Feeding preferences of an invasive Ponto‐Caspian goby for native and non‐native gammarid prey

Abstract

Summary When an invasive predator encounters native and invasive prey, two scenarios are possible: the predator may benefit from the presence of naïve native prey or choose prey from its region of origin, reflecting their common evolutionary history. To determine interactions between an invasive predator and native and invasive prey, we used the Ponto‐Caspian racer goby Babka gymnotrachelus as predator and gammarids as prey: native Gammarus fossarum and Ponto‐Caspian Dikerogammarus villosus and Pontogammarus robustoides. We hypothesised that prey origin would affect fish preferences and growth rate and conducted a series of laboratory experiments on fish predation and growth and estimated profitability of prey of different origin. The goby preferred native prey to the Ponto‐Caspian gammarids, irrespective of prey motility, the presence of shelters or waterborne chemical cues. Moreover, fish grew better when fed native prey. Thus, we suggest that fish selectivity was based on the assessment of prey quality during direct contact with gammarids. A diet consisting of Ponto‐Caspian gammarids did not facilitate an invader originating from the same region, which benefited more from the presence of a local prey species. Ponto‐Caspian gammarids and gobies are successful invaders in inland waters, usually main rivers. The gobies, in contrast to the invasive gammarids, enter smaller tributaries that serve as refugia for native gammarids. We show that the gobies may benefit from the presence of native prey species in such locations.