Ecosystems can exhibit multiple stable states at similar external conditions. Such systems shift from one stable state to another abruptly and discontinuously, when they cross certain threshold parameters. Some examples of such abrupt shifts include coral bleaching, woodland encroachment of grasslands and desertification in semi-arid ecosystems. These transitions in ecosystems are often associated with loss of biodiversity and economic impacts, therefore are important to predict. These systems with multiple stable states, in some cases, can be understood as systems with a free energy functional having multiple local minima. In this theoretical framework, these abrupt transitions in ecosystems are similar to the discontinuous or first order phase transitions. In this thesis, we use the tools from the theory of non-equilibrium phase transitions to understand the mechanisms that cause abrupt transitions in spatially extended ecosystems and the statistical properties of these systems which can help us predict them.

Previous studies have shown that strong local positive feedback among individuals is an important mechanism for systems to have multiple stable states. In our study, we use a lattice based model of vegetation dynamics with basic processes as birth, death and positive feedback among individuals. In its simple version, this model is in the same universality class as directed percolation which is well known to exhibit a continuous phase transition from an active state to an absorbing state. Using master equation expansion for finite sized systems, we construct stochastic differential equations for our discrete state lattice model. We analytically show that systems with finite size can have multiple stable states even in the absence of positive feedbacks. Our numerical simulations of the spatial models confirm these results. Small sized ecological systems, therefore, can undergo discontinuous transition from an active high density state to a bare state where larger ecosystems would have survived.

It is well-known that systems close to a continuous phase transition show slow recovery from the perturbations. This phenomenon is known as critical slowing down. Since ecological systems are finite in extent and rarely in steady states, signatures of critical slowing down are seen before the discontinuous transition as well. In spatial systems, critical slowing down manifests as increase in spatial correlations and spatial variance in the system. Theoretical studies have shown that these signatures can be used as early warning signals for the imminent transitions. These spatial signals have been tested in microbial systems in lab, but few studies show their validity in the field. We hypothesize that above spatial metrics increase when a transition occurs along the gradient of driver in space. We first test this “space-for-time substitution” in a lattice model where driver changes along space. This model shows a transition from one state to another across space. We show that spatial metrics like variance and correlations show an increase even before the transition along the spatial gradient of driver. We, then, test these theoretical predictions in a savanna ecosystem using remotely-sensed and the ground-truthed data. In this ecosystem, grassland and woodland states co-occur at similar rainfall values and the abrupt transition occurs along the rainfall gradient in space. We show that critical slowing down based spatial indicators show theoretically expected trends before the transition. Therefore, we argue that simple spatial metrics can be used to anticipate the abrupt shifts in large-scale ecosystems.

In addition to the early warning signals, it is important to quantitatively estimate the threshold parameter at which the system is likely to shift to another state. To estimate this threshold, we use the property of phase transitions that systems show diverging correlations at the critical point. Therefore, in finite ecosystems showing alternative stable states, we hypothesize that the spatial location at which variance and correlation in the state variable are maximum will be closest to the transition. We used a spatially-explicit model of vegetation dynamics in which the driver value shows a gradient in space. We show that the point at which spatial variance and correlation in vegetation are maximum, is indeed the critical point of the system. We then test this method of finding the critical point in real ecosystems by analysing spatial data from regions of Africa and Australia that exhibit alternative vegetation biomes.

In summary, we employ a model from non-equilibrium statistical physics to understand abrupt transitions in ecological systems. We show that stochasticity caused by finite sized systems can lead to abrupt transitions in spatial ecosystems. We suggest simple spatial metrics to quantify critical points in real ecosystems, offering a significant advance from current studies that only proposed qualitative metrics of proximity to critical points. This thesis presents an elegant example of how principles of nonequilibrium phase transitions can be applied to a complex biological system, by modelling and testing their predictions with data from ecosystems.

SPEEC-UP is a one day conference of student presentations (of 3 minute duration) on Ecology, Evolution and
Conservation.

Its organised by a bunch of folks from ATREE, IISc and NCBS and will be
held at NCBS on 31st August. Here is the link to abstract submission
*(deadline: 20th June).*

http://speecup-blr.weebly.com/

This is a Bangalore centric student event and we expect this will a way to
provide a platform for students and faculty to get together.

There are cash prizes to be won for best presentations!

Conservation of any concerned taxa in altered ecosystems requires an in-depth knowledge of their ecology, including key interdependent facets such as their physiology, behaviour, and habitat. In addition, ecological and anthropogenic perturbations are known to influence the stress status of free-ranging animals. Understanding and assessing the effect of such disturbances on the stress physiology of an animal, therefore, becomes important to gain a holistic picture about the animals’ well-being and to enable better conservation of that species. Hence, this study, being the first detailed assessment, addresses the proximate causation of influence of some of the fundamental ecological and human-induced stressors on the stress status of free-ranging Asian elephants of the Bandipur National Park, the Nagarahole National Park and Hassan district of Karnataka using the non-invasive technique for measuring faecal glucocorticoid metabolites (fGCM). We assessed the influence of intrinsic (age, sex, body condition and lactation) as well as extrinsic factors (seasonality, group size, and human-induced stressors) on the levels of fGCM. Our findings elucidate that the stress-response in a free-ranging elephant is synergistically influenced by various ecological, social and anthropogenic correlates. Such information can help not only in understanding the health status but also in addressing the causes of conservation problems, evaluating the effect of conservation models and formulating the better strategies for the welfare of elephants.

Division of labour plays a very important role in social insects and could
either be reproductive or non-reproductive in nature. The lack of
morphological differences among individuals in primitively eusocial species
lead to greater flexibility in their social roles making them very
interesting model systems to study division of labour. *Ropalidia
cyathiformis*, a primitively eusocial wasp was chosen as the model system
for the study of reproductive and non-reproductive division of labour. One
of the key findings reveals that while dominance behaviour is used as a
mechanism for reproductive division of labour, age is used for
non-reproductive division of labour. We also compared our findings with
what is already known in a related conspecific, *Ropalidia marginata*. Our
findings showed that *R. cyathiformis* maybe a more primitive species
compared to *R. marginata* and provide a glimpse into the origin of
eusocial insects.

More than 50 years after William Hamilton laid the mathematical foundations of kin-selection theory, how cooperation among genetically distinct individuals evolves and is maintained remains one of the most fundamental and fascinating themes of evolutionary research. Of particular importance to this broad theme is the question of how genetic and behavioural diversity within cooperative groups affects group productivity when the latter is a major component of group-member fitness.
Among animals, examples of within-group behavioural diversity that increase total group cooperative productivity abound. However, although research on microbial social evolution has burgeoned in the past two decades, no study has addressed whether cooperative microbes similarly evolve genetic diversity within natural social groups that increases group productivity. Hence, we tested the effects of natural diversity within fruiting bodies of the social bacterium Myxococcus xanthus on total group spore productivity.
This study demonstrates the first examples of chimeric synergy - i.e. positive effects of social chimerism on total group productivity - among conspecific microbes derived from the same natural social group. Moreover, the “social network” within one set of isolates derived from the same fruiting body were also examined in great detail. These analyses show that the chimeric synergy generated by interaction among the distinct members of this fruiting-body group is broadly distributed across genotypes and interactions rather than being (less interestingly) due to social responses by one genotype or a small minority of genotypes.
Interestingly, the chimeric synergy occurs almost exclusively among M. xanthus isolates derived from the same fruiting body. In contrast, forced chimerism among isolates derived from different fruiting bodies generates almost exclusively strongly negative effects on group productivity (chimeric load). Thus, this study not only document naturally evolved, within-group chimeric synergy among microbes, but also the stark dichotomy of such positive within-group interactions to pervasive between-group antagonism, a dichotomy common among cooperative animal species.
These observations therefore suggest both i) that group-level performance during fruiting body development is a major component of fitness for M. xanthus cells and ii) that such selection can operate to maintain within-group diversity of positive effect on group-level performance while purging within-group diversity of negative effect. These results also reveal the absence of selection for divergent lineages across groups to remain socially compatible, thus leading to the quantitative decay of cooperation as a function of spatial distance between isolate origins (and hence as a function of genetic distance between isolates) in experimental between-group chimeras. Thus, the findings from this study are consistent with an intuitively appealing model of selection operating at multiple levels of biological organization in natural populations of bacteria, with selection among higher-level units (in this case fruiting-body-forming groups) being strong enough to differentiate the fundamental social character of within-group versus between-group genetic variation.

Many species of tephritid flies (Diptera: Tephritidae) perform a wing waving display ('supination') to deter attacks from jumping spiders. This display, along with the dark bands on the wings, has been thought to deter spiders through a form of mimicry termed 'predator mimicry'. In a series of studies with jumping spiders and the Mexican fruit fly, I explored this interaction from a visual ecology perspective. Using an custom built eye-tracker that traces the movement of the retina in the principal eyes, I played videos of displaying flies and monitored the response. I describe the patterns of retinal movement of jumping spiders in three treatments: during fly display, fly walking and a still fly. We show that the deterrent effect is achieved by exploiting the sensory biases of the predator.

The pervasive effects of climate change on the biosphere are increasingly evident with many well-documented impacts on species ranges and phenological events. As ectotherms, the phenologies of plants and insects are highly sensitive to changes in temperature. The vast majority of studies of climate change effects on terrestrial organisms have focused on the responses of individual organisms to changes in temperature and precipitation patterns. Far fewer studies have examined the effects of climate change on biotic interactions, yet studies are vital for our understanding of how climate change has (and will continue to) alter communities and ecosystems. This talk explores how changing temperatures differentially alter the phenologies of members of a simple trophic community (cowparsnip, its insect herbivore – parsnip webworm, and its parasitoid wasp – Copidosoma sosares) across an elevational gradient, resulting in phenological matches in warmer years and mismatches in colder years. In cooler years, cowparsnips at higher elevations largely escape herbivory; in warmer years, cowparsnip populations at higher elevations experience reduced fitness due to substantially increased levels of herbivory.

The evolution and biogeography of various taxa in Peninsular India are of particular interest as this region, a Gondawanan fragment, is critical to our understanding of historical biogeography in the Oriental realm. Over the past decade, molecular tools have enabled testing of alternative historical scenarios of faunal exchange and consequent biogeographic patterns. The snakes of Peninsular India, despite their spectacular diversity, remain poorly known with regard to their biogeographic affinities. While most Indian snakes are considered to be Malayan relicts, this hypothesis remains unexplored. Hence, we explored historical patterns of dispersal and diversification within Peninsular India using two distantly related snakes with broad differences in ecology and biology; an arboreal, non-venomous genus, Ahaetulla (vine snakes), belonging to the family Colubridae, and the genus Trimeresurus (pit vipers) a group of terrestrial and arboreal, venomous snakes belonging to the family Viperidae.

First, using an extensive taxon sampling of snakes from Peninsular India and adjoining Northeast India, we delimited species using a coalescent method and a multi-criteria approach including genes, geography and morphology. The results reveal the presence of several new lineages of snakes, including morphologically cryptic lineages, in both genera. Second, using mitochondrial and nuclear DNA, we reconstructed the phylogenies of the delimited lineages. In vine snakes, we discovered a deeply divergent lineage (Proahaetulla gen. nov.) from the southern Western Ghats, that is sister to all remaining members of Ahaetulla. In Trimeresures, we recovered multiple clades, one of which is predominantly peninsular Indian with a few Southeast Asian lineages. Third, we tested for clade congruence in patterns of diversification and dispersal using ancestral range reconstruction of geographical ranges. In contrast to earlier hypotheses, Peninsular India emerged as a centre of snake diversification and Western Ghats as a major centre of in-situ radiation for both clades. Patterns of dispersal show signatures of congruence and contrast between the clades, with the Western Ghats acting as a major source for colonisation of ancestral lineages into the arid regions in Peninsular India and adjoining Sri Lanka as well as Southeast Asian regions.

Organizers: Dr. Maria Thaker (CES) and Dr. Meena Balgobal (Colorado State University)

Open to registered participants only.

Biocemented earthen structures like termite mounds are one amongst many examples of animal-built structures with exogenous and/or endogenous materials that have received scrutiny from architects, structural engineers and soil scientists. However, little is known about the process of construction at different length and time scales. In this interdisciplinary study between ecologists and engineers, we explore termite mound construction at micro-, meso- and macroscales represented by aggregation of soil into bricks with the help of termite secretions, cementation and curing of bricks, and densification and compaction of mound soil over its lifetime. The above processes occur over a wide range of time spans – from a few seconds to decades. This ongoing work provides us insights into the process of mound construction by close to a million termite individuals working in tandem without an architect or masterplan and leading to stable structures that are three orders of magnitude larger than individual termites and retain structural stability for decades.