguish between legitimate resource collection and deliberate timber extraction.

Behavioural observations totalling approximately 143 hours revealed significant behavioural plasticity in gibbons. Moderate disturbance levels were associated with increased vigilance, alarm vocalisations, and adaptive adjustments in foraging behaviour, whereas high disturbance suppressed key behaviours, including alarm communication and coordinated group movement. Population surveys recorded thirty gibbon groups across the sanctuary, with evidence of ongoing reproduction despite disturbance.

Ethnographic research revealed widespread forest dependence among local communities, with livelihood constraints and limited economic alternatives emerging as major drivers of timber extraction. The findings highlight complex interactions among habitat change, wildlife behaviour, and human livelihoods. By integrating ecological and socio-economic perspectives, this study provides new insights into disturbance ecology and emphasises the need for targeted, community-informed conservation strategies to safeguard the diversity of HGWS.

Coastal fisheries target select species but also catch several non-target or ‘bycatch’ species, which comprise ~40% of global catch. Large-bodied, slow-growing species such as elasmobranchs and cetaceans (marine megafauna) are particularly vulnerable to such mortality. Despite its importance, patterns and drivers of bycatch remain poorly understood. Species susceptibility to bycatch may depend on their traits, environmental conditions, and fishing practices, but it is unclear whether these patterns are governed by general rules or local variables. My thesis addresses these questions by examining interactions of elasmobranchs and cetaceans with fishing gear across multiple contexts in India.

My first chapter investigates drivers of elasmobranch capture in nearshore fisheries on India’s east and west coasts. By integrating fisheries landing data, fishing location information, and fisher interviews, we analysed 2,209 fishing trips recorded across three seasons in 2022–23 that caught 5,578 elasmobranchs from more than 20 species. Catch risk was higher at the eastern site, where species were likely targeted, while catch rates were highest on the west coast. Overall, drivers of elasmobranch capture were highly fishery- and site-specific, although some general patterns emerged, such as greater bycatch risk closer to the coast.

My second chapter addresses the lack of baseline knowledge on cetacean occurrence in the North Indian Ocean. I used species distribution models to map areas of high species richness for 18 species. The east coast of India, south Sri Lanka, and the Lakshadweep and Andaman–Nicobar archipelagos emerged as species rich areas. The central west coast of India emerged as a hotspot for two nearshore species - the Indian Ocean humpback dolphin (Sousa plumbea) and the Indo-Pacific finless porpoise (Neophocaena phocaenoides) - that overlap with high fishing activity, making it an ideal system to study cetacean–fisheries interactions.

My third chapter focuses on mortality dynamics of these two nearshore cetaceans along Goa. Using long-term stranding records (2017–2025), ocean current simulations, carcass decomposition experiments, and population surveys, we estimated their at-sea mortality, which was 42 ± 2.4 individuals for S. plumbea and 23 ± 1.8 for N. phocaenoides. Mortality hotspots were concentrated in coastal areas with high fishing and tourism activity, which have potentially caused a 30% decline in S. plumbea abundance over the past two decades.

While drones provide valuable perspectives on dolphin–fisheries interactions, quantifying movement and behaviour from aerial imagery remains challenging. In my fourth chapter, I combine machine learning with a mathematical approach to georeference objects in drone imagery, enabling automated GPS-like tracking without onboard tags. The method achieves a median positional error of 1.5 m - comparable to or better than GPS tags - and enables high-resolution, non-invasive tracking of free-ranging animals.

Finally, my fifth chapter applies drone-based tracking to examine behavioural responses of Indian Ocean humpback dolphins to fisheries, co-occurring with unregulated tourism in Goa. Drone focal follows of 90 dolphin groups were analysed using the above framework. Dolphins avoided tourist boats, while interactions with fishing nets were associated with increased foraging behaviour. Groups near fishing nets were more sensitive to the presence of tourism boats, revealing complex behavioural trade-offs faced by dolphins exposed to multiple human activities.

Together, my thesis combines ecological analyses with methodological advances to understand how marine megafauna interact with fisheries. By integrating empirical data, distribution modelling, methodological advances and drone-based tracking, it provides new insights into the mechanisms underlying bycatch risk and highlights opportunities for conserving threatened marine species in rapidly changing coastal ecosystems.

Snakes are among the most notable reptilian lineages ubiquitous in several ecosystems across the globe. The innovation of the venom system has strongly underpinned their evolutionary success. In India, the Indian spectacled cobra (Naja naja) is one of the “big four” medically relevant snake species responsible for most human envenomations and fatalities. Despite its near pan-Indian distribution and documented geographic variation in morphology and venom composition, its evolutionary history, phylogenetic diversity, and biogeographical origins are poorly understood. This work adopts an integrative framework combining phylogenetics, phylogeography, population genomics, and venomics to elucidate the evolutionary dynamics of Naja naja across its distribution range.
In Chapter 1, we reconstruct the evolutionary relationships of N. naja across geographically disparate populations. Using an expansive sampling, we test species monophyly, assess genetic diversity, and use time-calibrated phylogenies to place lineage divergence within the context of major geological and climatic events. Our results support an African origin for the genus Naja and a Miocene dispersal of N. naja into South Asia. Unlike many widely distributed snakes, N. naja shows no evidence of phylogeographic subdivision within India, indicating that it is a largely panmictic mainland species. In contrast, Sri Lankan N. naja forms a genetically distinct clade, separate from mainland populations.
In Chapter 2, we examined population structure, spatial genetic patterns, and demographic history of N. naja. Genome-wide analyses revealed geographically structured genetic variation across mainland India, with individuals broadly clustering by geography, albeit with variable ancestries. Interestingly, several clusters comprised of highly admixed individuals, suggesting shared ancestry across regions rather than strictly discrete populations. Furthermore, within a cluster, geographic distance explained genetic similarity, but this relationship diminishes at the species scale, suggesting that local dispersal processes operate within clusters while historical population structure shapes patterns at the species level. Demographic history inferred using representative individuals reveals long-term fluctuations in effective population size, providing an overview of their population dynamics. Together, these results point to a complex interplay between historical lineage differentiation and spatially variable connectivity in shaping genetic variation in N. naja.
In Chapter 3, we examine the geographic variation in venom composition across N. naja populations and evaluate the influence of ecological factors and the underlying genetic structure on venom phenotypes. Using biochemical and proteomics approaches, we characterize differences among populations and integrate these results with population-genomic data. Interestingly, no cluster-specific venom fingerprint was observed, and the changes were primarily due to proportional differences in venom components. Geographic origin explains the largest proportion of venom variation, followed by genetic population structure, while minimal contributions were also recorded from other ecological factors. A substantial proportion of venom variation remains unexplained, indicating pronounced within-population heterogeneity and additional ecological or regulatory influences shaping venom phenotypes.
By combining molecular phylogenetics, population genetics, and functional analyses, this work sheds new light on how evolutionary forces shape diversity in venomous reptiles. Our multifaceted approach provides a population genomic perspective on genetic variation in a widespread and ecologically flexible serpent, with implications for understanding regional differentiation in medically important snakes.

Pantala flavescens or the Globe Skimmer, a commonly available species of dragonfly, performs a fascinating multi-generational transoceanic migration between India and Africa (see Figure below). The intriguing annual migration was reported a century ago. The multi-generational, transoceanic migration circuit spanning 14000-18000 kms, from India to Africa is an astonishing feat for an insect few cms in size. Wind, precipitation, fuel, breeding, and the life cycle affect the migration, yet understanding of their collective role in the migration remains elusive. We identify the transoceanic migration route by imposing a time constraint emerging from energetics on Dijkstra’s path-planning algorithm. Energetics calculations reveal Pantala flavescens can endure 90 hours of steady flight at 4.5m/s. We incorporate active wind compensation in Dijkstra’s algorithm to compute the migration route from years 2002 to 2007. The prevailing winds play a pivotal role; a direct crossing of the Indian Ocean from Africa to India is feasible with the Somali Jet, whereas the return requires stopovers in Maldives and Seychelles. The migration timing, identified using monthly-successful trajectories, life cycle, and precipitation data, corroborates reported observations.Wind drift compensation is crucial for the dragonflies to reach their destination. We conducted tethered flight experiments in a wind tunnel on live specimens of P. flavescens. Specifically, we evaluated the tethered flight in the tailwind and headwind for different crosswind orientations by comparing the distribution of mean values of thrust, side force, and lift between the headwind and the tailwind. Further, we conducted high-speed Schlieren flow visualization to visualize two distinct flight modes and the associated vortical flow structures.

Amphibian populations worldwide face unprecedented decline rates, with UV radiation emerging as a significant but complex contributor to this biodiversity crisis. Studies have revealed that the impacts of UV are heavily modulated by co-occurring environmental factors. Temperature influences DNA repair rates, pH levels can synergistically increase mortality, and UV-induced immunosuppression enhances disease susceptibility, which is particularly relevant given the role of pathogens like chytrid fungus in amphibian declines. The evidence indicates that UV radiation contributes to amphibian declines not as a primary driver, but as a critical modulator that amplifies the effects of other anthropogenic stressors.
This multi-stressor perspective is essential for understanding the complex etiology of the amphibian crisis. This presentation explores the mechanistic pathways through which ultraviolet radiation influences amphibian physiology and survival and evaluates its potential
role in population declines.

Soil microbes are well known to affect plants by playing significant roles in nutrient and energy cycling. There is growing understanding of the full range of interactions and context-dependency of plant-soil microbe relationships. Modern genomics has further expanded our access to the microbial world, and the boom in microbial data requires strong theoretical frameworks for interpretation. Mathematical models that are tightly linked to data will allow us to scale up from individual plant-microbe interactions to plant growth, species coexistence and community-level trait and spatial distributions. I present two examples of mathematical models that incorporate plant-soil microbiome interactions and expand our understanding of plant communities and their response to management.

First, I present a new phenomenological model of plant-soil microbiome interaction in which the soil microbiome is represented along a one-dimensional axis (derived from multidimensional scaling or other dimensionality-reduction methods). I show how the outcomes of the dynamics of two plant populations shift dramatically when plants and soil microbiome interact reciprocally. Second, I describe a simple plant-nutrient model that exhibits hysteresis. Incorporating the soil microbiome, which mediates plant-nutrient interactions, leads to a new type of stable branch that I call “precariously stable”. Together, these models demonstrate the significance of plant-soil microbiome interactions in plant population and community dynamics.

Different nonlinear interactions extant among the numerous constituents of diverse systems give rise to several interesting phenomena and are responsible for the wide range of dynamics seen in nature. By construction of appropriate models that mimic observations, we can, to some extent, predict a system's behaviour in certain parameter regimes. A general understanding of a system based upon physical principles enables one to operate it in a "desirable" dynamical regime.

This talk will outline some of my past work in modelling & explaining the dynamics of some complex natural systems. We address questions such as- what causes certain insect infestation cycles to occur regularly like clockwork but sometimes cease suddenly & if we can predict their recurrence, how can we explain animal movement in human-modified landscapes, how do we predict tipping points, etc.

Group-living organisms across taxa coordinate their movement to evade threats or predators. However, how information about threats, often available only to a few individuals within the group, efficiently propagates among the group members, and how animals use the information of predator to coordinate their movement, remains less explored. In this thesis, our aim is to study collective escape responses, information propagation and context-dependent hierarchical leadership in collectively escaping groups, using both data and models.

We first investigate the collective responses of a sheep flock (Ovis aries) to a herding dog (border collie). We observed that the sheep flock remained highly cohesive throughout the herding events, consistent with the selfish herd effect, a known mechanism hypothesised to reduce predation risk. Sheep moved faster as the dog increased speed, while being highly polarised but less cohesive. This suggests that cohesion alone may not adequately explain anti-predatory benefits of group-living, especially in groups exhibiting synchronous collective motion as seen in our sheep flock experiments. Using lagged cross-correlation analysis of time series of direction of different individuals, we identified a clear hierarchy among sheep in terms of their directional influence on the flock. We found that the average spatial position of a sheep along the front-back axis of group velocity strongly correlates with its influence on group movement.

To explain these results, we developed a computational model where sheep follow simple interaction rules, namely, repulsion from the dog and a tendency to move towards and align with neighbours. This model can reproduce empirically observed patterns. Consistent with experimental findings, the model predicts that the individuals at the front of the flock had greater directional influence on the group. Furthermore, we developed a null model of herding in which the chasing behaviour of dog is not included. Such a model fails to reproduce the hierarchical information flow, suggesting that the observed empirical patterns are characteristic of collective escape response.

When animals collectively respond to threats, it is difficult to know if the individuals were directly reacting to the threat or to the response of their neighbors. We study high-resolution data from a controlled experimental set up of fish (tiger barbs) where an individual trained to a threat stimulus via aversive conditioning escapes the stimulus, thus precisely controlling the individual reacting to the threat (or thus, having information of the threat). We show that in a group of five fish with only one conditioned fish, the escape behaviour of one conditioned fish could trigger collective escape responses with all the fish. We use lagged cross-correlation analysis of speed of different fish to analyse information propagation and leadership. Under unperturbed conditions, we do not observe any hierarchical leadership. However, when we turn on the green light and the conditioned fish responds to the green light by crossing the barrier, we observe a hierarchical transfer of information from the conditioned fish to the naive ones. Further, by using spatially-explicit agent-based models, we show that the hierarchical transfer of information occurs because, once the green light is turned on, the conditioned fish reduces it’s interaction strength with all the naive fish until it crosses the barrier, while the naive fish respond to the conditioned fish due to its rapid change in speed and direction.

In summary, my thesis reveals that during the initial attack by predators, the information about the threat propagates via sudden changes in the speed of informed individuals. However, when the predator continuously chases the group, information spreads more strongly through changes in the direction of the individuals at the front. Further, we can use computational models to both explain these patterns, as well as make inferences about the broad nature of interactions among group members while they escape threats. Thus, combining results from all these studies, from highly controlled to natural settings, our study revealed some general principles of collective escape dynamics in group-living organisms.

Animals must consume nutrients in optimal amounts and ratios to maximize their fitness. However, most animals face various constraints to foraging optimally in their natural habitats. While studies conducted in the lab and mesic habitats suggest that animals can sense and meet their transient and long-term needs, we still have little understanding of the nutritional ecology of vertebrates in extreme environments. In this thesis, I attempt to fill this gap by examining the nutritional ecology of the desert-dwelling Indian spiny-tailed lizards Saara hardwickii under various ecological contexts.
In the first chapter, I adopt a global approach to understand whether variation in life-history traits across lizards can be explained by nutritional intakes. Lab based studies on multiple species suggest a strong link between nutrition and life-history traits. However, the results from my study suggest that these associations generally do not reflect in the relationship between nutrition and life-history at an inter-specific level. Absence of a significant relationship between nutrition and life-history at an evolutionary scale might indicate that nutritional responses are more sensitive to demands imposed at ecological timescales.
In the second chapter, I examine whether lizard diet is sensitive to specific nutritional requirements from key life-history events across seasons. For this, I quantified nutritional responses (nutrient consumption and retention) in Indian spiny-tailed lizards Saara hardwickii across four seasons in the Thar desert of northwest India. The results from this work show that S. hardwickii uses both behavioural diet choice and post-ingestive physiology to match seasonal nutritional needs by differentially consuming and retaining nutrients in an extreme environment.
In addition to the long-term demands of life-history traits, animal nutrition is also sensitive to more transient nutritional needs due to various ecological factors, such as predation risk. Lab based studies show that fear of predators can modulate nutritional responses via the physiological stress response. In the third chapter, I examine whether the risk of predation from a feral predator affects stress physiology, and consequently, nutritional responses in S. hardwickii in their natural habitat. Lizards in high-risk habitat adjust both intake and retention of carbon and nitrogen. The lack of physiological stress and changes in diet composition in this species hints to a significant role of behaviour, not physiology, in mitigating predation risk.
I test this in my final chapter by examining the mechanistic links between antipredator responses and their downstream costs on fitness in S. hardwickii. To this end, I quantified behavioural and physiological antipredator responses in S. hardwickii across habitats varying in predation risk and food resources. Using a structural equation modelling approach, I examine how the costs associated with these antipredator responses can result in varying fitness outcomes in heterogenous environments.
Together, this thesis integrates extensive field observations, lab experiments, modelling approaches and a global synthesis to understand the nutritional underpinnings of behavioural, physiological, and life-history trait variation. Understanding the nutritional ecology of these traits can provide mechanistic insights into species responses to various natural and anthropogenic changes in their environment.

Multiple traits, including antipredator responses, foraging behaviour, development rate and fecundity, contribute towards an organism's fitness. These diverse traits interact through the shared resources allocated to maximise fitness. Ecological conditions can affect these interactions by driving increased investment in a particular trait at the cost of other traits (inter-trait trade-off). How are these interactions affected when an individual goes through different development stages, which serve different functional roles? What are the consequences for an individual's fitness in such a complex life-cycle?
To understand the trade-offs that operate at multiple levels in a complex life cycle, I investigated the role of early predation risk conditions across the life cycle of the holometabolous insect – Aedes aegypti. Aedes aegypti has four major stages: egg, larva, pupa, and adult. Previous work suggests that ecological conditions experienced by the larval stage affect adult traits. However, we lack knowledge of how early larval conditions affect the pupal stage and the cumulative effects of both stages on adult traits.

To understand multistage, inter-trait trade-offs, I exposed the immature stages to a key selection pressure, predation risk. Leading to our aim of understanding the combined and individual roles of larval and pupal stages in managing trade-offs, I first unravelled the relationship between larval and pupal stages. I adopted behavioural approaches to examine (1) the carryover of larval predation-risk experience on the pupal stage to understand if a pupa independently responds to risk or whether the larval experience influences its response to risk conditions. I discovered that a pupa that has experienced predation risk as a larva modulates its response to predation cues, showing that the larval experience affects pupal traits. This experiment showed that a behaviour or experience with an adaptive value can overcome the barrier of metamorphosis. Since Aedes aegypti larvae and pupae are found in group settings, I also examined (2) the behavioural manifestation of predation experience in a group setting. This allowed me to understand the abilities of the pupal stage in responding to risk conditions under different contexts. I found that experience does not influence the behaviour of an individual pupa if it is in a group. This is probably because being in a group is an antipredator response itself. My first two chapters highlight the need to include the pupal stages in life history studies because of their ability to process different cues while responding to their environment.

After discovering the context-dependent antipredator response of the pupal stage, I examined (3) the multistage trade-offs, driven by early predation risk conditions, between larval-adult, pupal-adult and larval-pupal-adult stages. I performed lab-based controlled experiments where I followed all the life stages under risk and no-risk conditions. On analysing diverse morphological, biochemical and life-history traits of risk-experienced and naive individuals, I demonstrated that the fitness consequences differ for males and females, and it may start from larval-pupal trade-offs and accumulate as the risk persists. I also found that the pupal stage, like the larval stage, can respond to risk conditions both behaviourally and physiologically. However, it is less well-equipped than the larval stage to manage the trade-offs. Fitness consequences are worse when the pupal stage alone experiences risk. Hence, different stages can contribute to trade-offs that lead to various fitness consequences.

My thesis yields novel insights into life history evolution by displaying the ability of individual life stages to manage trade-offs. It highlights the importance of a poorly understood pupal stage, which can respond to different environmental cues, behaviourally and physiologically. It also explains how the abilities of individual stages to manage trade-offs independently and cumulatively can change the consequences for adult fitness.