Community assembly in subtidal epibenthic invertebrate communities in the Gulf of Maine: A community phylogenetic and functional trait approach

How organisms assemble to form a community is a central question in
ecology, with commonly inferred mechanisms including environmental
filtering, competitive exclusion, and random processes. Community
phylogenetic and functional trait analyses have been used to identify the
relative importance of these processes, most often in terrestrial
angiosperm systems consisting of a single taxon (e.g., class). Here,
community phylogenetic and functional trait analyses are applied to
multiphyletic subtidal epibenthic invertebrate assemblages at eight sites
in the Gulf of Maine, to investigate the relative importance of
deterministic or stochastic forces in structuring these communities. At
local sites, some communities were phylogenetically overdispersed,
suggesting community assembly via competitive exclusion. Five traits
exhibited phylogenetic signal and for these traits, phylogeny can be used
as a proxy for ecological similarity. Functional trait diversity was
overdispersed for one site and clustered for another, indicative of
assembly via competitive exclusion and environmental filtering
respectively. Regionally, taxonomic beta diversity was less than expected
by chance but phylogenetic and functional trait beta diversity were
greater than expected, indicating that species are not dispersal limited
and that different environmental conditions among sites select for
different species. These results suggest that subtidal epibenthic
invertebrate assemblages in the Gulf of Maine are structured by
deterministic forces and that different assembly processes operate at
different spatial scales: locally, competitive exclusion appears to be
important whereas regionally, environmental filtering plays a role.