Supplementary Information files for: 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 nonnative 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 villosus and Gammarus 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 species D. villosus, followed by G. tigrinus, and C. pseudogracilis, with the lowest survivorship recorded for the indigenous species G. pulex for
all substrates except cobble. However, total biomass
consumption of the indigenous G. pulex and the nonnative D. villosus by P. leniusculus were similar
suggesting that crayfish may have been satiated by
larger D. villosus individuals. Substrate size had a
significant influence on the predation success of P.
leniusculus, with larger substrate clasts typically
resulting in increased survivorship rates for all species
except C. pseudogracilis, which displayed lower
predation rates for sand substrates. The findings of
this study highlight the risks that naı¨ve 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