CONSUMER–RESOURCE BODY-SIZE RELATIONSHIPS IN NATURAL FOOD WEBS

TLDR

Differences in body size between consumers and their resources are thought to influence interaction strengths, population dynamics, and food‑web structure, yet the global distribution of consumer–resource body‑size ratios remains poorly understood. Across a global database, aquatic herbivores and detritivores exhibit body‑size ratios several orders of magnitude larger than carnivorous predators, and predator–prey ratios are higher in freshwater than marine or terrestrial systems, greater for vertebrate than invertebrate predators, and larger for invertebrate than ectotherm vertebrate prey, implying systematic variation in interaction strengths across habitats and consumer types.

Abstract

It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer–resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator–prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator–prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer–resource interaction strengths may vary systematically across different habitat categories and consumer types.