Ecosystems face unprecedented threats arising from extinctions, invasive species, and the accumulation of persistent contaminants.  The response of an ecosystem to these threats is mediated by the structure of the food web, and depends crucially on the food web's degree of compartmentalization. Despite its ecological importance, compartmentalization and the mechanisms that give rise to it remain poorly understood.  Here, we investigate several definitions of compartment, propose ways to understand the ecological meaning of these definitions, and quantify the degree of compartmentalization of empirical food webs.

Results/Conclusions

We find that the compartmentalization observed in empirical food webs is consistent with the predictions of models that do not explicitly introduce compartments, which indicates that the observed compartmentalization can be accounted for by the one-dimensional niche organization of species and their diets.  By uncovering the connection between compartmentalization and species' diet contiguity, our results help us understand which perturbations may entail catastrophic effects and which ones may lead to ecosystem fragmentation. Additionally, we show that the composition of compartments can be used to address the long-standing question of what determines the ecological niche of a species.