Baltimore Ecosystem Study Cary Institute of Ecosystem Studies

2012 BES Annual Meeting Presentation and Poster Abstracts

Local and regional constraints on diversity of an experimental urban metacommunity
Swan, Christopher
Co-Authors: Katherine Brundrett

Abstract: The complex urban landscape is hypothesized to mediate both the local and regional factors that influence species diversity of ecological communities. To begin to understand the mechanisms of how urbanization can shape biodiversity patterns, we focused on two regional constraints, source pool composition and dispersal, and one local environmental factor. We hypothesized that (1) dispersal should interact with local habitat conditions to mediate levels of biodiversity, and (2) a reduced species pool in urban habitats should constrain the response of communities to diverge along the local environmental gradient. To address these predictions, we manipulated each in a full-factorial design to estimate the response of zooplankton communities in pond mesocosms. Mesocosms were inoculated from either three rural or three urban stormwater ponds, and dispersal maintained in half of the mesocosms for 12 weeks. Local water quality was degraded by introducing road deicer as sodium chloride, a contaminant of rising local concern. We found that dispersal increased diversity significantly, and the presence of chloride significantly reduced diversity. Furthermore, the reduction in the number of taxa and constraints on composition of the urban species pool limited the ability for communities to diverge across the two deicer treatments. Our results suggest (1) dispersal played a strong role in shaping local diversity patterns, and (2) regional species pool composition constrains the ability of communities to respond to a shifts in local environmental conditions. This study provides one of the first experimental tests of local versus regional factors shaping urban metacommunities.