Annual variation of oilseed rape habitat quality and role of grassy field margins for seed eating carabids in arable mosaics

Promoting the weed seed predation service by carabids requires an understanding of the spatio-temporal distribution of carabid species during the cropping season. In the present study, we analyzed the spatio-temporal dynamics of three abundant seed-eating carabid species in oilseed rape (OSR) and its adjacent habitat (cereal crop or grassy field margin) with four indicators: activity density, nutritional state, the use of the interface with the adjacent habitat, and the proportion of carabids leaving OSR. The activity density and nutritional state of Poecilus cupreus decreased after harvest, comprising a period related to a decrease of resource availability and the end of life cycle. We detected a tendency of movement from OSR to the adjacent habitat after harvest for Amara similata, although this was not as strong as expected. The presence of grassy field margins influenced the spatio-temporal dynamics of Pseudoophonus rufipes and A. similata, suggesting that spillover processes exist for these two species but not for P. cupreus. Monitoring four complementary indicators gave a more thorough understanding of the perception of local and adjacent habitats by carabids, which is a prerequisite for the identification of landscape configurations that enhance the activity density of these natural enemies within crops.