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EXAMINATION OF HABITAT USE AND DISPERSAL OF EXOTIC BULLFROGS AND THEIR POTENTIAL IMPACT ON NATIVE AMPHIBIAN COMMUNITIES IN THE WILLAMETTE VALLEY, OREGON
Citation:
Heppell, S. EXAMINATION OF HABITAT USE AND DISPERSAL OF EXOTIC BULLFROGS AND THEIR POTENTIAL IMPACT ON NATIVE AMPHIBIAN COMMUNITIES IN THE WILLAMETTE VALLEY, OREGON. Presented at American Society of Ichthyologists and Herpetologists, Kansas City, MO, July 3-8, 2002.
Description:
Bullfrogs (Rana catesbeiana) are exotic in the west and have been implicated in the decline of western pond turtles and native ranids. Habitat alterations that favor bullfrogs have enhanced populations, particularly in agricultural areas such as the Willamette Valley. I will present results from field surveys, radio tracking and population modeling that show how bullfrogs have adapted to local conditions and where they are expected to occur on the landscape. Mark-recapture and telemetry shows that metamorph and adult bullfrogs travel long distances over land and utilize upland habitat far more than expected. Using a GIS-based habitat model with individual-based frog movement, I have mapped expected bullfrog distribution on the Valley floor and potential overlap with red-legged frogs (Rana aurora). Hypothetical reductions in survival of metamorph red-legged frogs caused by the presence of bullfrogs further reduces suitable habitat for the natives and creates additional ?sink? populations. However, habitat loss, deterioration and fragmentation for red-legged frogs is already so high that bullfrog presence may be a relatively minor additional stressor.