Scale-dependent environmental filtering of ground-dwelling predators in winter wheat and adjacent set-aside areas in Hungary

Agricultural intensification may act as an environmental filter shaping invertebrate assemblages at multiple spatial scales. However, it is not fully understood which scale is the most influential. Therefore, we utilized a hierarchical approach to examine the effect of local management (inorganic fertilization and soil properties; within-field scale), habitat type (winter wheat field and set-aside field; between-field scale) and landscape complexity (landscape scale) on assemblage structure and functional diversity of two important groups of natural enemies, carabids and spiders, in a cultivated lowland landscape in Hungary. Environmental filtering affected natural enemies at different spatial scales; likely as a result of enemies’ different dispersal ability and sensitivity to fertilizer use. Carabids were strongly affected at the within-field scale: positively by soil pH, negatively by soil organic matter and fertilization. At the between-field scale, carabids had higher activity density in the set-aside fields than in the winter wheat fields and simple landscapes enhanced carabids diversity, species richness and activity density at the landscape scale. Spiders were more abundant and species-rich in the set-aside fields than in the winter wheat fields. Although highly mobile (macropterous) carabids might disperse to arable crops from greater distances, while spiders possibly depended more on the proximity of set-aside fields, the winter wheat fields (where pest control should be delivered) were utilized mostly by common agrobiont species. Increasing crop heterogeneity within arable fields could be a potential option to increase the diversity of carabids and spiders in the studied region.