A mathematical model developed by Prof Cang Hui at Stellenbosch University has proven to be the single best method from several tested worldwide for estimating the diversity of plants over a large area.
Models are crucial tools that allow scientists to estimate the biological diversity of particular habitats, regions, countries and even continents, and to assess how this might be changing over time.
Prof Hui was part of an international effort involving five research groups who were asked to test the accuracy of their modelling techniques by applying it to small samples from the same dataset – the 1999 Great Britain Countryside Survey. Their predictions were then tested against data from the national database of British plant species.
This provided the “true" species-area relationship for British plants, enabling the research team to determine the best modelling technique. It is the first time that these mathematical techniques could be tested, and compared, on such a large scale. The results of the study were published in the journal Ecological Monographs this week.
Of all the models tested, the single best method for estimating the shape of species-area relationship was that of Prof Hui, based on his concept of species' occupancy ranking. It is also the first time for this model to be published.
Prof Hui's research group in the Department of Mathematical Sciences at SU focuses on developing models and theories for explaining emerging patterns in ecology: “As ecological processes are highly complex and adaptive, we rely on the simplicity of mathematical language to build models and theoretical frameworks," he explains
Another top performing model was that of Prof Fangliang He (University of Alberta, Canada) and Prof Tsung-Jen Shen (National Chung Hsing University, Taiwan), which provided estimates within 10% of the true value.
The other models performed less well; while there are around 2,300 plant species in area in question, some models' up-scaled species richness estimates were far off the mark, ranging from 62 to 11,593.
Prof William Kunin, an ecologist from the University of Leeds and lead author on the article, says policymakers are often concerned with the preservation of biodiversity at national, continental or global scales, but most biodiversity monitoring is conducted at very fine scales.
“This mismatch between the scales of our policies and of our data creates serious challenges, especially when assessing biodiversity change."
In this study, the task required estimating the biodiversity of an area five orders of magnitude larger than the total area sampled - equivalent to estimating the species richness of the land plants across the entire globe based on samples that cover only 3,000 km2.
The methods will greatly aid the work of the Intergovernmental Panel on Biodiversity and Ecosystem Services (IPBES). One of their aims is to provide policymakers with objective scientific assessments about the status of the planet's biodiversity and its services to people. The Convention on Biological Diversity (CBD) also requires countries to improve their monitoring and reporting of biodiversity, as set out in the Aichi Targets.
Prof Kunin believes mathematical modelling of biodiversity upscaling has come of age: “These methods will greatly facilitate biodiversity estimation in poorly-studied taxa and regions, and the monitoring of biodiversity change at multiple spatial scales," he concludes.
On the photo: Prof Cang Hui. Photo: Stefan Els
Prof Cang Hui
Department of Mathematical Sciences, Stellenbosch University
Prof William Kunin
University of Leeds
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