Trait-specific effects of habitat isolation on carabid species richness and community composition in managed grasslands

1. Isolation of natural and semi-natural habitats, a consequence of increasing management intensification, has been identified as a major threat to the diversity of many taxa in agricultural landscapes. Yet, it is increasingly apparent that the effects of habitat isolation vary not only among distantly but also closely related taxa, depending on their respective ecological traits. 2. We studied the effects of habitat isolation on carabid beetles with different dispersal potential in common perennial grasslands. The grasslands belonged to three isolation classes: (i) situated in a continuous belt of grasslands, (ii) in an arable matrix but connected to the continuous belt via corridors or (iii) completely isolated in the arable matrix. 3. Neither total carabid species richness nor richness of carabids with high dispersal potential was affected by habitat isolation. In contrast, richness of carabid species with low dispersal potential was more than two times lower in isolated than in continuous grasslands. Communities of isolated sites were characterised by species with high dispersal potential whereas species with low dispersal potential were associated with continuous or well connected grasslands. 4. Our results revealed trait-specific responses of carabids to habitat isolation and highlight the need for considering these differences when predicting effects of landscape structure on carabid diversity. Grassy corridors seemed to assist the dispersal of carabids with low dispersal potential, thereby allowing these species to persist also in non-continuous but connected habitats. Thus, corridors represent a suitable measure to maintain the diversity of carabids in spatially structured grasslands in agricultural landscapes.