Predator Out of Place : The Differential Impacts of Native and Non-native Crayfish on Bufo Tadpoles

Predators have been shown to alter important fitness components (larval period mass at metamorphosis and overall survivorship) of larval anurans. Uncommonly studied predators of tadpoles include crayfish. Both native and introduced crayfish occur in NC. To gain a better understanding of the effect of introduced crayfish in NC we examined the impact of native (Procambarus acutus) and introduced (P. clarkii) crayfish on Fowler's toad larvae (Bufo fowleri). We hypothesized P. clarkii would have a greater effect on fitness components of Bufo fowleri because it is larger more aggressive and invasive in many parts of the world. Because these two species can co-occur we conducted an experiment that allowed us to evaluate the independent and interactive effects of the two crayfish species at different densities (0 1 or 2 individuals present). We found that crayfish did not alter toad larval period but reduced toad survival and caused toads to metamorphose at larger masses. The effect of crayfish on toad survival and mass at metamorphosis increased with crayfish density. Interestingly native crayfish caused a stronger reduction in survival and a stronger enhancement in mass at metamorphosis than did introduced crayfish when present at similar densities. Although toad survivorship in ponds with both crayfish species was comparable to survivorship in ponds containing only native crayfish toads metamorphosed at larger sizes when both crayfish species were present. We caution however that P. clarkii can achieve higher densities than native species in some situations and likely have a more important effect under high-density conditions.