Hierarchical, multi-scale analysis of species-environment relationships
This dissertation presents several new approaches to analyzing species-habitat relationships in multi-scaled, hierarchical systems, and demonstrates their utility in analyzing a forest bird data set from the Oregon Coast Range. In the first chapter I present a review of past studies of species-habitat relationships at the landscape level. I then suggest a number of attributes that studies should include in order to rigorously analyze landscape-level relationships between species and their environments. In chapter two I introduce a new method of hierarchical, multi-scale decomposition of species-environment relationships. The approach translates a hierarchical, multi-scale conceptual model into a statistical decomposition of variance. It uses a series of partial canonical ordinations to divide the explained variance in species-environment relationships into its independent and confounded components, facilitating tests of the relative importance of factors at different organizational levels in driving system behavior. In chapter three I discuss the implications of how the species response variables are recorded for analyses of multi-scale species-environment relationships. In chapter four I demonstrate the use of this method in analyzing forest bird species-environment relationships. Chapter four demonstrates the hierarchical partitioning method for a large forest bird data set from the Oregon Coast Range. I found that plot-level factors were better predictors of community structure than either patch- or landscape-level factors. There were major differences among life-history groups in terms of the relative importance of factors at the three spatial scales. In chapter five I describe the landscape-level patterns of avian diversity in the Oregon Coast Range. I used a combination of factorial analysis of variance and partial discriminant analysis to quantify the relative importance of differences in mature forest area, fragmentation and basin in influencing each response variable and community diversity overall. Bird community diversity was influenced by both the extent and fragmentation of mature forest at the landscape-level. Species richness and density responded more strongly to mature forest area than to fragmentation, and were significantly lower in landscapes that were completely dominated by mature forest than in landscapes with a mixture of seral stages. Species evenness was more strongly related to fragmentation than to area of mature forest at the landscape-level.