Control of Keratella populations by interference competition from Daphnia1

The cladocerans Daphnia galeata mendotae and Daphnia rosea inhibit population growth of the rotifer Keratella cochlearis even when shared food is abundant. Keratella swept into the branchial chamber of Daphnia may be immediately killed, mortally wounded, or lose attached eggs before or while being rejected. The chance of a Keratella being injured decreases with its age and increases with its retention time in the chamber. Such mechanical interference competition, described for the first time among zooplankton, may be very important in controlling natural populations of some rotifers.