Natural floodplain dynamics shape grasshopper assemblages of meadows in the Donau-Auen National Park (Austria)

Flooding events are an important factor shaping arthropod communities on riverine meadows. We investigated to what extent species diversity and species composition of grasshopper assemblages on meadows in the Donau-Auen National Park (Lower Austria) are affected by annual floods. Grasshoppers were sampled between June and September 2012 on 12 meadows prone to yearly summer inundations, and 13 meadows protected from such floods by a levee. All acoustically and visually detected individuals were counted. Excluding one stray species not associated to meadows and representatives of the genus Tetrix, which cannot be recorded reliably with our sampling method, a total of 24 grasshopper species were recorded. Species richness was nearly identical on both meadow types. However, species composition differed prominently between regularly flooded and non-flooded meadows. Furthermore, we compared local incidence of all 24 species (quantified as percentage of colonized meadows) with their regional occurrence (quantified as percentage of 6250 m x 5550 m grids with records in Eastern Austria). Accordingly, hygrophilous species are more prevalent in the Donau-Auen National Park than expected from their regional occurrence. Our study provides strong evidence that natural floodplain dynamics still have a significant impact on species composition of meadow grasshopper assemblages in the Donau-Auen National Park. Hence, maintaining high hydrological dynamics (e.g. by river restoration measures) will be a precondition to successfully protect the characteristic fauna of floodplain meadows.