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

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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

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.

Media coverage of our winter school modern finance and macroeconomics

Along with my collaborators Srikanth Iyer and Srinivas Raghavendra, I am organising an ICTS conference on “Modern finance and macroeconimics” from Dec 22nd and Jan 2nd.

We are delighted that our school got a coverage from Deccan Herald, an important newspaper in southern India. My colleague Srinivas Raghavendra and a student participating in the conference are quoted in the article.

In this school, I will be teaching techniques related to our collaborative work on testing predictions of early warning signals of critical transitions in financial markets. This work was done with Srinivas Raghavendra and my former UG students Nikunj Goel and Quentin Hoarau.

And Happy new year to all!

Visit by Sonia Kefi and a workshop near Conoor

Dr Sonia Kefi, a researcher from the CNRS Montpellier and two of her students, Alex Genin and Miguel Berdugo, are visiting our lab for two weeks from 27th Nov to 10th Dec 2015. Our labs are collaborating on developing mathematical models of patterned ecosystems, especially the vegetation of semi-arid ecosystems.

 

The three visitors from France and the three folks from our lab (me, Sumithra and Sabiha) went to a tea estate resort near Conoor in Tamil Nadu, away from the distraction of Bengaluru, to assess the progress we have made so far on our projects.  We also had a guest – Krishnapriya Tamma, a PhD student from NCBS (Dr Uma Ramakrishnan’s student) who gave a fantastic talk on her superb phd thesis. It was a great scientific meeting discussing a number of ideas.

Sonia also gave a departmental seminar at CES on 7th Dec 2015 on ‘Identifying the building blocks of ecological networks

Visit by Sonia and her students is part of travel grant we were awarded early this year by the Indo-French Centre for Applied Mathematics. In the first visit, we visited Montpellier in June this year.

 

 

 

We have been awarded an Indo-French grant

We are delighted that we have been awarded a grant from Indo-French Centre for Applied Mathematics. This is a collaborative grant with Dr. Sonia Kefi, a researcher at the CNRS based Institut des Sciences de l’Evolution de Montpellier (ISEM), France. This will help us continue our collaborations on the topic of mathematical and computational models of self-organization in semi-arid ecosystems.

The grant is awarded for a duration of two years. It allows for visits of both of our labs working on this problem to travel to each other labs. The total funds for the first year is around 12,000 Euros.

For those interested in knowing more, see Kefi, Guttal, et cl 2014, Plos ONE for our previous work where, together with various leading researchers in the field, we developed a systematic methodology to detect early warning signals of ecological transitions.

Vishu presents at an Indo-US workshop on Environmental Statistics, ISI Kolkota

I am giving a talk at a workshop on Environmental Statistics at ISI Kolkata. This is jointly organized by SAMSI, am NSF funded institute in the USA on mathematics and statistics and ISI Kolkata. The workshop has various talks on using statistical models in studying environmental data. There are many talks on analyzing data related to climate and a few on spatial data as well.

I presented our own on devising early warning signals of critical transitions. My talk was a bit different compared to others in using dynamical systems models that helps us devise statistical measures for studying ecology. I also used our recent analysis of financial markets to illustrate statistical aspects of detecting early warning signals.