Evidence of decline for Bufo boreas and Rana luteiventris in and around the northern Great Basin, western USA

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Revisiting historical sites for patch-associated fauna can provide a relatively fast assessment of species status in a region. Between 2000 and 2003 the authors repeatedly surveyed historically documented sites for two amphibian species of concern in the northern Great Basin: the western toad (Bufo [Anaxyrus] boreas) and the Columbia spotted frog (Rana luteiventris). They estimated that B. [A.] boreas occupies 49.5% (34.1–65.0%) of 34 historical sites and R. luteiventris occupies 52.0% (43.5–62.3%) of its 30 historical sites. B. [A.] boreas was more likely to be detected at historical sites that were human-altered, whereas R. luteiventris was more likely to be detected at sites that had deeper water than other sites in the study. B. [A.] boreas was detected at three of 41 (7.3%) proximal sites (located near historical sites), whereas B. [A.] boreas was detected at one of 187 randomly selected sites, and R. luteiventris at three sites. Given that the number of historical sites available for resurveys was small, these results should be interpreted with caution. Moreover, a species can shift its distribution away from historical sites due to habitat succession or metapopulation dynamics without necessarily declining. The authors suggest that there is sufficient evidence to conclude that B. [A.] boreas and R. luteiventris have declined in and around the northern Great Basin. Comparatively high occupancy of proximal sites by R. luteiventris suggests this species may not have declined as much as has B. [A.] boreas in the study region.

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ELECTRONIC FILE - Zoology