Jitesh defended his thesis titled “Intrinsic noise in collective dynamics” – where he theoretically and empirically investigated how stochasticity plays a very counter-intuitive role and creates order!
The thesis was reviewed by Prof Martin Evans (Dept of Physics, Edinburgh, UK) and Prof Malay Banerjee (Dept of Math, IIT Kanpur)! We thank them for their very constructive comments and their valuable time.
As you can see, although this work is from CES and we look at fish schools, it was reviewed by physicists/mathematicians! This is because there are lots of links between physics and schooling fish.
Jitesh is continuing as a short-term post-doctoral fellow in the lab. He will soon join Max Planck Institute for Collective Behaviour in Konstanz for his postdoctoral work on honey bees and collective cell migration.
Hearty congratulations to Dr. Sabiha Majumder who is all set to join ING in Amsterdam on a new exciting career path of banking/finance.
Sabiha got a PhD from the Physics department of IISc in 2017/18, working jointly with me and Sriram Ramaswamy. Her thesis applied ideas from nonequilibrium statistical physics and stochastic systems to analyse risks of ecological collapse. She published a number of excellent papers on this topic, in prestigious ecology journals. After her PhD, she joined ETH-Zurich for a postdoc, where she continued for two years.
In her new job, Sabiha will be employing her interdisciplinary skills as a Risk analyst in the banking/finance sector!
This shows how skills learnt in PhD are highly transferable. One need not continue in the traditional academic set up after PhD — something that a lot of PhD aspirants are unaware of. There are a large number of opportunities outside the academic set up where skills of PhD are going to be extraordinarily useful.
I receive a very large number of applications for summer internships from all over India (and occasionally one or two from abroad). I usually take 2-4 students every year.
Unfortunately, this year (2020), I have decided not to take any summer interns due to a rather hectic schedule I have in summer.
I had informed many students to contact me in early February to know about my decision on interns this year. If you see this message, I know this will be disappointing, but I hope we will find ways to work together later. I wish you all the best in finding alternative internships.
I am on the core-committee of KVPY from July this year and got an opportunity invite speakers for the KVPY Vijyoshi camp.
I (and everyone else involved) was thrilled that Prof Marlene Zuk accepted the invitation! She visited India to deliver spectacular talks at KVPY-2019 on sexual selection. She also attended and gave a talk at a mini-symposium/discussion on animal signals in CES.
Here is a picture of her with our lab:
L to R: Archana Prakash, Priya Iyer, Shuaib, Tanveen, Vishwesha, Marlene Zuk, Ashwin, Arun and Jitesh.
Here is my thread, attempting to explain some aspects of the new paper by former students Sumithra Sankaran, Sabiha Majumder and Ashwin – published in Methods in Ecology and Evolution.
It looks really pretty in the formal formatted version 🙂
Before I go further, we are so happy that there is Kannada Abstract to this paper! I will do a Kannada thread as well later.
Thanks to Kolleagala Sharma @kollegala for the help with Kannada abstract. Incidentally, the paper came out on Nov 1st!
Some background: Many ecosystems can ‘suddenly’ switch states, also called regime shifts or tipping points. This can happen in semi-arid vegetation, mussel beds, lakes, corals, etc. Therefore, we want to know which ecosystems are prone to sudden tipping.
An ideal way to find this is to perturb the ecosystem & measure how it returns. But this is difficult & in many cases, such a perturbation may cause the tipping! So this is not even desirable.
A paper in Nature 2007 proposed that we may infer stability by measuring properties of spatial patterns. Specifically, they focused on semi-arid vegetation. Here is an image from Google Earth, in Rajasthan. Note that not all clusters of plants are of same size.
Basically, they argued that the resilient (or stable) ecosystems do not have any ‘typical size’ of clusters. Broadly, they claimed that cluster-size distribution and its properties can inform us about ecosystem resilience.
Mathematically, this means that the frequency distribution of cluster sizes is a power-law. Power-laws are fascinating because their mean & variance are infinitely large!
This is in quite a contrast to distributions we regularly use – like Gaussian/normal or exponential.
To make this clear, we show a graph in the paper tries to explain how power-laws are fundamentally different from normal or exponential decay functions.
Power-laws have a large tail, and hence you are likely to find very large-sized patches in such systems.
These are not just mathematical fantasies! Many empirical systems do show power-law distribution of clusters.
Here is Figure 1 from our paper with empirical examples of power-law clustering.
Does it mean they are highly stable ecosystems? There were several follow up studies, that found mixed evidence to this overall claim.
That’s the background to Sumithra’s work.
The main result from Sumithra’s work is that the above-proposed link between resilience and cluster-size distribution is NOT robust. So it’s a NEGATIVE result!
To show this, she used a simple computational model of ecosystems
Here is a pictorial representation of the spatial-model.
The model itself is directly taken from a statistical physics paper (Lubeck, J Stat Phys 2006) but with ecological interpretation thrown in!
Sumithra showed that power-law cluster-size distribution can occur even when systems are very close to tipping points. Hence, power-laws are not indicators of ecosystem resilience. Here is a conceptual diagram and result that explains the results.
Power-law cluster-sizes are also studied extensively in the context of ‘percolation’ in the physics literature. We showed that power-law cluster-size distribution in our ecology models relates to percolation of physical systems!
We also talk about what else can be measured to infer resilience. There are more technical aspects! Because this paper uses ideas from many areas – ecology, physics, math, computer simulations and statistics of fitting distributions – we explain many technical aspects.
Finally, I must say that handling Editor Dr Hao Ye at Methods in Ecology and Evolution gave extensive comments that really helped the clarity and presentation of the manuscript.
If you came this far, press the like button (for me know how many really read this!) and Thanks a lot! ..END!!
During the visir of Guy Theraylaz, our lab members (Pritha, Jitesh, Akanksha) and collaborator Dr Danny Raj organized an interdisciplinary one-day symposium titled Collective behaviour at CES, IISc. Here is the full schedule:
Around 10 faculty members from IISc and other institutions gave presentations. Prof Theraulaz also gave a fascinating special seminar at the Collective behaviour symposium on self-organized nest architecture.
There was also a very lively poster session where a number of students presented their work.
The symposium was very well attended, including two IT folks who saw the notice on Twitter and joined the entire day of talks!
During the visit of Prof Theraulaz, we organized an intense workshop on collective behaviour at Valparai, Tamil Nadu from 08.09.2019 to 10.09.2019.
Many students working on collective behaviour from our lab and our collaborator Dr Danny Raj attended the workshop. The workshop focused on the discussion of existing research in the field of collective behaviour and potential future advances in the same.
The team also did a number of field visits to observe wildlife, assisted by extraordinary scientists and staff from Nature Conservation Foundation.
As I mentioned in an earlier post, Guy Theraulaz visited CES and our lab as Infosys Chair Professor.
During the visit, the lab members of Dr Vishwesha Guttal organized an interdisciplinary one-day symposium titled Collective behaviour. Around 10 faculty members from IISc and other institutions gave presentations. Prof Theraulaz also gave a fascinating special seminar at the Collective behaviour symposium on self-organized nest architecture.
In addition, Prof Theraulaz attended a workshop on collective behaviour was organized by Dr Vishwesha Guttal at Valparai, Tamil Nadu from 08.09.2019 to 10.09.2019. Many students working on collective behaviour from our lab attended the workshop. We discussed the state of research in the field of collective behaviour and potential future advances in the same. The team also did a number of field visits to observe wildlife, assisted by superb staff and volunteers from Nature Conservation Foundation.
Apart from faculty members at CES, Prof Theraulaz held a whole range of discussions with faculty members spread across the Institute as well as neighbouring institutions such as NCBS and ICTS. Some faculty members he met included: Prof Ashish Verma (Civil engineering), Prof Renee Borges (CES), Prof Rohini Balakrishnan (CES), Prof Sanjay Sane (NCBS), Prof Axel Brockmann (NCBS), Dr Danny Raj (Chemical engineering), etc.
Akanksha Rathore, a final year PhD student in our lab, conducted a workshop on the timely topic of using image processing in ecological studies (formally titled “Image processing for animal census and movement studies”; my name is listed as organiser but quite shamelessly I wasn’t even present on the day of workshop). She was ably assisted by Preethi (a former project assistant of our lab and current PhD student of my colleague Kavita Isvaran) and Arun (system admin of our lab).
This was a day-long workshop and covered the basics of the topic. Here is a brief description of the same.
Camera traps, aerial imagery vehicles and top-mounted cameras are becoming popular modes of data collection in wildlife and ecological studies. Videos and images captured using these approaches aid in the studies of space-use patterns, animal movement, and animal census. This mode of observation can help us gather Spatio-temporal data at unprecedented detail and thus aid in answering a novel set of questions that were previously difficult to address. However, when collected data is huge it becomes difficult to manually extract useful information from the videos/images. For eg, identifying animals in the images captured from camera traps, locations of individual animals within a group, fine-scale movement trajectory of an animal or even identifying a particular type of flower or vegetation from the images. These tasks can be automated up to some extent using techniques from Computer Vision field. In this workshop, we will be covering case-scenario for which video or image-based data collection can be useful and then some basic concepts from computer vision field which can be used to extract meaningful information from the images. we will also cover the concepts of some of the available software for animal detection and how to choose the software for a particular type of data.
Here are some pictures from the workshop!
The workshop was partially supported by a UGC-UKIERI grant on collective behaviour of blackbuck herds.