Abstract
Among small organisms, it is often difficult to distinguish native from alien species because we cannot easily determine where they originate. They are often labelled cosmopolitan or cryptogenic, euphemisms that indicate that we are uncertain of their origin. This lack of infor- mation obscures our understanding of biogeography and ecosystem functioning, thus limiting our ability to control biological invasions. Here, we propose a simple method using existing data to improve assessments of freshwater Rotifera. We tested the usefulness of 8 of 10 attributes of alien species, taken from a framework originally designed for distinguishing alien marine crustaceans, and added one new attribute. We used this framework to verify the origin status of 16 rotifers referred to in the literature as alien, cosmopolitan, tropicopolitan, or new to Europe. We assigned the alien status to 11 species that scored positively for at least half of the attributes; only 3 of these species were previously classified as alien in the literature. Cryptogenic status was assigned to 5 species, including 1 previously considered to be alien in Europe. The most efficient predictors of alien origin status were 2 attributes: appearance in areas where not previously found, and rela- tively restricted distribution in the assessed area compared to the distributions of native species. We propose this method as a first step towards assessing the status of a species whose origin is unclear, before more labour-intensive tools such as genetic analysis are employed. The use of a formal protocol to screen the existing data makes the origin status assessment transparent, open to discussion and subject to revision as new information becomes available.
Highlights
Much effort has been put into developing scientifically sound risk-assessment protocols for different taxa and environments, formalizing the process of distinguishing between ‘good’ and ‘bad’ alien species; the latter having negative ecological or economic impacts (Brunel et al 2010, Essl et al 2011, Kumschick & Richardson 2013, Vanderhoeven et al 2015)
The level of certainty of this assessment differed among the species; and in addition to the terms used in the search criteria, some of them were described in the literature using the descriptive terms new, cosmopolitan or tropicopolitan
For species described by multiple terms, we extracted the one that was closest to suggesting its alien European status
Summary
Much effort has been put into developing scientifically sound risk-assessment protocols for different taxa and environments, formalizing the process of distinguishing between ‘good’ and ‘bad’ alien species; the latter having negative ecological or economic impacts (Brunel et al 2010, Essl et al 2011, Kumschick & Richardson 2013, Vanderhoeven et al 2015). Such a process must be rigorous and transparent, since listing species as alien may be legally binding and may have significant economic consequences, including import bans and/or high environmental management costs (European Commission 2014). It is even harder to determine whether each of the few records known for a given species lies within its natural range or whether some of them result from human-mediated introductions (Pyšek et al 2004)
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