Interannual rainfall variability promotes species coexistence primarily through relative nonlinearity in interaction strength

Combating the effects of global change and biodiversity loss requires a deeper understanding of species coexistence across variable environments. Little is known, however, about how drivers of coexistence respond to environmental change.

Using a greenhouse competition experiment, we examine how interannual rainfall variation influences competitive dynamics in an old‐field annual plant community in southern China. We parameterize a competition model for eight species to assess coexistence outcomes under constant and variable rainfall conditions, partitioning variation‐independent and variation‐dependent mechanisms of coexistence.

We show that species are more likely to coexist under variable rainfall conditions. Of the coexistence mechanisms examined, relative nonlinearity of the interaction strength most strongly promotes coexistence, followed by a lesser positive contribution from relative nonlinearity of the vital rates, while the interaction effect between these nonlinearities tends to destabilize coexistence.

Synthesis . Our study provides novel evidence that rainfall variability promotes pairwise species coexistence in a multispecies plant community, driven primarily by the relative nonlinearity in interaction strength. These findings highlight the necessity of incorporating environmental variability into coexistence studies to better predict and manage biodiversity in a changing world.