Effects of carbaryl on species interactions of the foothill yellow legged frog (Rana boylii) and the Pacific treefrog (Pseudacris regilla)
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Amphibian species worldwide are being confronted with novel anthropogenic stressors such as contaminants and invasive species. While much work has been done to examine these factors individually, less is known about how these stressors might interact. No studies to this point have examined the potentially synergistic impacts between these two stressors on a threatened amphibian species. We present the results from three separate laboratory studies focusing on two species of frogs, the Pacific tree frog (Pseudacris regilla) and a federal species of concern, the foothill yellow legged frog (Rana boylii). These experiments examine the toxicity of an insecticide, carbaryl, on each species, on their competitive interactions, and on their interaction with a non-native crayfish predator (Pacifastacus leniusculus). R. boylii were more susceptible to pesticide exposure than P. regilla and exposure reduced their ability to compete. This differential effect of the pesticide resulted in a remarkable increase in mortality (50%) for R. boylii with an invasive crayfish predator present while P. regilla exhibited no change. These results add to concerns over the utility of single species toxicity tests in determining safe levels for environmental exposure and advocate for the use of multiple species tests that focus on key species interactions.
KeywordsPesticide Multiple stressors Predation Competition Sub-lethal effects
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