Invasive plant distributions: Lessons from native and exotic ranges

Invasive exotic plants are both symptoms and agents of global change, having diverse effects on ecological and economic systems. The roles of propagule pressure and ecosystem invasibility are key in understanding the mechanisms of biotic invasion and the factors that determine invasion success. In this dissertation, I use spatial distribution and environmental data to make inferences about the ecological niche and current and potential distributions of invasive plants. Chapter one focuses on the analysis of spatial data in biogeographic studies, such as used in the balance of the dissertation. This chapter illustrates numerous ways that spatial heterogeneity can be a rich source of information yielding insights on important ecological processes. In chapter two, I examine the role of various biotic, abiotic, human, and historic factors measured at a variety of spatial scales in shaping the distribution of Celastrus orbiculatus Thunb. (Asiatic bittersweet), an exotic invasive vine, in the Southern Appalachians of Tennessee (TN) and North Carolina (NC), USA. This chapter demonstrates the important legacy of introduction sites in shaping the distribution of exotic plants many years after their introduction. Finally, in the third chapter, I identify and compare the ecological niche and distribution of an invasive tree, Ailanthus altissima (P. Mill.) Swingle (tree-of-heaven) in both its native Chinese range and introduced range in the US and predict its potential US distribution based on Chinese occurrence data. The predicted distribution is compared with actual US occurrence information and found to indicate a broadening of the ecological niche in the introduced range. Collectively these chapters illustrate the relative importance of factors related to the ecological niche and propagule pressure in determining the distribution of invasive species in their native and exotic ranges and suggest evolutionary and ecological hypotheses related to the invasion process.