Print PageWhat determines invasiveness of alien organisms is among the most interesting and urgent questions in ecology. In attempts to answer this question, researchers compare invasive alien species either to native species or to non-invasive alien species, and this is done in either the introduced or native ranges. However, inferences that can be drawn from these comparisons differ considerably, and failure to recognize this could hamper the search for determinants of invasiveness. To increase awareness about this issue, we present a framework of the various comparisons that can be used to test for determinants of invasiveness, and the specific questions each comparison can address. Moreover, we discuss how different comparisons complement each other, and therefore should be used in concert. For progress in invasion biology, it is crucial to realize that different comparisons address different biological questions and that some questions can only be answered unambiguously by combini ng them. We illustrate our framework with results from recent studies which have tested differences in plant survival in a grassland sward among native rare and common plant species, and alien invasive and alien non-invasive plant species in Switzerland.
Results/Conclusions
We found that alien plants survived in grassland swards better on average than native species, but invasive and non-invasive alien species did not differ in survival rates, and native common and rare species also did not differ significantly in their survival. Thus, whilst alien species may survive under competition better than native species, differences in survival do not explain why some alien species are more invasive than others. This result emphasizes the importance of considering non-invasive, invasive and native species together.
