Understanding how species coexist despite competition is an enduring challenge in community ecology, with a rich history of theory, empirical work and controversy. In 2000 AD, Peter Chesson published a seminal paper in which he used Lotka-Volterra models of two-species interactions to derive the conditions for coexistence in terms of the relative strength of intra- vs. interspecific interactions. Modern coexistence theory or MCT, as this is termed, also incorporates the role of temporal and spatial factors on coexistence and offers a unifying theoretical framework to understand the processes that maintain diversity. In the years since, MCT has attracted much attention with key theoretical and empirical advances. It has been extended to multi-species systems and applied to questions of species distributions, invasive species, species persistence with climate change, and habitat fragmentation. MCT integrates previous work on species coexistence and is today a key paradigm in community ecology. In this lecture, we will go over the basic components of MCT, relate it to other theories of species coexistence, link to established frameworks of species interactions, and explore empirical applications and limitations. The goal of the lecture is to provide an overview of modern coexistence theory as a conceptual basis to contextualize questions regarding community assembly. 

We live in a human-dominated Earth. Human activities have broken up many once contiguous terrestrial habitats into smaller fragments—where ecological communities lose diversity. Patterns of diversity loss in forest fragments have been widely documented. Yet, we know surprisingly little about how the mechanisms that maintain diversity fare in fragments. Long-standing theory and growing empirical evidence indicate that in plant communities, pests and pathogens—natural enemies—help maintain diversity via negative feedbacks on host plant populations. The diversifying effects of enemies are especially strong during the early life-stages of seedling establishment and survival, but its imprint can last many generations. Could weaker enemy effects explain reduced plant diversity in forest fragments? In a human-modified forest, I found that enemies such as insects and fungi were less able to maintain diversity of tree seedlings near forest edges compared to interiors. Weaker effects of enemies also changed the functional characteristics of recruiting seedlings. Simulations using this field data show that changes to seedling dynamics can compromise the long-term ability of fragments to maintain diversity. Contrary to common expectation, canopy openness, a correlate of light availability, did not correlate with spatial variation in diversity of species or traits. With nearly 20% of the world’s forests being within 100 m of an edge, loss of cryptic biotic interactions may pose a widespread threat to plant diversity. In my future work, I will delve deeper into the mechanisms that link enemy-mediated feedbacks to species performance and diversity in forest edge vs. interior. Furthermore, I will expand on my ongoing work that examines how a changing climate (drought) will interact with edge effects to shape performance of tree species, and hence their fitness, in human-modified forests. Mechanistic insights that combine ecological theory with observation and experiment can help predict the trajectories of human-modified ecosystems in a fast-changing world.

Urban lakes in India suffer from different types of problems. Lakes which are filled with sewage due to heavy inflows of wastewater through storm-water drains, lakes which remain dry due to a combination of diversion channels (bypass drains) and blocked storm-water drains and lakes which overflow and cause flooding, because they are already filled with partially treated sewage. Paradoxically, many cities in India have engaged citizen communities. Why then despite the considerable investment of money and citizen engagement do problems persist? The answer is quite complex. It has in equal parts to do with what we understand (and don't) about urban lakes, how government agencies work (and don't), and how citizens engage (and don't). In this talk, I will offer some lessons from having engaged with lakes for the last few years and a roadmap for change.

Plants and insects have co-evolved since the appearance of phytophagous insects and their interactions can be beneficial or detrimental. Galls are pathologically developed tissues or organs on the plant that arise mostly by hypertrophy and hyperplasia usually under the influence of parasitic organisms. Thus, leaf galls are the result of specific interaction of the leaves with the host and the galling organism and are an excellent example of parasitism of insects on plants.  

Ficus benjamina, known as the weeping fig, is grown worldwide for aesthetic purposes in interior and outdoor landscapes. The thrips species Gynaikothrips uzeli is a major pest and exclusively associated with the weeping fig (Ficus benjamina) across its cultivated spaces worldwide. 

In my research, I will examine the cost incurred by F. benjamina upon leaf gall initiation by G. uzeli with reference to leaf area damaged, choice of infesting cells during gall initiation, and its impact on the ontogeny of both the leaf and the leaf gall. I will also investigate the host-selection behaviour of G. uzeli, inquilines present in the leaf gall microcosm, and natural enemies present within the leaf gall community. I will examine the distribution of laticifers (constitutive resistance) in galled and ungalled leaves, a little explored area in insect–gall interactions, and examine the effect of laticifers on leaf gall initiation. 

Mutualisms are omnipresent across all life-forms; from prokaryotes to higher organisms. In a mutualistic interaction, one or both the partners provide services to the other, in exchange for which they receive rewards. Lately, mutualisms have also been considered as consumer–resource interactions, where, a host receives some service from its partner and provide resources in exchange as rewards. Resources, hence can be regarded as a currency in the operation of mutualism and are therefore central to the working of most mutualisms. However, resource allocation within a mutualism has rarely been studied. 

The Fig–Fig wasp interaction provides us with an excellent model system to study resource allocation in a mutualism. It is a typical example of an obligate brood-site pollination mutualism, wherein the pollinator wasps provide figs with pollination services in exchange for which the developing pollinator offspring receive nutrition.  

I aim to look at the patterns and strategies of resource allocation in the mutualism between figs and fig wasps. First, I will look into the patterns of resource allocation across the developmental phases of figs, and to the different occupants of the figs. I will then look at how different factors like position of the syconium and different occupants within the fig, that also include parasites, can influence resource allocation. I will also look into another potential, but completely unexplored factor, i.e. photosynthesis rate of the figs, which can also influence the amount of nutrition a fig can acquire.  

https://teams.microsoft.com/l/team/19%3abfb48615d561409380167f6365cae6e5...

Genetic variability in an organism allows us to assess its ability to respond to changing environmental conditions or disease epidemics. Hence, preserving this genetic diversity is an essential aspect of conservation biology. Phylogenetic tools are often used to study this variation within and between groups and build strategies for management of Evolutionarily Significant Units. Population genetics, in addition, provides us information on the gene flow between populations, signatures of inbreeding and other aspects of their genetic condition. Studies in the past decade have brought up yet another angle of looking at biodiversity, in the form of the microbiome. Since microorganisms have a faster turnover than eukaryotic genes, the microbial diversity could potentially show signatures of change at much smaller time frames. For my PhD, I studied the variation in Antilope cervicapra or blackbuck across its range, both in terms of genetics of the animal and its gut microbial diversity.

The first chapter tries to clarify the phylogenetic position of Antilope cervicapra with respect to other antelope lineages. Both concatenated and coalescent based methods were used, on data from 12 nuclear markers, to resolve the phylogenetic relationships between multiple species of antelope belonging to the four genera, Gazella, Nanger, Eudorcas and Antilope. I find that both coalescent and concatenated based phylogenetic analyses consistently place A. cervicapra as sister to Gazella dorcas, thus making Gazella a paraphyletic group. Divergence dating using fossil calibrations and biogeographic analyses, show that the Antilope lineage diverged around ~2 mya and dispersed from the Saharo-Arabian realm into India, post the expansion of grasslands. Unlike the gazelle found in India, A. cervicapra was better suited to grasslands and semi-arid conditions and did not extend their range beyond the Indian subcontinent.

The second chapter looks at phylogeography and population genetics of A. cervicapra across its geographic range. Using both mitochondrial and microsatellite genetic information, I find that different markers shed light on different aspect of their evolutionary history. The blackbucks seem capable of travelling much longer distances than expected, although habitat fragmentation in recent times have probably restricted their movement, as seen by the lack of shared haplotypes between locations. Both microsatellite (nuclear) and mitochondrial data indicate that the population from the Eastern part of India is genetically distinct and the species as a whole shows signatures of having undergone a bottleneck and recent genetic expansion. Further the microsatellites indicate the presence of 3 genetic clusters in this species, pertaining to the Northern, Southern and Eastern regions of India. The study also indicates the most likely demographic scenario where an ancestral population separated into two groups that gave rise to the North and South clusters and the East population was derived from the South at a later time period.

In the third chapter, I compare the gut-microbiome of blackbucks from ten different locations, to understand what drives their alpha and beta diversity. Metagenome information from the V3-V4 region of 16S rRNA were used to delineate different taxonomic orders of gut bacterial communities, to determine whether host genetics or the host environment has a stronger influence in structuring gut microbial community. Results show that although distance to human settlement and precipitation affect species richness of gut microbes, the correlations between nucleotide diversity and Shannon and Simpson alpha diversities were significant. Further the pairwise dissimilarity between the gut microbial composition increases with both increasing geographical distance as well as pairwise microsatellite distance. This study sets a baseline for further research on how animal gut microbiomes associate with host genes and potentially influence fitness.

Largely, my thesis looks at diversity in an endemic ungulate from different angles and also tries to elucidate its taxonomic position among Antilopinae.

Phoresy is the dispersal of small organisms on larger ones to move out of an unfavourable habitat. Although these interactions are transient, phoretic organisms can form tight associations with mutualistic systems if they are dependent on both mutualistic partners, one serving as a vehicle with the other providing a substratum for development. These linked tripartite interactions may further lead to increase in host specificity in phoretic organisms. Therefore, to understand the effects of phoretic interactions on the entire mutualistic system and factors that can help the phoretic organisms to gain host-specificity, I investigated the phoretic nematode community associated with the fig–fig wasp brood-site pollination mutualism. I chose Ficus racemosa, a wide-spread and a common tropical keystone fig species, which shows a mutualistic relationship with a unique pollinating fig wasp species and harbours a host-specific phoretic nematode community. Ficus racemosa has an Indo-Australian distribution and is known to be associated with several nematode species throughout its range. A few nematode species have also been reported from India, but they lacked comprehensive detail on their morphology and also molecular characterization, thus making it difficult to carry out further species-specific studies. Therefore, we firstly characterised the phoretic nematode community associated with the Ficus racemosa system in south India, using both morphological and molecular approaches and found a mixture of plant-parasitic, animal-parasitic and possibly omnivorous taxa. We found that the nematode community consisted of three new nematode species out of which one of the species showed phenotypic plasticity. The phylogenetic analysis based upon near-full-length small subunit (SSU) and D2–D3 expansion segments of large subunit (LSU) rRNA genes showed that the species have close affinities with sister nematode species reported from Ficus racemosa from other geographical locations outside India. To determine the effects of phoretic nematodes on the entire mutualism, we performed various bioassays and determined the fitness effects of phoretic organisms on both mutualistic partners, i.e. figs and pollinator fig wasps. We found that not only did the nematodes negatively affect the survival, flight ability, offspring number and predation risk faced by their fig wasp vehicles, but they also negatively impacted fruit seed number and size in a density-dependent manner. Furthermore, wasps arriving at their destinations carried lower phoretic nematode load compared to dispersing wasps suggesting that there is selection on hitchhiker numbers within a vehicle during the dispersal process. Using choice experiments with single nematodes and employing conspecific as well as heterospecific co-travellers, we showed that these phoretic organisms were able to distinguish between vehicles with different hitchhiker density and physiological states. Plant-parasitic nematodes preferred vehicles devoid of conspecifics and likely hitchhiked in pairs, while animal-parasitic nematodes preferred vehicles with conspecifics within a certain density range. Both types of nematodes were insensitive to the presence of heterospecific co-travellers. The nematodes used volatiles and carbon dioxide for this intra-specific vehicular discrimination. We also characterized the volatiles emitted by the pollinator wasps and identified the possible set of compounds that might elicit an attraction response in the nematodes towards their vehicles. Overall, we show that phoretic nematodes have a density-dependent negative effect on the mutualism between figs and their pollinating fig wasps and that they use parameters such as vehicle physiology and existing traveller load within the vehicle to select a vehicle for their dispersal.

Collective movement is a fundamental process affecting the survival and reproductive success of group-living animals. Many of the hypothesized benefits of grouping such as predation evasion and foraging efficiency require the individuals in a group to move in a coordinated way. While moving in groups, animals are not only responding to the environment but also interacting with each other. These interactions give rise to emergent collective movement and behavioral patterns. A novel aspect of emergent behavior is that a group can exhibit properties that no individual displays on its own.

Most studies on emergent properties of collective behavior are conducted in controlled conditions. However, in natural settings, habitat is heterogeneous in terms of resource distribution, availability of hiding places and substrate for movement. Empirical studies have rarely investigated such fine-scale interactions (e.g. alignment, attraction among individuals) in their natural habitat. One reason for the dearth of such studies is the difficulty of data collection. Recent advances in techniques of aerial imagery allow us to observe and record such fine-scale data. For my PhD project, I studied collective behavior of blackbuck herds in their natural habitat. More specifically, I investigated the collective response of blackbuck herds during predation-like events. By analyzing multiple interactions among group members simultaneously, I aimed to understand the role of social interactions in shaping the collective response of blackbuck herds when faced with predation-like threats.

First, we overcome the difficulty of observing fine-scale interactions in animal groups (in their natural habitat) by using UAVs. We recorded blackbuck herding behavior at high spatio-temporal resolutions (30 frames per second). Using this technique we were able to record blackbuck herd’s collective escape behavior in the context of predation using controlled-simulated threats.

Tracking animals in the videos recorded in natural habitat is extremely difficult due to varying background and light conditions and clutter in the background. Relatively basic image processing methods and default tools don’t perform satisfactorily in such scenario.

Hence, we developed a machine learning method and GUI tool to extract the spatial locations and movement trajectories of all the individuals in a group from the videos recorded in natural field conditions.

Once we were able to obtain the movement trajectories from the videos, I then analysed these trajectories and interactions between individuals to explore - how the information about predatory risk spreads through a group in natural conditions. Broadly, our results suggest that transient leader-follower relationships emerge in these groups while performing high-speed coordinated movement. Also, males and females respond differently to the threat scenario: adult females are more likely to be the response initiators whereas adult breeding males are more likely to influence the group movement during the escape response. Our results indicate that in fission-fusion groups associations are likely to last for short time scales and spatial positions of the individuals only affect their response-time (vigilance behavior) but not their influence on the group.