How does ecological variation among grazer species constrain community assembly?


For species to exist in the same place, they often need to have similar habitat requirements but different resource use or feeding strategies.  In Bodega Bay, CA, I combined trait data with surveys of community composition throughout bay habitats (eelgrass beds, mudflats, fouling communities) to understand the relative importance of habitat filtering vs. niche partitioning in structuring amphipod communities.

Best, R.J., and J.J. Stachowicz. Phenotypic and phylogenetic evidence for the role of food and habitat in the assembly of communities of marine amphipods. In press @ Ecology: preprint.

What is the relative value of trait vs. phylogenetic diversity for predicting species interactions and community composition in experimental vs. field contexts?

Trait data is time consuming to collect, subject to phenotypic plasticity, and dependent on biases about what traits we think might be important.  This has led to increasing interest in using phylogenetic proxies for the ecological variation between species.  However, the link between phylogenetic relationships and species coexistence varies with both trait lability and ecological context.

Ultrametric tree for Bodega Bay grazers

By combining a Bayesian phylogeny of northern CA amphipods, data on a range of traits, a mesocosm experiment, and observations of community composition in the field, I found that competitive interactions in experimental mesocosms were driven by labile feeding traits, and therefore not predictable from phylogenetic relationships. In contrast, at the scale of community assembly in the field phylogenetic relationships do predict coexistence via different, more conserved traits.

Best, R.J., and J.J. Stachowicz. Phenotypic and phylogenetic evidence for the role of food and habitat in the assembly of communities of marine amphipods. In press @ Ecology: preprint.

Best, R.J., N.C. Caulk, and J.J. Stachowicz. 2013. Trait vs. phylogenetic diversity as predictors of competition and community composition in herbivorous marine amphipods. Ecology Letters 16:72-80.

Best, R.J., and J.J. Stachowicz. 2013. Phylogeny as a proxy for ecology in seagrass amphipods: which traits are most conserved? PLoS ONE In press.

How does trait variation affect ecosystem function?

ulva in eelgrassGlobally, seagrass meadows are declining, and this is often due to overgrowth by algae.  One possible cause of this overgrowth is increased predation on the invertebrate grazers that control that algae.


However, using trait data for the grazer species in the Bodega Bay eelgrass system, I found that this kind of trophic cascade can be weakened by a mismatch between species-specific feeding rates on algae and species-specific predation susceptibility.

Best, R.J., and J.J. Stachowicz. 2012. Trophic cascades in seagrass meadows depend on mesograzer variation in feeding rates, predation susceptibility, and abundance. Marine Ecology Progress Series 456:29-42.

What trait combinations permit species invasions?

In Bodega Bay, a few species of amphipods are introduced from Asia or the North Atlantic. In bays with more shipping, introduced species now make up a much larger proportion of the community. To understand what this means for the health of eelgrass ecosystems, I am testing whether the introduced species succeed by having different feeding strategies than the native species, or by simply being physiologically suited to environmental conditions in the bays where they are found.