Browsing and grazing by cladoceran filter feeders

Abstract

If different Cladocera have similar minimum requirements for suspended food, the capacity to utilize sedimented material would shift the competitive advantage to facultative bottom foragers in ponds, shallow lakes, and laboratory cultures with fluctuating levels of planktonic food. In laboratory cultures, Daphnia pulex browses or forages on the bottom of its culture vessel when suspended food concentration is too low to support reproduction or high rates or ingestion. Suspension feeding or grazing is the primary feeding mechanism only above the incipient limiting food concentration when ingestion rate is maximal, although a proportion of the animal's time is spent swimming (and therefore suspension feeding) at all food concentrations. Limited evidence suggests that different species of Cladocera have similar food levels at which reproduction is zero, yet not all are facultative browsers. Daphnia magna exhibits a similar behaviour to D. pulex but D. galeata and Ceriodaphnia quadrangula do not. These results show that the switch from grazing to browsing may be a determinant of competitive success among Cladocera.