Effects of small-scale grassland fragmentation and frequent mowing on population density and species diversity of orthopterans : a long-term study

1. Habitat fragmentation is considered one of the major threats to invertebrate diversity in semi-natural grassland. However, the effects of habitat fragmentation through mowing on the rich insect fauna of these grasslands have not been sufficiently investigated and experiments are especially rare. 2. We studied the impact of small-scale grassland fragmentation on orthopterans over 7 years in an experiment which allowed us to additionally investigate the effect of frequent mowing on Orthoptera communities. 3. Overall, Orthoptera density and species richness increased over time. This was likely a result of increased small-scale habitat heterogeneity and the provision of a short-turf habitat suitable for xerophilous species. The fragmentation affected orthopteran density and species composition but not species richness whose response lagged behind the changes in abundance. 4. Responses differed between suborders. Ensifera density was higher in fragment than in control plots. Caelifera density did not differ between fragment and control plots. The mown matrix was an unsuitable habitat for most of the species, particularly within the Ensifera. 5. Our experiment shows that even small-scale fragmentation can affect Orthopteran communities and that the effects became more pronounced over time. As the mown matrix was unsuitable for many Ensifera species, they may go locally extinct when large areas are mown simultaneously.