Invasiveness of Oenothera congeners alien to Europe: Jack of all trades, master of invasion?

The genus Oenothera includes a number of species alien to central Europe, which differ in their invasion success. The present study was designed to investigate how fecundity, growth rate of seedlings and competitive ability contribute to the invasion potential within this genus. The relative growth rate and response to interspecific competition from neighbouring vegetation were determined for 15 species. Relations between these characteristics and other species traits identified in previous studies (germination, seed production and seed mass) were examined and used to explain the invasion success of particular species in Europe. Ability to germinate in the light was the only significant predictor of invasion success in six European countries. Fecundity is another trait contributing to invasion success. The most successful invaders within the genus are poor at competing with native vegetation, and an ability to escape from competition seems crucial for invasion success. Oenothera biennis, the most successful invader, is not outstanding in any of the characteristics assessed but is well placed in most of them. We suggest that a ‘Jack-of-all-trades’ strategy may be beneficial for an invader. The parental chromosomes of the species studied had no effect on the distribution of traits; hence the conclusions drawn at the species level are not biased by the specific banding pattern within the genus (permanent translocation heterozygosity). The present study indicates that comparative studies of closely related species may indicate the determinants of invasion success if they include many characteristics of the complete life cycle.