Urban arthropod communities: Added value or just a blend of surrounding biodiversity?

Urban areas are species-rich ecosystems. The question remains, however, whether urban species constitute a unique community, and thus add value to landscape biodiversity, or whether they are just a mixture of species from surrounding ecosystems. In this study, the occurrence and abundance of arthropods were analysed according to trophic guilds (Cerambycidae and Buprestidae as xylophagous species, Apiformes as pollinators, Neuroptera as flying predators, Araneae and Carabidae as surface-dwelling predators) in urban, agricultural and forest ecosystems in Switzerland. To assess the likely origin of arthropod fauna in Swiss cities, we identified character species (regular and constant occurrence) for ecosystems and performed ordination and cluster analyses. In total, we studied 10,034 specimens from 497 species and found that 13% of all species and 10% of the character species were predominately found in the urban ecosystems. Community analyses showed that the three ecosystems harbour distinct species assemblages. While communities at forest sites are quite dissimilar from those at urban and agricultural sites, these latter share more than one third of all character species, which indicates either that agricultural areas function as source habitats for urban communities or that agricultural species have survived urbanisation in situ. Overall, our study identified a distinct urban arthropod community that enriches landscape (gamma) diversity in Switzerland. Urban sites may provide novel habitats for species of former extensive agriculture, or species otherwise not, or scarcely, occurring in the region. The present study illuminates the value of urban arthropods for overall biodiversity which should be incorporated in planning decisions.

► We analysed 497 arthropod species in cities, agriculture, and forests. ► 10% are unique to the urban ecosystems. ► Urban communities are closer to agricultural areas than to forests. ► Distinctive urban communities add to beta and gamma diversity. ► The value of urban arthropods should be incorporated in urban planning decisions.