Extinction potential from invasive alien species

Abstract

Biological invasions pose significant threats to biodiversity, while impacting ecosystem services, human health, and cultural heritage. Despite these far-ranging effects, their impacts are generally underappreciated by both the public and policymakers, resulting in insufficient management and inadequate conservation outcomes. Recognizing the gap in effective quantitative measurement tools, we introduce the Extinction Potential Metric (EPM) and its derivative, EPM for Unique species (EPM-U; adjusted for phylogenetic uniqueness) to quantify the ecological damage caused by invasive alien species (IAS). These metrics estimate the number of current and projected extinct species within a 50-year horizon under a business-as-usual scenario due to specific IAS. We applied EPM and EPM-U to assess threats to native terrestrial vertebrates from IAS, examining impacts on 2178 amphibians, 920 birds, 865 reptiles, and 473 mammals. The analysis identified that damage mostly stems from a limited number of IAS, notably two pathogenic fungi affecting amphibians (up to 380 equivalent extinct species) and primarily cats (139 equivalent extinct species) and rats (50 equivalent extinct species) impacting other groups, through mechanisms such as predation, disease, and reduced reproductive success in birds. The proposed metrics not only provide a standardised measure of ecological impacts but are sufficiently versatile to be tailored for specific spatial and temporal scales or taxonomic groups. Furthermore, EPM could serve as a model for developing unified indicators to monitor global biodiversity targets, such as those defined in the Kunming-Montreal Global Biodiversity Framework (GBF), by assessing the ecological effects of various individual and combined anthropogenic stresses. Also, EPM and EPM-U could support the enforcement of Target 6 of the GBF, by establishing lists of IAS requiring urgent prevention and control. Thus, EPM and EPM-U offer critical tools for improving the management of biological invasions and enhancing global conservation strategies.