Print PageCentaurea solstitialis and C. calcitrapa are two closely related species with highly overlapping native and non-native ranges in Spain and California, respectively. Centaurea solstitialis is highly invasive in California whereas C. calcitrapa is naturalized but has not become invasive. We sampled seeds from eight populations per species and region and grew plants alone and in competition with seven species of grasses from both ranges in a common garden greenhouse experiment. After 92 days plants were harvested and dried and weighed.
Results/Conclusions
For both species, Californian populations were larger than Spanish conspecifics when grown with no competition. When plants were grown in competition with grasses, Californian populations of C. solstitialis out-performed their Spanish conspecifics in every treatment. While Californian populations of C. calcitrapa also tended to be larger than their Spanish conspecifics, these intercontinental differences were consistently smaller than those for C. solstitialis.
Other studies indicate that some traits of C. solstitialis and C. calcitrapa have been selected on in their new, non-native ranges over the last two centuries. We cannot exclude potential founder effects, but our results suggest that such selection may extend to greater competitive abilities for both species in at least one non-native range. The invasive C. solstitialis and the non-invasive C. calcitrapa demonstrated similar competitive responses to other species, thus we found no evidence that species-specific, per capita competitive abilities contribute to the greater invasive success of C. solstitialis.
