Evaluation of habitat suitability models for elk and cattle
Hohler, Deborah Dorothea
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Managing elk (Cervus elaphus nelsoni) and cattle habitats in the western United States is confounded by the complex interactions of these species and by diverse private and public land management goals. Managers often use quantitative models as tools in land resource management yet many of these models have not been validated. I evaluated modified versions of existing elk and cattle habitat suitability index (HSI) models on four ranches in Montana and Wyoming to evaluate their ability to predict feeding site selections on non forested habitats. Animal locations were determined from aerial surveys conducted 0.5 to 3.0 hours post sunrise, and marked using GPS. The models were used to categorize landcover grids based on suitability for cattle and elk using data gathered from georeferenced spatial information on cover types, elevation, aspect, slope, distance from water, and roads. I hypothesized that elk and cattle feeding site selection would increase with increasing suitability levels. Chi squared analyses were conducted on 1,076 independent elk group locations and 806 independent cattle group locations collected during 2001 and 2002. Selection ratios (S) determined selection (i.e., S > 1.0), avoidance (i.e., S < 1.0), or non selection (i.e., S = 1.0) within a given habitat suitability category. Preference for specific habitat classes was determined using Bonferroni confidence intervals. I found little evidence that the modified elk model consistently predicted seasonal feeding site selection and failed to reject the null hypothesis. Elk selection during the fall season on one ranch satisfied my hypothesis, but the model performed poorly on the other ranches. The modified cattle HSI model was mostly a poor predictor of cattle use on all four ranches. Inaccuracies in the GIS based data used in the models may have contributed to the failure of the models to predict elk and cattle use. Variables used in the models may have not accurately portrayed relationships among habitat variables and habitat use by cattle and elk. The poor performance of the elk and cattle models underscores the need to test habitat models before they are used in resource planning.