Ground beetle dynamics in intensively managed agricultural landscapes

Sammanfattning: In this thesis I have focused on studying dynamics of ground beetle assemblages in intensively managed agricultural landscapes. By definition, the land cover of these landscapes is dominated by annually tilled farmland, comprising a range of different crop types, in the context of the southern Swedish province of Scania mostly winter wheat, spring barley, winter rapeseed, and sugar beets. This background begs the question: can the presence of ground beetles in intensively managed agricultural landscapes be facilitated without sacrificing land dedicated to crop production? Crop diversification has been mentioned as a possible greening measure to mitigate agricultural intensity. Our results show that semi-natural grasslands and leys may not function as source habitats at a landscape-scale if they comprise a low proportion of the total land-use, while increasing crop diversity is correlated to ground beetle richness and diversity in agricultural landscapes dominated by arable land. Autumn breeding ground beetles were indicative of low crop diversity landscape. This is likely a result of high proportions of winter sown cereals that increase dominance of the species Pterostichus melanarius Illiger. Larger species were absent from assemblages emerging ground beetle assemblages in intensively managed crops such as sugar beet. Further, our results suggest that winter wheat fields are less adverse habitats for overwintering larger ground beetles as compared to sugar beet fields. Sugar beet management reduces emergence of larger ground beetle species that dominate actively moving assemblages, indicating that especially larger species are drivers of local ground beetle dynamics. Differences in isotopic composition between emerging and colonizing individuals of Trechus quadristriatus Schrank suggests that a significant proportion of individuals of this species came from remote locations, perhaps crossing the Baltic Sea with easterly winds.