Feeding choice and predation pressure of two invasive gammarids, <Emphasis Type="Italic">Gammarus tigrinus</Emphasis> and <Emphasis Type="Italic">Dikerogammarus villosus</Emphasis>, under increasing temperature

In most European freshwater ecosystems, the invasive gammarids Gammarus tigrinus and Dikerogammarus villosus strongly impair recipient communities through predation of a wide range of native invertebrates. Due to the effects of temperature on both the physiology and the behaviour of such ectotherms, understanding how global warming may influence their ecological impact is a research priority. These species were therefore exposed to three different food types to determine their detritivorous, herbivorous and carnivorous characters, and predation was measured characterizing the Holling’s functional response. The effect of increasing water temperatures (15, 20, 25°C) on both the food choice and predatory activities was investigated. Both species showed a significant preference for animal tissues at all temperatures. The total food intake increased with temperature for G. tigrinus but did not change for D. villosus, which may result from specific species differences in metabolic requirements. The consumption of live prey strongly increased with temperature. The main differences were an increased searching efficiency in G. tigrinus and a decreased handling time in D. villosus as temperature increased, which may result from differences in foraging strategies. These results suggest that climate change is likely to increase the predation pressure of both invasive gammarids on prey species.