Plant competitive interactions and invasiveness: searching for the effects of phylogenetic relatedness and origin on competition intensity

The invasion success of introduced plants is frequently explained as a result of competitive interactions with native flora. Although previous theory and experiments have shown that plants are largely equivalent in their competitive effects on each other, competitive non-equivalence is hypothesized to occur in interactions between native and invasive species. Small overlap in resource use with unrelated natives, improved competitiveness and production of novel allelochemicals are all believed to contribute to the invasiveness of introduced species. I tested all three assumptions in a common-garden experiment by examining the effect of plant origin and relatedness on competition intensity. Competitive interactions were explored within 12 triplets, each consisting of an invasive species, a native congeneric (or confamilial) species and a native heterogeneric species that are likely to interact in the field. Plants were grown in pots alone or in pairs and in the absence or presence of act...