A meta‐analysis of biotic resistance to exotic plant invasions

TLDR

Biotic resistance is the ability of resident species to limit exotic plant invasions, yet the processes driving it and their strength remain uncertain, with classic theory emphasizing competition and the enemies‑release hypothesis. The study aimed to quantify how resident competitors, diversity, herbivores, and soil fungal communities contribute to biotic resistance in plant invasions. The authors performed a meta‑analysis of published plant invasion studies to assess the effects of these biotic factors. The analysis showed that resident competitors, diversity, and herbivores all exert strong negative effects on invader establishment, herbivores being as effective as competitors, while fungal communities had little impact, and overall biotic resistance limits but does not prevent invasion, merely constraining invasive abundance.

Abstract

Abstract Biotic resistance describes the ability of resident species in a community to reduce the success of exotic invasions. Although resistance is a well‐accepted phenomenon, less clear are the processes that contribute most to it, and whether those processes are strong enough to completely repel invaders. Current perceptions of strong, competition‐driven biotic resistance stem from classic ecological theory, Elton's formulation of ecological resistance, and the general acceptance of the enemies‐release hypothesis. We conducted a meta‐analysis of the plant invasions literature to quantify the contribution of resident competitors, diversity, herbivores and soil fungal communities to biotic resistance. Results indicated large negative effects of all factors except fungal communities on invader establishment and performance. Contrary to predictions derived from the natural enemies hypothesis, resident herbivores reduced invasion success as effectively as resident competitors. Although biotic resistance significantly reduced the establishment of individual invaders, we found little evidence that species interactions completely repelled invasions. We conclude that ecological interactions rarely enable communities to resist invasion, but instead constrain the abundance of invasive species once they have successfully established.