Extinction risk in vascular plants and vertebrates is negatively correlated with family size

Understanding the pattern of species extinction risk is key to biodiversity conservation. Previous studies showed extinction risk correlates strongly with taxon species richness. However, there is no consistent conclusion to this hypothesis, and patterns differ among different taxonomic groups. Here, we collated lists of vascular plant and terrestrial vertebrate species information on their threatened status in Yunnan Province and performed the first systematical analysis to test the relationship between the proportion of threatened or extinct species and species richness at the family-level of the two above taxa in Yunnan Province, China. We found that extinction risk was not randomly distributed among families and the estimated extinction risk was higher among closer phylogenetic families than expected by chance. Moreover, there were significant negative correlations between extinction risk and family size in vascular plants and terrestrial vertebrates. Our results suggest that family size is a good predictor of extinction risk and extinction risk is related to evolutionary history at family-level among vascular plants and terrestrial vertebrates in Yunnan.