Die postglaziale Besiedlung Mitteleuropas durch Libellen, mit besonderer Berücksichtigung Südwestdeutschlands (Insecta, Odonata). The postglacial colonization of Central Europe by dragonflies, with special reference to southwestern Germany (Insecta, Odonata)

The migratory routes along which the Central European species of dragonflies probably immigrated from their periglacial refuges into Central Europe are reconstructed. Due to the topographical configuration in Central Europe, the postglacial invasions were confined to only a few routes. Mountain chains and also small river valleys, i.e. the Rhine valley between Lake Constance and Waldshut, acted as barriers; while geotectonic depressions, such as the ‘Geneva Gate’, ‘Burgundian Gate’ and ‘Moravian Gate’, played an important role as ‘gateways’ in overcoming these obstacles, the wide river plains were used as corridors to invade the hinterland. The extent of the immigration into Central Europe by the dragonfly species depended on the one hand on the distances which had to be covered from the refugial areas, but, on the other hand, also on the distinct postglacial climatic periods (Preboreal, Boreal, Atlantic, Subboreal, Subatlantic). Depending on their thermal requirements each species started expanding from their refugial areas at different times. Due to variable postglacial climatic conditions, progressive migratory phases alternated with regressive phases. The very different recent distribution patterns of the Central European dragonflies can only be understood if all the climate history, landscape morphology, the thermal requirements of the species, their origin (refugial areas) and history of colonization are considered. Because many Central European dragonfly localities currently lie at the periphery of the range of many species, these species can only survive in these areas if individual ‘reinforcements’ from their centres of distribution are possible. They still take place mainly along the old routes. Thus, disruption of the migratory routes, especially at the gateways, due to anthropogenic actions may influence the fauna of large Central European regions. Due to many anthropogenic influences, the routes already often seem to be interrupted over long distances and the connections to the centre of distribution already broken. As a result of precise knowledge of the courses of the migratory routes a better prediction is possible as to whether species conservation measures or recolonization projects will be successful.