A fundamental question of long standing in the study of life on Earth is, “Why are there so many species?” This question concerns the distribution of and relationships among species in the present day, but also requires an understanding of the history of diversity. Patterns of diversity result from multiple, interconnected ecological processes operating at different spatial scales. The goal of this research is to gain knowledge about processes that control diversity by using fossil data to provide a temporal perspective that is unavailable when studying modern ecological communities. The fossil record provides the only natural historical account of changes in the diversity of ecological communities in Earth’s past. This research examines the taxonomic composition and diversity of brachiopod paleocommunities in the Delaware Basin of west Texas (Guadalupe Mountains National Park). The study interval is the Bell Canyon Formation, a 5.4-Myr interval of upper Middle Permian (Capitanian) siliciclastic and carbonate rocks deposited on the toe-ofslope of the basin. Silicified brachiopods extracted from the carbonate rocks provide the basis to test two hypotheses: (1) the taxonomic composition of local fossil brachiopod paleocommunities remains uniform, and (2) the changes in diversity of local fossil brachiopod paleocommunities reflects the relative importance of regional processes. Multivariate analyses of clustering analysis and ordination, diversity partitioning, and rank abundance plots are used to evaluate brachiopod taxonomic composition and diversity within an ecological framework. Sequence stratigraphic analysis provides the means to place the results within an environmental context related to sea-level changes. Results indicate that the reorganization of brachiopod paleocommunity structure coincides with major basinal-scale disruptions. Large disruptions allowed rare taxa and invaders from outside the basin to become dominant within paleocommunities. The dynamics within paleocommunities do not appear to prevent the replacement of the incumbent taxa with new taxa. The importance of these findings indicate that paleocommunities are not static through this interval and can be perturbed into configurations with new dominant taxa. Therefore, ecological responses of paleocommunities are resolvable at the geological time scale.

<p>Dispersal has been long recognized as an important process in metacommunity dynamics, allowing isolated communities to interact with each other through the movement of individuals. Metacommunity theory and its four models (species-sorting, mass-effects, patch-dynamics and neutral) emphasize the significance of dispersal in the structure and composition of local community. Therefore, quantifying movements of individuals between patches is necessary to understand how systems will respond to varying degrees of connectivity and resulting species interactions. Many studies that have attempted to quantify dispersal, particularly of aquatic invertebrates, found conflicting results with respect to the intensity with which dispersal occurs. Moreover, investigations of invertebrate dispersal factors aquatic habitats have neglected to consider the influence of multiple factors such as life cycle stage, species, and external environmental features on dispersal rate via three vectors (wind, overflow, and animal transport). Colonization experiments have largely emphasized the importance of dispersal in influencing species richness, abundance and diversity but have yet to demonstrate direct comparisons between composition of dispersing species and local community structure. I investigated dispersal of aquatic invertebrates in a rock pool metacommunity, its possible influencing factors (species, life stage and the surrounding rock pool environment), and potential impact on species composition in local communities. To explore this, I used a combination of dispersal interception traps, colonization experiments and long tern biotic community surveys. I found dispersal occurs both rapidly and in high abundance across rock pools, particularly using wind and flow vectors, with minimal influence of connectivity, vegetation and ocean on dispersal rate. Although species and life cycle stages were highly variable and differed in their dispersal intensity, a high degree of similarity existed between composition of dispersing species and local community structure. Regional processes (i.e., dispersal), despite its unpredictability, is important for species assemblage and local community composition and necessary in the colonization of newly created habitats.</p> / Master of Science (MS)

<p>The identification of processes governing genetic structure at different spatial scales remains a major challenge in evolutionary biology and is of considerable applied interest in conservation biology. In <i>Euphrasia stricta</i> five varieties have been identified (<i>brevipila</i>, <i>gotlandica</i>, <i>stricta</i>, <i>suecica</i> and <i>tenuis</i>) based on differences in habitat, phenology and morphology. In this thesis, I examined genetic variation at AFLP and microsatellite marker loci in relation to variation in habitat and morphology within and among varieties of <i>E. stricta</i> on the island Gotland in the Baltic Sea. The results are discussed in relation to evolutionary processes acting within this species complex. </p><p>In a study conducted at the regional scale, the two early-flowering varieties <i>suecica</i> and <i>tenuis</i> each formed a genetically distinct group, while the three late-flowering varieties <i>brevipila</i>, <i>gotlandica</i> and <i>stricta</i> formed a third group. The results suggest that <i>suecica</i> and <i>tenuis</i> have ancient origins since they are genetically different both from the <i>brevipila</i>/<i>gotlandica</i>/<i>stricta</i> group and from each other despite their similar habitat preferences. This pattern was obtained using both marker systems. Discrepancies between AFLP and microsatellites were found in patterns of isolation by distance and in estimates of expected heterozygosity, <i>H</i>_e.</p><p>Focusing on the mixed genetic group <i>brevipila</i>/<i>gotlandica</i>/<i>stricta</i> and the causes behind their clustering together despite differences in morphology and habitat preferences, I performed a study at a smaller geographic scale. Studying a population of <i>E. stricta</i> I found that, although gene flow within the population was strong, it had not prevented the formation of genetic groups associated with micro-habitat properties. </p><p>An important result for conservation of the rare variety <i>suecica</i> is its distinct genetic separation from variety <i>tenuis</i>. If the aim of conservation is to preserve the uniqueness of <i>suecica,</i> the two varieties should be treated as separated entities. </p>

The identification of processes governing genetic structure at different spatial scales remains a major challenge in evolutionary biology and is of considerable applied interest in conservation biology. In Euphrasia stricta five varieties have been identified (brevipila, gotlandica, stricta, suecica and tenuis) based on differences in habitat, phenology and morphology. In this thesis, I examined genetic variation at AFLP and microsatellite marker loci in relation to variation in habitat and morphology within and among varieties of E. stricta on the island Gotland in the Baltic Sea. The results are discussed in relation to evolutionary processes acting within this species complex. In a study conducted at the regional scale, the two early-flowering varieties suecica and tenuis each formed a genetically distinct group, while the three late-flowering varieties brevipila, gotlandica and stricta formed a third group. The results suggest that suecica and tenuis have ancient origins since they are genetically different both from the brevipila/gotlandica/stricta group and from each other despite their similar habitat preferences. This pattern was obtained using both marker systems. Discrepancies between AFLP and microsatellites were found in patterns of isolation by distance and in estimates of expected heterozygosity, He. Focusing on the mixed genetic group brevipila/gotlandica/stricta and the causes behind their clustering together despite differences in morphology and habitat preferences, I performed a study at a smaller geographic scale. Studying a population of E. stricta I found that, although gene flow within the population was strong, it had not prevented the formation of genetic groups associated with micro-habitat properties. An important result for conservation of the rare variety suecica is its distinct genetic separation from variety tenuis. If the aim of conservation is to preserve the uniqueness of suecica, the two varieties should be treated as separated entities.