| Ecologists recognize two components of biodiversity: inventory diversity, the species composition of a single place, and differentiation diversity, more commonly called beta-diversity, which is derived by several different methods from the change in species composition between places. Beta-diversity is determined through a complex array of processes relating to the interaction of species traits and characteristics of the physical landscape over time. Geographic variation in beta-diversity reflects past and present differences in environment, ecological interactions, and biogeographic history, including barriers to dispersal. As beta-diversity quantifies the turnover in species across space, it has important applications to the scaling of diversity, the delineation of biotic regions and conservation planning. Despite the importance of beta-diversity, relatively little is known about diversity's "other component", particularly at broad scales.; In this dissertation, I trace the conceptual evolution of beta-diversity in order to reconcile the different views surrounding it, and examine empirical patterns of terrestrial vertebrate beta-diversity at broad spatial scales in order to gain insight into this important diversity component. I use range data for amphibians, birds, and mammals within the Western Hemisphere to produce the only maps to date of beta-diversity at this scale for multiple classes of terrestrial vertebrates and test for cross-taxon congruence in broad-scale beta-diversity. I also examine the strength and geographic variation of the relationship between beta-diversity and species richness. In a third empirical chapter, I analyze whether beta-diversity of amphibians at a global scale varies systematically across biogeographic realms and biomes.; My results show that vertebrates classes have congruent patterns of beta-diversity across the Western Hemisphere. Further, beta-diversity and richness exhibit disparate patterns for these taxa. I demonstrate, however, that the strength of beta-diversity congruence and the relationship of beta-diversity to species richness vary with spatial extent, geographic location, and between taxa. Amphibian beta-diversity at a global scale also shows complex variation across biogeographic realms and biomes. These findings illustrate the influence of environmental, historical, and taxonomic differences on ecological relationships, and stress the need for stringent tests across multiple taxa and regions. |
