Microbial decomposers are the unseen majority that determine ecosystem processes, and perform biogeochemical functions which translate into essential services, and regulate global climate. In grazing ecosystems that represent over 40% of the terrestrial realm, soil microbes respond to aboveground interactions between plants and herbivores. In this thesis, I analyse different aspects of soil microbial functions in the high-altitude grazing ecosystem of the Trans-Himalaya, and quantify the implications for biogeochemical cycles and sustainability under climate change.

In the first chapter, I explore how large mammalian herbivores alter foraging strategies of soil microbial decomposers. Soil microbes forage by releasing extracellular enzymes (EE) into their environment to break down organic matter. Long-term herbivore-exclusion experiment revealed that herbivores improve quality of biomass-input to soil. This reduced microbial deployment of generic-depolymerizing EE relative to specialised-EE that release assimilable end-products. I validated the underlying role of quality of detrital input to soil by a reciprocal transplant experiment using laboratory incubations. I synthesised 860 soil-EE profiles from across the world to establish that this response to quality of detrital-input to is soil is both widespread and general. These observations provide evidence of a continuum between herbivores and decomposers that is relevant to global nutrient cycles and can also explain how microbes control soil-C sequestration in grazing ecosystems. In other words, soil microbial decomposers forage more efficiently in the presence of large mammalian herbivores.

In the second chapter, I explored how microbes alter the stability of the soil-carbon pool when humans replace wild-herbivores with livestock in grazing ecosystems. I found microbial-respiration was lower in soils under grazing by wild-herbivores than under livestock, with corresponding differences in fungal:bacterial ratio, microbial-biomass, and metabolic-quotient. Direction and magnitude of these inter-related microbial responses were driven by reduced soil microbial carbon use efficiency (CUE) under livestock. Since CUE is a fundamental microbial trait, wild-herbivores sequestered twice the soil-C than livestock despite comparable ecological settings. This implies that investments in wildlife conservation in multiple-use landscapes can help decarbonise the atmosphere to mitigate some of the negative environmental impacts of livestock-production.

In the third chapter, I addressed the relationship between functional diversity of decomposer functions in soil and the stability of ecosystem processes under land-use change. Unlike producers and consumers, decomposer functions are common between natural and agroecosystems. I take advantage of alternative land-use in the Trans-Himalaya where the native reference state with wild plants and wild herbivores is repurposed into two distinct agroecosystems—to grow livestock, or crops. I find that the extent of human-alteration of the reference state is reflected in the degree of homogenization of decomposer functions. Relative to the native state, magnitude of individual functions was often higher under crops but remained unchanged under livestock, such that land-use had no net effect on multifunctionality. However, univariate and multivariate measures of functional heterogeneity were lower under crops but were unaffected under livestock. Stability of decomposer biomass, measured as invariance through time, was comparable across land-use types. These results show that previous knowledge on diversity-relationships in producers and consumers are not easily extended to decomposers, and there are fundamental differences. Although agroecosystems in the Trans-Himalaya show remarkably high degree of ecological resistance, homogenization of their decomposer functions can make them susceptible to environmental fluctuations, such as those foreseen by future climate projections.

In summary, this thesis explains how soil microbes contribute to the functioning of grazing ecosystems.

In mixed-species bird flocks (flocks hereafter), participants vary in their degree of similarity with each other. Flock participants can gain group size (supplementary) benefits by choosing similar flock partners, or complementary benefits from dissimilar partners. The nature of benefits, therefore varies based on overall similarity in the flock. Earlier research has shown that flocks world-over tend to be phenotypically clumped and that intraspecifically gregarious species are important benefit providers. In this thesis, I examine changing patterns of associations and species importance with respect to group size, in mixed-species bird flocks.

In my first chapter, I examine the relationship between flock size and phenotypic clumping. I find that small flocks are more phenotypically clumped than expected by chance but as flocks become larger, the phenotypic variation does not differ from what’s expected by chance. I also find that, at a global scale, flocks in regions with lower average flock size are more phenotypically clumped. In the second chapter, I examine the importance of intra-specifically gregarious species. I find that flocks with less than or equal to two gregarious species have lower richness of non-gregarious species than expected by chance. I also study traits of intra-specifically gregarious species that are linked to functional importance and find that individual behavioural traits are not directly correlated to species importance. In the third chapter, I construct emergent networks of flock participant species based on flock co-occurrence. I find that a few species are structurally important in flocks of all sizes, while a few are important only in networks of large flocks. I also find that flock components that are unconnected in smaller flock networks, merge in large flock networks. Overall, I find that species similarity and presence of important species is crucial in smaller flocks whereas large flocks are heterogenous groups that resemble random phenotypic assemblages of flocking birds.

TBD

Here I review the connections between animal movement and seed dispersal. Modelling seed dispersal by animals seems straightforward, we need a way to keep track of the position on the animal trough time and a clock for how long seeds travel with the animal. Simple models show how changing parameter combinations can result in very different seed dispersal kernels, including fat-tailed ones. When movement is more realistic, in the sense that is tied to the spatial distribution of resources, both seed consumption and dispersal kernels vary according to the neighborhoods of focal plants. Plants with many fruiting neighbors have high fruit removal rates but shorter dispersal distances. We empirically tested these theoretical predictions with a mistletoe species exclusively dispersed by an arboreal marsupial in Northern Patagonia. However, this is an unusual system because in general, plant communities interact with many species of frugivores. Recent empirical work shows that some frugivores may favor the consumption of rare fruits with important consequences for plant diversity maintenance. The mechanisms behind such patterns are still speculative but they could be related to frugivore physiology. Progress in hierarchical data analysis tools allows us to fit joint species frugivory models where species-level movement and foraging parameters are modeled as a function of species traits and their phylogenetic relationships. We have parameterized such models with bird movement and foraging data from tropical and temperate communities. In our model, plant-frugivore interactions emerge from frugivores’ behavior in a spatially explicit setting. This allows predicting how interactions rearrange after extinctions, and hence, to better quantify the vulnerability of plant species to partner loss. We can also have good estimates of frugivores’ role in seed dispersal. Overall, there has been great progress in data collection and modelling but we still need a better understanding of seed retention times, and of how bird physiology influences fruit choice. Further improvements in our ability to understand and predict seed dispersal by animals would probably also require considering within and among species agnostic behaviors

TBD

TBD

Natural history is the cornerstone of ecology from time immemorial. Anyone who been intrigued by some naturally occurring phenomena would agree that observing ecological systems or organisms in their natural settings is both incredibly challenging and, equally rewarding. Surely, there is also a subtle something about being out in the wilderness which drives a naturalist. Is it the satisfaction of seeing momentary truths? Is it the thrill in acquiring an intimate knowledge of the mysterious ways in which nature works? Is it the tranquility of the wild, away from the chaos and madness of our city life? Is it a quest for adventure? Or, an overzealous enthusiasm bordering crazy? I will take this opportunity with you all to look at a part of my life when I got on to the roof of the planet—the forest canopy. We shall briefly examine some of the aforementioned aspects and by doing so, I hope to shed light on how natural history has continued to shape my career as a biologist; assuage any feelings of “having taken the wrong turn” and, punch above my weight to draw out the field biologist in you.

Colobines are group of primates known to inhabit different habitats. These habitats pose diverse challenges which they have coped up physiologically and behaviourally. Primates in such environments are subjected to prolonged scarcity of food due to phenological variations and low temperature in winters. They are expected to allocate their time to various activities optimally in order to balance their energy requirements. One such primate inhabiting the harsh weather condition of Himalaya is Himalayan gray langur. Himalayan gray langur, Semnopithecus ajax, is little-known endangered primate, initially reported to be present in few parts of north-western Himalaya. To understand their survival strategies in these habitats one must know about the whereabouts of this species.

Therefore, I first accessed the spatial distribution and occurrence of Himalayan gray langur in Kashmir region. This was achieved by using well-structured questionnaire and on-ground surveys in the region. It was followed by identifying sites which face human-langur conflict. My results suggest a wider range of Himalayan gray langur in Kashmir which was previously thought to be restricted in a small range. Langurs were found distributed in the protected mountainous forest areas of Kashmir by showing a preference for broad-leaved deciduous and coniferous habitat types within 1600-3000 m. Conflict in the form of crop raiding was found in the villages around protected areas.

Based on the knowledge of the distribution of these primates in forests, I tried to address how this primate survives the seasonality and cold temperatures of Himalaya in the next chapters of my thesis. I have addressed this by investigating the behaviour patterns and the strategies they have adopted to balance the energy requirements. I used observational methods of instantaneous scans for different behaviour categories. My results suggest Himalayan langurs spend more time feeding during lean winter when high-quality food is less available and rest more during hotter months. Moreover, they have greater home range sizes in winter than in summer. These results suggest an energy maximizing strategy by these primates when resources are scarce by feeding more on less profitable food sources and expanding their home range size.

I further investigated the diet and feeding behaviour of langurs. They were found to shift their diet with seasonality. They feed on a variety of plant items ranging from bark, buds, young leaves, mature leaves, ripe fruits and seeds. I used resource selection functions to test for plant species preference. A seasonal preference for certain plant species and plant parts suggest that availability of plant parts influences their choices. From these results one can conclude that Himalayan gray langur has adapted to explore a variety of food sources other than leaves. This study helps us in understanding the ability of colobines to explore such versatile diets which has helped them colonize many habitats, one of them being the Himalaya.

Overall, this study provides a baseline information for conserving Himalayan gray langur through comprehensive understanding of its distribution, activity budget, home range, diet and feeding preference in Kashmir Himalaya. The current distribution serves as a base-map for various management policies towards the conservation of this high-altitude primate. Moreover, insights about the conflict will help managers in developing ideas to reduce and prevent conflict. Due to the presence of this species in the broad-leaved deciduous and coniferous forests of Kashmir, it becomes important to preserve and protect these habitats for its survival. The key findings of this study are expected to benefit directly towards the conservation of this species and in understanding the survival strategies of these high-altitude primates.

CES IHS 2020
Talks, Posters, Short documentaries, Panel discussion, Science and Creativity stalls

Territoriality associated with lek-mating systems is unique in that males defend small, heavily clustered territories that lack resources usually thought to attract females, such as food and water. Females visit these male aggregations (leks) solely for the purpose of mating. Males compete intensively to defend mating territories and male mating success is typically highly skewed. Males in this system face the complex problem of making decisions on how much effort to allocate towards territory defence and mate attraction efforts versus maintenance activities and how to time this effort, as the duration of territory tenure in relation to the peak in number of females visiting the lek has important fitness consequences. Associated with the high variance in mating success, there is extensive variation in the behaviour of males holding territories on leks. In my thesis, I attempt to understand this variation in male lekking behaviour, by examining patterns of territorial investment in relation to patterns of expected payoffs, estimating underlying hormone correlates and analysing the social context of male territorial decisions. Using a lekking population of blackbuck (Antilope cervicapra) as a model system, I took an integrative approach to study the variation in male territorial and mating behaviour on lek.

In the first chapter, I investigated a principal blackbuck lek to understand the fine scale patterns of variation in male territorial investment and test whether they may arise from associated variation in mating benefits. I found that patterns of male investment in lek attendance, signalling and interactions closely track patterns in payoffs, supporting the hypothesis, that due to the large costs of lekking-related behaviour males should tailor their investment in this behaviour to predictable cues of mating benefits. Apart from responding to indirect spatial and temporal cues of potential mating benefits, males also appeared to modulate their lekking behaviour directly in response to a female visiting their territory.

In the second chapter, I examined relationships between lekking behaviour and testosterone and glucocorticoids on a blackbuck lek. I used a non-invasive technique of monitoring endocrine status by measuring concentration of hormone metabolite in blackbuck faeces using enzyme immunoassays. I found that time during the mating season predicted variation in faecal testosterone and cortisol metabolite concentration, but there was no clear relationship between testosterone/cortisol metabolite concentrations with distance from lek-centre.

In the third chapter, I examined the influence of local interactions on male behaviour by quantifying correlation of behaviours at the male neighbourhood level in the short-term (immediate) and long-term (over the mating season). I found that, in the short-term, neighbourhoods show correlated behaviour suggesting that males respond to the behaviour of neighbouring males when making decisions related to displays and how much time to spend on their territory. I found that, over the long-term, lekking male blackbuck appear to locally influence each other’s investment in intensive displays.

Overall my thesis findings indicate that male investment in high-cost signalling is sensitive to diverse factors, including fine-scale spatial and temporal patterns in potential mating benefits, immediate cues of mating benefits, and to social environment. My findings also suggest that taking an integrative approach and examining hormonal mechanisms may provide insights into trade-offs generating variation in costly male behaviour.