Cordulegaster heros and Somatochlora meridionalis in Ukraine: solving the zoogeographical puzzle at their northern range limits (Odonata: Cordulegastridae, Corduliidae)

The first records of Cordulegaster heros and Somatochlora meridionalis in Ukraine completed their distribution picture, thereby allowing the zoogeography of Balkan Odonata species at their northern range limit in Eastern Europe to be better understood. Five localities of C. heros in the Khotyn and Chernivtsi Uplands showed the eastern colonisation route to have proceeded north through the eastern Subcarpathians and adjacent hilly areas in Romania and southern Ukraine. A habitat and zoogeographical analysis mostly solved the Cordulegaster-puzzle in Ukraine and drew a picture of a northern C. boltonii-zone divided from a southern C. heros-zone by the extensive Podolian Upland. The population of S. meridionalis found in the extreme southwestern Ukraine completed the northernmost range limit in Eastern Europe between the known Slovakian and Romanian localities. It occurs in the Transcarpathian Lowland, i.e., the northernmost part of the Great Hungarian Plain in the direct foreground of the Carpathian foothills. Thus, it perfectly follows the species distribution pattern largely based on an extensive border zone of great basins and low foothills of the adjacent mountain ranges of the Carpathians and Alps. The situation and habitat of Ukrainian and eastern Slovakian localities suggest the Tisa River system as the main colonisation route of S. meridionalis for Central and Eastern Europe. Clear differences in the population sizes between streams suggested the optimal, acceptable, and marginal habitats of C. heros, which differed in the grain size of the bottom sediments, the stream morphology, and water current. Somatochlora meridionalis occurred in a several-metre-broad slow flowing and largely shaded canal-like river where specific habitat conditions were responsible for the concentration of species activity near the levee and pipe culvert.