Through decades of experimental and observational research, ecologists have sought to understand how changes in biodiversity affect ecosystem productivity. While most small-scale experiments report positive effects, evidence from non-experimental settings is mixed. These conflicting results reflect challenges in developing empirical designs that permit credible, generalizable causal inferences from ecological systems. These challenges can, however, be overcome through recent advances in data and methods. To estimate how changes in species richness affect productivity, we leverage multi-site, longitudinal data from over 1200 unmanipulated plots in 43 grassland ecosystems around the world, and apply methods from public health and economics specifically designed for inferring causality from observational data.
Results/Conclusions
We find that losses in species richness cause productivity to increase: a 10% decline in richness leads to a 2.4% increase in productivity We find that losses in species richness cause productivity to increase: a 10% decline in richness leads to a 2.4% increase in productivity (i.e., an effect size of -.24 of biodiversity on productivity with a 95% CI of [-0.397, -0.083]). This result cannot be explained by observable or unobservable confounding factors but could be explained by plausible ecological mechanisms and the types of biodiversity changes happening in the Anthropocene as non-native species invade new areas and rare species are preferentially lost from ecosystems. As new sources of longitudinal ecological data become available, our methods can be applied more broadly to improve causal inferences about ecological relationships from observational data.
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