A global-scale collaborative study published this week in the prestigious journal Science shows that plant biodiversity within the world’s grasslands peaks at intermediate levels of productivity, lending support to a long-standing but controversial ecological hypothesis.
Three members of UBC Okanagan’s Institute for Biodiversity, Resilience, and Ecosystem Services (BRAES) — Jason Pither, John Klironomos, and former Biology graduate student David Ensing — are among 62 co-authors on the international study.
The paper quantifies how the number of plant species within the world’s grasslands varies as a function of plant biomass – a measure of ecosystem productivity.
More than 40 years ago, a seminal study hypothesized that diversity should peak at intermediate levels of productivity within herbaceous plant communities, such as grasslands.
If correct, this hypothesis would mean that the world’s grasslands – most of which are already impacted by human activities – could be managed to maintain or enhance biodiversity, itself a driver of ecosystem services upon which humans depend.
“Hundreds of studies have tested the ‘humped-back’ hypothesis, but results have varied widely, engendering vigorous debate in the literature,” says Pither.
The challenge is one of logistics.
“Achieving the geographic and environmental scope necessary to obtain a full picture requires remarkable effort,” says Pither, who led all the statistical analyses for the study and, along with Klironomos and Ensing, provided field data from the Okanagan region.
Enter “HerbDivNet” – an international consortium of researchers, coordinated by lead author Lauchlan Fraser, Professor of Biological Sciences and Canada Research Chair in Community and Ecosystem Ecology at Thompson Rivers University. Fraser enlisted investigators from around the world, including Pither and Klironomos, to help test the hypothesis at a global scale, across an enormous gradient of ecosystem productivity.
This was key, Pither explains, because they were able to show that previous studies, including a high-profile 2011 Science paper that refuted the hypothesis, likely lacked the power and sampling scope to detect and accurately quantify the relationship between biodiversity and the productivity of grasslands.
“Human activities are resulting in unprecedented rates of biodiversity loss,” says Pither, “so it’s crucial that if biodiversity does systematically vary with something manageable, such as productivity, we need to know.”
The HerbDivNet consortium continues to grow, and to collaborate on biodiversity research.
“We anticipate many more publications out of this remarkable collaboration,” Pither notes.
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