DISTRIBUTION, DIVERSITY, LIFE-CYCLE AND GROWTH OF A MAYFLY COMMUNITY IN A PREALPINE STREAM SYSTEM (INSECTA, EPHEMEROPTERA)

Within the framework of a study on the ecology of Dippers in a prealpine stream system, the macroinvertebrate communities were also investigated, especially Ephemeroptera. Ten stations were sampled qualitatively, of which two (Saane and Turbach streams) were investigated quantitatively for 16 months (April 1983-July 1984). Fifteen mayfly species were found. The faunistic affinities among the 10 streams investigated reflect the main abiotic characteristics. There was no significant difference in species richness, diversity and evenness for Saane and Turbach streams. Life cycles of nine species were studied in these two watercourses. Those of Rhithrogena degrangei, Rh. hybrida, Rh. savoiensis and Ecdyonurus helveticus are described for the first time. Baetis alpinus is the only species to exhibit a bivoltine cycle, whereas all others have a univoltine summer or winter cycle. Specific growth rates were measured for most species. The summer generation of B. alpinus presents the highest growth rate (4.51% dry weight d(-1)), whereas the lowest values were recorded for Rh. degrangei (0.76% dry weight d(-1)). The importance of abiotic variables, especially water temperature, is also discussed.