Agri-environmental schemes promote ground-dwelling predators in adjacent oilseed rape fields: diversity, species traits and distance-decay functions.
Rising demands for agricultural products and high environmental costs of intensive agriculture reinforce the need for ecological replacements in agricultural management. In Europe, agri-environmental schemes (AES) are implemented to enhance species richness and provision of ecosystem services, but the effectiveness of different AES types and the spatial extent of possible beneficial effects are little understood. In this study, we assessed the effects of different AES types on diversity, species traits and distance-decay functions of ground-dwelling predators in adjacent crop fields. On 31 study sites with winter oilseed rape (OSR) adjacent to four types of AES differing in management intensity and habitat age, we recorded ground-dwelling predators (carabid beetles, staphylinid beetles and spiders) during OSR growth from April to July. Effects of the AES on species richness, activity densities and different traits of these taxa were examined with transects of pitfall traps running along a continuous distance gradient from the AES across the habitat border into the OSR fields. Ground-dwelling predator communities benefitted similarly from the different AES types. In adjacent OSR, activity densities, carabid species richness and the proportion of predatory carabid beetles declined from the field edge, while mean body size increased. Adjacent AES increased the proportion of predatory species and simultaneously decreased the proportion of granivorous or frugivorous species in adjacent OSR fields. Synthesis and applications. Our results indicate a beneficial effect of adjacent agri-environmental schemes (AES) on ground-dwelling predators in oilseed rape (OSR), mostly irrespective of agri-environmental schemes type and therefore management intensity and habitat age. The short-ranged distance-decay effects on natural enemies in oilseed rape underpin that a strategic spatial placement of agri-environmental schemes in agricultural landscapes is required to maximize biological pest control. This could help replace anthropogenic input in modern agriculture and secure adequate yields.