Nikunj Goel wins Volterra Award and Damman Award at ESA 2016

Nikunj Goel has won two awards at the Ecological Society of America (ESA) 2016 Annual Meeting, Volterra Award by the Theoretical Ecology section and Ton Damman award from the Vegetation section. He was given these for his excellent presentation titled “Spatiotemporal dynamics of savanna-forest distribution”. Both of these awards are given to best graduate student presentation at the Annual meetings of ESA.

Congratulations to Nikunj!

Nikunj graduated with BSc(Research) from IISc in 2015 and worked in our lab for his final year project working on early warning signals of financial meltdowns that resulted in a publication. He is currently a PhD student with Dr Carla Staver at Yale University. We continue to collaborate after he has moved to Yale and I serve on his PhD thesis committee.

Visit by collaborators

Our friends from France, Sonia Kefi and two of her group members Miguel Berdugo (currently a student of Prof Fernando Maestre in Spain and soon moving as a postdoc with Sonia) and Angeles Mayor (a postdoc with Sonia) visited Bengaluru for about a week. They enjoyed the tree festival Neralu and other small fun events in the town.

Of course, we all met them to have exciting discussions and how to take our collaboration forward. Here is a group picture at a cafetaria.

photo_2017-03-01_22-02-22

Our new paper testing theory of spatial indicators of ecological transitions published in Global Ecology and Biogeography

We are happy to announce that our new paper on testing theory of spatial indicators of critical slowing down and ecological transitions has appeared in the online early version of the journal Global Ecology and Biogeography.

Congratulations to Amit Agrawal (former project assistant of our lab) and Sabiha Majumder (PhD student) for their first research publication! This project began during conversations between Stephanie Eby, Andrew P. Dobson and myself. That was back in 2010, when I was a post-doc at Princeton. They had this excellent high resolution data that made sense in the context of a theory paper from my thesis in 2009.

So what is this paper about? 

Ecosystems like clear lakes or forests can abruptly collapse to ‘unhealthy’ states like toxic-turbid lakes or deserts with low vegetation. Our lab uses ideas from physics of phase transitions (e.g., water boiling to become vapour) to develop statistical tools of early warnings of such abrupt transitions. For example, two papers of my PhD thesis (Guttal and Jayaprakash 2008 and 2009) were on developing such tools to analyse time series and spatial data from ecosystems. The underlying theory is now popularly known as ‘Early warning signals of critical transitions’, “Theory of Critical slowing down”, etc.

In this paper, we were testing such tools using spatial data of large scale ecosystems. There were earlier efforts to test these quantitative tools, but mostly in simple laboratory conditions or controlled lake experiments.

Specifically, we test the prediction that the following metrics show stronger signatures of transitions ‘before a collapse of an ecosystem’

(A) Spatial variance (proposed in Guttal and Jayaprakash, 2009)

(B) Spatial skewness (proposed in Guttal and Jayaprakash, 2009)

(C) Spatial autocorrelation (proposed in Dakos et al 2010)

(D) Spatial spectra (proposed in Carpenter and Brock 2010).

This graph below shows how theoretical predictions and real data match.

spatial-csd-theory-data-comparison

There were a few subtle and insightful aspects related to analysing this dataset. First, we didn’t have an ideal dataset, so we had to make an approximation called ‘space-for-time substitution’ to compare theory with real data. We justified this approach using a model. Second, the data were discrete-state (occupied/unoccupied), unlike what the models typically assumes continuous variables (like biomass density) in each of the above papers. We developed a data preprocessing method called coarse-graining, inspired from the physics literature. We thought the method to be sufficiently important and hence the details of the method will be published separately. Analysing this dataset has motivated various thesis chapters in our lab’s PhD student Sabiha Majumder, who is from Physics department and works jointly with me and Prof. Sriram Ramaswamy.

I should add that reviewers gave detailed comments that helped the manuscript a lot. This was also our first manuscript where we used services of Axios.

All codes and some data associated with this manuscript are available on our Github page: https://github.com/tee-lab/spacetime-csd

Recent visitors to lab: Silvia de Monte, Nikunj Goel and Vivek Hari Sridhar

Our lab has begun the (relatively) new year 2017 with a burst of visitors!

Prof Silvia de Monte from Institut Biologie de l’Ecole Normale Supérieure, Paris visited our lab today (9th Feb 2017). Our lab spent the entire morning through afternoon discussing exciting research works going on in both our laboratories. Thank you for dropping by Silvia! Do visit us IISc again.

Nikunj Goel visited us from Yale University for three weeks (13th Jan to 5th Feb) to discuss his ongoing thesis research plan on Savanna-Forest dynamics. Nikunj is no stranger to our lab, having done his undergraduate thesis, that led to a publication, with us! He is currently a PhD student with Dr Carla Staver at Yale University. I am also on his PhD thesis committee – so we expect our interactions and collaborations to continue.

In the first week of Jan, Vivek Hari Sridhar, a PhD student at the Department of Collective Behaviour at the Max Planck Institute of Ornithology, visited our laboratory. He gave a lab talk on his thesis research plan on how individual level heterogeneity influences collective behaviour. He also discussed the possibilities of using GPU based parallel programming for his research work. We hope to be in touch in the future too. Do give a shout anytime, Vivek.

These visitors have added burst of energy and enthusiasm to all of our group members. Now, we are getting ready to receive our next visitor from France next week!

Recent conferences and talks

It’s been a really long time, almost 7 months, since I have posted any updates on lab website. So let me post some of the conference and talks that our lab members have been involved with.

In March 2016,  a bunch of us that mostly included younger generation of ecologists, launched a new conference called India – Behaviour, Ecology and Evolution, in short I-BEE at Ramnagar, Uttarakhand, near the Corbett National Park. Three of us from the lab, me and two my of PhD students, Sumithra Sankaran and Jaideep Joshi, presented our work there. One key feature of the conference was that all talks were contributed talks which were peer-reviewed before acceptance. The conference was attended by around 100 people and was very well received.

A few folks from NCBS and ICTS have started a seminar series called Dynamics Fridays, that happens once on four weeks and rotates between NCBS and ICTS. I gave one of these dynamic talks in May 2016 on a very preliminary work on building models based on dynamics of fish school from real experiments.

In May 2016, I gave an invited talk at a national conference on Advances in Mathematical & Computational Biology held at IIT-Ropar. The event was only for two and a half days and was small. It had a great mix of physicists and mathematicians working on biological problems. I really enjoyed this small event.

In June 2016, I gave an invited talk at an International conference organised by ICTS, Bengaluru on Games, Epidemics and Behaviour. The conference had an interesting mix of applied mathematicians and computer scientists. I was one of the few ‘biologists’ among speakers. It was interesting to see applied mathematician’s way of approaching contact process based models, which we extensively use in our lab.

In Aug/Sept, I gave an invited talk at a symposium on “Spatiotemporal patterns as early warnings of possible catastrophic shifts in stressed ecological systems at the conference EcoSummit held at Montpellier, France.The symposium had a bunch of folks whose papers I had read from my student days, but had never met! It was fantastic. In the same conference, my student Sumithra Sankaran gave a talk on how to detect criticality in patchy ecological systems whereas my other PhD student Sabiha Majumder presented a poster on estimating criticality from real spatial ecological data.

Following this conference, my collaborator at CNRS Montpellier had organised a one day workshop on “Early Warning Signs of ecosystem degradation: Theory and applications on ecological data”. I gave the introductory talk on the “Theory of tipping points and their indicators”.

That seems quite a bit for an year where I had put breaks on travelling! I am not attending any conferences for the rest of this year. I expect these numbers to be even smaller for 2017.

 

ISRO meeting and poster award

The National Centre for Remote Sensing at Hyderabad, an ISRO centre focussing exclusively on remote sensing related activities, organised a one day ‘Academica and student interaction meeting’ on 5th Feb 2015. Myself and my PhD student Sumithra Sankaran attended this meeting.

We had very good interactions with scientists at NRSC. We discussed our requirement of high resolution data of various ecosystems for our research work for which they offered lot of support. We hope to build strong collaborations with the ISRO scientists.

Congratulations to Sumithra Sankaran who won a best poster award for her poster on ‘Characterising vegetation of semi-arid ecosystems’. She presented her modelling work on based on simple cellular automata models and how one can use spatial metrics of remote sensing data to infer ecological features underlying the system.

New paper on financial market crashes and media coverage

Our new paper showing “Lack of Critical Slowing Down Suggests that Financial Meltdowns Are Not Critical Transitions, yet Rising Variability Could Signal Systemic Risk” is out in PLoS ONE!

Nature India carried out a very nice article on our work, written by Mr Varma. National University of Ireland, Galway issued a press-release (an initial draft of which was written by Rajashree of Science Media Centre, IISc). and featured it on their website. Here is a media article at Deccan Herald, but whats written there just does not make sense.

This work was done in collaboration with Dr Srinivas Raghavendra, an economist at the National University of Ireland, Galway. We started the work sometime in mid-2012. Nikunj Goel, a Physics undergraduate student at IISc, joined this work in early 2014 and did enormous contributions to the manuscript. Quentin Hoarau, an undergraduate itern from CNS, France, was also a co-author on the manuscript.