AbstractInvestigations on the life histories of two cladocerans,Moina brachiataandDaphnia obtusa, in a small, nearly temporary pond in South Germany revealed thatM. brachiatais better adapted to fluctuating environmental conditions; the species dominated from May to October.D. obtusawas present in spring and autumn/winter but disappeared completely during the summer months. Both species coexisted for extended periods in spring and autumn; abundance ofD. obtusawas generally by an order of magnitute lower. Four periods of low water level were slightly preceded by or coincided with a decrease of clutch size, a decrease of the proportion of egg bearing females indicating that both species suffered from food shortage.Laboratory investigations on life history parameters showed that the two species have different temperature tolerances and preferences.M. brachiatashowed its highest reproductive success at 25 and 30°C but died at temperatures<15°C and ≥ 35°C.D. obtusaexperienced a broader temperature range (2 to 25°C) but could not withstand temperatures ≥ 30°C. Short term starvation periods (3d) caused the death ofM. brachiatafemales, whileD. obtusasoon recovered and reproduced when being refed.M. brachiatais a typicalr‐species with early reproduction, rapid development, high population growth rates and a high tendency to produce resting eggs;D. obtusapursues more the concept ofk