“Cosmopolitan” species are often alien invaders

Posted on June 1, 2016

Our ability to manage species invasions is often compromised by a lack of knowledge as to which species are actually aliens and which are natives. This is especially true in the case of animal groups containing small, poorly- studied species. In the absence of solid information, many such taxa have been uncritically assumed to have cosmopolitan distributions. Polish researchers used a multi-point protocol to assess the chance that a given species is invasive. They tested their system on freshwater rotifers, and awarded “invasive” points to a species if it: (1) appeared in areas where it wasn’t previously found; (2) showed an increase in local records after the species appeared in a new area; (3) was associated with human methods of dispersal or (4) other alien species; (5) had a high prevalence in human-transformed habitats; (6) had a relatively limited spread in the assessed area compared to distributions of native species; (7) possessed isolated populations on different continents; (8) had an exotic evolutionary origin, with its closest related species on another continent; and (9) first appeared in the assessed area in new or artificial environments. Test species were assigned alien status if they satisfied most (i.e., at least five) of the nine criteria. Of the 16 species of European rotifers examined, 11 had scores of 5-7 and were therefore assigned as aliens. In contrast, prior to the study, only four species were regarded as alien, one incorrectly so. The assignment protocol can be used as a first step in assessing the status of species, before more intensive (e.g., genetic) analyses can be carried out.

Reference: Pociecha, A. et al. 2016. Native, alien, cosmopolitan, or cryptogenic?
A framework for clarifying the origin status of rotifers. Aquatic Biology 24, 141–149. http://www.int-res.com/articles/ab2015/24/b024p141.pdf