Habitat modeling and movements of the Yosemite toad ( Anaxyrus (=Bufo) canorus) in the Sierra Nevada, California

The Yosemite toad (Anaxyrus (=Bufo ) canorus) is a high-elevation species endemic to the Sierra Nevada mountain range in California and is part of the world-wide amphibian declines phenomenon. The toad is thought to have disappeared from over 50% of its historic range even in seemingly undisturbed areas, and remaining populations appear to be in decline. The causes of the disappearance and decline are unknown, and this poses a particular challenge for management and conservation since there is little understanding on how to ensure the survival of remaining populations. In order to provide information that can be used to inform management and to aid in the conservation of the species, my research on the Yosemite toad consisted of three parts: (1) constructing species distribution models to identify environmental correlates; (2) identifying environmental correlates associated with different habitat patch types; and (3) determining movement patterns and habitat use in the terrestrial environment. In the first study, I used Yosemite toad survey data from over 2,200 sites in the Sierra National Forest in the southern part of the toad's range and related them to 54 environmental variables. I found that the Yosemite toad has a complex relationship with the environment and is correlated with both biophysical and management related variables. In the second study, I looked at 49 consistently occupied sites versus 27 intermittently occupied sites throughout the range of the Yosemite toad and related the two site types separately to 26 environmental variables. I found that the different site types were correlated with different environmental variables. In the third study, I radio-tracked 42 adult Yosemite toads and collected data on their movements and habitat use. I found that toads traveled up to 1.26 kilometers away from breeding sites, and the average distance moved was 275 meters. The toads were often found in burrows and extensively used the terrestrial environment. The results from my research help elucidate the environmental requirements of the Yosemite toad both in and away from breeding sites, and can be used to inform management decisions for protection of the species and its habitat.