A synthesis on alien mammals threatened in their native range

Many alien species are safe in their native ranges; however, some are threatened, posing a challenging conundrum for conservation and invasion science. We focused on alien threatened mammals, examining their distribution, pathways, threats, and conservation strategies. We also reassessed their IUCN Red List category to evaluate the effect of including alien populations in extinction risk assessments. Of 242 alien mammals, we identified 41 aliens that are threatened, classified as critically endangered (19%), endangered (27%), or vulnerable (54%). They were primarily introduced for hunting and exchanged within Asia, with introduced ranges concentrated in eastern Australia. They were subject to multiple threats, most notably biological resource use. Including alien populations in the categorization assessments reduces extinction risk of 22% of the species. We highlighted the conservation value of alien populations for threatened mammals. However, conservation managers and extinction risk assessors shall carefully consider their use, to avoid negative impacts on native biodiversity.