Food Web Complexity Underlies Biodiversity Effects on Ecosystem Functioning

Abstract

Biodiversity change has elicited widespread concern over the consequences for functions and services provided by ecosystems1–3. Despite extensive evidence for a positive effect of biodiversity on ecosystem functioning within a single trophic level4,5, how this biodiversity effect varies with multitrophic food web structure remains unresolved6 even though most ecosystems contain two to six trophic levels7. We investigate how food web complexity modulates biodiversity-ecosystem functioning (BEF) relationships in nature by quantifying energy fluxes as proxies for two major ecosystem functions8—primary consumption and predation—in 318 highly-resolved, complex food webs from marine, lake, stream, and soil ecosystems. Ecosystem functioning increased consistently with taxon richness across all trophic levels and ecosystems, which arose from greater vertical diversity (i.e., maximum trophic level9) and trophic complementarity of predators in more taxonomically diverse food webs. Furthermore, predator trophic complementarity10,11 increased predation fluxes in all freshwater ecosystem types. These findings highlight the threat of trophic downgrading to critical ecosystem functions (e.g., biological control and maintenance of biodiversity and ecosystem stability) provided by predators12,13, which are typically most vulnerable to anthropogenic disturbances14,15. Our study demonstrates that the consequences of biodiversity change are deeply entangled within the web of life, emphasizing the need to conserve the trophic complexity underlying positive biodiversity-ecosystem function relationships.