The negative impact of urban sprawl on biodiversity: A simulation approach to genetic diversity in European cities

Current urbanization trends pose multiple challenges to biodiversity conservation and the provision of ecosystem services to city dwellers. Beside attempts to halt urbanization, urban planners can control urban forms, i.e., the spatial configuration of artificial areas within and around cities. Yet, a lack of consensus on their influence on biodiversity hinders appropriate decision-making. It is commonly predicted that compact cities should exhibit low biodiversity levels at their center while preserving the biodiversity of peri-urban areas, whereas the opposite pattern should be observed in sprawled cities. To test whether these trade-offs can actually emerge from existing urban forms, we simulated the genetic diversity of urban and peri-urban animal populations in 325 European cities. We delineated them by standardizing the proportion of artificial areas to 20 %, and distinguishing urban green spaces from forest habitats. We then modeled the indirect interplay of urban forms (irrespective of the degree of urbanization), the connectivity of these two habitats, and their respective genetic diversity. Our statistical path modeling results revealed an overall negative effect of urban sprawl on habitat connectivity, and consequently on genetic diversity in both habitat types. Interestingly, forest habitat connectivity was a better predictor of genetic diversity in the urban populations of the simulated species than was urban green space connectivity. This reflected the importance of preserving peri-urban habitats from urban sprawl, as they may act as biodiversity sources for city centers. Accordingly, efforts to foster biodiversity within cities should not overshadow the large-scale impacts of urban sprawl on peri-urban biodiversity. • We simulated the effect of European urban forms on animal population genetic diversity. • Urban sprawl indirectly affects genetic diversity by altering habitat connectivity. • This results in a negative impact on both urban and peri-urban genetic diversity. • Peri-urban habitat connectivity is key to maintain biodiversity within cities. • Urban biodiversity management should consider both cities and their surroundings.