Characterization of invasive potential of Cleome hassleriana and Polanisia dodecandra: Assessment of population establishment, herbivory effects, and germination

Invasive species of ornamental origin are of significant concern among ecologists, land managers, and floriculture breeders. Ecologists and land managers are concerned by the negative ecological impacts of invasive species in natural habitats, while floriculture breeders are troubled by the detrimental impact restrictive legislation would have on continued importation of exotic crop taxa. At present, the methodology to assess invasive potential of ornamental crops is based on performance in cultivated environments, while invasive biology research supports inclusion of both species- and habitat-specific analyses. The objectives of this dissertation were to characterize invasive potential of ornamental, annual Cleome hassleriana and Polanisia dodecandra cultivars in terms of (1) population establishment in cultivated, non-cultivated and competitive habitats, (2) compensatory ability in response to simulated-herbivory, and (3) germination response to light, stratification and temperature regimes. Habitat-type and disturbance level affected invasive potential in these cultivars. Germination, survival and growth were lower in non-cultivated and disturbed habitats than in garden and greenhouse conditions. The native species (Polanisia dodecandra ) exhibited greater invasive potential in terms of competitive ability than the non-native species (Cleome hassleriana). Cultivars showed different norms of tolerance to herbivory ranging from undercompensation to overcompensation, depending on the type of herbivore damage and the trait studied. Polanisia dodecandra had low compensation compared to Cleome hassleriana, but cultivars within series differed in their response. Significant interactions of herbivory and cultivar complicate the ranking of cultivars in terms of invasive potential. Significant effects of three-way interactions among seed lot, age and depth of planting (Expt. l.), duration of stratification, temperature and photoperiod and seed lot (Expt. 2 and 3) complicate the ranking of cultivars. The implications for a plant breeding program attempting to reduce invasive potential are several. First, there is a need to evaluate traits associated with invasiveness in target environments or under conditions that simulate natural environments. Second, the differences among cultivars and seed lots cautions against making broad generalizations within taxa.