Local, neighbor and landscape effects on the abundance of weed seed-eating carabids in arable fields: A nationwide analysis

Recent studies suggest that weed seed predation by carabid beetles may partly substitute for chemical weed control in agriculture. Promoting this weed regulation service would require enhancement of the in-field abundance of seed-eating carabids, yet, the diversity of the habitat, trophic requirements and spatial scales of response of different species are complex and our understanding of how management at different spatial scales affects the abundance of seed-eating carabids is limited. Using data collected in 161 arable fields and four crop types across the UK, the factors affecting the abundance of nine common seed feeding carabid species at three spatial scales (local, neighboring, landscape) were investigated using GLMMs. Locally, crop type strongly affected the abundance of individual species, in a species-specific manner and the intensity of field management had a negative effect on the abundance of several species, irrespective of their trophic guild. The occurrence of oilseed rape and grasslands in the neighborhood was found to decrease the abundance of generalist seed-eating carabids but was the main factor positively affecting the abundance of the mainly granivorous Amara aenea, which occur almost exclusively in our sampled oilseed rape fields. At the landscape scale, a generally positive effect of the cover of grassland and oilseed rape demonstrated that in-field carabid abundance responds to the spatial distribution of agricultural land-use in the wider landscape. These findings suggest that management options could be implemented at multiple spatial scales to promote weed seed predation in arable fields.