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 im- pacts (Current Zoology 57 (6): 836-843, 2011).