Farmland versus forest: comparing changes in Odonata species composition in western and eastern Sweden

Despite the loss of natural ecosystems in the developed world during the past millennia, anthropogenic landscapes still sustain much biodiversity. Our question was, whether ten year changes in regional Odonata faunas are comparable between farmland and forested areas, or if the species pool of farmland areas respond in other ways than that of forest. We used data of dragonfly larvae collected from 16 lakes in a farmland area in south-western Sweden in the years 2002 and 2011/12, and compared these to data from 34 lakes in a forest area in south-eastern Sweden in the years 1996 and 2006. The species-richness in the agricultural region increased by 17% but decreased by 13% in the forested region. The changes in occurrence and regional distribution were similar in both areas, affecting 71% and 69% of the species pool. Average extinction rates were comparable between the agricultural and the forested region (38% and 43%) while colonisation rates differed greatly (64% and 114%). The species composition differed between the regions; the forest lakes harboured a 29% larger species pool. It is possible that in the forested region, the regional species pool in areas surrounding the study sites could stabilise the extinction and have a positive effect on changes in species composition. We assume that the different habitat structures of the waters in the agricultural and the forest regions and changes in temperature are the main driving forces behind the shifts. The mean seasonal air temperature has increased by circa 0.5 degrees C in both regions, when comparing ten-year periods before each sampling year.