Primary consumer body size and food-chain length in terrestrial communities

Using 21 community food webs, we tested Elton's two hypotheses regarding the main factors limiting food-chain length in terrestrial communities, namely, energy (energy limitation hypothesis-ELH) and body size (size limitation hypothesis-SLH). As predators tend to be larger than their prey, food-chains are size-structured: animal size increases with trophic position. We found a negative correlation between the size of the primary consumer and the length of the chain. Food-chains based on small primary consumers are longer than those based on large primary consumers, and size rather than energetic efficiency is the main contributing factor. We found no correlation between habitat productivity and mean food-chain length. All these findings support the SLH over the ELH. Our results suggest that, as in aquatic communities, a single factor-a predator/prey size-ratio greater than 1-governs the structure of terrestrial communities.