Substrate mediated predator-prey interactions between invasive crayfish and indigenous and non-native amphipods

The increasing number of taxa being translocated across the globe is leading to many non-native species encountering indigenous taxa as well as other non-native species. Environmental heterogeneity may strongly influence the spatial distribution, habitat use and refuge availability for these taxa. Using a series of 24-h mesocosm experiments we examined the predator-prey interactions between an invasive crayfish (Pacifastacus leniusculus) and four amphipod taxa, one indigenous (Gammarus pulex) and three non-native species (Crangonyx pseudogracilis, Dikerogammarus villosusandGammarus tigrinus) to Great Britain.The potential mediating effect of physical habitat on predator-prey interactions was examined via the use of different substrate particle sizes; cobbles, gravels and, sand. Survivorship of amphipods in response to crayfish predation varied significantly with the highest rates recorded for the non-native speciesD. villosus, followed byG. tigrinus, andC. pseudogracilis, with the lowest survivorship recorded for the indigenous speciesG. pulexfor all substrates except cobble. However, total biomass consumption of the indigenousG. pulexand the non-nativeD. villosusbyP. leniusculuswere similar suggesting that crayfish may have been satiated by largerD. villosusindividuals. Substrate size had a significant influence on the predation success ofP. leniusculus,with larger substrate clasts typically resulting in increased survivorship rates for all species exceptC. pseudogracilis,which displayed lower predation rates for sand substrates. The findings of this study highlight the risks that naive indigenous taxa may face from new invasive species and the importance of characterising physical habitat (complexity and refugia potential) when considering the potential ecological effects of invaders on predation success.