Prioritization of introduction pathways is seen as an important component of
the management of biological invasions. We address whether established alien
plants, mammals, freshwater fish and terrestrial invertebrates with known
ecological impacts are associated with particular introduction pathways
(release, escape, contaminant, stowaway, corridor and unaided). We used the
information from the European alien species database DAISIE (www.europe-
aliens.org) supplemented by the EASIN catalogue (European Alien Species
Information Network), and expert knowledge. Plants introduced by the pathways
release, corridor and unaided were disproportionately more likely to have
ecological impacts than those introduced as contaminants. In contrast, impacts
were not associated with particular introduction pathways for invertebrates,
mammals or fish. Thus, while for plants management strategies should be
targeted towards the appropriate pathways, for animals, management should
focus on reducing the total number of taxa introduced, targeting those
pathways responsible for high numbers of introductions. However, regardless of
taxonomic group, having multiple introduction pathways increases the
likelihood of the species having an ecological impact. This may simply reflect
that species introduced by multiple pathways have high propagule pressure and
so have a high probability of establishment. Clearly, patterns of invasion are
determined by many interacting factors and management strategies should
reflect this complexity