Conservation priorities for functionally unique and specialized terrestrial vertebrates threatened by biological invasions

Invasive alien species (IAS) continue to pose a significant threat to biodiversity, leading to native population declines, which can ultimately disrupt ecosystem processes. Even though there is growing evidence of the impacts of IAS on functional diversity, most of the existing conservation prioritization approaches still focus on taxonomic diversity, neglecting the ecological role of species.We have refined the FUSE-IAS score to fill this gap by combining functional irreplaceability (measured by uniqueness and specialization) of species with their extinction risk due to IAS. Applying this score to 3,642 terrestrial vertebrates exposed to IAS, we found that 38% of those species showed high functional irreplaceability, making them priority species for conservation actions targeting IAS. These priority species were concentrated in specific areas in the case of amphibians (Central America and Madagascar) and lizards (Caribbean islands, North Australia, New Zealand, and New Caledonia), whereas birds (mostly coastal and on Pacific islands, North India, and New Zealand) and mammals (Southwest Europe, Central, East and South Africa, Southeast Asia, and East Australia) were more widespread. We further identified 79 species that were also highly irreplaceable but not yet threatened by IAS, suggesting that preventive conservation measures can ensure the protection of these species and their future biodiversity value. Finally, focusing on the Top 50 priority birds, we found that 64% of species still require the implementation of conservation actions to mitigate the IAS threat. This score helps prioritize species that represent large amounts of functional diversity and thus contribute to the conservation of global functional diversity. Incorporating functional diversity into the conservation prioritization of species and associated areas is key to accurately reducing and mitigating the impacts of IAS on native biodiversity, a target defined in the Kunming-Montreal Global Biodiversity Framework.