Distance functions of carabids in crop fields depend on functional traits, crop type and adjacent habitat: a synthesis

Natural pest and weed regulation are essential for agricultural
production, but the spatial distribution of natural enemies within crop
fields and its drivers are mostly unknown. Using 28 datasets comprising
1,204 study sites across eight Western and Central European countries, we
performed a quantitative synthesis of carabid richness, activity densities
and functional traits in relation to field edges (i.e. distance
functions). We show for the first time that distance functions of carabids
strongly depend on carabid functional traits, crop type and, to a lesser
extent, adjacent non-crop habitats. Richness of both predators and
granivores and activity densities of small and granivorous species
decreased towards field interiors, whereas the densities of large species
increased. We found strong distance decays in maize and vegetables whereas
richness and densities remained more stable in cereals, oilseed crops and
legumes. We conclude that carabid assemblages in agricultural landscapes
are driven by the complex interplay of crop types, adjacent non-crop
habitats and further landscape parameters with great potential for
targeted agroecological management. In particular, our synthesis indicates
that a higher edge-interior ratio can counter the distance decay of
carabid richness per field and thus likely benefits natural pest and weed
regulation, hence contributing to agricultural sustainability.