University of Salzburg, Department Environment & Biodiversity, Austria
In the last few decades insects have been facing steady declines. In addition to other anthropogenic stressors, land use change is one of the main drivers. Urbanization is an ongoing land-use change worldwide due to constant human population growth. However, urbanization can have detrimental effects on insects, especially through habitat loss, altered resource availability and via dispersal barriers. To protect biodiversity and to fulfil human needs in urban spaces, it is important to understand if and how urbanization affects insect species, especially understudied ones such as insects occurring in small standing waters in tree holes, tires, graveyard vases, flowerpots and others. These waters serve as breeding habitats for insects and may contribute to urban biodiversity. They can provide ecosystem services like decomposition and the production of pollinators (adult pollinating insects with aquatic larvae) or ecosystem disservices like the production of mosquitoes. In a four-year study, we (1) investigated the species assemblages of waterbodies in the city of Salzburg, Austria and how different urbanization measures affect aquatic insect community composition, abundance, species richness and litter decomposition. (2) To understand energy fluxes and to disentangle food web structure in these systems, we measured trophic positions of inhabitants using stable isotope techniques. (3) Using camera traps, we aimed to shed light on how small standing urban waterbodies are used by terrestrial animals such as birds. (4) Finally, we investigated if urbanization effects apply to other cities in Europe. First results clearly reveal soil-sealing as positive and green structures as negative predictors for abundance of aquatic larvae (mostly midges), while imperviousness also affects species composition. Higher temperatures in urban spaces significantly increased decomposition. Additionally, we give first insights into the trophic positions of larvae within these aquatic microhabitats, confirming detritus as main resource and a lack of predators. Using preliminary data, we could show negative effects of urbanization on the use of water systems by terrestrial animals (feeding, bathing, drinking). Further analyses in different cities will provide detailed information on how our results are applicable to urban spaces more generally. Concluding, this study contributes to a broad understanding of how urban spaces and their structures contribute to biodiversity (loss) and how certain management measures like the promotion of green structures might help to strengthen urban biodiversity.
