Species distribution models are commonly used to identify the environmental characteristics that allow for the persistence and survival of a species in the landscape. This information is particularly valuable for sensitive species, such as the Yosemite toad (Bufo canorus = Anaxyrus canorus) in California. The toad appears to have disappeared from over 50% of its historic range even in seemingly undisturbed areas, and the cause(s) of its disappearance and decline are not known. In order to manage for and conserve the Yosemite toad, information on its distribution and environmental requirements are needed. A species distribution model was created to identify environmental characteristics that are suitable for the existence of the toad, using known occurrences from a comprehensive field survey conducted in the Sierra National Forest, California. Toad occupancy data were analyzed using logistic regression, with toad presence or absence (i.e., not detected) as the response variable. Predictor variables were derived from a combination of field surveys and geographic information system data sources. Two common presence-absence modeling methods, generalized linear models and generalized additive models, were used for this study.
Results/Conclusions:
Results show that the distribution of the Yosemite toad in the Sierra National Forest is related to a number of environmental factors and no one variable or reduced subset of variables is the main predictor of toad presence-absence. Instead, a combination of eco-physiological factors, resources and disturbances correlate with toad occurrences. This indicates that the species has a complex relationship with the environment but exhibits a wide range of latitude in its requirements. It is not dependent on a single set of environmental variables and can persist within a suite of conditions. This may indicate that the species is relatively insensitive to environmental conditions and might have a low phenotypic plasticity. While this may be favorable for Yosemite toads in stable environments, it may mean that the toad does not fare well in variable or changing environments due to an inability to respond rapidly to the changes.
