Effects of road density on regional food webs.

Roads stand as major threats to biodiversity because they affect the functioning of ecosystems and the provision of ecosystem services. Understanding how the effects of roads affect the dynamics of ecological interactions is essential to managing human impacts on biodiversity, but such studies are few. We investigated species vulnerability to road density and effects of road density on food webs across Europe. Using species-specific road density thresholds, beyond which local populations may not persist, and trophic interaction data (predator-prey interactions), we constructed regional food webs to assess the potential loss of trophic interactions due to roadkill. We analyzed data on 551 species across top, intermediate, and basal trophic levels. Effects of roads varied spatially. In areas near major cities, species lost >90% of their trophic interactions. We found 191 species that were affected by loss of prey or predators. Apex predators exhibited lower direct impacts from road density than predators at lower trophic levels, and basal-level species seemed more exposed to direct road-related effects (roadkill), which could trigger a cascade of interaction disruptions. Our findings emphasize the need for informed road infrastructure development and targeted conservation strategies to mitigate the negative impacts of roads and traffic and thereby preserve the integrity of ecological networks. Our identification of critical areas where road-induced cascade effects may be most pronounced and of groups of species that may be at higher risk from roads can inform policy and conservation planning.