Science Leadership

George Mercer Award (2025)

May 20, 2025

Congratulations to Assoc Prof Ryan A Chisholm and Dr Lynette HL Loke on receiving the prestigious 2025 George Mercer Award (2025). The accolade recognises their groundbreaking ecological study which tested competing theories about ecological community assembly using experiments conducted on intertidal communities in Sentosa, Singapore. 

Classic theory suggests that niches set a ceiling on the number of species coexisting in a community, and that only low immigration of new species keeps communities from reaching this ceiling. An alternative theory proposed in Assoc Prof Chisholm’s previous work suggests the opposite: that niches set a floor on the number of coexisting species, with immigration typically maintaining the number of species above this floor. 

The field experiment used a novel community assembly design to manipulate immigration rates; thereafter, the authors applied mathematical models to the data to test alternative hypotheses for community assembly. The results support the novel theory, indicating that niches provide a low floor on species diversity and suggesting that in nature, where immigration is typically high, most species coexist only transiently. These conclusions can be adapted for other ecological systems and used as a ‘niche detector’ for assessing when communities are niche versus dispersal assembled. This work was published in Nature (7 June 2023).

Each experimental unit comprised a custom-built habitat tile with a stainless steel cage and polycarbonate panels containing several holes, the number of which was adjusted across units to modulate immigration (Photo credit: Lynette Loke)
A selection of intertidal animals observed in the experiment (Photo credit: Lynette Loke)
The relationship between species richness and immigration rate in the experiment exhibited a low floor at low immigration rates, consistent with the novel theory (red), rather than a high ceiling at high immigration rates, as predicted by the classic theory (blue)

The awards committee noted: “Deftly integrating field experiments with clear hypotheses and mathematical modelling, 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.” 

Assoc Prof Chisholm heads a theoretical ecology and modelling laboratory at the Department of Biological Sciences, Faculty of Science. Dr Loke is a former graduate of the department who currently heads a spatial and community ecology laboratory at the University of Melbourne.

The George Mercer Award was established in 1948 and is awarded annually by the Ecological Society of America for an outstanding ecological research paper published in the last two years whose lead author is under 40.