Invasion of high alpine ecosystems by the exotic dandelion Taraxacum officinale (Asteraceae)

Over the last century, an increase in global human movement has dramatically increased the number of exotic invasive species. Invasive species are the second leading threat to biodiversity and control measures result in an exorbitant economic cost to society. Exotic plant species can threaten related native congeners through asymmetric hybridization and subsequent backcrossing, a process known as genetic assimilation. I explore the initial stages of this process in Taraxacum ceratophorum, the native alpine dandelion, and the invasive asexual T. officinale. Results indicate that sexual T. ceratophorum throughout central Colorado co-occur and flower simultaneously with T. officinale. Insects move pollen indiscriminately between these Taraxacum species and interspecific hand-pollinations result in hybrid offspring. Although native pollen out-performs foreign T. officinale pollen in T. ceratophorum styles, factors reducing pollen accrual rates may partially remove barriers to natural hybridization, which may promote the genetic assimilation of T. ceratophorum.; I further explore if T. officinale's ability to alter its morphology in response to environmental variation (phenotypic plasticity) and physiological performance (drought tolerance) relative to the native benchmark, T. ceratophorum, are useful in predicting invasiveness. Results show that differences in plasticity between species are not systematic, but instead vary among traits. In fact, my results suggest that the absence of plasticity in seed dispersal traits enhances the colonization potential of T. officinale. Physiological measurements demonstrate that T. officinale plants and interspecific hybrids do not out-perform T. ceratophorum plants under drought stress. Physiological data indicates that periods of extreme drought should help limit invasion, and when considered with plasticity data demonstrate the need for further study of mechanisms promoting invasion.