Comparing habitat and landscape effects on carabid (Coleoptera: Carabidae) traits in cereal fields and grasslands

Carabids are important natural biocontrol agents for pest regulation in agricultural landscapes. Their role in the ecosystem is related to functional traits, which are themselves filtered by both the degree of habitat disturbance and the landscape composition and configuration that distribute ecological resources. Here we aim at sorting out the influences of habitat and landscape context on carabid traits in permanent grasslands and winter cereal crops (wheat or barley). We sampled carabids in adjacent grasslands and cereal fields in three agricultural plains of south-eastern France. We analysed the links between carabid traits and their occurrence in the studied habitats using regression models. We also characterised the influences of habitat and landscape context on trait distribution using multivariate analyses. Polyphagous species were more likely than others to be shared by both adjacent grassland and cereal fields. Granivorous carabids were strongly related to grasslands, while predatory and polyphagous species were more often captured exclusively in cereal crops when exclusive to one habitat. Small apterous carabids were more likely to be found in grasslands only. Concerning the influence of the landscape, polyphagous species were related to cereal crops surrounded by higher grassland coverage or lower compositional heterogeneity. Smaller carabids were more likely to be found in the vicinity of high grassland coverage, and apterous carabids in grassland-dominated landscapes. Grasslands thus not only provide resource and habitat complementation for generalist carabid species from neighbouring croplands, but they also host distinctive species showing particular traits. It is therefore important to maintain or restore grasslands in agricultural landscapes to support species and functional diversity in farmland.