Conservation paradoxes and challenges in invasive alien species with economic costs

Several studies have revealed species that constitute conservation paradoxes because they are invasive in some areas and threatened in others. However, those studies only considered ecological impacts of invasions and species' threat category as a criterion that makes them conservation priorities. Here, our aim was to highlight further species that cause economic costs because of their invasiveness in some areas while being in need of priority protection in their native ranges. We used the InvaCost database to calculate an economic cost for each invasive alien species (IAS) in this database and explored the threat category, as well as the phylogenetic and functional distinctiveness of these IAS. We also focused on the costliest IAS to reveal their threat category and distinctiveness. Among the 355 species of mammals, birds, and plants constituting IAS with sufficient data on economic costs, we found that 10 species are also conservation priorities because they are threatened in their native range, therefore constituting conservation paradoxes. We further found that 27 IAS with economic costs are also conservation priorities because they are among the most phylogenetically or functionally distinctive, thus constituting conservation challenges. One IAS with economic costs is a conservation priority both because it is threatened in its native range and phylogenetically distinctive: the koala. Finally, we found three conservation paradoxes or challenges among the costliest IAS. Our work stresses to an unprecedented level that some species simultaneously need to be controlled in their invasive range and protected in their native range. • 10 invasive alien species (IAS) with economic costs are also threatened • 27 IAS with economic costs are among the most distinctive species of their group • One IAS with economic costs, the koala, is both threatened and distinctive • Those 36 IAS with economic costs are in need of priority protection in their native ranges • Coordinated management at population-level would maximise conservation outcomes