The effect of field boundary type on the community structure, spatial distribution and physiological condition of overwintering arthropods, with special reference to Carabidae and Staphylinidae (Coleoptera)
The potential of different field boundary types in lowland farmland to contribute to arthropod biodiversity and sustainable agriculture was investigated. Field boundaries, categorised according to nationally applicable definitions, were found to represent ecologically differing habitats based on their woody abundance and the frequency of young and mature emergent trees. These habitat characteristics were determining factors in the community structure and composition of overwintering epigeal arthropods. Hedgerows supported the most species rich carabid and staphylinid assemblage. Degraded hedgerow boundaries supported the most equitable carabid community, and provided a refuge for carabid species with poor dispersal power to a greater extent that hedgerows or post and wire fences. The grassy and natural regeneration vegetation associated with post and wire boundaries supported high densities of all taxa particularly overwintering carabid and staphylinid polyphagous predators. A subset of all field boundary types was required for complete species representation, indicating that maximising the heterogeneity of field boundary habitats represented at the farm-scale will enhance arthropod biodiversity in farmland. Carabidae and Staphylinidae actively selected overwintering sites and the physiological condition of polyphagous predators was generally high. It was concluded that heterogeneous distributions in field boundaries were more likely to be the result of differential microhabitat selection rather than differential survival overwinter. This indicated that favourable overwintering microhabitats occurred in all field boundary types. Generally, overwintering survival did not appear to be a regulating factor in the population dynamics of polyphagous predators. Margins adjacent to pre-existing boundaries may contribute to enhanced densities and physiological condition of some polyphagous predators, both over winter and in early spring. The results were discussed in relation to field boundary management and agri-environment policy.