Lack of Evidence for Epidemic Disease as an Agent in the Catastrophic Decline of Australian Rain Forest Frogs

Recent concern about declining amphibian populations has stimulated an extensive effort to quantify the population status of amphibians throughout the world, and to elucidate the causal factors associated with declines (Stebbins & Cohen 1995). Many declines are attributable to anthropogenic factors, but others are less readily explained (Vial & Saylor 1993). The causal factors associated with population declines in Australia's rain forest frogs continue to be elusive despite an intensive program of research over the last 5 years. The species most affected are restricted to patches of upland rain forest where they breed in lotic environments (Richards et al. 1993). Many potential explanations have been advanced to account for frog declines (Stebbins & Cohen 1995). Among these hypotheses is the idea that some declines might be caused by epidemic or endemic disease, possibly in combination with damage to the immune systems of frogs (Carey 1993). It is becoming recognized that research into species declines needs to use the same rigorous experimental protocols to distinguish among competing hypotheses that are used in basic ecological research (Blaustein et al. 1994; Caughley & Gunn 1996). Laurance et al. (1996) suggest that eight lines of evidence support the conclusion that a virus is responsible for catastrophic declines of some Australian rain forest frogs. We reassess these lines of evidence and provide alternative interpretations.