Article,
Modeling habitat of the desert tortoise (Gopherus agassizii) in the Mojave and parts of the Sonoran deserts of California, Nevada, Utah, and Arizona
US Geological Survey open-file report, (2009)
Abstract
Habitat modeling is an important tool used to simulate the potential distribution of a
species for a variety of basic and applied questions. The desert tortoise (Gopherus agassizii) is a
federally listed threatened species in the Mojave Desert and parts of the Sonoran Desert of
California, Nevada, Utah, and Arizona. Land managers in this region require reliable information
about the potential distribution of desert tortoise habitat to plan conservation efforts, guide
monitoring activities, monitor changes in the amount and quality of habitat available, minimize
and mitigate disturbances, and ultimately to assess the status of the tortoise and its habitat toward
recovery of the species. By applying information from the literature and our knowledge or
assumptions of environmental variables that could potentially explain variability in the quality of
desert tortoise habitat, we developed a quantitative habitat model for the desert tortoise using an
extensive set of field-collected presence data. Sixteen environmental data layers were converted
into a grid covering the study area and merged with the desert tortoise presence data that we
gathered for input into the Maxent habitat-modeling algorithm. This model provides output of
the statistical probability of habitat potential that can be used to map potential areas of desert
tortoise habitat. This type of analysis, while robust in its predictions of habitat, does not account
for anthropogenic changes that may have altered habitat with relatively high potential into areas
with lower potential.
