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The anuran family Bufonidae is a large, cosmopolitan group comprising of almost 400 species that inhabit a great variety of environments. Three bufonids with relatively limited distribution in the United States are federally listed as “endangered:” Wyoming toads (Bufo baxteri), arroyo toads (B. californicus), and Houston toads (B. houstonensis); golden toads (B. periglenes) from Central America are perhaps the best known example of an anuran that has recently declined. By contrast, marine toads (B. marinus) are one of the most successful anuran introductions , having spread throughout much of the Southern Hemisphere . In spite of the attention these forms have received, many bufonids remain relatively “understudied,” and their conservation status is unknown. Twenty-one bufonid species are recognized in the United States, and eleven of these occur in the arid Southwest (Collins, 1997; see also Crother et al., 2000). Although most of the desert dwelling forms have not been surveyed in any detail, a number have been superficially inventoried (Table 32-1). My purpose here is to review what is known about the status of bufonids of the arid southwestern United States and, in so doing, to draw attention to emerging general patterns regarding their status. I first review case histories of some bufonids that have been surveyed over the past decade. Spring Breeding, Perennial Streams, and Arizona Toads Arizona toads (B. microscaphus) occur in extreme southern Nevada and southwestern Utah, northwestern, central, and eastern Arizona, and far west-central New Mexico (Stebbins, 1985; Sullivan, 1993). Throughout this region they are associated with riparian systems from desert scrub at low elevations to pine forest habitats over 2,500 m. They typically breed in running water during the early spring, although the breeding period varies depending on rainfall, temperature, and elevation (Stebbins, 1985; Schwaner et al., this volume, Part Two). Arizona toads are members of the Bufo microscaphus complex , which includes three species: arroyo toads (B. californicus) of southwestern California and extreme northwestern Mexico; Arizona toads of central Arizona; and Mexican toads (B. mexicanus ) of north-central Mexico. Regarded as subspecies (of B. microscaphus) by many workers, recent analysis indicates substantial genetic divergence among the three lineages; given their allopatric distribution and diagnosability, they should be regarded as full species (Gergus, 1998; Crother et al., 2000). Interestingly , the genetic divergence among these lineages occurred without divergence in mating calls used by males and females during courtship (Gergus et al., 1997). Although speculative , this may be related to the similarity in habitats occupied by the toads in these three geographic areas or to the absence of other syntopically breeding bufonids. Arizona toads have been documented at a number of new sites over the past 10 years. Of the 98 element occurrences for the Arizona toad listed in the Arizona Game and Fish Department Heritage Data Management System, 55 (56%) are new localities recently (relatively) documented (1986–96; Anonymous, 1996a). All these localities are within the historic range of the species and suggest that additional search efforts will document these anurans in other appropriate habitats throughout their suspected range in the Southwest. Long-term viability of any of the recent or most historic populations is unknown, but, given their persistence at many historic localities and the documentation of occurrence at many new sites, it is reasonable to conclude that substantial declines have not occurred. Three historic sites are no longer occupied by Arizona toads in central Arizona: Alamo Lake on the Bill Williams River, Lake Pleasant on the lower Agua Fria River, and the Verde Valley. All three sites are similar in having experienced dramatic alteration of the native riparian communities due to construction of impoundments. Each area is now occupied by Woodhouse’s toads (B. woodhousii), a close relative that hybridizes with Arizona toads in all areas of distributional overlap . Interestingly, in southwestern Utah and northwestern Arizona spatial dynamics of hybrid zones between these toads have been stable over the past 50 years (Sullivan, 1995). However , in central Arizona the hybrid zone between these two toads along the lower Agua Fria River (near Phoenix) appears to have expanded over the past 40 years from the vicinity of Phoenix north to Black Canyon City (about 60 km; see Lamb et al., 2000; Malmos et al., 2001). It remains for future study to determine if Woodhouse’s toads can supplant Arizona toads in the absence of major habitat alterations, such as the development of impoundments. 237 TH I RTY-TWO Southwestern Desert Bufonids BRIAN K. SULLIVAN 238 SOUTHWESTERN DESERT BUFONIDS TABLE 32-1 Bufonid Status...

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