Energetic constraints to food chain length in a metacommunity framework

Abstract

As metabolism increases with body size, populations of large-sized species can become constrained to relatively low trophic positions within a local community due to their high energetic demands combined with the limited efficiency with which energy is transferred up the food chain from primary producers. In a metacommunity context, dispersal can become a major driver of population dynamics and persistence, having also the potential to ameliorate the aforementioned energetic constraints due to its effect on colonization and energy subsidies from connected patches. Here, we derive a size-dependent model for food chain length in communities subjected to migration and show that populations with higher influx of migrants are able to persist at higher trophic positions. Simulations of random, dendritic, and real aquatic metacommunities corroborate this result and further indicate that community location in the landscape (relative centrality or isolation) may determine local food web structure. More central patches contained larger populations and were less constrained in trophic position. This effect was particularly strong in dendritic metacommunities, which are representative of freshwater watersheds in general. Furthermore, the role of spatial processes is nonlinearly intensified with increases in body size, indicating that larger organisms have a much stronger dependence on landscape attributes.