Extending trait dispersion across trophic levels: predator assemblages act as top-down filters on prey communities

Studies of community assembly typically focus on the effects of abiotic
environmental filters and stabilizing competition on functional trait
dispersion within single trophic levels. Predation is a well-known driver
of community diversity and composition, yet the role of functionally
diverse predator communities in filtering prey community traits has
received less attention. We examined functionally diverse communities of
predators (fishes) and prey (epifaunal crustaceans) in eelgrass (Zostera
marina) beds in two Northern California estuaries to evaluate the
filtering effects of predator traits on community assembly, and how
filters acting on predators influence their ability to mediate prey
community assembly. Fish traits related to bottom orientation selected for
more clustered epifauna communities, and epifauna were generally
overdispersed while fishes were clustered, suggesting that prey may be
pushed to disparate areas of trait space to avoid capture by benthic
sit-and-wait predators. We also found correlations between the trait
dispersions of predator and prey communities that strengthened after
accounting for the effects of habitat filters on predator dispersion,
suggesting that habitat filtering effects on predator species pools may
hinder their ability to affect prey community assembly. Our results
present compelling observational evidence that specific predator traits
have measurable impacts on the community assembly of prey, inviting
experimental tests of predator trait means on community assembly, and
explicit comparisons of how the relative effects of habitat filters and
intraguild competition on predators impact their ability to affect prey
community assembly. Integrating our understanding of traits at multiple
trophic levels can help us better predict the impacts of community
composition on food web dynamics as regional species pools shift with
climate change and anthropogenic introductions.