Spatial organization of desert tortoises and their burrows at a landscape scale

We thoroughly surveyed two 9 km 2 study plots using 624 km of transect lines in the south- central Mojave Desert, California, mapping with a precision global positioning system the location of desert tortoises (Gopherus agassizii) and their burrows. We found 98 desert tortoises and 1463 tortoise burrows. Three separate geospatial methods (quadrat-variance, nearest neighbor, and 3 geospatial functions) confirmed that active and total desert tortoise burrows were aggregated on the landscape at multiple spatial scales. Desert tortoises also displayed an aggregated pattern, although results were not consistent between the two plots. We also found a significant positive association between desert tortoises and their burrows using Type II linear regression and Ripley's K 12(t) function. A strong positive association between active burrows/km 2 and tortoises/km2 (r2 = 0.88) and between total burrows/km2 and tortoises/km2 (r2 = 0.80) and the supporting results of Ripley's K 12(t) geospatial function suggest that, within a given year and locality, desert tortoise burrows can be used to determine relative desert tortoise density patterns.