Assessment of predatory ability of native and non-native freshwater gammaridean species： A rapid test with water fleas as prey

Predation rate with relation to species, sex and water temperature was tested among four different gammaridean spe- cies： Dikerogammarus villosus, Gammarus roeselii, Gammarus pulex and Gammarus fossarum. Tests were performed in micro- cosms in climate-controlled rooms at five different temperatures. Daphnia magna, a common water flea, served as prey. On ave- rage D. villosus showed the highest consumption rate of Daphnia magna over the entire temperature range, followed in decreas- ing order by G pulex, G roeselii and G fossarum. The predation rate of all species showed a distinct peak at 20~C. Correction of predation rates for body size gave somewhat different results. D. villosus is then still the most predatory of all gammaridean spe- cies tested followed by G. pulex, G. fossarum and G roeselii. The outcome of the Daphnia tests is consistent with results of other studies with different prey. This supports that the Daphnia test is a good and quick indicator of the predatory abilities in gam- maridean species at varying temperatures, and allows the prediction of how changing temperature regimes influence invasion impacts