Unravelling the correlates of species richness and ecological uniqueness in a metacommunity of urban pond insects

Abstract

City ponds have the potential to harbour a rich biodiversity of aquatic insects despite being located inan urban landscape. However, our current knowledge on the correlates of pond biodiversity is limitedand even less is known about the factors that influence the ecological uniqueness of urban ponds. Themultiple environmental gradients, at different spatial scales, that may affect biodiversity and ecologi-cal uniqueness of urban ponds can thus be seen both as an opportunity and as a challenge for a study.In this study, we aimed to fill this gap by focusing on aquatic insect assemblages in 51 ponds in theSwedish city of Stockholm, using a metacommunity perspective. We found that species richness wasprimarily determined by the density of aquatic insects, water depth and proportion of buildings aroundthe pond. The uniqueness of ponds was estimated as local contributions to beta diversity (LCBD), and itwas primarily related to the proportion of arable land and industry around the ponds. With regard tothe metacommunity we found two interesting patterns. First, there was a negative relationship betweenrichness and LCBD. Second, biodiversity was spatially independent, suggesting that spatially-patterneddispersal did not structure species richness or LCBD. These last two patterns are important when consid-ering conservation efforts of biodiversity in city ponds. We hence suggest that the conservation of insectbiodiversity in urban pond should consider the surroundings of the ponds, and that high-richness pondsare not necessarily those that require most attention because they are not ecologically the most unique.