Identifying functionally distinctive and threatened species

Functional traits determine species' responses to environmental change and/or determine species' effects on ecosystem functions. When species with distinctive functional traits are threatened, there is a risk that ecosystem properties are also threatened. This is because functionally distinctive species may be those that have irreplaceable roles in an ecosystem and/or those that would be able to survive unusual environmental disturbances. To include functional distinctiveness as a criterion in conservation strategies, we need formal quantification of species' degree of distinctiveness while incorporating extinction risk. Based on previously developed quantitative methods, we develop a framework that links different metrics of functional distinctiveness and accounts for all species' extinction probabilities. Our framework is particularly relevant at the local scale, where species extinctions impact ecosystem functioning and where conservation policies are developed. As a case study, we thus applied our framework to the mammals of Indian dry forests known to be threatened with a drastic decrease in functional diversity and identified top-priority species as the threatened, most functionally distinctive species. We notably highlight that although some of the top-priority species we identified are charismatic and targeted by conservation actions, others are not. On the basis of this case study, we note that less charismatic, less known species that may be key for ecosystems could be revealed by applying our framework to a range of ecosystems and taxa.