The effect of Daphnia interference on a natural rotifer and ciliate community: Short‐term bottle experiments

Abstract

Two bottle experiments were conducted using water from a small, eutrophic lake to assess the impact of Daphnia interference (encounter) competition on the dynamics of the rotifer and ciliate populations dominating the zooplankton community. Indirect effects of Daphnia exploitative competition were minimized by adding food resources and using short incubation periods. The introduction of Daphnia pulex (16 liter−1) to Cryptomonas‐enriched (3–3.5 × 104 cells ml−1) water for 2 d significantly suppressed numbers of the ciliate Campanella sp.; the rotifers Kellicottia bostoniensis, Keratella cochlearis, Keratella crassa, Polyarthra vulgaris, and Synchaeta pectinata; and total rotifers. The presence of Daphnia did not affect numbers of the rotifers Asplanchna girodi, Polyarthra euryptera, and Trichocerca similis. Daphnia‐induced death rates of significantly suppressed, common species were highest for K. cochlearis (0.79–1.14 d−1), intermediate for S. pectinata and Campanella (0.23–0.33 d−1), and lowest for K. crassa and P. vulgaris (0.14–0.28 d−1). The most marked effects of Daphnia on community structure were 61–77% reductions in the relative abundance of K. cochlearis and up to 100% increases in the relative abundances of K. crassa and T. similis. The observed effects of Daphnia on the rotifer species are consistent with, and largely explicable by, previously conducted laboratory experiments and behavioral observations on interference between Daphnia and these or closely related species. Interference from Daphnia can rapidly reduce the abundance and shift the species structure of rotifer and ciliate assemblages in natural communities.