Response of ground beetle (Coleoptera, Carabidae) communities to changes in agricultural policies in Sweden over two decades

• Carabid species richness or evenness did not differ in samples separated by 24 years.
• Carabid community and trait composition changed after mitigation of intensification.
• More omnivorous, mobile, spring breeding, and large species were found after mitigation.
• A functional approach provided a more mechanistic view of carabid response to land use changes.

Agricultural intensification has been recognized as an important driver of declines in biodiversity and ecosystem services. Changes in agricultural policy aims to mitigate these declines, but little is known about actual outcome of large scale changes in agricultural policy on communities of service-providing organisms. Two data sets containing captures of ground beetles (Carabidae) collected at an interval of 24 years were analyzed; the data were collected in the same area in Sweden under different environmental conditions before and after the introduction of a national pesticide risk reduction program. Environmental changes were analyzed by considering indicators of land use and agricultural management over time. Ground beetles collected over the whole season were considered and species were categorized according to functional traits. Environmental changes between the two time periods were characterized by increases in fallow and organic farming and a strong reduction in the amount of pesticide active ingredients sold and risk factors associated with pesticides. Although there were no changes in ground beetle species richness and community evenness after mitigation of agricultural intensification, there were differences in dominance distribution and functional composition. Ground beetles collected in the 1980s had higher proportions of carnivorous, cursorial, and small and intermediate size beetles than those collected in 2003. Communities sampled in 2003 had increased proportions of omnivorous, mobile, spring breeding, and large beetle species. These shifts in functional characteristics of ground beetle communities may improve biological control of cereal aphids and reduce variability in this ecosystem service over time.