FWS Desert Tortoise Connectivity Areas

The output of this model depicts the areas of contiguous, highest value habitat for the Mojave desert tortoise. The areas of highest value are those of highest habitat potential (as modeled in Nussear et al. 2009) which are adjacent to other areas of highest habitat potential. Nussear et al. (2009) developed a model of habitat suitability for the tortoise using presence data and 12 environmental variables to predict potential areas of desert tortoise habitat throughout its geographic range at a 1km2 scale. Their analysis did not account for anthropogenic changes that may have altered habitat with relatively high potential into areas with lower potential. We therefore utilized 1) National Landcover Datasets" Impervious Surfaces layer and 2) The Nature Conservancy's "highly converted areas" (TNC Mojave Ecoregional Assessment 2010; TNC Sonoran Ecoregional Assessment 2009) to change heavily developed areas where tortoises cannot occur to zero habitat potential. The highly converted layer depicts urban, suburban and agricultural lands that have been heavily altered. Our model first finds areas with a 1.0 habitat potential probability, then iteratively adds adjacent areas with a lower potential starting with 0.9 down to 0.6. The output consists of all areas down to 0.6 that can be reached from any 1.0 area, with no unconnected "habitat islands".