Seasonal differences in predation risk among seagrass epifauna species stabilize community-level predation over time

Predation risk varies through space and time due to changing refuge quality, predator communities, and prey traits. Despite this, ecological research is often focused on measuring average predation risk at the community level. While this can give important information about overall trophic transfer and ecological efficiency, it ignores differences in predation risk among prey species within a community, which may be important determinants of species coexistence and local diversity. We used crustaceans associated with temperate seagrass in Northern California to explore the relationship between seasonal variation in among-species and community-level predation risk for a community of morphologically distinct prey. We measured predation risk of the four most abundant and widespread prey species at six field sites every two to six weeks for one year. At the community level, sites differed significantly in their annual variation in predation risk, and these differences were correlated with the amount of variation in the among-species predation risk. When there was more within-year variation in predation risk among the four prey species, predation risk at the community level was more stable across the year. On the other hand, when each prey species in the community had similar levels of predation risk throughout the year, predation as a community-level process was much more seasonal and variable. Variation in predation risk also changed across a gradient of seagrass cover, a proxy for refuge quality. Sites with greater seagrass cover had less annual variation in community-level predation risk and more variation in predation risk among the four species at any given time point. In contrast, at sites with less eelgrass, all species were consumed at the same rate throughout the year, suggesting previously demonstrated differences in antipredator strategies among species are less relevant in the absence of habitat-forming species. We suggest that larger species-specific differences in predation risk throughout a year result in a more stable level of predation risk for the whole community, and that this may be driven by increased refuge provided by seagrass habitat mediating different prey species relative levels of susceptibility to predation.