Invaders eating invaders: potential trophic interactions between the amphipod

We investigated potential interspecific predation between two invasive crustacean species, currently widespread and co-occurring in European inland waters: the Ponto-Caspian amphipod Dikerogammarus villosus (Gammaridae) and the North American spiny-cheek crayfish Orconectes limosus (Cambaridae). We evaluated interactions of adult specimens of D. villosus and juvenile O. limosus (from the 3rd developmental stage – DS) under conditions with and without feeding. We used two different experimental setups: short-term (one-week) rearing in aquaria each containing 30 specimens of either single-species or mixed stock, and 20-daylong rearing in small circular plates with one individual of each species. In the aquaria, a significant effect of D. villosus presence on survival of O. limosus stocks was found, with stronger influence on unfed stocks. Survival of D. villosus was not influenced by either O. limosus presence or feeding. Direct predation of D. villosus on juvenile O. limosus, predominantly on the 3rd DS, was often observed in the small plates. The 5th DS O. limosus was killed only a few times and was already able to feed on adult D. villosus. Our results show that both species are able to affect each other negatively through intra-guild predation: D. villosus may successfully feed on juvenile O. limosus (3rd and 4th DS), but larger crayfish can resist predation by the amphipod.