Competition between Rotifers and Daphnia

This study examined the ability of two rotifers to coexist with a large cladoceran. Laboratory competition experiments using daily renewed batch cultures showed that Brachionus calyciflorus and Keratella cochlearis were excluded by Daphnia pulex from mixed—species cultures in 1—3 wk. The Daphnia populations removed increasingly disproportionate shares of the daily algal food supply, leaving the rotifer populations to gradually starve to extinction, and also may have mechanically interfered with the Keratella. Daphnia appeared unaffected by the presence of the rotifers. Rotifers, whose food niches are included with those of cladocerans, may be rapidly excluded by large cladocerans through both exploitative and interference competition; they are unlikely to abound in zooplankton communities with large cladocerans unless food is abundant or environmental factors differentially inhibit the cladocerans.