Abstract:
How forests respond to anthropogenic climate change raises challenging
questions that are both fundamental and urgent. Vulnerability of forest to
changing rainfall patterns and increasing extreme events such as droughts
is clear from wide-spread tree mortality and can have large scale consequences
on forest diversity, services and global climate sysetm. However, underlining
processes such as
how meteorological drought translates into tree mortality, species-specific
vulnerability are unclear.

This thesis begins with addressing some perplexing issues in assessing
forest tree growth response vis-à-vis rainfall gradients, both in space and time.
It then addresses some fundamental questions as to where do trees source water from,
and what is the dynamics of water availability by depth that species actually
respond to
in terms of growth and survival. It employs a novel method to assess species-specific
water uptake in a forest over two decades and evaluates how belowground
“hydrological niches”
operate for these long-lived organisms that are trees; assisting their co-existence,
but
leading to differential fates under extreme drought.

Insects have for millennia presented human society with some of its greatest development challenges by spreading diseases, consuming crops and damaging infrastructure. Despite the massive human and financial toll of invasive insects, cost estimates of their impacts remain sporadic, spatially incomplete and of questionable quality. We compiled the most comprehensive database of economic costs of invasive insects, expressing historical estimates in annual 2014-equivalent US dollars. Taking all reported goods and services estimates, invasive insects cost a minimum of US$70.0 billion year-1 globally, while global health costs directly attributable to invasive insects exceed US$6.9 billion year-1. Total costs rise as the number of estimates increases, although many of the worst costs have already been estimated (especially those related to human health). A lack of dedicated studies, especially for reproducible goods and services estimates, implies gross underestimation of global costs. Global warming as a consequence of climate change, rising human population densities and intensifying international trade will allow the costliest insects to spread into new areas, although substantial savings could be achieved by increasing surveillance, containment and public awareness.

Understanding the processes that influence spatial patterns in species richness and composition is central to ecology. A wide range of mechanisms have been proposed but the struggle to find a universal explanation for these patterns continues. The wet evergreen forests of the Western Ghats provide an ideal setting to test the drivers of large scale variation in species richness. We collected primary data comprising 20,400 occurrences of 450 species of woody plants, and built a biome-wide species database, to examine patterns of richness and composition along the entire latitudinal extent of the Western Ghats. This study uses a macroecological approach with a focus on species geographic range to uncover the mechanisms that shape the diversity and distribution of woody plants in the Western Ghats. We then use spatial, edaphic, topographic and climatic variables to test the relative importance of niche based and dispersal based processes in structuring spatial variation in species composition. Finally, using the primary data collected on species occurrence and range size, we establish for the first time, baseline data on the status and distribution of woody plants and, following the IUCN criteria, carry out
species assessments for 250 species of endemic woody plants of the Western
Ghats.

Acoustic communication in orthopterans and anurans is a suitable model system to study sexual selection because the acoustic signals are generally produced by males to attract females over long distances for mating. Such systems provide an opportunity to explore the two operative mechanisms of sexual selection, male competition and female mate choice. In studies of sexual selection in these systems, the common approach has been to quantify male acoustic signal variation and to measure female preferences for different features of the acoustic signal using playback experiments, generally under laboratory conditions. A lack of ecologically relevant information on signal variation and female mate sampling strategies in wild populations, however, makes it difficult to assess the strength of selection and distinguish between the two mechanisms of sexual selection. Thus, for my thesis, I first quantified variation in male acoustic signals in a wild population of the field cricket species Plebeiogryllus guttiventris, in terms of amount of calling activity across multiple nights and the acoustic features of the advertisement signal within and across nights. I then went on to study female preferences for individual call features and the possible trade-offs when features co-varied. Finally, I explored female sampling strategies using experimental and computational approaches.

Collective behavior is a phenomena present ubiquitously in biological systems. Collectively moving animals show complex patterns and dynamics. The behavior leading to such patterns could confer evolutionary advantage to animals. Therefore, it is important to study how such patterns are formed and what function they provide to an animal. This has been a subject of many theoretical and empirical studies. Theoretical models have shown that a mobile group self-organizes by virtue of simple local interactions among near-neighbors. These models are constructed based on theoretical insights (sometimes intuitive) of mechanistic processes underlying these patterns. However, many of the model assumptions may not hold true in reality. Moreover, the nature of these findings has largely remained qualitative. Therefore, in our work, we wish to derive a mathematical model using empirical data that can provide a quantitative framework for understanding the scales of interaction in a mobile group.
Broadly, this thesis aims to provide a quantitative framework of the mechanistic drivers of collective motion and ecological conditions under which such behavior evolves.
In the first objective, we model a group level property (average orientation) that describes the state of the system. We derive a stochastic ordinary differential equation model by applying a coarse grained approach to real data from fish schools. The model predicts a change in the group level property as a function of group size. Future work involves making a general model applicable over a range of group sizes.
In the second objective, we aim to understand dynamics over smaller spatial scale within the group. Therefore, we will monitor a local level property of the group that varies both across space and time. Using this data we will derive a stochastic partial differential equation that can describe the spatio-temporal evolution of the locally varying property within the group.
In the third objective, we aim to decipher interaction rules between individuals using an evolutionary approach. Our premise is that those set of rules that result in the system showing an expected state, might also be the rules operational in real world systems. Therefore, we will explore different situations leading to the evolution of the system to an expected state. This thesis thus uses multiple approaches to investigate the mechanisms driving collective motion in animals.

The nest of social insects is considered the locus of their social lives. Although several ants and honeybees show site specific task performance; paper wasps usually are devoid of well-defined sites for task performance on their nest. It would be exciting to investigate thus, how and why wasps would organize themselves spatially on their nests in order to fulfill their reproductive and/ or non-reproductive motivations. Each female on the nest of Ropalidia marginata has several options at her disposal including 1. abandoning the parent nest and founding another, 2. joining another foundress, 3. waiting patiently to overthrow an existing queen to take over a fully functional colony or 4. gauging the meek chances of salvaging direct fitness throughout her life and retaining a sterile worker status to rely entirely on indirect fitness. In the light of the variety of strategies employed, we expect great variation in the space use patterns of these females. While this expectation was met, several more engaging questions arose.

Foraging strategies of a predator are shaped by numerous ecological variables. One aspect of foraging strategy focuses on an individual’s space use, which could be driven either by resources or group living. However, not many studies have examined how both resources and group living could together contribute to the space use decisions made by a predator. Moreover, in the group-living context, influence of group sizes on an individual’s space use decisions has rarely been studied. The first objective would be to address these research gaps using the group-living bat species, Megaderma spasma as a model organism.
On a smaller spatial and temporal scale, foraging strategy of a predator could be determined by the distribution and detectability of its prey resources. Previous studies have shown that predators are attracted towards prey aggregates due to increased detectability but their capture success in aggregates might reduce due to the confusion effect. Most studies have examined such predator behaviour in the visual and not in the auditory context. My second objective would be to address this research gap using the bat species, Megaderma spasma as a model organism since they can use both echolocation and prey-generated sounds to capture their prey.

Both intraspecific and heterospecific animal groups are common in nature. Heterospecific animal groups allow individuals to be similar to group members so as to avail the benefits of group living but be dissimilar enough to avoid competition. Mixed-species flocks of birds are one of the most common heterospecific associations in different regions of the world. My aim is to determine how mixed-species flocks assemble and how interactions within these affect participation of flock members. Although similar species tend to associate more with each other in flocks in general, large flocks are often composed of species that are very different from each other. Moreover, some species in mixed-species flocks are important for benefit provision and maintenance of the flock – known as nuclear species. Intraspecifically gregarious species are very often nuclear species in flocks and are also known to be the main benefit providers in flocks. Some other species, although attractive to flock participants, may impose costs on flock participatnts by stealing food found by them (eg. the greater racket-tailed drongo *Dicrurus paradiseus*). We aim to study each of these functional types to understand what traits make them attractive to other species and what factors influence their presence in flocks.
My specific objectives are: 1) To understand the process of formation of mixed-species flocks by examining the changes in flock composition at different stages in flock formation. 2) To understand what traits of intraspecifically gregarious species predict their importance in mixed-species bird flocks. 3) By using the greater racket-tailed drongo as a model for species that impose costs on flock participants, I aim to understand what flock features influence the drongo’s behaviour (whether to steal or forage independently) and what influences the participation of species which are common targets of the drongo in mixed-species flocks.
My study site is Anshi National Park situated in the Uttara Kannada district of Karnataka. I will use a combination of primary and secondary data to address the different objectives in this study.

Ecosystem resilience is defined as the ability of the system to remain
unchanged or regain its prior state after subjected to perturbations. In
this study, we have considered two kinds of perturbations namely; climate
factors and above-ground trophic interactions. As plants form a bridge
between above-ground and below-ground trophic interactions, plants are
considered as an assay to evaluate the status of an ecosystem. In the
current scenario of global warming, the temperature and precipitation
patterns have shown increasing variation, with a shift in mean global
temperature and precipitation patterns. Researchers have documented
increase in temperature and changes in precipitation patterns in
Trans-Himalayan region. Thus Trans-Himalaya is a model ecosystem to
examine vegetation-climate relationships. We hypothesize changes in
phenology considering plant-soil interactions, with the background of
on-going climatic changes in the Trans-Himalayan landscape. In this study,
phenology is used to understand the vegetation state. Phenological changes
can be detected by examining time series data on vegetation. Hence remote
sensing data is used to understand large scale vegetation changes due to
climatic conditions in Trans-Himalayan landscape. Our preliminary analysis
shows that the majority of the area of Trans-Himalayas has not changed
from 2002-2015. We address this resilience of the Trans-Himalayan
vegetation to climatic variations through resource co-limitation
hypothesis.
Above-ground trophic interactions like herbivory and carnivory can have
direct (consumption) and indirect (non-consumption) effects on vegetation.
These above-ground trophic interactions determine the chemical composition
and quantity of detritus. The nutrient in the detritus is recycled back to
plants by soil microbes, and this ecosystem process depends on the abiotic
conditions like soil temperature and moisture. Hence it is important to
understand the interaction between climate factors and above-ground
interactions in determining vegetation structure and composition. The
interactions between above-ground organisms and plants are highly complex.
Trophic cascade provides a framework to understand these complex
interactions. We apply the concept of trophic cascade by conducting
herbivore, carnivore exclusion experiments in grassland ecosystem. These
field experimental plots are set-up across a gradient of rainfall to
capture the interactions between above ground interactions and water
availability. Here I present preliminary results of grass biomass
subjected to different scenarios of above ground trophic interactions.

Tropical habitats face a diverse range of threats. Two common and important threats are invasive species and roads. Invasive plants are proposed to be a major threat to biodiversity worldwide, yet not much is known about their impacts on higher trophic levels, such as insects. Roads and other linear intrusions such as power lines and railway tracks are another common aspect of human disturbance in natural landscapes, including tropical forests, and are often linked to the spread of invasive plants. I studied impacts of these two important proximate drivers of habitat disturbance, namely invasive plant species and roads, on habitat use of butterflies in a tropical moist deciduous forest in Western Ghats. Invasive plants and roads are expected to modify micro-habitat structure, resources and other aspects of the local ecology of butterflies and thereby influence how they use space (micro-habitats within the larger habitat). Because systematic ecological information on tropical butterflies is comparatively limited, I adopted a multi-species approach. I examined space use responses of butterflies to a gradient in lantana cover in the forest, and to the presence of road. The abundance of different species of butterflies in different micro-habitats was taken as a measure of habitat use. Data was collected over two seasons and at two spatial scales. The two habitat disturbances were found to influence local habitat use by butterflies. But, interestingly, species appeared to respond differently, with some showing positive, others negative and some no strong association with road edge or lantana gradient. I then examined whether this variation in response could be understood in terms of species-specific functional traits. Correlating the responses of species to a habitat disturbance with functional traits may provide a way of arriving at general patterns and increasing the ability of studies to predict responses. Species with similar trait values are expected to respond similarly to a habitat change driver. I measured morphological traits in 254 butterfly species from India and classified them according to their micro-habitat preferences (based on expert opinion). I first examined relationships between morphological traits, ecology and evolutionary relatedness. I then examined patterns of correlation between these traits and responses to the two habitat disturbances and found that certain traits can help predict responses. Overall, my study suggests that butterfly space use is influenced by roads and lantana but the response varies across species. These changes in habitat use might have further population or community level consequences that need to be examined.