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.

acroevolution provides a lens to investigate how species originate, adapt, diversify, respond to environmental change, and go extinct over deep time. However, many of the processes that generate large-scale biodiversity patterns ultimately operate through population-level demographic and genetic dynamics. This doctoral thesis leverages tarantulas (family Theraphosidae)—one of the most iconic and globally distributed groups of spiders, as a model system to integrate macroevolutionary, macroecological and population genetic perspectives, thereby linking evolutionary processes across temporal and biological scales.
The first chapter reconstructs the complex biogeographic history of tarantulas, addressing the paradox of decoupled centres of origin and centres of diversity. Using fossil-calibrated phylogenies and model-based ancestral range reconstructions, it reveals how plate tectonics, and asymmetric dispersal shaped their global distribution, challenging classical expectations of diversification centered around regions of origin.
The second chapter examines the drivers of asymmetric species richness among tarantula subfamilies. By disentangling the effects of evolutionary time and trait-mediated diversification, it demonstrates that clade age is the primary determinant of species richness, while defensive innovations such as urticating hairs elevate net diversification rate. This chapter presents an empirical support for “key innovations” correlating with higher diversification.
The third chapter explores the interplay between morphology and ecology, focusing on patterns of miniaturization. It links repeated transitions to non-burrowing terrestrial microhabitats with reduced body size and altered limb proportions, illustrating how ecological opportunity can disrupt long-term stabilizing selection and generate novel phenotypes.
The fourth chapter investigates how recent climatic change has shaped genetic diversity and demographic history across latitudes in tarantulas. By integrating mitochondrial genetic data with ecological niche models projected onto past climatic conditions, it reveals latitudinal variation in demographic responses since the Last Glacial Maximum, connecting macroecological patterns with population-level processes.
The final chapter extends this framework using whole genome sequencing of a Western Ghat endemic tarantula species to show that long-term climatic instability can generate fine-scale genetic structure even in the absence of physical barriers. By linking paleoclimate dynamics to genomic diversity and demographic history, this chapter demonstrates how past habitat dynamics leave enduring signatures at the genomic scale.
Together, these chapters integrate deep-time evolutionary history with contemporary genetic processes, highlighting how geography, traits, ecological transitions, and climate interact across scales to shape biodiversity.

Our ability to collect large amounts of data is improving and so is the urgency to answer ecological questions in the face of global change. As ecologists, we can embrace the inherent complexity and noise in ecological data and leverage statistical tools, often used in other fields, to answer these urgent ecological questions. The overarching theme of this talk will be how to use statistical tools such as time series analysis, hierarchical models, simulation studies, and likelihood profiles. I will use my work on Pacific salmon, that are ecologically and culturally important in North America, as examples of these statistical tools and talk about the lessons I learnt while trying to answer:
1) Do Pacific salmon use social information while migrating and how do hatchery salmon releases in Washington affect the timing of migration of wild salmon?
2) What is the impact of logging on Pacific salmon populations on the West Coast of Canada?

Predators are key drivers of ecosystem function. Animals must continuously assess the risk of predation and adopt strategies to minimise danger by modifying behavioural and functional traits such as habitat use, foraging time, and prey selection. Humans, however, represent a unique class of predators and exert disproportionate lethal pressure across ecosystems, while their non-lethal activities such as recreation or tourism further alter animal behaviour through disturbance and perceived risk. My thesis investigates how direct and indirect human interactions shape animal behaviour and, by extension, ecosystem processes.
In Chapter 1, I conducted a systematic review and meta-analysis synthesising global evidence of behavioural responses of wild animals to both lethal and non-lethal human activities. Lethal activities such as hunting and fishing elicit strong and consistent anti-predator responses from wild animals, including heightened vigilance and reduced foraging. Non-lethal interactions such as tourism and recreation produce similar but weaker effects while passive activities such as roads produce more variable behavioural effects. These findings suggest that the magnitude and direction of behavioural responses depend on the type, intensity, and context of human activity, though significant geographic and taxonomic gaps remain.
In Chapter 2, I developed an agent-based model to explore the population-level consequences of humans as lethal versus non-lethal “superpredators” within a multi-trophic system. The model incorporates different types of predator and prey agents that interact through both consumptive and non-consumptive pathways. I compared scenarios involving human-mediated lethality (targeting mesopredators, prey, or both) against non–lethal interactions. Results show that lethal interactions profoundly alter population dynamics, increasing coexistence probabilities and reducing extinction risk, whereas non-lethal interactions alone exert minimal long-term influence. This theoretical framework highlights that the consumptive component of human predation drives ecological restructuring to a far greater extent than fear of humans alone.
In Chapter 3, I investigated the indirect effects of human activity through selective predator removal by fishing. I compared predator assemblages and prey behaviour across protected and unprotected coral reefs in the South Andaman Islands. Predator abundance, coral cover, and structural complexity were significantly higher within marine protected areas (MPAs). Correspondingly, prey fish in MPAs displayed increased vigilance and modified foraging consistent with a foraging–safety trade-off, whereas individuals in fished reefs exhibited homogenised behavioural patterns indicative of reduced predation pressure.
In Chapter 4, I tested for erosion of anti-predator responses through an in-situ behavioural experiment employing 3D-printed decoys of predatory fish. Prey fish in protected reefs responded strongly to predator models by increasing vigilance and foraging rates, while those in unprotected reefs showed limited responses. These results provide direct evidence that sustained predator removal may in turn alter perceived predation risk and weaken anti-predator behaviour among prey individuals.
Collectively, my thesis integrates global synthesis, theoretical modelling, and empirical field experiments to demonstrate that human predation fundamentally reshapes animal behaviour and ecosystem function. Lethal human activities generate potent landscapes of fear, while chronic predator removal leads to behavioural homogenisation. Humans as superpredators thus alter ecosystem processes both directly and indirectly. However, the overall impacts of human activities depend strongly on the intensity and nature of human pressure, local ecological context, and management regimes. Understanding these context-dependent outcomes is therefore essential to balance conservation goals with sustainable human use of natural ecosystems.

Circadian rhythms in physiology and behaviour have near 24h periodicities that must adjust to the exact 24h geophysical cycles on earth to ensure adaptive daily timing. Such adjustment is called entrainment. One major mode of entrainment is via the continuous modulation of circadian period by the prolonged presence of light. Although Drosophila melanogaster is a prominent insect model of chronobiology, there is little evidence for such continuous effects of light in the species. In this talk, I will describe my research demonstrating the effects of prolonged light exposure at specific times of the day on the timing of sleep/activity rhythms. Further, I will discuss results that show that certain spectral compositions of light lengthen the circadian period of Drosophila and provide evidence that this is produced by the combined action of multiple photoreceptors which includes the cell-autonomous photoreceptor cryptochrome. Finally, I introduce ramped light cycles as an entrainment paradigm that produces light entrainment that lacks the large light-driven startle responses typically displayed by flies and requires multiple days for entrainment to shifted cycles. These features are reminiscent of entrainment in mammalian models systems and make possible new experimental approaches to understanding the comparative mechanisms underlying timing of sleep rhythms in the fly.

Prof. Athreya will discuss an investigation into the intraspecific diversity in three frog species of a rhacophorid genus along an elevation gradient spanning 400-2400 m in Eaglenest wildlife sanctuary. First, he will describe an inexpensive procedure to sequence tens of thousands of DNA bases using a hybrid of the "Sanger" and "NGS" approaches. This sequence data was used to investigate genetic diversity in the three species and genetic relatedness of their elevational populations.

Migration is a behavioural strategy that species use to track 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. Despite seasonal elevational migration being a dominant life history strategy in montane birds on every continent, little is known about migratory patterns and drivers. The majority of existing research comes from the Neotropics, where a handful of studies have shown that migrants are frugivores or nectarivores tracking peak fruiting and flowering seasons across the elevational gradient. However, outside of this region, like in the Himalaya, most elevational migrants (~70%) are insectivorous. My thesis aims to understand how and why birds migrate in the Himalaya and how resource availability and dietary specialisation can potentially explain elevational migration in Himalayan 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 examine how diet, habitat, territoriality, body mass and wing morphology might best explain these patterns.
In the second chapter, I try to understand how arthropod availability varies seasonally along the Himalayan elevation gradient. Aerial and terrestrial arthropods decline with elevation in the winter but increase with elevation in the summer while foliage arthropods show a similar mid-elevation peak in abundance across seasons. This pattern appears to influence bird migration; salliers and terrestrial gleaning insectivores seem to track prey abundance, migrating to different elevations seasonally. In contrast, foliage-gleaning birds are more likely to be residents.
Given patterns in arthropod availability with elevation and season, in the third chapter I examine whether dietary specialisation can explain why some high elevation breeding birds migrate to lower elevations in winter (where arthropods abundances do not fluctuate) while others overwinter at high elevations despite the lack of arthropod resources. Using a combination of faecal DNA metabarcoding and stable isotope analysis, I show that elevational migrants are likely to be dietary specialists that track arthropod resources, while high-elevation residents are dietary generalists that supplement their winter diet with fruit and nectar, likely because of the scarcity of arthropods in winter.
In summary, using a combination of citizen science datasets and field- and lab-based methods, my thesis attempts to improve our understanding of elevational migration and its ecological mechanism in the Himalaya. Understanding the drivers of elevational migration is a crucial first step in predicting how tropical montane avifauna will fare in an increasingly warm world.

Plant-pollinator interactions have molded the stunning diversity of flower forms in nature. The flowers’ morphology determines their accessibility for foraging pollinators. In some plant species, flower parts fuse to form elaborate structures. Consequently, insects require intricate motor routines to access their nectar and pollen. Learning to handle such ‘complex’ flowers efficiently requires much practice in the short term, but successful foragers often reap high long-term rewards. How may the short-term barriers to exploiting complex flowers be overcome, allowing the evolution and radiation of such flowers? Despite much research on pollinator responses to specific floral features, an integrative view of flower accessibility to insects is still missing. Laboratory experiments with real and artificial flowers suggest that bumblebees innately prefer morphologically complex shapes over simple ones and that success with one complex morphology increases their tendency to forage on flowers with other complex shapes. A game-theoretic evolutionary model predicts a stable coexistence of simple and complex flowers in plant communities. The expected steady-state frequency of complex flowers is influenced by the flowers’ spatial aggregation and by the pollinators’ flying distances and learning abilities. We are currently testing these predictions using a large database of published pollination networks. In conclusion, our research suggests pathways to the evolution of morphologically complex flowers by considering the behavior and life history of their pollination partners.

In this talk, I will give an overview of recent work by my collaborators and myself looking at the origins, current knowledge, and future of species richness. First, I will describe our work on the origins of species richness patterns, especially those related to differences in species richness among clades (e.g. the dominance of angiosperms in plants and arthropods in animals), over space (e.g. the latitudinal diversity gradient), and among traits (e.g. the preponderance of species with sexual reproduction). Second, I will describe our recent work looking at how our knowledge of biodiversity is changing over time, including rates and patterns of discovery of new species, genera, and families. Third, I will talk about our recent work on the loss of biodiversity, including the rates, patterns, and causes of recent extinctions and the current and future impact of climate change.

Colors in animals can be produced either chemically by (usually diet-acquired, costly) pigments or physically by the constructive interference of light scattered by endogenous, cost-free, photonic nanostructures and sometimes as a combination of both. Fade-proof, saturated structural colors have evolved convergently in diverse animal taxa, including birds, insects and arachnids. However, given that the underlying nanostructures are overwhelmingly diverse in form and function, their characterization has suffered for over a century. I have pioneered the use of synchrotron Small Angle X-ray Scattering (SAXS) as a high throughput technique to structurally and optically characterize integumentary photonic nanostructures from hundreds of species across diverse animal orders in a comparative fashion. This led to the discovery of the first single gyroid crystals in biology within the iridescent green wing scales of certain papilionid and lycaenid butterflies, and recently in the feather barbs of the Blue-winged Leafbirds (likely driven by female preference for saturated hues). But broadly, this wealth of structural knowledge has led to the realization that these diverse photonic nanostructures share a unifying theme – they all appear to be self-assembled within cells by the co-option of fundamental intra-cellular processes: membrane invagination in insect scales and liquid-liquid phase separation in bird feather barb cells. In this talk, I will broadly summarize our current state of knowledge about the structure, function, development and evolution of self-assembled animal structural colors using examples from birds, butterflies, beetles, bees and tarantulas, including in the fossil record.