The significance of a grassy field boundary for the spatial distribution of carabids within two cereal fields

This paper investigated how distance from the field edge affects overall activity-density, species richness and distribution of individual carabid (Coleoptera: Carabidae) species. Carabid beetles were sampled using pitfall traps at six different locations: grassy field boundary, 0 (field edge), 4, 11, 24 and 49 m distance from the field edge, in two fields of winter wheat (Wageningen, the Netherlands) during the spring and early summer of 2004. The assemblage of carabid beetles was highly diverse, consisting of 75 species. Carabid activity-density was low in the boundary compared to the field. Within the field, it was highest at the edge and decreased towards the field centre. Species richness, standardized to the number of individuals, did not differ between sampling locations. Based on the within-field distribution three ecological groups of carabids were distinguished: (i) boundary species; (ii) field-interior species and (iii) field-edge species. Because species within one genus differ in their response to the boundary, the importance of studies at species level is stressed.