A test for a cost of opportunism in invasive species in the Commelinaceae

Many invasive species can respond opportunistically to favorable growing conditions. In a previous work, we found that invasive species in the family Commelinaceae were more opportunistic than their noninvasive congeners and could therefore outperform noninvasive relatives in an environment with abundant resources and no competition. Contrary to the expectation that superior performance under favorable conditions comes at the cost of reduced performance under stressful conditions, invasive species did not perform more poorly relative to noninvasive congeners under any conditions we examined. Here we expand our search for potential costs of opportunism in invasive species to additional environmental conditions in which invasive taxa have been shown or predicted to perform poorly. We grew four invasive and four noninvasive species in environments consisting of all possible combinations of high and low soil resources and presence and absence of clipping (removal of aboveground biomass). We also fed leaves of each species to a generalist herbivore to assess resistance to herbivory. We found that the advantage of invasive species is reduced but not eliminated by low soil resources and clipping. At low soil resources, invasive species produced softer leaves than noninvasive species and might therefore be less resistant to generalist herbivory than noninvasive species, although a direct comparison of resistance in a no-choice bioassay revealed no difference. The invasive species outperformed noninvasive species only under the most favorable conditions, and the noninvasive species did not outperform the invasive species in any environment.