Environmental variables drive differences in the beta diversity of dragonfly assemblages among urban stormwater ponds

Stormwater ponds are beneficial to urban landscapes because these man-made systems can reduce the negative effects of flooding in urban areas and restrain the distribution of pollutants. In addition, these systems are especially important to maintain the biodiversity of urban landscapes. Here, we sampled a set of 18 stormwater ponds in the city of Uppsala in Sweden to test the relationship between beta diversity of adult dragonflies and environmental factors (local and land use variables). We analysed the total beta diversity and its two components: replacement and richness difference. We recorded 31 species of Odonata, comprising 61% of the Odonata species in the province of Uppland in Sweden. By itself, this result indicates the importance of stormwater ponds in contributing to biodiversity in urban areas. The richness difference component of beta diversity was higher than the replacement component. Results from generalized dissimilarly models indicated that the richness difference component was mainly related with pond area and total vegetation cover (aquatic vegetation plus vegetation surrounding ponds). Focusing on different vegetation variables separately, models indicated that the beta diversity components were significantly correlated with percentage cover of floating algae scums, emergent aquatic macrophytes and tall shore vegetation. These results are consistent with what is known about the ecology of dragonflies, including the importance of aerial plant structures for perching, shelter from terrestrial and aquatic predators, and for providing oviposition sites. We also found that the stormwater ponds harboured a large part of the regional species pool. These systems are therefore important havens of biodiversity in urban landscapes. Our results also indicate that the management of different types of vegetation is key to maximize the potential of these systems in maintaining regional biodiversity.