Evaluating the empirical basis for threat attribution in the IUCN Red List

Understanding the impacts of different threats on species is key to successful conservation interventions and policies. The International Union for Conservation of Nature (IUCN) assesses threats to species, and the organization's Red List of Threatened Species is a key conservation tool. We quantified the degree to which threats in IUCN assessments for 3 vertebrate groups (birds, amphibians, and ray-finned fishes) were based on species-specific quantitative empirical data. To do this, for 2142 IUCN species assessments, all listed references were reviewed to determine whether they contained species-specific quantitative data linking a listed threat and the assessed species. Only 7.5% of listed threats across all taxa and categories were based on species-specific quantitative data. For species with at least one threat listed, only 12.5% of species had species-specific quantitative data underlying at least one threat. There were more data on threats for some taxa, and there was a trend toward having more information on threats that are generally considered less predictable, such as "invasive/problematic" species and climate change. Understanding how a lack of species-specific data may affect understanding of extinction processes is crucial for continued improvement of conservation outcomes.