Biotic mechanisms contributing to the stability of productivity differ along a gradient of rainfall variability

Productivity increases with precipitation across spatial gradients but does not as closely track precipitation over time, nor does high variability in precipitation lead to highly unstable productivity. Patterns of precipitation variability may be associated with different biotic mechanisms controlling the stability of productivity. We used nine long-term (>10 years) datasets of species composition from LTER grasslands across a US climate gradient to relate two stabilizing mechanisms – stable dominant species and negative species covariance – with precipitation variability. We found that dominant species were more stable in sites characterized by low precipitation variability, whereas negative species covariance increased with precipitation variability. Considering biotic stabilizing mechanisms in light of environmental conditions may help unify previous conflicting reports on the relative importance of biotic mechanisms for ecosystem stability.