| One of the greatest factors contributing to the worldwide decline in biodiversity is habitat destruction leading to the loss and fragmentation of populations of many species. Knowledge of the genetic and demographic factors that are affected by and influence rarity advances our understanding of the consequences of habitat degradation, and this knowledge is crucial for creating management plans for rare or endangered species. In this dissertation, I address these factors in a rare sunflower species, Helianthus verticillatus , through studies of its population genetics and taxonomic status, the assessment of population size, and the evaluation of fitness. A population genetic study, employing a novel genetic marker, demonstrated that this species is not the product of recent hybridization and, surprisingly, harbors high levels of genetic diversity despite its small number of populations and disjunct range. A study of the clonal diversity and structure in this species revealed far fewer numbers of individuals than were previously reported; these results led to the upgrading of the species' priority status for the Endangered Species Act. Finally, populations differed with respect to phenotypic fitness related traits; this was not predicted by population genetic data and further highlights the need for comprehensive studies of endangered species in order to fully evaluate the effects of rarity and fragmentation on population viability. |
