The distribution pattern of mire specialist butterflies in raised bogs of the northern lowlands of Central Europe
Raised bogs are extreme and azonal ecosystems with a characteristic hydrological balance, microclimatic conditions and a specific flora and fauna. Recently, these ecosystems have increasingly become the focus of scientific and general attention because of their important ecosystem roles in the face of global warming and providing biodiversity refuges. From a biogeographical and evolutionary context, the peat bogs of the European Lowlands serve as palaeorefugia, acting as cold, edaphic island habitats for arcto-alpine or boreo-montane insect species in temperate biomes. Analysing 105 peat bog sites in the northern lowlands of Central Europe, we compare the diversity and geographic distribution pattern of a subset of six butterfly species, which appear to be tyrphobiontic or tyrphophile mire specialists. We demonstrate a decrease in mean species number in the European Lowlands on a gradient from the east (Northern Belarus, about 4 species) to the west (Northern Germany, about 1 species), and suggest that the decreasing species number may be mainly caused by human impact in the past. The individual distribution pattern shows a nearly complete gap in occurrence of the sensitive bog specialist species Colias palaeno and Boloria eunomia in Northern Germany and an increasing presence of those species in peat bogs of eastern Europe. Boloria aquilonaris shows a different pattern, which, in contrast to C. palaeno, is continuously distributed in all sampled regions and seems to be the more tolerant of tyrphobiontic butterflies in the face of human impact on peat bogs. In the light of other recent findings our results also suggest that Boloria aquilonaris and Plebejus optilete may serve as target species reflecting success in ecological restoration of peat bog ecosystems.