Behavioural responses of invasive ( Gmelinoides fasciatus ) and native ( Gammarus lacustris ) amphipods to predators on different bottom substrates

The amphipod Gmelinoides fasciatus has invaded and established in numerous large lakes in Eurasia and, in the process, has displaced the native amphipod, Gammarus lacustris . The mechanism behind its invasion success is unclear and remains an important topic for invasion ecology. Three laboratory experiments were conducted to determine if superior predator avoidance and different types of bottom substrate could be important factors contributing to the invasion success of G. fasciatus . Our results indicate that, on gravel and sand substrates, G. fasciatus exhibited superior digging behaviour to avoid predation by fishes (perch and common roach), contrary to G. lacustris . On sandy substrate, only 9% of G. fasciatus individuals were consumed, whereas G. lacustris were consumed much more intensively at 74%. In addition, G. fasciatus exhibited a more substantial reduction in activity, where the time spent in motion reduced from 37.6 to 20.8% compared to G. lacustris (from 21.8 to 17.4%) when in the presence of predatory fish kairomones. G. fasciatus movement speed was also reduced in the presence of kairomones (from 57.1 to 39.3 mm/s). However, the presence of kairomones had little effect on digging behaviour of G. fasciatus . G. fasciatus consistently demonstrated superior predator avoidance abilities over G. lacustris , suggesting that this mechanism might play an important role in the invasion success of G. fasciatus .