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Species-habitat relationships are a central tenant to ecological theory and are critical in species management. Yet, despite a long-standing tradition of utilizing species-habitat relationships in both theoretical and applied ecology, there remains to be no clear predictors of how species relate to habitat. In order to further our understanding of the habitat selection process, we must begin to comprehend what spatial scales species form habitat decisions and what potential behavioral or life-history predictors underlie the scale of habitat decisions. During 2010-2012, I conducted point counts for grassland birds across Nebraska and assessed habitat relationships over multiple spatial scales to construct predictive species distribution models. Results indicated that landscape scale habitat variables drastically constrained or, alternatively, facilitated the positive effects of local land management for Ring-necked Pheasants. Hierarchical theory suggests that ecological processes function concurrently over multiple spatial scales and not all scales may be appropriate in determining species occurrence. I predicted that the spatial scale in which a species forms habitat decisions would correlate with body size, a predictor of life-history expression, if the scale is a function of how the species interacts with its environment. I tested this hypothesis on 10 obligate grassland bird species in Nebraska, USA. For seven species, I found evidence of a characteristic habitat selection scale, but no relationship to body mass. To quantify local habitat quality, a predictor of species occurrence, I assessed the precision of five methods of measuring plant structure using ground-based imagery and processing techniques. I recorded standing herbaceous cover using digital imagery at two locations in a mixed-grass prairie. I compared the precision of the digital imagery vegetation analysis (DIVA) methods and quantified variability within each technique using the coefficient of variation. Vertical herbaceous cover estimates varied among DIVA techniques but the precision of four of the five techniques was consistently high. Overall, DIVA techniques are sufficient for measuring standing herbaceous cover and can adequately reduce measurement error associated with multiple observers.
Advisor: Joseph J. Fontaine