Influence of warming on the functional responses of invasive omnivores, Procambarus crayfishes

The red swamp crayfish (Procambarus clarkii) and the marbled crayfish (Procambarus virginalis) are congeneric invasive species whose potential impacts in the Great Lakes basin have generated concern. In laboratory experiments, we tested the functional responses of these omnivores to two common food resources, insect larvae (Chironomus bloodworms) and aquatic macrophytes (Eurasian milfoil Myriophyllum spicatum), to gain predictive information on their per capita effects under present (18°C) and projected future (26°C) climate scenarios for the basin. The maximum feeding rate of P. virginalis was higher at 18°C than at 26°C when presented with bloodworms but did not differ between temperatures when presented with macrophytes. By contrast, the feeding rate of P. clarkii did not change with temperature for either food resource. Due to their larger mean size, P. clarkii exhibited higher rates of resource (bloodworm and macrophyte) consumption than P. virginalis at both temperatures. These results suggest that trophic impacts of P. virginalis will dampen with increased warming, whereas P. clarkii will sustain larger impacts irrespective of temperature within the range tested.