Category Archives: Uncategorized

Sankar’s paper on squamate extirpations and recoveries in Singapore published in Biological Conservation

Singapore has experienced substantial habitat and biodiversity loss since 1819. Nevertheless, the last century has also seen some forest recovery, as well as the natural re-establishment of several previously extirpated species like oriental pied hornbills and smooth-coated otters. Animals that can fly and swim can re-establish from source populations in Malaysia, but snakes and lizards—also known as squamates—are not able to recolonise as easily. How can we use mathematical models to think about which species to reintroduce to recovering forests? In 2023, we published a paper applying the novel MODGEE (matrix-of-detections-gives-extinction-estimates) model to detailed historical bird, butterfly and plant datasets from Singapore to study extirpation rates for these groups. In a new study, led by Sankar and just published in Biological Conservation, we applied this model to squamates in Singapore.

We compiled a detailed historical dataset for squamates in Singapore (largely based on records from Figueroa et al., 2023) and used the MODGEE model first to generate an extirpation timeline. Our estimated extirpation rate for squamates was 17%, which was lower than previously estimated rates for birds (40%) and butterflies (46%). This implies that squamates may be more resilient to habitat degradation than birds, perhaps because birds generally have lower population densities, and butterflies, perhaps because of butterflies’ reliance on host plants.

Our model estimated that about 17% of squamates have been extirpated from Singapore over the last two centuries. Primary forest species (red) experienced higher extirpation rates than secondary forest-tolerant (green) and parkland species (yellow).

We also used the results to inform a conservation translocation triage for extirpated squamates in Singapore. Given that squamates were never systematically hunted at scale (no pun intended) in Singapore, their extirpation timeline can serve as an indicator of each species’ sensitivity to habitat loss. Since highly sensitive species would have been lost early on in Singapore’s developmental history, recently extirpated species would likely be better candidates for reintroduction to Singapore’s recovering forests. Through this method, we identified the hulk forest gecko (Gekko hulk) as a fitting potential candidate species for reintroduction to Singapore from stock populations in Peninsular Malaysia.

We identified the hulk forest gecko (Gekko hulk) as a candidate for reintroduction to Singapore.

Sankar, A., R. A. Chisholm. 2026. Where will they come from, when did they go? Squamate extirpations and recoveries in Singapore. Biological Conservation, 315:111721

Ho Ning and Tricia attend Biological Sciences Graduate Congress in Chulalongkorn University, Thailand

The Biological Sciences Graduate Congress is an annual event bringing together Master’s and PhD students from NUS; University of Malaya, Malaysia; and Chulalongkorn University, Thailand. Ho Ning and Tricia recently attended the 2025 congress at Chulalongkorn University. Ho Ning presented her work on modelling sea turtle population dynamics in Southeast Asia. Tricia presented her work on estimating dark extinctions for freshwater taxa in Singapore.

Tak attends the International Society for Ecological Modelling Global Conference in Kashiwa, Japan

Tak attended The International Society for Ecological Modelling (ISEM) Global Conference, held over 19–23 October in Kashiwa, near Tokyo. This conference is a congregation of researchers who apply mathematical and statistical models to ecological problems, thus providing insights for effective natural resource management and conservation. At the conference, Tak presented a talk on modelling the effects of fragmentation on extinction risk of populations, which is a collaboration with Ryan and Nao Takashina from the University of Tokyo. Tak attended other talks and poster presentations related to ecological modelling, and networked with numerous other researchers.

After the conference, Tak spent ten days visiting Nao and colleagues at the Department of International Studies at the University of Tokyo’s Kashiwa campus. Nao constructs and uses mathematical models to explore ways of balancing human extraction and conservation in socioecological systems, such as fished marine ecosystems. Nao has previously collaborated with Chisholm Lab on the effects of environmental variability on tropical tree biodiversity. During his visit, Tak worked with Nao on our fragmentation–extinction project as well as a project on how the effectiveness of protected areas changes with spatial grain.

The Graduate School of Frontier Sciences, which houses the Department of International Studies, at the University of Tokyo’s Kashiwa campus

Ryan attends OceanX summit

Last week Ryan attended the OceanX summit in Singapore. OceanX is a nonprofit organisation dedicated to marine research and conservation. The summit was held aboard the organisation’s research vessel, the OceanXplorer. The summit brought together scientists, creative professionals, and philanthropists to brainstorm new ways to further ocean science and communicate it to the public.

Ryan attends the Ecological Society of America annual meeting in Baltimore

Ryan has just returned from the Ecological Society of America’s 110th annual meeting in Baltimore, Maryland, USA. In addition to partaking of the stimulating smorgasbord of seminars, Ryan attended the awards ceremony to receive the George Mercer Award on behalf of himself and Lynette Loke, and he launched his new textbook. The textbook is titled Theoretical Ecology: Concepts and Models with R and is available from Princeton University Press in paperback and hardback.

Tak’s new paper on testing model predictions of higher-order species diversity on islands published in Ecology Letters

The ability of a scientific model to make accurate predictions is an important criterion for assessing its validity, but in ecology there are relatively few studies that have made and tested true a priori predictions, i.e., predictions of unseen data. In a study led by Tak and just published in Ecology Letters, we tested several ecological models’ predictions of unseen higher-order diversity patterns in island archipelago data.

Specifically, we (i) fitted a suite of mechanistic models to observed values of alpha diversity (i.e., number of species on each island) for each of 17 archipelagos, (ii) used the fitted models to make quantitative predictions of three higher-order patterns of island biodiversity, and (iii) quantitatively tested the predictions. The 17 datasets represented a wide range of taxa (including plants, birds and mammals) and archipelago types (including marine and inland water) (Fig. 1). Importantly, the predicted patterns of biodiversity represent higher orders of diversity that contain information absent in alpha diversity, namely the number of species shared between each pair of islands, the number of species shared among each triplet of islands, and the occupancy–frequency distribution that shows the frequency distribution of the number of islands occupied by species in an archipelago.

Our central finding is that an individual-based neutral model of island community dynamics produced fairly good predictions of island biodiversity (e.g., Fig. 2). This suggests that stochastic neutral competition among species together with dispersal limitation is a parsimonious explanation for multiple patterns of island biodiversity. A non-neutral version of the model that included coarse niche structure had worse predictive ability, probably due to overfitting. Our study is a clarion call for further efforts to test true predictions in ecology, in particular using mechanistic models to shed light on the processes structuring ecological systems in nature.

Fig. 1. An aerial view of Baltrum, one of the Frisian Islands in the North Sea. The Frisian Islands form one of the 17 archipelagos that we examined. This photo was taken by Carsten Steger and used in an unaltered form under a CC BY-SA 4.0 license.
Fig. 2. For ant communities on the Frisian Islands (17 islands), the observed relationship between number of species shared between each pair of islands and the average area of the islands (points) is accurately predicted by an individual-based neutral model fit only to the observed relationship between the number of species on each island and island area (this information by itself imposes only very weak constraints on the quantity being predicted). The proportion of points that fall within each confidence interval (shaded regions) closely tracks the nominal coverage of the interval (see text at right). The photo shows an ant of the species Formica fusca, which is found on the Frisian Islands. The photo was taken by Mathias Krumbholz and used in an unaltered form under a CC BY-SA 3.0 license.

Lynette and Ryan receive the George Mercer Award from the Ecological Society of America

The Ecological Society of America (ESA) has awarded Lynette and Ryan the George Mercer Award for their paper testing theories of community assembly using an experiment on intertidal communities in Singapore (Loke & Chisholm 2023). The George Mercer Award was established in 1948 and is given annually for an outstanding ecological research paper published in the last two years whose lead author is under 40. The ESA announcement wrote, “Deftly integrating field experiments with clear hypotheses and mathematical modeling, this study provides novel insights into an ecological question that has been debated for decades. The results of the paper advance our understanding of the forces structuring ecological communities, and the authors combine theory and empirical evidence in a creative and exceptionally well-written way.”

Lynette has collaborated with our lab on several projects in recent years. She moved to the University of Melbourne last year to start a spatial and community ecology lab.

Nadiah’s new paper on many-strategy games and the evolution of co-ordinated co-operation published in the Journal of Theoretical Biology

Co-operation is pervasive in human societies, but the evolutionary origins of co-operation are still incompletely understood. One prominent hypothesis for explaining co-operation is kin selection, whereby individuals accrue fitness benefits by helping close relatives who share many of their genes. Evolutionary game theory has been used to study the evolution of co-operation and kin selection, but until now it has been technically challenging to analyse scenarios where the benefits scale nonlinearly with the number of co-operators, which can occur, e.g., when there are economies of scale in a group activity such as a hunt.

In a new paper led by Nadiah Kristensen, we present a new mathematical method for rigorously accounting for relatedness in evolutionary models with an arbitrary number of players and an arbitrary number of discrete strategies, e.g., co-operators and defectors. We demonstrate the method with an application to a game in which the benefit to individuals rises sharply once some threshold number of co-operators is passed, representing, e.g., a successful hunt. In addition to unconditional co-operators and unconditional defectors, we allow a cognitively advanced strategy: co-ordinated co-operators, who conduct a lottery prior to each game to ensure that the threshold number of co-operators is attained. We find that co-ordinated co-operation is favoured by kin selection. However, if we allow homophily to decline, as happened over the course of human evolution, co-ordinated co-operators can be invaded by another cognitively advanced strategy, the liar, who participates in lotteries but does not follow through on commitments to co-operate. For coordinated cooperation to resist invasion by liars, either some level of homophily must be maintained, or following through on the agreement after a lottery must be in players’ self interest.

Our approach will be broadly useful for exploring the evolution of co-operation in other scenarios involving cognitively advanced strategies that arise from leaps of insight into how the game works. Such scenarios could include, for example, the evolution of punishment and enforcement institutions.

Nadiah was until last year a Research Fellow in our lab, and she is now working at the University of Queensland. This paper was part of an ongoing collaboration with Hisashi Ohtsuki at The Graduate University for Advanced Studies in Japan.


Kristensen N.P., Chisholm, R.A. & Ohtsuki, H. (2025). Many-strategy games in groups with relatives and the evolution of coordinated cooperation. Journal of Theoretial Biology, 605:112089.