Predatory rotifer Asplanchna brightwellii mediated competition outcome between Brachionus calyciflorus and Brachionus patulus (Rotifera)

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In the present study, we evaluated the effects of a graded series of different intensities of predation by predatory rotifer Asplanchna brightwellii (0, 1, 2, 5, 10 and 20 ind. per 50 ml) on the competition outcome between two herbivorous rotifers, Brachionus calyciflorus (196 ± 12 μm in length) and Brachionus patulus (145 ± 8 μm in length), at high (3 × 106 cells ml−1) and low (0.5 × 106 cells ml−1) algae food (Chlorella pyrenoidosa) levels. Under low predation intensity (0, 1, 2, 5 predators), B. patulus was able to outcompete and coexist with B. calyciflorus at low and high food level, respectively. Further, increased predation intensity decreased competitive ability of B. patulus at each food level, and it was eliminated from the culture assemblage at high predation intensity (20 predators). However, B. calyciflorus could persist under the highest predation intensity in this experiment. Population growth rate of B. calyciflorus was affected by food level, not by predation intensity, while that of B. patulus showed a reverse result. The maximum population density of B. patulus was significantly influenced by both predation intensity and food level, but for that of B. calyciflorus, food level was the only influence factor. The results suggest that the competition outcome between herbivorous rotifer species with different body sizes are not only affected by food level but also influenced by the predation intensity.