Evolutionary and Ecological Drivers of Invasion in the Annual Thistle, Centaurea melitensis

Invasive species have resulted in enormous economic and ecological costs and are considered a major cause of the global loss of biodiversity. The causes of invasion are complex, involving characteristics of the invading species and properties of recipient communities. Processes driving invasion are both evolutionary and ecological. Understanding the mechanisms of biological invasions is essential to reducing the threats from ongoing introductions, preventing new invasions, and controlling the spread of existing invaders. Centaurea melitensis, a widespread invasive plant that has established globally from its western Mediterranean center of origin, offers a unique opportunity to examine the processes that enhance invasiveness of plant species. The overall objective of this research is to examine the ecological and evolutionary factors that produce invasive populations of C. melitensis. The approach uses ecological and genetic data, a common garden, and species distribution modeling to compare characteristics of individuals and environments from the native range in Spain with those from two invasive ranges of similar Mediterranean climate type: one in central Chile and the other in California. Chapter One introduces the problem and gives a background overview. Chapter Two compares population densities and dominance among regions. Chapter Three addresses variation in phenotypic plasticity and life history traits among regions by comparing plants grown in a common greenhouse. In Chapter Four, molecular genetic markers are tested for applicability to C. melitensis. Chapter Five examines the role of fire and other disturbances on community dynamics. Chapter Six uses species distribution modeling to project a potential invasive range onto a non-native range to identify niche evolution. Results of this project indicate that C. melitensis is more abundant and more dominant in the invasive range than in the native range; that invasive populations are genetically differentiated from native ones for several life history traits and their plasticities; that microsatellite markers developed for other Centaurea species are not applicable to C. melitensis; that fire promotes the recruitment of C. melitensis; and that the niche of invasive plants has shifted from those of native plants. The questions in this study are not only important in terms of basic research in ecological and evolutionary processes such as how species interactions and local adaptation affect species distribution and abundance, but also are relevant to management applications by informing strategies to prevent and limit the impacts of species invasions