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.

An important goal of ecology is to predict how natural populations respond to perturbations. Natural populations are nonlinear and exhibit substantial variability. In this talk, I will present a theoretical framework showing how transient responses to one-time perturbations accumulate over time, providing a unified framework for pulse-press perturbations. I will draw conceptual links across systems, from traditional farming landscapes in the Indian Himalaya to natural populations of Trinidadian guppies. Together, these examples illustrate how stochasticity and disturbance structure shape resilience, predictability, and vulnerability across ecological and socio-ecological systems.

Foraging is essential for animals, providing energy for all fitness-related activities. While foraging decisions are often viewed as maximizing intake and minimizing costs, this food-centric view overlooks the role of specific nutrients. In the wild, animals face various environmental challenges that trigger physiological responses, such as glucocorticoid-driven metabolic shifts altering nutritional demands and should therefore directly influence dietary choices. Hence, foraging decisions should be readily explicable at the nutrient levels. In my thesis, I examined how environmental risks, such as resource uncertainty, seasonal changes, and predation risk affects foraging behaviour and nutritional intakes in the tropical lizard, Psammophilus dorsalis, highlighting strategies employed to meet changing nutritional needs.
Reptiles exhibit physiological adaptations for torpor, helping them combat energetic shortages in the wild. Hence, I first tested whether tropical lizards adjust foraging choices in response to resource uncertainty risk by manipulating their starvation levels. I found that satiated lizards avoided risk while starved lizards took greater risks, providing novel evidence of risk-sensitive foraging in a tropical reptile. I then explored how seasonal variation in glucocorticoids is linked to life-history stages of lizards and affect their dietary nutritional intakes and excretion in the wild. I found that, despite seasonal variation in stress-induced glucocorticoids, lizards maintained a consistent carbon:nitrogen intake ratio. However, glucocorticoids negatively correlated with faecal compositions, suggesting post-ingestive nutritional retention as a possible strategy to meet physiological demands.
Expanding on the findings from my previous chapters, I explored post-ingestive elemental retention in response to physiological stress as an adaptive strategy to meet energetic demands during challenging states. In a lab experiment, I manipulated stress levels and measured carbon and nitrogen retention. Although lizards from all treatments retained similar amounts, potentially due to the masking effects of captivity itself, my study highlights the need to study compensatory strategies that animals employ to achieve their nutrient goals. In my final chapter, I explored how predation risk affects prey dietary choices by testing two hypothesis – the food safety trade-off and nutritional optimization. By manipulating ‘what to eat’ and ‘where to eat’, I studied dietary choices and measured macronutrient intakes by lizards. Results revealed novel support for both hypotheses in governing dietary choices of lizards when faced with predation risk, offering new insights into how fear shapes nutritional decisions of prey.
Overall, my thesis shows how animals integrate environmental cues with physiological needs to guide foraging decisions and optimize nutrient intakes under diverse ecological challenges.

This session will explore the diverse career paths available to science graduates, including academia, industry, entrepreneurship, and public policy. Drawing on my own journey from PhD research at IISc to roles in industry and at the Indian Institute for Human Settlements, and my colleagues, I will share practical insights on navigating career transitions, spotting opportunities, and developing skills for impact-driven work. The talk will also highlight strategies and support systems that can help students make informed career decisions, followed by an interactive discussion to address individual questions and aspirations.

Migration is a behavioural strategy that species use to deal with seasonal variation in climate and resources. A common form of migration is elevational migration, which is a short-distance movement undertaken by mountain birds, typically between high-elevation breeding grounds and low-elevation non-breeding grounds. Although common in mountain birds, little is known about the potential drivers of elevational migration. By studying Himalayan birds, my thesis aims to understand how and why birds migrate elevationally and how resource availability and dietary breadth can potentially explain elevational migration in birds.
In the first chapter, I use a large citizen science dataset (from eBird) to quantify the summer and winter elevational ranges of 377 Himalayan bird species and describe five patterns of elevational migration. I then describe how diet, habitat, territoriality, and body mass might best explain these patterns.
In the second chapter, I examine how arthropod prey availability for birds varies seasonally along the Himalayan elevation gradient. Aerial (eaten by salliers) and terrestrial arthropods (eaten by terrestrial gleaners) decline in abundance with increasing elevation in the winter but increase with elevation in the summer. Whereas the abundance of foliage arthropods (eaten by foliage gleaners) declines with elevation in both seasons. The abundance of avian foraging guilds and their specialised arthropod prey corresponded closely. The relative abundance of sallying and terrestrial gleaning insectivores also increases with elevation in summer and declines in winter; seasonal movements of these species therefore correlate with fluctuations in prey abundance. In contrast, foliage-gleaning birds are more likely to be residents, showing little change in abundance across seasons and elevations. These results point towards potential relationships between food availability and elevational migration in different kinds of insectivores.
Given patterns in arthropod availability with elevation and season, in the third chapter, I examine whether dietary breadth can explain why some high elevation breeding birds migrate to lower elevations in winter (where arthropod abundances do not fluctuate greatly) while others overwinter at high elevations despite the apparent lack of arthropod resources. Using a combination of faecal DNA metabarcoding and stable isotope analysis, I show that high elevation residents have a lower trophic position in the winter possibly due to a decline in the consumption of arthropods and the supplementation of their diets with fruit and nectar. Elevation migrants on the other hand have a similar trophic position across seasons by maintaining a largely consistent arthropod diet as they migrate elevationally. Whereas these data cannot directly test for food limitation as a causal mechanism, the observed dietary consistency in migrants, contrasted with the shifts seen in residents, is consistent with the hypothesis that seasonal fluctuations in food availability may be an important predictor of elevational movement in these species.
In summary, this thesis uses a combination of citizen science datasets, field- and lab-based methods to describe migratory patterns and processes at multiple scales, ranging from an entire mountain range to a single elevational gradient in the eastern Himalayas.