Relative importance of competition with Daphnia (Cladocera) and nutrient limitation on Anuraeopsis (Rotifera) population dynamics in a laboratory study

1 In the laboratory, the growth and reproduction of Anuraeopsis fissa were measured when fed on Scenedesmus species grown in nutrient-sufficient, nitrogen-limited and phosphorus-limited media and in the presence or absence of one adult Daphnia longispina per vial. 2 Poor food quality may reduce the effect of competition on rotifers. Competition from Daphnia was stronger with nutrient sufficient algae than with nutrient limited algae. P-limitation significantly reduced Anuraeopsis population growth rate and fecundity. The effect of nutrient limitation on Anuraeopsis was stronger than that of competition with Daphnia. The Anuraeopsis population declined with P-limited food in both the presence and absence of Daphnia. 3 Exploitative competition by Daphnia on Anuraeopsis was stronger in the nutrient-sufficient treatment than in the N-limited one. Density, fecundity and population growth rate of Anuraeopsis were negatively affected by Daphnia in the nutrient-sufficient treatment, while only fecundity was reduced by Daphnia in the N-limited treatment. Consequently, in the N-limited treatment, mortality should be lower in the presence of Daphnia. This result could suggest that Anuraeopsis lives longer when short of nitrogen. 4 Nutrient limitation may affect to the competitive interactions between zooplankton species. P-limitation decreased the quality of algae as food for Anuraeopsis while N-limitation decreased the susceptibility of this rotifer species to exploitative competition by Daphnia.