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ASYMMETRICAL EFFECTS OF INTRODUCED BULLFROGS (RANA CATESBEIANA) ON NATIVE RANID FROGS IN OREGON
Citation:
Pearl, C. A., M. J. Adams, R. B. Bury, AND B. McCreary. ASYMMETRICAL EFFECTS OF INTRODUCED BULLFROGS (RANA CATESBEIANA) ON NATIVE RANID FROGS IN OREGON. COPEIA. American Society of Ichthyologists and Herpetologists, 1:11-20.
Impact/Purpose:
To investigate whether microhabitat and behavior differences predict species susceptibility to predation
Description:
Introduced American Bullfrogs (Rana catesbeiana) have become widely established in the Pacific Northwest over the last century and are throught to be an important predator of native amphibians throughout the western United States. The Northern Red-Legged Frog (Rana aurora aurora) and Oregon Spotted Frog (Rana pretiosa) historically coexisted in portions of the Pacific Northwest now invaded by R. catesbeiana, but R. pretiosa has declined more severely than R. a. aurora. We investigated whether microhabitat and behavior differences that facilitate sympatric coexistence of the natives predict which species is more susceptible to predation by introduced R. catesbeiana. Our laboratory experiments demonstrate that R. catesbeiana adults prefer aquatic microhabitats, that R. pretiosa juveniles are more aquatic than R. a. aurora, and that adult R. catesbeiana consume more R. pretiosa than R.A. aurora juveniles. Meana and maximum jump distances of R. pretiosa were shorter than equally sized R. a. aurora, and the difference between these two species increased with larger frog sizes. Our examination of field survey data indicates that R. pretiosa coexist with R. catesbeiana less frequently than R. a. aurora. We conclude that R. catebeiana is a greater threat to survival of R. pretiosa than to R. a. aurora and suggest that microhabitat use and escape abilities of native ranid frogs may be linked to this asymmetrical effect. Analysis of behavioral and microhabitat differences among related native species may be a useful tool in predicting the effects of introduced predators on amphibians and can assist in developing conservation priorities for these species.