are especially susceptible to other stressors, such as introduced species and disease. Tropical montane species are at special risk because of global warming. These already stressed species, reduced to a few populations, also are likely to be hit hardest by Bd. However, a paradoxical fact is that new species of amphibians are being described at an unprecedented rate. In 1985, the first comprehensive account of all amphibian species reported ≈4,000 species (Frost, 1985). That number has now risen to >6,300, and species are being named at a rate exceeding 2% per year. Some of these species are cryptic forms that were found as a result of molecular systematic studies, but the vast majority are morphologically distinctive species mainly from tropical regions (Fig. 2.5). These biologically unique species often have been found as a byproduct of the heightened interest in amphibians and consequent field research. Field surveys in still relatively unstudied parts of the world (e.g., New Guinea and nearby islands, Madagascar) have resulted in many new discoveries. Among the most spectacular discoveries during this decade are a frog from India that is so distinct that it was placed in a new family (Biju and Bossuyt, 2003) and a salamander from South Korea that is the only member of the Plethodontidae from Asia (Min et al., 2005). It is impossible to know what has been overlooked or has already been lost to extinction, but there is every reason to think that the losses have been substantial.
The rate of extinction of amphibians is truly startling. A recent study estimates that current rates of extinction are 211 times the background extinction rate for amphibians, and rates would be as high as 25,000–45,000 times greater if all of the currently threatened species go extinct (McCallum, 2007).
Despite these alarming estimates, amphibians are apparently doing very well in many parts of the world, and many thrive in landscapes heavily modified by human activities. Species such as the cane toad (Bufo marinus), the American bullfrog (Rana catesbieana), and the clawed frog (Xenopus laevis) have proven to be potent invasive species, and they have not yet been shown to be afflicted by chytridiomycosis. Attempts are being made to mitigate anticipated losses of amphibian species. Promising research on bacterial skin symbionts of amphibians suggests that they may have antifungal properties (Harris et al., 2006; Woodhams et al., 2007), possibly opening pathways for research on changing the outcomes of fungal attacks. Local extinctions have been so profound and widespread in Panama that a major initiative has been launched to promote in situ as well as ex situ captive breeding programs. Species will be maintained in captivity until solutions to problems such as chytridiomycosis, local habitat destruction, or others can be mitigated, at which time reintroduction programs will be developed (Gewin, 2008). Although amphibians are suffering declines and extinctions, we predict that at least some frogs,