Predicting extinction risk by range loss: Evidence from the fossil record

Climate change is one of the main drivers for the wave of species extinctions predicted for this century. IPCC extinction risk assessments are based in part on predicted climate-driven reductions in the geographic ranges of focal species (range loss). This builds on the well-established IUCN (2022) Red List criterion, in which a species is considered critically endangered (>50% extinction risk) if it loses ≥80% of its geographic range. However, while there is clear evidence that extinction risk is related to the absolute geographic range of a species, the empirical relationship between range loss and extinction risk is not well understood. Using fossil evidence of true extinctions over the past 23 million years, with 2600 range change observations of 1215 marine genera, this study implements a Bayesian hierarchical weighted generalized additive model to investigate how extinction risk changes with the percentage decrease in geographic range of a genus. Results clearly indicate how extinction risk increases non-linearly with range loss. Taxon dependent differences in the relationship between extinction risk and range loss indicate great potential for adapting its application in extinction risk predictions and the IUCN criteria.