Trophic position of consumers and size structure of food webs across aquatic and terrestrial ecosystems

Do large organisms occupy higher trophic levels? Predators are often larger than their prey in food chains, but empirical evidence for positive body mass - trophic level scaling for entire food webs mostly comes from marine communities based on unicellular producers. Using published data on stable isotope compositions of 1093 consumer species, we explored how trophic level scales with body size, food-web type (green vs. brown) and phylogenetic group across biomes. In contrast to widespread assumptions, the relationship of body size on trophic level of consumers, from protists to large vertebrates, was not significant per se, but varied among ecosystem types and animal groups. The correlation between body size and trophic level was strong in marine, weak in freshwater and absent in terrestrial consumers, which was observed also at the scale of local food webs. Vertebrates occupied higher trophic positions than invertebrates and green trophic chains were longer than brown in aquatic (prim...