FOOD-DEPENDENT AGGREGATION AND MOBILITY OF THE WATER FLEAS CERIODAPHNIA-DUBIA AND DAPHNIA-PULEX

In this paper, we show that two freshwater cladoceran zooplankters (Ceriodaphnia dubia and Daphnia pulex) differ in swimming speed and ability to locate local regions of high food concentration in a flow-through circular chamber. This comparison is of general interest, since models of spatially structured predator-prey dynamics have predicted that differences in individual mobility and foraging behaviour may affect spatial distributions and, consequently, population dynamics. Daphnia pulex was more mobile than C. dubia, and also located the high end of a food gradient while C. dubia did not. It seems likely that the mechanisms used by D. pulex to locate these regions are related to ingestion and (or) filtering rates. It was hypothesized that individuals reduce their swimming speed in order to linger in regions of high food concentration. Differences in mobility and behaviour between C. dubia and D. pulex were used to generate hypotheses about the distribution and stability of their respective populations. Specifically, it was predicted that C. dubia populations would have a more aggregated and, consequently, a more stable population in smaller environments than D. pulex.