Carabid distribution in a farmland mosaic: the effect of patch type and location

The distribution and abundance of carabid beetles was studied in a large pa tch of farmland of 150 fields. If the species pool is supposed to be the sa me over the study area, differences between the occurrence of beetles on th e fields are probably due to habitat choice. We investigated the carabid co mmunities of 27 fields by pitfall trapping. The community composition of th e green set-asides differed from those of the tilled fields. In the set-asi des, the proportion of the autumn-breeding individuals was almost 70% at th e beginning of June, while the potato fields and bare set-aside field suppo rted mostly spring breeders. Morisita's index indicated that there was a re lationship between the similarity of the communities and the distance betwe en them. However, the distance was found to be an important factor in expla ining dissimilarity only in barley fields. This may be because colonization of tilled fields occurs early in spring and is dependent on the species po ol of neighbouring fields and field margins.