Neutral theory reveals the challenge of bending the curve for the post‐2020 Global Biodiversity Framework

In October, nations of the world will begin negotiations for the post‐2020 Global Biodiversity Framework under the Convention on Biological Diversity. An influential ambition is “bending the curve of biodiversity loss,” which aims to reverse the decline of global biodiversity indicators. A second relevant, yet less prominent, milestone is the 20th anniversary of the publication of The Unified Neutral Theory of Biodiversity and Biogeography. Here, I apply neutral theory to show how global biodiversity indicators for population size (Living Planet Index) and extinction threat (Red List Index) decline under neutral ecological drift. This demonstrates that declining indicators are not solely caused by deterministic species‐specific or geographical patterns of biodiversity loss. Instead, indicators are sensitive to nondirectional stochasticity. Thus, “bending the curve” could be assessed relative to a counterfactual based on neutral theory, rather than static baselines. If used correctly, the 20‐year legacy of neutral theory can be extended to make a valuable contribution to the post‐2020 Global Biodiversity Framework.
Global biodiversity indicators for populations (Living Planet Index) and extinction threat (Red List Index) decline under random ecological drift. The consequence of this is that prominent aspirations to “bend the curve of biodiversity loss” may be untenable, at least in terms of current biodiversity metrics. The Unified Neutral Theory of Biodiversity and Biogeography—which celebrates its 20th anniversary this year—could be used as a counterfactual against which to measure progress toward the post‐2020 Global Biodiversity Framework.