Integrating functional and phylogenetic perspectives reveals new priorities for bird and mammal conservation

Finite resources dictate that conservation biologists must prioritise some species over others. Conservation metrics, such as EDGE (Evolutionarily Distinct and Globally Endangered; EDGE1) and FUSE (Functionally Unique, Specialised and Endangered), make prioritisation based on species evolutionary or functional distinctiveness, respectively, and degree of threat. EDGE is in part based on the rationale that the evolutionary distinctiveness it captures serves to maximise biodiversity in form and function. However, doubts exist as to whether or not evolutionary distinctiveness truly serves as a proxy for functional distinctiveness, and, therefore, if the prominent use of EDGE lists by conservation practitioners adequately protects functional distinctiveness. To address this, we conducted a direct global comparison of EDGE against FUSE. Unlike EDGE, FUSE directly measures and prioritises functional distinctiveness. Here, we compare EDGE and FUSE scores for two well-studied groups: mammals (n = 5319 species) and birds (n = 7932 species). These groups are central to global conservation and, until now, have not been assessed under FUSE. We find that species rankings under EDGE and FUSE differ significantly, highlighting that these two metrics capture distinct, complementary aspects of biodiversity. This suggests that conservation strategies based solely on EDGE may overlook species with critical functional roles. Rather than assuming alignment between evolutionary and functional distinctiveness, we propose integrating both within a single measure, leveraging the strengths and benefits of each. To this end, we present a new conservation metric - EFUSE (Evolutionarily and Functionally Unique, Specialised, and Endangered) - which incorporates both evolutionary and functional distinctiveness into a single measure. EFUSE ensures that important components of biodiversity, which relate to ecosystem functioning, natures future contributions to people, and the intrinsic value of species, are adequately maximised in conservation decision-making.