Feeding environment and other traits shape species' roles in marine food webs.

Food webs and meso-scale motifs allow us to understand the structure of ecological communities and define species' roles within them. This species-level perspective on networks permits tests for relationships between species' traits and their patterns of direct and indirect interactions. Such relationships could allow us to predict food-web structure based on more easily obtained trait information. Here, we calculated the roles of species (as vectors of motif position frequencies) in six well-resolved marine food webs and identified the motif positions associated with the greatest variation in species' roles. We then tested whether the frequencies of these positions varied with species' traits. Despite the coarse-grained traits we used, our approach identified several strong associations between traits and motifs. Feeding environment was a key trait in our models and may shape species' roles by affecting encounter probabilities. Incorporating environment into future food-web models may improve predictions of an unknown network structure.