Thesis Defense: Christopher F. Jorgensen

Christopher Jorgensen will defend his master thesis, "Assessing Local and Landscape Constraints on Habitat Management for Grassland and Upland Birds," at 9 a.m., Monday, Nov. 5, in 901 Hardin Hall. His adviser is Joseph Fontaine.

Abstract
Biodiversity loss is an increasing threat and while habitat restoration is beneficial, management actions do not always demonstrate the desired outcome. Understanding why management actions fail is critical, yet often the focus is directed towards assessing habitat relationships at a single scale, failing to consider the importance of ecological mechanisms that act across scales. 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. While identifying habitat relationships at multiple spatial scales is important for conservation, understanding the mechanisms underlying habitat selection is critical for ecological theory. 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.