Long-term population trends in three grassland insect groups: a comparative analysis of 1951 and 2009

Development of farming practices has caused drastic changes in European agricultural landscapes during the past 50 years. As a consequence of these changes, insect diversity is widely expected to decline. We performed a comparative analysis with long-term data of three insect groups: Auchenorrhyncha, Heteroptera and Orthoptera. In 2009, we revisited nine grassland sites in northern Germany that were originally sampled in 1951 using the same techniques and during a similar time frame. We found that the insect community exhibited no consistent trends between years. Species richness of Auchenorrhyncha and Heteroptera increased on plot level as well as on landscape level but remained unchanged for Orthoptera. Abundance of Auchenorrhyncha and Orthoptera significantly decreased, while Heteroptera increased. There is a strong trend towards homogeneity in community composition for Heteroptera and a weak one for Auchenorrhyncha. The frequency and abundance of species preferring disturbed and/or eutrophic habitats increased, whereas the number of species preferring low-productive habitats declined. This trend is especially pronounced in Auchenorrhyncha. Generalistic species were more abundant in relative proportions as well as in absolute numbers. We hypothesize that these trends arise from alterations of Central European landscapes because of agricultural intensification over the last several decades.