Population-dependent dispersal potential of freshwater invasive amphipods: a case study of Dikerogammarus villosus

Biological invasions add a novel context to studies on animal dispersion mechanisms. Invasive Ponto-Caspian species are widely distributed in Europe and well known for their fast spreading. Therefore, they can be used as a good model for studying the mechanism of dispersion in disturbed ecosystems. Some invasive species may show similar preferences towards habitats, which leads to competition between them. Consequently, weaker competitors may be displaced and forced to move elsewhere to avoid direct competition. In this study, the dispersal ability of the Ponto-Caspian gammarid, Dikerogammarus villosus , was tested. This species has spread in Europe through two invasion routes (Western and Eastern) from two genetically differentiated source populations (the Danube and Dnieper deltas, respectively). In addition, the spread of gammarids in single- and mixed-group treatments in aquaria was experimentally compared. Whether gammarids stayed in the initial part of the aquarium or moved forward over the course of 22 h depending on their origin and the presence of competitors of particular origin was determined. The individuals remaining in the initial part as stronger competitors and those that emigrated as weaker were also considered. Gammarids from both groups (particularly larger individuals) tended to move slightly more in the presence of competitors from the Eastern group, pointing to the stronger competitive capability of the latter. Moreover, the local sampling site (i.e. local population) had a stronger effect on dispersal than the origin of the invasive group. Our study suggests that the higher competition capacity of the Eastern group may lead to a more intense spread of the weaker Western group in their contact zone, including the colonization of suboptimal habitats, but this correlation will also depend on local population traits. These findings highlight the importance of individual traits such as body size and the significance of involving multiple populations in behavioural studies and research on biological invasions. • Invasive amphipod populations differ in dispersal potential. • Competition among individuals is the main driver of dispersal. • Larger individuals are more likely to disperse.