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Greater Yellowstone Ecosystem Report

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To understand the impacts of an herbivorous invasive species on native herbivores, it is critical to quantify the relative impact of the invasive and the native species on shared resources. In a field experiment, we compared grazing efficacy of periphyton by the invasive New Zealand mudsnail, Potamopyrgus antipidarum, and 3 native macroinvertebrate grazers. Depending on the measure of periphyton biomass, P. antipodarum removed as much or more periphyton than any of the native grazers. When we examined diatom genera individually, P. antipodarum also suppressed the relative abundance of the greatest number of diatom genera and suppressed those diatoms more than the native grazers. As a result, P. antipodarum should compete strongly for periphyton with native grazers. In particular, because Ephemerella mayflies were the second most effective grazers and grazed many diatom genera similarly to the invasive snails, these mayflies may be competing with P. antipodarum in the introduced range. Overall, grazing ability may contribute to the invasion success of P. antipodarum.