invasiveness of an introduced species does not predict its impact

Inconsistent use of terminology plagues the study and management of biological invasions. The term “invasive” has been used to describe inter alia (1) any introduced non-indigenous species; (2) introduced species that spread rapidly in a new region; and (3) introduced species that have harmful environmental impacts, particularly on native species. The second definition in various forms is more commonly used by ecologists, while the third definition is pervasive in policy papers and legislation. We tested the relationship between the invasiveness of an introduced species and its impact on native biodiversity. We quantified a species' invasiveness by both its rate of establishment and its rate of spread, while its impact was assigned a categorical ranking based on the documented effects of the invader on native species populations. We found no correlations between these variables for introduced plants, mammals, fishes, invertebrates, amphibians and reptiles, suggesting that the mechanisms of invasion and impact are not strongly linked. Our results support the view that the term “invasive” should not be used to connote negative environmental impact.