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The Ponto-Caspian gammarids Dikerogammarus villosus SOVINSKIJ and Echinogammarus ischnus STEBBING have invaded Central-European streams in the early 1990s. Declines in macroinvertebrates have been observed since the arrival of invasive species. To elucidate the predatory impact of gammarids on the macroinvertebrate community, we conducted laboratory experiments with macroinvertebrate prey taxa and native and invasive gammarids as predators. Dikerogammarus villosus, which is known to be a strong predator, consumed more and a broader range of prey than E. ischnus or the native gammarids, Gammarus pulex L. and Gammarus roeseli GERVAIS. Echinogammarus ischnus consumed a somewhat higher amount of prey organisms than G. pulex and a higher number and a broader range than G. roeseli. Adult D. villosus consumed up to 25 mg macroinvertebrate biomass (wet weight) per day which corresponds to approximately 1/3 of their own biomass. Chironomid larvae were preferred by all gammarids tested. Taking into account that gammarids density may surpass 1000 ind m-2, our results suggest that the predatory behaviour of invasive gammarids, in particular of D. villosus, may have contributed to the decline of some macroinvertebrate taxa in some European streams.
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