No evidence for an evolutionary increased competitive ability in an invasive plant

We tested whether Solidago canadensis, which was introduced from North America into Europe from the 17th century onward, has evolved an increased competitive ability (EICA) at the cost of tolerance against herbivory in its new ranged We grew plants from nine introduced European and 10 native American populations in a common garden in Europe. In half of the plants, we simulated herbivory by removing 50% of the leaf area and by spraying them with jasmonic acid. Although plants from Europe had 30.5% larger leaves, they had 27.4% smaller inflorescences and tended to grow less tall (-7.0%) and produce fewer vegetative offspring (-5.0%) than plants from North America. The simulated herbivory treatment did not result in any significant differences in height, inflorescence biomass, or number of vegetative offspring between treatment and control plants. Moreover, there were no significant differences in the response of European and American plants to simulated herbivory, indicating that they did not differ in their tolerance against herbivory. We conclude that the EICA-hypothesis does not hold in the case of the S. canadensis complex, and the worldwide invasion success. of this species must be based on other mechanisms.