Predation rates on semi-natural grasslands depend on adjacent habitat type

Spillover in ecological systems, that is the dispersal or foraging of organisms across habitat borders, can affect ecosystem functioning and food web interactions of local communities. While spillover of organisms from perennial habitats into agricultural fields received some attention in the context of ecosystem service provisioning, the spillover into semi-natural habitats has rarely been addressed, although spillover of generalist predators or competition for pollinators can have consequences for nature conservation. We studied predation rates of ground-dwelling predators on 20 calcareous grasslands, with either coniferous forest or a crop field as adjacent habitat. As prey items we exposed 32,000 ladybird eggs on the grasslands. Within two study periods (June to September) predation rates were higher at warm compared to cool days, but did not depend on the study period itself or the distance from the edge where prey items were placed. In each study period we found higher predation rates when coniferous forest was the adjacent habitat, however, only on cool days. On warm days, prey items were consumed to very high extents (often 100%), which did not allow the detection of possible differences between adjacent habitat types. The higher predation rates on grasslands adjacent to forests can be explained by predator spillover from forests to grasslands. We conclude that semi-natural habitats provide not only ecosystem services in adjacent human dominated habitats, but are also exposed to antagonistic spillover effects. Such antagonistic spillover should be considered in conservation strategies for semi-natural habitats.