Local vs. landscape-scale factors affecting habitat occupancy of Eastern Collared Lizards (Crotaphytus collaris) in tallgrass prairie

Background/Question/Methods Grassland management, such as grazing and burning, has the potential to alter habitat structure and quality, and may influence the probability of site occupancy for native species occupying naturally patchy habitats. Estimating habitat occupancy is a key step for understanding a species' ecology and response to disturbances, particularly within an intensively managed landscape such as the tallgrass prairie of the Flint Hills in eastern Kansas, where some 90% of managed grasslands is grazed by cattle, with up to two-thirds of the region burned annually. The main objective of this study was to determine how local-scale patch attributes vs. landscape-scale management influence habitat occupancy of collared lizards (Crotaphytus collaris) at the Konza Prairie Biological Station, an experimental landscape with watershed-scale burning and grazing treatments. Collared lizards occupy rocky outcrops along limestone ridges that fringe the hilly topography of the region. Suitability of outcrops may depend upon the amount of cover. However, landscape-scale management effects may be less important than local-scale patch attributes. Rock outcrops were surveyed twice from May-July 2008. We used Program Presence to model patch occupancy as a function of grassland management within watersheds, geomorphological features and habitat cover at outcrops, along with environmental factors (e.g., temperature, wind).

Results/Conclusions Of the six models chosen a priori, the best-fit model indicated that detection probability remained constant throughout the season (p = 0.60), and that the probability of occupancy was best modeled as a function of the number of refuges within rock outcrops rather than the fire/grazing regime of the surrounding landscape. Thus, site occupancy of collared lizards is more influenced by local site characteristics than the surrounding landscape. This research underscores the importance of evaluating management effects and the relative importance of factors operating at local vs. landscape scales on site occupancy, especially if the aim is to determine what management actions might be appropriate for boosting habitat occupancy. In the case of collared lizards in tallgrass prairie, site suitability is apparently related to refuge availability, which is a function of the underlying geology, and thus not under the control of land managers and conservationists.