Density versus per capita impacts of an introduced crayfish on stream communities.
Pintor, Lauren*,1, Sih, Andrew1, 1 University of California-Davis, Davis, CA, USA
ABSTRACT- Invasive species often devastate native communities and ecosystems through the invader's ability to attain high densities. Increased densities often lead to larger effects on a community often despite a reduced impact per individual. In northern California streams, the exotic signal crayfish, Pacifasticus leniusculus, has large negative impacts on native communities. However, the degree of their impact differs from stream to stream. We conducted a mesocosm experiment measuring the density and per capita impacts of signal crayfish populations collected from low and high density sites on a typical stream prey community (snails, benthic invertebrates and algae). Additionally, we evaluated the behavioral mechanisms underlying differing impacts between signal crayfish populations. Results indicate that signal crayfish significantly reduce prey densities and that impacts are significantly higher at high crayfish densities. However, behavioral observations suggest high densities also shift behavior (increased aggression and foraging rate) possibly leading to an increase in per capita effects. This synergistic effect (of density and behavior) may in part explain the devastating effects to native communities often found at high density crayfish sites, and also provide insight to mechanisms of invasion in general.
Key words: invasive species, crayfish, impacts, behavior
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