Graduate Thesis Or Dissertation
 

Using a species-centered approach to examine patterns and drivers of avian species richness in the Rogue Basin, Oregon

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A 'bird's eye view' : using a species-centered approach to examine patterns and drivers of avian species richness in the Rogue Basin, Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rf55z988p

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  • The combined effects of habitat loss, degradation, and fragmentation pose a serious threat to Earth's biodiversity, imperiling even relatively common species. 'Habitat' is necessarily a species-specific concept, and investigations of bird diversity relationships and subsequent efforts to prioritize conservation areas, are challenged by the difficulty of estimating complex habitat gradients for multiple species across broad spatial scales. Technologies such as fine-resolution remote sensing combined with enhanced species distribution modeling techniques hold promise for more accurate assessments of multi-species habitat distributions. In this research, I focused on forest bird species which utilize and/or are highly associated with threatened Oregon white oak and California black oak (Quercus garrayana and Q. kelloggii) vegetation types in the Rogue Basin of southwest Oregon. I created individual species distribution models (SDMs) for 48 bird species as a function of fine-resolution (30 x 30 m) remotely sensed land cover and other environmental variables using boosted regression tree (BRT) models. I then 'stacked' SDMs for spatially explicit regional estimates of multi-species avian richness. In my first chapter, I examined the potential for site-level species richness to be influenced by local vegetation and environmental conditions (e.g. the "local vegetation heterogeneity hypothesis") or by landscape-level dispersal potential (e.g. the "regional species pool hypothesis"). I summarized 'stacked' SDMs for indices of 1) habitat amount at a local scale relevant bird territory use and 2) habitat amount at a broad scale relevant to forest bird dispersal, and ask whether local- or landscape-scale habitat amount is relatively more important to site-level bird species richness. I hypothesized that greater importance of either habitat amount metric would indicate greater influence of local or landscape drivers to local richness. I found evidence that for a large pool of bird species with diverse habitat associations, landscape-scale habitat amount may be relatively more important to local (i.e., territory level) richness of forest birds than is local habitat amount. In contrast, for more specialized (i.e., oak-associated) guilds, local-scale habitat may be considerably more important than amount of habitat within the surrounding landscape. My results suggest the importance of local- and landscape-scale processes in structuring bird communities, supporting both 'local vegetation heterogeneity' and 'regional species pool' hypotheses. In my second chapter, I examined the relationships between landownership, oak vegetation distribution, and bird diversity, with the objective of determining which of five primary landownership types contribute most strongly to bird species habitat in the Rogue Basin. I asked whether individual bird species distributions and estimated richness are 'additive' or 'redundant' among land ownership types, hypothesizing that differences among owners will be apparent and related to the amount of oak-dominant vegetation held by each owner regionally. I found that estimated local mean species richness of oak-associated birds in private non-industrial (PNI) ownerships is approximately double that of other Rogue Basin public and private ownerships examined. This result may be driven by disproportionate PNI ownership of limited oak cover types, and/or by hypothesized variation in management goals and activities among owners which influence local vegetation structure. Relatively greater importance of territory-scale habitat to local oak-associated species richness suggests management for these species should maximize site-level habitat amount and quality. The importance of private non-industrial owners to oak-associated avian richness validates current focus on engaging private landowners in bird-focused oak conservation and restoration. Overall, my research links efforts to conserve avian habitat with efforts to understand multi-scale drivers of bird diversity, using a novel methodology that embraces the complexity of species' habitat gradients.
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file details HalsteadKatherineE2013.pdf 2017-08-07 Pubblico Scaricare