The coexistence of three species of Daphnia in the Klostersee : II. The stabilizing effect of selective mortality and conclusions for the stability of the system.

Data are presented which make it most probable that selection according to relative visibility (represented by body size and egg ratio) and relative mortality stabilize the coexistence of Daphnia hyalina hyalina Leydig, D. galeata gracilis Hellich and D. cucullata Sars in the prealpine Klostersee. The results are based on multiple and partial correlation analyses which showed positive partial correlation between relative size and/or relative egg ratio and/or relative abundance, and the index of selectivity (W) according to Vanderploeg and Scavia (1979). Further it turned out that besides size, abundance, and egg ratio, the lake temperature but not other environmental parameters are related with the mortality of Daphnia. From these data a verbal descriptive model is derived which explains the seasonal segregation and stable coexistence of the three species.