Anaxyrus exsul

The genus Anaxyrus was split from Bufo by Frost et al. (2006). However, taxonomy within the genus Bufo remains controversial and many references still use the long-established Bufo. Considered by some authors to be a subspecies of Anaxyrus boreas.

Molecular data indicate that Bufo exsul is phylogenetically nested within Bufo canorus; further data are needed to determine whether Bufo exsul should be subsumed with Bufo canorus (Shaffer et al. 2000).

Phylogenetic analyses of mtDNA data from throughout the range of the Bufo (Anaxyrus) boreas species group (including boreas, canorus, exsul, and nelsoni) by Goebel et al. (2009) identified three major haplotype clades. The Northwest clade (NW) includes both subspecies of boreas (boreas and halophilus) and divergent minor clades in the middle Rocky Mountains, coastal, and central regions of the west and Pacific Northwest. The Southwest (SW) clade includes exsul, nelsoni, and minor clades in southern California. Bufo (Anaxyrus) canorus, previously identified as paraphyletic, has populations in both the NW and SW major clades. The Eastern major clade (E) includes three divergent lineages from southern Utah, the southern Rocky Mountains, and north of the Great Basin at the border of Utah and Nevada. Goebel et al. (2009) tentatively suggested that some or many of the clades might warrant recognition as distinct species. However, the authors refrained from delineating new species circumscriptions, noting that additional research might suggest different taxonomic outcomes (e.g., recognizing the traditionally defined Bufo canorus as two distinct species or, conversely, combining it with other minor groups and thus broadening its scope).

Small range in Deep Springs Valley, Inyo County, California; habitat is appropriately managed, and population has been relatively stable in recent decades; molecular data suggest that A. exsul may be conspecific with A. canorus--further study is needed.

Range includes several springs feeding Deep Springs Lake (playa), in Deep Springs Valley, Inyo County, California: Buckhorn Spring, Corral Spring and adjacent pond (Schuierer and Anderson 1990), and Bog Mound Springs at an elevation of 1,520 meters (about 5,000 feet). A population at Antelope Springs at about 1,710 meters, about 7 kilometers northwest of Deep Springs Lake, may have been introduced (Schuierer 1962, Murphy et al. 2003, Stebbins 2003). An introduced population occurs in a flowing well near Salt Lake in Saline Valley, Death Valley National Park, Inyo County, California (Murphy et al. 2003). Black toads were introduced at Cottonwood Springs in the Owens Valley in the 1960s (Schuierer 1962), but no there are no subsequent records for that area (Fellers 2005). The species was introduced at Batchelder Spring, Westgard Pass, Inyo County, but apparently it is extirpated there.

Entire range can be regarded as one occurrence; or perhaps subdivided into a half dozen subpopulations.

"Kagarise Sherman (1980) noted tadpole mortality associated with water diversion and a low level of adult mortality presumably caused by cattle trampling. In response, Deep Springs College abandoned irrigation ditch maintenance and related agricultural practices (e.g., raking and burning) that were potentially detrimental to the toads. Cattle exclosures were built around the spring sources in the early 1970s, presumably to protect toad hibernacula from disturbance." (Murphy et al. 2003). Since then, Deep Springs College has abandoned all agricultural practices within black toad habitat, except periodic cattle grazing (Murphy et al. 2003). Cattle exclosures and other areas at Corral Springs have become thickly vegetated; the impact of this on the toads deserves further study (Murphy et al. 2003). Trampling by cattle occurred at Antelope Spring in at least the 1970s.

In addition to habitat concerns, potential threats include chytridiomycosis and introduction of non-native species such as bullfrogs. The small range of the species makes it highly vulnerable to sudden declines that could occur with the introduction of a non-native predator or disease (Fellers 2005).

These toads appear to tolerate periodic droughts and other climate variations (Schuierer 1972) and so may not be highly vulnerable to climate change unless it results in significant reductions in spring outflows.

Excessive collecting by herpetologists may have been a threat in the early 1970s (Schuierer 1972).