Promotor: Prof.dr. P.G.L Klinkhamer, Co-promotor: K. Vrieling
|Links||Thesis in Leiden Repository|
Although the introduction of invasive plant species in a given area causes economic and ecological problems, it still provides an ideal opportunity for ecologists to study evolutionary changes. According to the Evolution of Increased Competitive Ability hypothesis and Shifting Defense Hypothesis, the release from specialist herbivores after introduction is expected invasive plants to shift their costly defense against specialist herbivores to cheaper defense against local generalist herbivores. A net gain can be saved to increase plant growth and competitive ability. In this thesis I used Jacobaea vulgaris as a model plant species to study the evolutionary changes in plant anti-herbivore defenses and growth ability. I found that invasive Jacobaea vulgaris populations indeed have evolved better growth and competitive ability, higher chemical defense but decreased structural defense and regrowth ability compare to the native populations. In addition, we show that all studied traits of invasive populations from multiple geographically distinct regions changed toward the same expected direction. It indicates parallel evolution took place in these invasive regions since they all differed significantly in climatic conditions. Such parallel evolution is most likely due to the disappearance of selection pressures from specialist herbivores rather than the adaptation to local abiotic factors after invasion.