Termite mounds are iconic examples of earthen structures that can withstand the forces of nature such as weathering and remain intact for decades if not centuries. We have discovered that moisture alone, at levels close to the liquid limits of the construction soil, which is a residual red soil in Bangalore, is sufficient to give termite mound soils its incredible strength. However, in the absence of the manipulation of soil by termites, this soil has no weathering resistance.
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.
The termite mound is an iconic example of earthen construction. It is a self-organised structure built by thousands of blind termite workers that build a stable soil structure with extremely high safety factors and resistance to slope failure. Using finite element modeling, tomography, porosity measurements and experimental determination of air permeability, we show that the termite mound is a bilayered structure with a solid core and a porous shell.
List of Selected students for the PhD program at CES (2020)
1 20119079 TARUN SURESH MENON
2 20100046 ARITRA BISWAS
3 20100767 SURANSE VIVEK PREMNATH
4 20115553 JOSHI MIHIR MAKARAND
5 20110421 PRANAV BALASUBRAMANIAN
6 20104684 AMANDA BEN
7 20110076 KAJAL KUMARI
8 20108394 AYAN DAS
9 20111917 PRATIK DAS
1 20102390 ANUBHAV DHAR
2 20113281 JASPREET KAUR
The effects of invasive plant species on ecosystems are manifested in various ways which might often be counter-intuitive and confusing. Existing literature has largely stressed upon the negative impacts of invasive species on certain ecosystem properties, like suppression of growth of native seedlings. However, the holistic view of the effects of such species on ecosystems is still not clear. There is a need to understand that invasive species are a structural and functional part of invaded ecosystems. Studying ecosystem functions like nutrient cycling and regulation, in relation to invasion, is necessary because it directly linked to all organisms in an ecosystem and it is modified by the characteristics and abundance of the invasive species.
In this study, we aimed to understand the effects of plant invasion on nutrient stocks in biomass, litter and soil. First, we aimed to estimate for resident carbon and nitrogen pools, in a tropical dry deciduous forest (considered to be one of the most at-risk ecosystems in the world) in Mudumalai Tiger Reserve, India, over a period of one year. Then, we tried to understand how pools of these elements are modified under the influence of increasing abundance of the invasive shrub species Lantana camara.
This study reinforces the fact that it is difficult to predict the impacts of invasive plants on soil nutrient cycling processes. Through time, we see areas of higher density of Lantana camara showing more pronounced effects on parameters like soil microbial biomass carbon and nitrogen as compared to lower densities. In other parameters like litter carbon and nitrogen, soil carbon and nitrogen and biomass carbon and nitrogen, the results vary among the density categories through time. For most of the study, the carbon and nitrogen stock changes under different density of infestations did not vary significantly from the mean values of the forest. Expected patterns do emerge in certain cases, but do not remain consistent both throughout the course of study as well as the density categories. In many cases, places with low or intermediate levels of the shrub show more significant effects. These results validate the need of more consolidated research on such issues to gain in-depth understanding of ecosystem functions for better forest management and policy formulations.
Vaibhav's Protanilla, Protanilla flamma a small subterranean ant measuring just 2.5mm has been described from the forests of Netravali Wildlife Sanctuary in Goa, India. This ant is completely blind and uses chemical cues for navigating in their dark subterranean world. The species is named after Prof. Vaibhav Chindarkar from Goa. The word “vaibhav” means eminence – like the glow of a flame in the dark in Sanskrit and incidentally, this species is also yellowish-orange in colour and hence, the species is named "flamma".
Effective communication in animals comprise emission of a signal by a signaller and a response by a receiver, such that the interaction is beneficial to either only the signaller, or both the signaller and the receiver. Although animals often communicate using a single sensory modality, use of multimodal signals is very prevalent, possibly to increase the efficacy of communication. The evolution of signalling traits in new sensory modalities, in the presence of signals in pre-existing sensory channels is intriguing, as it requires co-evolution between signals and receiver psychology. Furthermore, environmental conditions and energetic constraints of signallers, may govern the type and intensity of signals, as well as, their efficacy in reaching the sensory systems of the receivers.
In the first chapter, I studied the general ecology of a single species of a diurnal gecko in the genus Cnemaspis to understand its habitat use, activity patterns, and composition of population. I found that individuals of Cnemaspis mysoriensis are active throughout the day and found in areas with broad trees and numerous crevices. I also found that males of this species have colour morphs, which differ in their relative abundance in areas of high and low density. The population of this species has highly skewed adult to juvenile numbers in areas of high density. Finally, I found that individuals show low site fidelity and males avoid cohabiting.
In the second chapter, I determined the presence of multimodal signalling and the relative importance of signal components in chemical and visual sensory modalities for intraspecific communication in a single species of Cnemaspis. I found that male and female receivers differed in responses to signal components. Chemical stimuli were necessary and sufficient for female receivers; however, male receivers required both the chemical and visual stimuli as a multimodal signal to elicit a response.
In the third chapter, I determined whether complexity and elaboration of various components of a multimodal signal across multiple species of Cnemaspis were associated with environmental parameters. I also investigated whether components in different modalities had trade-offs in their expression and intensity, possibly due to constraints. I found that some visual and chemical traits of signallers were well-associated with the environment to either increase the conspicuousness of signallers to conspecifics (visual traits) or decrease the loss of signal in the environment (chemical traits). I also found some evidence for trade-offs between components of signals between the two sensory modalities.
Finally in the fourth chapter, by comparing receiver responses of two closely related species of Cnemaspis, one with unimodal signals and another with multimodal signals, I investigated whether the evolution of receiver responses were associated with elaboration of traits in a new signal modality. I found that movement-based responses of male receivers of the species with multimodal signalling were highest towards multimodal signal, providing some support for the evolution of receiver response with trait elaboration.
Overall, I found that in multiple diurnal gecko species, the elaboration of traits in the visual sensory channel shows some trade-off with chemical trait expression, and seems to have evolved to enhance interactions among males.
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.
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.