The response of carabids to landscape simplification differs between trophic groups.

We studied the response of carabid species richness and density to landscape simplification (measured as percentage cover of non-crop habitat surrounding each study site) in 36 wheat fields using pitfall traps. Carabids were divided to trophic groups following the literature. The number of species from different trophic groups declined with increasing landscape simplification in the order: carnivores > phytophages > omnivores. Density compensation of both carnivores and phytophages suggests that species decline is caused by the loss of specific resources rather than by an overall reduction in food availability. Increasing evenness indicates that a greater share of phytophagous species contributes to density compensation at poorer sites. A comparison with data from complementing studies shows that marked differences in species numbers (carnivores > omnivores > phytophages) are due to a different sensitivity of trophic groups to agricultural management. Since our findings seem to be partly due to increasing sensitivity to landscape changes with trophic rank, and partly to decreasing sensitivity of depauperate communities to local environmental stress, species loss can best be explained by the co-action of factors at local and regional scales. Species richness decline might significantly alter the role of carabids as biocontrol agents.