UNC Ecology Seminar: James Stegen

Dispersal, Environmental Niches, and Oceanic-Scale Beta-Diversity in Deep-Sea Bivalves

Elucidating processes responsible for the structure of ecological communities is one of the longest standing questions in ecology. To gain insight, studies have related the degree of turnover between pairs of communities (beta-diversity) to the spatial and/or environmental distances between them. Strong relationships between beta-diversity and spatial or environmental distance suggest important roles of dispersal limitation or environmental filtering, respectively. Available evidence shows that dispersal limitation and environmental filtering operate simultaneously. However, studies only examine the relative magnitudes of these processes, and we have yet to uncover the quantitative scales at which dispersal limitation and environmental filtering operate. In the current study we qualitatively and quantitatively estimate the scales at which these processes operate in deep-sea bivalve communities spanning the Atlantic Ocean. We combine data on community composition with species phylogenetic and functional trait data. These data were used to characterize taxonomic, phylogenetic and functional trait beta-diversity among all sites. We also take a pattern-oriented modeling approach by comparing empirical beta-diversity patterns with predictions from a novel community assembly simulation model. Our results indicate that environmental filtering based on limiting resource supply is more influential than dispersal limitation. We also find that turnover in taxonomic composition occurs at a much higher rate than turnover in phylogenetic or functional trait composition. Species composition may thus be highly stochastic while physiological and morphological attributes of community members are governed by relatively deterministic processes. In addition, through our theoretical-empirical comparison we estimated that dispersal limitation occurs at a scale between 240-750 km and environmental filtering operates at a scale of 1.2-2.1 g C / m^2 / day. That is, an individual has a 5% chance of a propagule dispersing to a location that is 750 km away from its location and surviving in a location that has resource supply 2.1 g C / m^2 day-1 away from its optimal resource supply. In sum, by coupling taxonomic, phylogenetic and functional trait beta-diversity to process-based theoretical predictions we have provided highly novel information on the relative and absolute magnitudes of dispersal limitation and environmental filtering in deep-sea bivalves.