Habitat Gradients and the Effects of Non-Endemic Fish on Amphibians: Are There Lessons From the Lowlands?

Michael J. Adams USGS Forest and Rangeland Ecosystem Science Center, Corvallis, OR

Amphibian declines in high-elevation parks of western North America are of concern because of the relative lack of human disturbance to these areas. Predation by introduced fish is one hypothesis to explain these declines, and could also explain declines in low-elevation areas. In lowlands, habitat alterations and bullfrog introductions are additional concerns that are difficult to separate from fish effects. Literature from across North America on the role of fish in lowland ponds suggests that behavioral tradeoffs faced by individuals play an important role in determining the composition of amphibian communities. These tradeoffs determine how a species responds to various types of predators as well as the ability of a species to persist under a range of hydrological regimes. However, these predictions are largely untested in western North America. Regional studies support the importance of fish effects to amphibian community composition in lowlands but, in the context of the pond permanence gradient, it is not clear how important fish predation is to regional distribution patterns of amphibians. There is also experimental evidence that some western amphibians may be able to develop behaviors that can allow them to coexist with an introduced predator. But costs associated with those behaviors may still be detrimental. Pond permanence, habitat complexity, and indirect effects all appear to interact in determining the importance of fish effects.

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