Direct assessment of the independent effects of exploitative and interference competition between Daphnia and rotifers
It is well established that large Daphnia can markedly reduce rotifer populations in both natural communities and laboratory cultures, but the mechanism for this reduction has been debated. Both exploitative competition for resources and interference have been invoked, but experiments have not directly assessed the independent roles of these mechanisms. Using laboratory chambers divided with 53-µm Nitex screen, I have separated the effects of interference from exploitative competition by Daphnia pulex on Keratella cochlearis and Keratella crassa. At both high and low food levels, K. cochlearis is strongly affected by interference competition but not exploitative competition, and K. crassa shows no evidence of suppression by Daphnia through interference competition. These results suggest that laboratory studies examining the effects of Daphnia on rotifers are correct in attributing much of the reduction in rotifer numbers to direct interference competition.