Interactive effects of local and landscape factors on farmland carabids
1. As a result of migration and spillover from noncrop habitats, predacious insects in agricultural fields respond locally to adjacent field margins and on a larger spatial scale to habitats in the surrounding landscape. However, the relative importance of local and landscape effects and their possible interactions have rarely been studied.
2. We studied carabids in 18 pumpkin fields bordered by different field margins, along a gradient from simple to structural rich landscapes. Carabids were caught in pitfall traps along transects from the adjoining semi-natural habitat towards the field centre.
3. Although estimated species richness generally increased towards the field edges, carabid abundance increased towards adjacent woody margins and other crop fields. By contrast, abundance decreased towards adjacent herbaceous margins. Estimated carabid species richness in organically managed fields increased with increasing landscape heterogeneity, whereas this effect was absent in conventional fields. However, estimated species richness did not differ between organic and conventional fields.
4. The differential response of carabid abundance to distance from the field edge in accordance with the type of field margin may explain the variability of patterns reported in the literature. The results of the present study show that both local and landscape parameters must be taken into account to promote carabids as natural enemies of crop pests.