Trophic Island Biogeography

Background/Question/Methods

Historically, the structure of ecological food webs has been attributed to the availability of resources and the interactions between species. However, the role of spatial processes in driving food web structure remains poorly understood. Recent theory predicts that food web structure should vary predictably with island size and isolation. Here, we test this theory of “trophic island biogeography” by describing variation the food web structure of reef fish communities on 55 islands in the South Pacific. We show that the predator-prey ratio is highest in low diversity systems and that the ratio varies strongly and predictably with biogeographic characteristics.

Results/Conclusions

 Importantly, our data exhibit opposite patterns from those predicted by the theory of trophic island biogeography. Specifically fish communities on larger and less isolated islands contain two prey per predator, whereas food webs on smaller and more isolated islands have approximately 1 prey per predator. Our study provides novel empirical evidence for spatial process in governing food web structure, which substantially alters our current understanding of the role of spatial process in driving large-scale variation in community structure. Given the known links between structure and function of ecosystems we suggest that the observed variation in structure of food webs may also have implications for conservation and management. Specifically, lower diversity systems that house a smaller standing biomass of fish and have high predator prey ratios may be particularly sensitive to human-induced alterations of food web structure.