Tobias Bauer

• Urbanization drives environmental change at multiple scales and negatively effects biodiversity in several ways. Nonetheless, urban areas concomitantly offer resources and habitat for an array of different organisms and represent a still mostly unutilized opportunity for biodiversity conversation. On the other hand, cities have been identified as hotspots for alien plant species and facilitator for invasive plants. As a result, many urban habitats are dominated by non-native species. Green spaces represent the most important habitat analogue for organisms in cities. In this regard, urban grasslands have one of the greatest potential for conservation. With a majority of urban grassland still excessively managed solely for ornamental purposes, recent research demonstrated that extensively managed urban meadows with only one or two cuts per year facilitate a great diversity of arthropods, including species of conservation concern (cc). Nonetheless, the role of urban grassland in the applied conservation of arthropods at the local scale is still little investigated. The first part of the dissertation therefore aimed at disentangling the effects of management, local and landscape parameter on spiders (Araneae) and ground beetles (Carabidae) that occur in urban grassland situated in a large city of Southern Germany (Karlsruhe, Baden-Württemberg). For both taxonomic groups national recording schemes as well as local red lists are available. 27 urban grasslands in two management intensities (1-2 cuts with biomass removal, 3-5 cuts with self-composting) along an urbanization and humidity gradient were sampled with pitfall traps and sweep net. The results demonstrate that local parameters such as humidity and vegetation height had the strongest effects on the abundance of species of cc as well as assemblage composition, while intensive management negatively effected the abundance of both groups. Landscape parameters such as urbanization or isolation had comparatively minor effects on diversity and abundance. Dry and sparsely vegetated urban grassland hosted the largest number of species of cc, while the assemblages of mesic and humid grasslands mostly consisted of common species. In part, species of cc were sampled in high numbers on dry grasslands, indicating flourishing populations. If biodiversity-friendly management is financially or otherwise limited, it should primarily target dry grassland in urban areas. A further comparison with a large nearby grassland reserve (<Alter Flugplatz=) revealed that urban grasslands mostly harboured a subset of the spider diversity already present at the reserve, with only a few species exclusively found in urban grassland. Several specialists of xerothermic conditions remained restricted to the reserve with only a fraction of species of conservation cc recovered from urban grasslands (13 out of 37 species, 4 exclusive to urban grasslands). This comparison demonstrates that small urban grasslands may harbour several species of cc, but also exclude other, potentially area-sensitive specialists. To further address effects of urbanization and the urban matrix on organisms, we compared urban, suburban and rural populations of a common grasshopper (Chorthippus biguttulus) and analysed whether morphological and behavioural differences between them exist. Urban populations showed increased boldness and higher rates of fluctuating asymmetry, which may be explained by higher environmental stress in urban habitats during development and selection for bolder individuals in the urban landscape. The last part of the project focused on the effects of two invasive plant invaders. American species of goldenrod (Solidago canadensis and S. gigantea) and Himalayan balsam are common invasive plants in Karlsruhe, however, virtually nothing is known on their effects on vegetation-dwelling predators during flowering season. Spiders and potential prey items sampled from dense stands of both invaders showed contrasting effects on sampled specimens and functional groups in comparison with mixed stands of native plant species, demonstrating that both invaders altered spider abundances in different ways.