Two Ponto-Caspian amphipods, Dikerogammarus villosus and Dikerogammarus haemobaphes , have expanded their geographical ranges from eastern Europe into Great Britain in recent years. This study represents one of the first examining the distribution and habitat preferences of coexisting populations of D. haemobaphes and D. villosus via field and laboratory experiments in the UK. Field surveys of a recently invaded lowland reserv...