FOOD EFFECTS ON LIFE-HISTORY TRAITS AND SEASONAL DYNAMICS OF CERIODAPHNIA-PULCHELLA

1. This paper describes the effects of differences in food quantity an d quality on selected life history traits of Ceriodaphnia pulchella. A nimals were fed with four concentrations of two green algae, Scenedesm us obliquus and Chlamydomonas globosa, given separately as well as in a 1:1 mixture. 2. In most cases growth, reproduction and condition of the animals and consequently the rate of population increase, r, incre ased with food concentration. Life history parameters of animals raise d on S. obliquus were lowest, whereas no significant differences were found between animals fed with C. globosa and with the mixture of the two algal species. 3. In contrast to the large effects of food quantit y and quality found in the laboratory, an analysis of the population d ynamics of C. pulchella in Lake Tjeukemeer showed that the effect of c hanges in food conditions during the growing, season of this species w as limited, although overall food levels seemed to be poor throughout the year. 4. Changes in the birth rate of the population are mainly go verned by changes in temperature, and possibly by changes in the densi ties of the invertebrate predator Leptodora kindtii.