Biogeographical patterns, ecological drivers, and evolutionary mechanisms of plant invasions

Understanding and predicting organisms’ responses to novel environments is a key issue for global change biology. In this dissertation, I study biogeographical patterns of plant invasions in Brazil, explore some of their ecological drivers, and disentangle the gene-level mechanisms that cause introduced organisms to become successful or failed invaders. I found that, for the invasive flora of Brazil, species were not introduced to new regions at random and that a species’ reason for introduction and continent of origin were associated. Asian ornamental and African forage plants are overrepresented, and two families (Poaceae and Fabaceae) dominate the invasive flora of Brazil. To address the reason for the observed patterns, I studied 18 Pinus species introduced to Brazil. I found that biotic resistance reduced the rate of spread, but did not prevent invasions from happening. Also, mean values of species traits did not explain which species would have become naturalized or invasive. The number of source populations introduced for each species was the factor that best explained the observed pattern of invasion. These findings indicate that forests might not resist invasion by Pinus and support the hypothesis that propagule pressure is a driver of invasions with propagule diversity being a component of this mechanism. Next, I surveyed the ecological literature to explore reasons why invasive species are not always invasive. I found intraspecific variation in invasion success and explanations for this variation: low propagule pressure, abiotic resistance, biotic resistance, genetic constraints, and mutualist release. Finally, to understand mechanisms leading to variation in invasion success, I analyzed the spread of Pinus taeda in six forestry provenance trials. I found that range expansions of introduced P. taeda resulted from an interaction between genetic provenance and climate and that temperature and precipitation predict the invasive performance of particular provenances. Further, I found genotypes can occupy climate niche spaces different from those observed in their native ranges. Overall, my work demonstrates genotypes respond to climate in distinct ways, and these interactions affect the ability of populations to expand their ranges. The introduction of adapted genotypes is a key driver of naturalization of populations of introduced species.