Spillover of arthropods from cropland to protected calcareous grassland - the neighbouring habitat matters.

Spillover effects of organisms from semi-natural habitats to adjacent crops have been frequently reported, yet evidence for the reversed process and associated functional consequences remains scarce. We examined the spillover of carabids, rove beetles and spiders from agricultural lands to protected, high-nature value calcareous grasslands by comparing two neighbourhood types: seven calcareous grasslands neighbouring intensively managed winter wheat fields and seven calcareous grasslands neighbouring intensively managed meadows in Germany. We examined arthropod activity density with repeated pitfall trapping in both the edge and the interior of all three habitat types (14 study sites). All three arthropod groups showed consistently higher activity density in calcareous grasslands adjacent to wheat fields than calcareous grasslands adjacent to meadows, apparently through spillover effects. Activity density of carabids and spiders exhibited a decline from the interior to the edge of the wheat fields and to even lower density at the edge and lowest density in the interior of the calcareous grassland. Carabid spillover from both neighbouring habitats to grasslands was driven by a dominant predatory species, Pterostichus melanarius, whereas Oedothorax apicatus was the dominant contributor to spider spillover from wheat to grasslands. Our results show that neighbourhood identity (wheat or meadow) can shape arthropod density and community composition in semi-natural habitats due to spillover of carabid beetles, spiders and rove beetles from adjacent crop fields. Neighbourhood effects on spillover are thus more accentuated at the cropland-grassland interface compared to the meadow-grassland boundary, with small grasslands being particularly affected due to their high edge-to-interior ratios. Our results suggest that meadows around high-nature value, protected grassland reserves, may be important conservation elements by attenuating arthropod spillover from arable crops. Such spillover may compromise the identity, structure and functioning of endangered communities.