Das Habitatspektrum von Aeshna juncea (L.) in der Schweiz (Anisoptera: Aeshnidae)

About 120 breeding sites were investigated with regard to certain biological and physical features. The upper vertical distribution (2240 m a.s.l.) coincides approximately with the natural tree line; the occurrence of larvae depends on the presence of aquatic vegetation and organic mud. The sp. colonises a great variety of habitats such as moorland pools, peat diggings, ditches, slowly running rivulets in inclined bogs and alpine lakes of different sizes. The water surface at a breeding site may vary from a few square metres to several hectares; the mean depth is 29 cm (range 1 -120 cm; range in 66% of the sites 1 -20 cm). On average the water is slightly acid (mean pH 5.0, range pH 3.3-93), the concentration of electrolytes is low (mean electric conductivity 64(iS, range 5-370pS, range in 66% of the sites 5- -35pS). The same is true of the concentration of carbonate (mean 34 ppm CaCOj, range 0-243 ppm CaCOj, range in 67% of the sites 0-18 ppm CaCO,). The vegetation consists of various aquatic plant communities, characterised by emergent, stalky plant structures (mean height 29 cm above the water, range 10-70 cm; coverage 5-100%, mean 48%). A. juncea appears more versatile with respect to its habitat requirements than other alpine odon. spp., but it cannot be considered a generalist. The observations are compared with those from the Black Forest bogs, Germany.