One of the desirable – and arguably essential – states for a tropical rainforest ecosystem is that it is resilient to perturbations, ensuring it can continue to provide ecosystem services in the face of global change. In this seminar, I will use data from more than a decade of observations on Malaysian tropical rainforests to examine rainforest resilience. I will outline the biodiversity and carbon status of logged forests, present a suite of studies that have quantified aspects of resilience and identified the taxa that are critical to generating resilience, and examine thresholds in logging intensity at which point resilience may be lost. I will end by introducing ongoing work designed to further quantify and understand the origins of resilience in tropical rainforest ecosystems.

Insects represent the most diverse group of animals on Earth and form critical links in terrestrial and freshwater food webs. Alarmingly, recent studies have reported dramatic insect declines in several parts of the world putting insect conservation firmly on the public and policy agenda. Gathering standardized and quantitative data on insects is time-consuming, labor-intensive, and requires large amounts of sustained funding that can rarely be met by conventional conservation-research funds. Technological and computational advances in remote sensing, which provide potential new solutions to this global challenge, will be discussed with a special emphasis on computer vision and radar entomology.

The mutualistic link between plants and pollinators plays a key role in ecosystem functioning. The topology of a native plant-pollinator network can be altered as alien plant species invade. Invasive (plant) species can displace native plants, reducing the number of plant species available for pollinators to visit and potentially affecting the reproductive success of native plants. Invasive plants can thrive in a variety of climates, and so are often difficult to control once they establish. Effective management strategies are necessary to prevent the spread of alien plants to protect native ecosystems.  I aim to compare plant-pollinator in primary forest versus invasive-dominate habitats (IDH), within Eaglenest Wildlife Sanctuary (EWS) in Arunachal Pradesh. In EWS, low-elevation settlements were abandoned over 15 years ago, and the land is now dominated by three main invasive plants - Ageratum conyzoides, Chromolaena odorata, and Micania macrantha. In the first chapter, I will compare the structure of plant-pollinator networks, with respect to their composition, diversity, abundance, and seasonal differences. For chapter 2, I propose to explore various invasive species management practices to lessen the adverse effects of invasive plants on native plants and to restore native vegetation on IDH. For the third chapter, I propose to conduct pollination exclusion experiments to quantitatively estimate pollinator efficiency and to determine plants’ fitness. For my final chapter, I propose to explore the impacts of invasive plants as neighbouring competitors/facilitators to native plants, to attract pollinators. I will compare native floral visitors' frequency and reproductive success of native plants in the forest interior (away from invasives) with forest edges (closer to invasives). The outcomes from this research will help us to better understand the influences of invasive plants on native habitats, and this will enhance our knowledge to restore invasive-dominated landscapes to native forests.

Small isolated populations are a raw material for speciation. Populations that get isolated from the main population are often small and soon begin evolving independently. However, small populations are prone to impacts of drifts and inbreeding which makes them vulnerable to extinction. With whole genome sequences of several endangered populations of tigers and rhinoceros we show that small isolated populations often purge some of their deleterious allele loads. However, whatever deleterious alleles remain in the population, are in high frequency and homozygosity. This might lead the population to extinction. We further observe with simulations and emperical observations that migrations from a different population although increases the deleterious allele load, also lead to decrease in the frequency of deleterious alleles and their homozygosity. Does this indicate that allopatric species also need mild gene flow from other populations?

 Long-term dynamism in forest vegetation composition has significant implications for biodiversity and conservation. In the mid-hills of Kumaon in the Western Himalaya (1500 m -2400 m asl), the expansion of pine into oak-dominated hardwood forest has been of concern, due to its possible impact on biodiversity and livelihoods. Yet this vegetational shift is poorly studied in terms of spatial extent, the underlying drivers or the ecological consequences. We used field-based and remote-sensing methods to quantify oak-to-pine transition over three decades and studied the effect of this shift on forest bird communities in a 1285 sq.km multiple-use forest landscape in Kumaon. Our analysis indicates a gradual replacement of hardwoods with pine over the period of study: specifically, 22% decline in dense (protected) oak, a 29% decline in degraded oak and 74% increase in pine- over their original extents respectively- from 1991 to 2017. We found significant roles for micro-scale spatial variation in habitat, topography and climate in driving the oak-to-pine transition. Spatial analysis of forest bird communities further suggests that the transition of hardwood forest to pine may result in significant defaunation over time. For instance, pine forests support 33-46% lower forest bird species richness than hardwood oaks. Hardwood forest specialists could be especially vulnerable to forest change, showing 93-97% lower abundance in pine forest sites in comparison to dense oak sites. Additional effects of warming and degradation may further intensify species losses at the regional scale, and require further study.

Not yet received.

Sahas will share his research that uses state-of-the-art radio tagging and 50 years of long-term population data to draw insights into the evolution of cooperative breeding behavior in acorn woodpeckers.

Altitudinal migration is the seasonal movement of organisms between higher-elevation breeding grounds and lower-elevation wintering grounds. Despite altitudinal migration being a common phenomenon (for instance, 70% of birds in the Himalayas migrate altitudinally), the abiotic and biotic drivers of altitudinal migration remain poorly understood. This is important because 85% of global terrestrial biodiversity is concentrated in mountains, and these species are vulnerable to the impacts of climate change. I propose to describe avian altitudinal migration in the Himalayas and determine the role of diet and thermal niche tracking in driving these seasonal movements.

The study site for my thesis is Eaglenest Wildlife Sanctuary, Arunachal Pradesh, which is part of the Eastern Himalayan Biodiversity Hotspot and is home to >350 breeding bird species. I first use a large open-source citizen science dataset to describe various altitudinal migration strategies across the Himalayas. I then go on to assess the various eco-morphological and functional traits as predictors of avian altitudinal migration. I then plan to determine whether migratory birds are tracking their thermal niche or dietary resource availability. For various species, I will assess and compare the degree of overlap in temperature and arthropod availability in their breeding and wintering grounds. Finally, I plan to investigate if diet can explain why certain birds migrate while others prefer to stay back in the harsh winter. I will determine bird diets using DNA metabarcoding on bird faecal samples. Given the various limitations of the DNA metabarcoding technique, I plan to use a complementary method to investigate diet – I will use stable isotope ratios of carbon and nitrogen in whole blood to compare the seasonal trophic niches of resident and altitudinal migrants in the eastern Himalayas. Results from this work will thus help improve our understanding of how and why birds migrate altitudinally, and will have implications for the conservation of montane biodiversity in the face of climate change.

A dramatic increase in global mean temperature and rapid thermal fluctuations are predicted to hit the earth in the coming decades. Anthropogenic activities are accelerating the thermal variations and it can have significant impacts on organisms worldwide. Tropical ectotherms are considered to be more vulnerable to climatic changes as they are adapted to relatively stable, aseasonal conditions of the tropics and are dependent on environmental temperature for all aspects of behaviour and physiology. While several studies have investigated the effect of climate warming on the behaviour and physiology of temperate ectotherms, studies on tropical ectotherms are lacking, though they’re predicted to be at high risk from global temperature increases. For my thesis, I propose to study the thermal responses of tropical agamid lizards in India. Furthermore, I propose predictions for organismal responses to future climate warming.

The first chapter looks at the effect of environmental temperature on the body colouration and regional heterothermy of P. dorsalis in a rural-urban context. The UV- visible colouration and body temperature patterns of both sexes will be measured on a range of temperatures (15, 20, 25, 30, 35 and 40 °C). The second chapter investigates the influence of environmental temperature on physiological and motor performances at a community level. The metabolic rate, sprint speed, endurance and bite force of the three species- P. dorsalis, P. blanfordanus and C. versicolor will be measured across the temperature range. In the third chapter, metabolic rate and motor performances of the three species will be used to predict how the species will respond to accelerated climate warming in the coming decades. The fourth chapter focuses on the developmental plasticity of thermal limits. The effect of thermal fluctuations experienced by the P. dorsalis eggs during the time of incubation on the thermal tolerance range of the hatchling will be examined. Overall, the thesis provides insight into the thermal ecology of tropical agamid lizards and the impact of climate change on their fitness.

A general quiz for the department members.