Many complex ecological and social-ecological systems are capable of nonlinear feedbacks. These can result in abrupt and unanticipated shifts in the dynamical regime of a system, as environmental conditions move the system beyond a tipping point. Research in early warning signals of tipping points focusses on ways to predict these tipping points ahead of time by looking for telltale signatures of noise in the data before the tipping point is reached. In this talk, I will describe some research research in our group that (1) characterizes how conventional early warning signals in ecological systems change in the face of social-ecological feedbacks, and (2) explores new types of early warning signals that predict not only the presence, but also the type, of tipping point that is being approached. I will also discuss some opportunities to find early warning signals of social-ecological transitions in social media data, such as tweets on climate change and vaccines.

A body of work is emerging wherein simple mathematical models of ecological dynamics are coupled to simple mathematical models of human behaviour to examine long-term sustainability of these systems. There are pros and cons to the use of simple models, as has been argued for decades in science. I will review these pros and cons in the context of several recent and ongoing studies of ours where we examine widely-ranging contemporary human-environment problems including forest pest control, coral reef endangerment, forest-grassland mosaic sustainability, human disease spread, land-use management, and climate change mitigation. Wicked problems such as these require the kind of basic understanding of alternate stable states, feedback strengths, and parameter influences that simple mathematical models can provide. I argue that the value of our models is one of complementarity: strengths of simple models may compensate for weakness of other approaches. Indeed when the level of complexity of the human and environmental submodels that constitute a coupled model are mismatched, then a ‘lower common denominator’ coupled model may be the most parsimonious way to start. Simple models can inform policy and other decision makers by revealing the mechanisms behind emergent properties and critical transitions. I prove examples of such insights from our recent and ongoing case studies.

Animal groups exhibit many emergent properties that are a consequence of local interactions. Linking individual-level behaviour to group-level dynamics has been a question of fundamental interest from both biological and mathematical perspectives. However, most empirical studies have focused on average behaviours ignoring stochasticity at the level of individuals. On the other hand, conclusions from theoretical models are often derived in the limit of infinite systems, in turn neglecting stochastic effects due to finite group sizes. In our study, we use a stochastic framework that accounts for intrinsic-noise in collective dynamics arising due to (a) inherently probabilistic interactions and (b) a finite number of group members. We derive equations of group dynamics starting from individual-level probabilistic rules as well as from real data to understand the effects of such intrinsic noise and the mechanisms underlying collective behaviour.

First, using the chemical Langevin method, we analytically derive models (stochastic differential equations) for group dynamics for a variable m that describes the order/consensus within a group. We assume that organisms stochastically interact and choose between two/four directions. We find that simple pairwise interactions between individuals lead to intrinsic-noise that depends on the current state of the system (i.e. a multiplicative or state-dependent noise). Surprisingly, this noise creates a new ordered state that is absent in the deterministic analogue.

Next, focusing on small-to-intermediate sized groups (10-100), we empirically demonstrate intrinsic-noise induced schooling (polarized or highly coherent motion) in fish groups. The fewer the fish, the greater the intrinsic-noise and therefore the likelihood of alignment. Such empirical evidence is rare, and tightly constrains the possible underlying interactions between fish. Our model simulations indicate that fish align with each other one at a time, ruling out other complex higher-order interactions.

Further, we analyze the method to derive the group-level dynamical equation using simulated data from two different models of collective behaviour. In doing so we resolve important time-scale related issues with deriving the deterministic and stochastic components of the mesoscopic description from the data.

Broadly, our results demonstrate that rather than simply obscuring otherwise deterministic dynamics, intrinsic-noise is fundamental to the characterisation of emergent collective behaviours, suggesting a need to re-appraise aspects of both collective motion and behavioural inference.

The evolution of flamboyant traits in animals is typically attributed to the selective force of sexual selection. However, natural selection can constrain the degree of elaboration of such traits. Therefore, animal signals reflect a balance between natural and sexual selection. I examined the role of these forces in the maintenance of a complex visual signal: dynamic colour change. Males of the Indian rock agama (Psammophilus dorsalis) exhibit rapid dynamic colour changes on their dorsal and lateral body regions during social interactions. The costs, benefits and adaptive significance of this relatively rare signal type is yet unknown.

Using a combination of visual modelling and field experiments, I first examined the predation risk on social colours and found that the courtship signal of males is costlier than the aggression signal. I then tested whether male colours expressed during aggression convey information about individual physiology and performance measures. Apart from a negative association between testosterone levels and the yellow colour expressed during aggression, body size and bite force were correlated, suggesting that body size could be an honest predictor of fighting ability. In the third chapter, I examined differences in health parameters of males and females that occupy dramatically different habitats as a consequence of urbanization. My results suggest that lizards in urban areas appear to have shifted their innate physiology in order to cope with urban stressors. Finally, I examined the response of receivers to different components of the male colour signals by assessing attention paid by conspecific receivers to each signal component independently and together. Both males and females responded equally to all male social colours although females showed difference in response to achromatic signals. Overall, I conclude that dynamic colour change may have evolved in this species to actively balance the costs of predation risk with the benefits of social signalling.

This workshop will be led Prof. Marlene Zuk and will focus on reasons for why women representation in careers in science is so poor, issues faced by women pursuing careers in science, and also what we can all do as individuals, professionals and as institutions to address these issues. The workshop will consist of a presentation by Marlene, small-group and larger group discussions, and examining several common real-life situations and discussing how these can be successfully handled.

A one day symposium on Animal Signals: Functions and Evolution to be held on Thursday, 12th December, at CES, IISc. Prof. Marlene Zuk from University of Minnesota will be delivering the opening talk.

Sexual selection has long been known as the force underlying the evolution of male ornaments and armaments that males use to gain access to mates. However, what is less understood is what happens when females mate with multiple males, causing sperm of different males to compete for fertilization. Selection for sperm that are both more competitive and better able to overcome the challenges of the female reproductive tract has brought about tremendous variation in sperm size and shape. I will discuss recent comparative work on the causes and consequences of variation in sperm form and function, including the evolution of the longest sperm ever measured. I will further discuss how males trade off the allocation of their limited resources between producing copious high-quality sperm and the costly ornaments and armaments to gain mating opportunities in the first place.

From a million giant wildebeest crossing political borders in the Serengeti to a minuscule bacterial colony moving across an agar gel in a petri-plate, migratory behaviour can be seen at all scales. Migration has evolved multiple times independently in many animal groups, such as birds, fish, mammals (including marine mammals and bats), reptiles (e.g. sea turtles), amphibians, insects and marine invertebrates. Although the evolution of migration in most cases is a response to seasonal fluctuations, its occurrence and extent depends on many physical, geographical, historical, and ecological factors which are likely to facilitate and/or constrain the evolution of migration. My thesis work broadly revolves around understanding the pattern of evolution of migration in birds. I use a meta data analysis approach to estimate global patterns in evolutionary history using ancestral character state reconstruction.

In my study, we target two aspects of migration: Group migration (where individuals of a species migrate together in groups) and Long-distance migration. In the chapter where we focus on Group migration, I test the idea that the evolution of group formation in ecological contexts other than migration may facilitate the evolution of migration in groups. In the other chapter where the focus is on Long-distance migration, we are trying to understand the plausible evolutionary trade-offs between the costs of elaborated traits and costs of long-distance journey. Before carrying out these two sets of comparative analyses, I have also carried out simulations to test for the efficiency of the phylogenetic method that I use in my study. I will briefly discuss the results of those simulations and will focus mainly on the work on group migration in this presentation.

Animals across taxa and habitats are known to use available space nonrandomly.

They are known to concentrate their space use around locations rich

in food, mates or refuges. There could also be cascading effects of such

disproportionate use for the individual itself, its conspecifics or even the

landscape it inhabits. In addition to using their habitats non-randomly for

foraging, avoiding predators and optimizing homing routes; some social insects

were also discovered to use their nest space non-randomly. We tested if the

primitively eusocial paper wasp Ropalidia marginata used its nest space nonrandomly

and indeed found a majority of individuals using parts of the nest

more intensively than expected by chance (spatial fidelity). We tested several

hypotheses that were primarily based on studies on ants, to understand the

relationship between the social and spatial organization of individuals in social

insect colonies. We found that the non-random space use by adults within R.

marginata nests is a result of maximizing nutritional exchange and minimizing

disease spread in the densely populated colonies. In addition, in order to

understand the role of non-random space use by adults on task performance, we

tracked individuals while they performed the task of food distribution, as it is the

most conspicuous and important task in social insect colonies. We found that

wasps within a feeding bout cooperatively (and often repeatedly) fed the

randomly distributed larvae, thus minimizing the chances of any larvae going

hungry. Each wasp that fed larvae in a feeding bout optimized its feeding route

by minimizing the distance per unit larvae it fed. We conclude that

understanding the spatial organization of adults might help us better understand

the mechanism of efficient division of labour on social insect nests.

The Indian subcontinent has been exposed to radical geological and climatic variations over geological time. Contact with other major landmasses, and the dispersal events that resulted from them, have made India and the rest of South Asia a fascinating natural laboratory for biogeography.

Snakes constitute ideal model systems for biogeographic studies given their almost cosmopolitan distribution, the ecological influence they wield, and their evolutionary age. Snakes of the Family Homalopsidae are of special interest given their semi-aquatic habits, and the behavioural and morphological adaptations unique to this clade. Homalopsids exhibit stark differences in their distributions, abundances, and feeding ecologies. This makes them ideal for addressing questions pertaining to phylogeography, ecology, and subsequently biogeography.

I aim to study the ecological and evolutionary determinants of homalopsid distribution. First, I aim to unravel the location of origin of this family and the ancestral state (fossorial/terrestrial, or aquatic) of the crown group. This will serve as a precursor to addressing questions on how homalopsids dispersed and colonized the Indian subcontinent. I will then utilize comparative phylogeography of select species to estimate how population structure varies as a function of tolerances of these snakes to abiotic factors. This would provide insights into factors that have allowed this clade to colonize their range given the geology and paleoclimate of the Indian plate and South-East Asia. Finally, I propose to utilize species distribution models to elucidate how these and other semi-aquatic snakes respond to gradients of abiotic stressors as well as their response to other sympatric snakes.