Summer floods shape meadow butterfly communities in a floodplain nature reserve in Central Europe

Abstract

How flooding regimes shape temperate-zone butterfly communities has received little attention. At the river Danube in eastern Austria, a levee has largely interrupted natural river dynamics since the late nineteenth century. Only a fraction of the floodplain area still experiences annual summer inundations after snow-melt in the Alps. We surveyed meadow butterfly communities on either side of the levee in a year with an unusually strong flood (2013), and in a season with a weak flood typical for the region (2012). Altogether we observed 67 butterfly species. Butterfly abundance and species richness were lower on meadows with stronger flood impact, but differences were modest. In contrast, species composition differed prominently relative to flooding regime and nectar availability. Grass-feeding species tended to be rarer on flooded meadows, while Brassicaceae-feeding species were more prevalent on nutrient-rich flood-prone meadows. Highly dispersive butterflies made up a larger share on flooded meadows, whereas highly philopatric species were relatively more common at sites with little or no inundation. These results indicate that summer inundations at the river Danube act as filters for the local species composition of butterflies on floodplain meadows. Local resource availability and the differential potential of species to re-colonize meadows after catastrophic floods are likely drivers of these differences. Effects of inundations were not consistently stronger in a year of a catastrophic flood than in a normal season. Butterfly communities on non-flooded meadows had a higher regional conservation value.