Author Archives: ryanchisholm

Nadav Shnerb visits the lab

Last week Prof. Nadav Shnerb from Bar-Ilan University in Israel visited the lab. This visit was part of a collaboration between our two labs under a recently awarded Singapore–Israel research grant. The purpose of the grant is to allow us to unify and further develop models of ecological community dynamics that incorporate temporal environmental variance. Our two labs have been working independently on these models for the past several years. During Shnerb’s visit last week, we spent many stimulating hours working through mathematics on the whiteboard and engaging in vigorous conceptual discussions. We look forward to a reciprocal visit in the coming year or two.

Tak attends the Ecological Society of America Annual Meeting in New Orleans, USA

Tak attended the Annual Ecological Society of America (ESA) Meeting, held in New Orleans from 5th to 10th August. This is one of the biggest conferences in the field of Ecology, with thousands of attendants.

During the conference, Tak presented new work from our lab on the spatial scaling of relationships between species richness and productivity. The work involves using a neutral community model to make quantitative predictions on how these relationships change with increasing spatial scale. These predictions form a baseline against which to compare results from more complex models. Tak obtained valuable feedback during and after his presentation.

The conference was also a good opportunity for Tak to meet up with colleagues and collaborators. These included Nadav Shnerb from Bar-Ilan University, who is collaborating with us on the effects of temporal environmental variation on patterns of biodiversity in plant communities.


Tak attends the Annual Meeting of the Society for Mathematical Biology in Sydney, Australia

Tak attended The Annual Meeting of the Society for Mathematical Biology & the Japanese Society for Mathematical Biology, which was held from 9 to 12 July at the University of Sydney, Australia (

After acclimatising to the austral winter, Tak presented new work by the Chisholm Lab that uses mathematical models to explain the shape of species–area relationships on islands, and obtained valuable feedback. He also re-united with researchers he had met in previous years, as well as engaging with other researchers: there were interesting conversations on hot topics in theoretical ecology and mathematical biology in general. Furthermore, Tak attended many talks and poster presentations, where he absorbed fresh ideas that could serve as inspiration for his own work.


Sydney University


Association for Tropical Biology and Conservation annual meeting in Kuching, Malaysia

The annual meeting of the Association for Tropical Biology and Conservation came to our part of the world this year: it was held in Kuching, Sarawak, Malaysia from 1 to 5 July. Lahiru, Catharina and Ryan attended. Lahiru presented his recently published work on estimating emissions from peatlands. Catharina presented her ongoing work about altitudinal shifts of frogs on Mount Kinabalu. Ryan presented our recently published work on fragmented species–area relationships. The conference was a great success with 800 attendees from around the world, ample networking opportunities and, in particular, fascinating keynote lectures.


James Rosindell visits the lab

James Rosindell from Imperial College London recently visited the lab for two weeks. James is a theoretical ecologist with an interest in biodiversity patterns and neutral models. James played an instrumental role in our recent paper on fragmented species–area relationships. He is also the joint advisor of Sam Thompson, our Imperial–NUS PhD student. During his visit, James gave a fascinating seminar covering a range of topics from microbial invasion to natural language processing. He also talked about the fractal-based tree-of-life visualisation software developed by his independent non-profit organisation OneZoom.


Nadiah’s new paper on carryover effects has been published in Ecology Letters

What allows a population in a heterogeneous landscape to become locally adapted? In general, adaptation to a rare habitat type is difficult because divergent selection is counteracted by the homogenising effects of gene flow. One well-established condition under which adaptation to a rare habitat type may occur is if the rare habitat has higher quality, so that a greater number of offspring can be produced there, to compensate for the habitat’s relative rarity in the landscape. In our new Ecology Letters paper led by Nadiah, we focus on an alternative way in which a habitat may be considered to have higher quality: by increasing the quality, rather than the quantity, of offspring produced. We show, using simulation models, that such “carryover effects” can indeed permit adaptation to a rare habitat type, counteracting gene flow from a more common but lower-quality habitat type.

We also propose an empirical example of carryover effects: the Blue Tit (Cyanistes caeruleus) on the island of Corsica. Blue Tits utilise two habitat types: deciduous and evergreen. There is evidence that the deciduous habitat is higher quality. On the mainland, the deciduous habitat type is more common, and thus Blue Tits who settle in the rarer evergreen patches are maladapted, resulting in source–sink dynamics. On Corsica, however, evergreen habitat dominates, but the source–sink pattern is not simply reversed. Instead, trait divergence into two ecotypes has been documented. We propose that this is because the deciduous habitat, though rare on Corsica, still has higher quality, and that offspring raised there gain advantages that carry over to their fitness later in life. These carryover effects then explain the observed divergence of the Blue Tit on Corsica into two ecotypes.

Tantalisingly, the carryover effects we study provide a potentially novel ecological mechanism whereby two subpopulations can become isolated. Nadiah gives a more comprehensive summary of the paper on her blog.

Kristensen, N. P., Johansson, J., Chisholm, R. A., Smith, H. G., Kokko, H. (2018) Carryover effects from natal habitat type upon competitive ability lead to trait divergence or source-sink dynamics, Ecology Letters (in press)


The divergence of Blue Tits (Cyanistes caeruleus) on Corsica into two ecotypes may have been driven by carryover effects. Image credit: © Francis C. Franklin / CC-BY-SA-3.0