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Abstract:
Two field experiments examined the effects of cyclopoid copepods on ciliates. The presence or absence of Cyclops abyssorum, Cyclops kolensis, and zooplankton >64 mu m was manipulated to determine the relative importance of direct cyclopoid predation on protists vs. indirect effects mediated through cyclopoid predation on other metazooplankton. In the second experiment, presence or absence of C. abyssorum was cross-classified with five concentrations of the metazooplankton community. Cyclopoid effects on ciliates were dependent on predator and prey species and on the abundance of alternate prey for cyclopoids. A trophic cascade was also observed, but only for two small ciliates, and only with the larger C. abyssorum. C. abyssorum had a stronger predation effect on oligotrich ciliates when metazooplankton had been removed, and this effect appeared at a lower metazooplankton concentration with a larger ciliate, compared to a smaller species of the same genus. These results suggest that for cyclopoid-ciliate interactions, switching behavior in the predator may be at least as important as a trophic cascade
