Vergleichende ökologische Untersuchungen an Epitheca bimaculata Charpentier 1825 im Saarland und in der Uckermark (Odonata: Corduliidae).

Abstract

Between 1988 and 1998, more than a hundred habitats of the supposedly rare corduliid dragonfly Epitheca bimaculata were studied in the western parts of the Saarland (SW- Germany), in the adjacent parts of Luxembourg and France (especially the valleys of the rivers Saar and Mosel) and in the Uckermark ('Biosphärenreservat Schorfheide-Chorin', NE- Germany). In the Saarland, the species inhabits eutrophic to polytrophic artificial backwaters, gravelpits and fish-ponds, whereas in the Uckermark it occurs in small natural, predominantly eutrophic lakes. Relevant characteristics of the Epitheca-habitats in both regions were the following: - still waters of small area: 85% of the habitats were less than 10 ha, 63% less than 4 ha; - relatively shallow water body without distinct stratification: maximum water depth between 1.1 and 12 m (91% less than 8 m, 67% between 2 and 6 m, only 12% with complete temperature stratification; - low oxygen content in deeper strata: usually less than 2 mg O2/l below 4 m; - water clouded by phytoplankton, eutrophic to polytrophic: breeding sites between 0.5 and 3.1 m median Secchi-depth (68% with visibility of less than 2 m); - water surface with abundant floating or submerged vegetation, more rarely also tree trunks or reed: substrates for oviposition and habitats of the younger larvae; - water surrounded by shrubs and/or deciduous woodland; - water inhabited by fish populations; - the dragonfly communities are dominated by Orthetrum cancellatum, Cordulia aenea and Erythromma species; aeshnids usually occur a low densities. - The typica habitats of Epitheca in central and western Europe are not large, oligotrophic lakes or slightly acetous bog ponds, but still waters in the flood plain (river lagoons or gravel pits) and small lakes inhabited by fish populations.

Keywords

Corduliidae, limnology, Uckermark, Saarland Germany, co-existence, fish, habitat structure, broad-leavered tree, forest, water vegetation, dragonfly community, lake, flood plain, optimal habitat, primary habitat, threat, negative factor.