Landscape structure and the biological diversity of the North American avifauna
Patterns of biological diversity are influenced by macroscale processes as well as localized ecological conditions, including the spatial distribution of landscape elements. Describing and quantifying the effect of landscape structure on ecosystem attributes such as biodiversity patterns is a research priority in modern ecology. This dissertation examines the connections between patterns of landscape structure and patterns of avian biodiversity in North America. The first goal of my dissertation was to identify metrics of landscape structure that are appropriate for describing the link between the spatial heterogeneity of landscapes and the spatial patterns of biological diversity. Then, using long-term species occurrence data from the North American Breeding Bird Survey, I tested the hypothesis that the body size distributions of species assemblages display discontinuities. I found that not only are there discontinuities, but the position of species in the body mass distribution relative to the location of the discontinuities has ecological consequences. I then used lacunarity analysis to test the hypothesis that discontinuities in landscapes structure correspond to discontinuities in body mass distributions. To accomplish this I again used species occurrence data from the Breeding Bird Survey and forested habitat distribution data from the National Land Cover Data set. The results of this analysis suggest that the forest habitat of eastern North America is not hierarchically structured and therefore is not the likely cause of the observed discontinuities in avian body mass distributions. Finally, I examined the hypothesis that the composition of avian species assemblages conforms to the distribution of ecoregions across North America. Using seven beta-diversity metrics to describe the species assemblages, I found that the distribution of the North American avifauna appears to be spatially autocorrelated and independent of ecoregion distribution.