The functional role of biodiversity in ecosystems: incorporating trophic complexity

TLDR

Biodiversity’s impact on ecosystem functioning hinges on both horizontal and vertical diversity, with complexity shaped by consumer dietary generalism, competitive trade‑offs, intraguild predation, and migration, yet mechanisms remain poorly documented. The review aims to synthesize theoretical and experimental progress on how biodiversity shapes ecosystem functioning, emphasizing integration of simulations and network‑based approaches. The authors conduct a comprehensive review of theoretical models and experimental studies to assess biodiversity effects across trophic levels. Findings indicate that horizontal diversity boosts biomass and resource use, prey diversity improves resistance to predation, predator diversity can cascade to plant biomass depending on omnivory and prey behavior, and adding trophic levels qualitatively alters diversity effects, yielding richer diversity‑functioning relationships than single‑trophic‑level predictions.

Abstract

Understanding how biodiversity affects functioning of ecosystems requires integrating diversity within trophic levels (horizontal diversity) and across trophic levels (vertical diversity, including food chain length and omnivory). We review theoretical and experimental progress toward this goal. Generally, experiments show that biomass and resource use increase similarly with horizontal diversity of either producers or consumers. Among prey, higher diversity often increases resistance to predation, due to increased probability of including inedible species and reduced efficiency of specialist predators confronted with diverse prey. Among predators, changing diversity can cascade to affect plant biomass, but the strength and sign of this effect depend on the degree of omnivory and prey behaviour. Horizontal and vertical diversity also interact: adding a trophic level can qualitatively change diversity effects at adjacent levels. Multitrophic interactions produce a richer variety of diversity-functioning relationships than the monotonic changes predicted for single trophic levels. This complexity depends on the degree of consumer dietary generalism, trade-offs between competitive ability and resistance to predation, intraguild predation and openness to migration. Although complementarity and selection effects occur in both animals and plants, few studies have conclusively documented the mechanisms mediating diversity effects. Understanding how biodiversity affects functioning of complex ecosystems will benefit from integrating theory and experiments with simulations and network-based approaches.