Functional Redundancy and Climate Resilience

Abstract

Functional redundancy -- the number of species performing the same ecological function, providing an insurance buffer against the loss of any individual species -- has long been proposed as the primary mechanism by which biodiversity stabilises ecosystem functions across environmental perturbations. Communities with high functional redundancy are buffered against functional loss from species extinction because co-occurring species with similar functional roles can compensate for the lost species' contribution. Under climate change, functional redundancy takes on additional significance: when one functionally redundant species is eliminated by warming or drought, others with different but overlapping thermal tolerance ranges can maintain the function -- making redundancy across thermal niches (response diversity to temperature) the specific component of functional redundancy most relevant to climate resilience. This study quantifies functional redundancy and response diversity across 247 plant and animal communities in 84 ecosystem types across 18 biomes, and tests whether redundancy predicts ecosystem function stability across a 28-year climate variability record. Functional redundancy (measured as mean number of species per functional entity; FRed) was the strongest predictor of function stability under interannual climate variability (partial R2 = 0.54; p < 0.001). Response diversity -- the variance in species' individual responses to temperature across functionally equivalent species (RDiv) - added significant independent variance (R2 = 0.28; p < 0.001) beyond FRed alone: communities with both high FRed and high RDiv maintained ecosystem functions across 94.7% of the climate variability range observed over 28 years, while low FRed-low RDiv communities maintained functions across only 47.4% of this range