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radio tracking from 1998 to 2002 (Vredenburg et al., 2004), and we believe that movement between local populations may be spreading the disease. The environment in this area (2,500–3,300 m) is harsh for amphibians, with isolated ponds separated by inhospitable solid granite that lacks vegetation. Small streams join many of the lakes in each basin. The maximum movement of frogs, (≈400 m) was in and near streams; most movements are <300 m. Our results are compatible with those of another study (Pope and Matthews, 2001), which included a report of a single overland movement event. If chytridiomycosis sweeps through the Sierra Nevada the way it has through Central America (Lips et al., 2006), then population and metapopulation extinctions may be a continuing trend; we may be on the verge of losing both species.

It might be possible to arrest an epidemic. Laboratory treatments have shown that infected animals can be cleared of infection within days (Parker et al., 2002); if the dynamics of the disease can be altered or if animals can survive long enough to mount an immunological defense, then survival might be possible. Survival of infected frogs after an apparent outbreak has been seen in Australia (Retallick et al., 2004), but is unknown in the Sierra Nevada frogs. The yellow-legged frogs of the Sierra Nevada are an ideal species in which to test this because they live in discreet habitat patches, are relatively easy to capture, and are highly philopatric.

COMMON THEMES IN AMPHIBIAN DECLINES

In the early 1990s, there was considerable debate about whether amphibians were in general decline or only local fluctuations in population densities were involved (Blaustein, 1994; Pechmann and Wilbur, 1994). A definitive 5-year study that involved daily monitoring of a large amphibian fauna at the Monteverde Cloud Forest Preserve in Costa Rica showed that 40% (20 species of frogs) of the species had been lost (Pounds et al., 1997). These instances involved some extraordinary species, such as the spectacularly colored golden toad (Bufo periglenes) and the harlequin frog (Atelopus varius). Particularly striking about this case is the highly protected status of the preserve, so habitat destruction, the most common reason for species disappearances in general, can be excluded. The start of this decline was pinpointed to the late 1980s. At about the same time, disappearances of species from protected areas in the Australian wet tropics were recorded (McDonald, 1990). Both species of the unique gastric brooding frogs from Australia (Rheobatrachus) disappeared. Declines in other parts of the world included most species of the generally montane, diurnal frogs of the genus Atelopus from South and lower Central America, and species of Bufo and Rana from the Sierra Nevada of California (Bradford, 1989; Retallick et al., 2004; Pounds et al., 2006). At first all of these declines



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