Effects of predation by Chaoborus flavicans on crustacean zooplankton of Lake Lenore, Washington

After Chaoborus flavicans became established in 1974, the species composition of zooplankton in Lake Lenore changed. Diaptomus nevadensis disappeared and densities of Diaptomus siciliswere reduced. 2. A transplant experiment showed the D. nevadensis could survive in Lake Lenore water in the absence of Chaoborus. The disappearance of D. nevadensis was probably a consequence of Chaoborus predation. 3. Although densities of Daphnia pulicaria† were similar before and after the colonization of C. flavicans, juvenile D. pulicaria began producing neck‐teeth during the first summer Chaoborus was present. 4. The seasonal pattern of neck‐teeth production by juvenile D. pilicaria did not correlate with density of Chaoborus but rather with a combination of water temperature and Chaoborus density, suggesting that metabolic processes are a component of induction of neck‐teeth in this species.