Linking the seven forms of rarity to extinction threats and risk factors: an assessment of North American fireflies

Abstract

Two key problems in trying to link rarity to extinction risk have been conflating threats with risk factors, and over-reliance on a rarity construct that fails to capture many relevant risk factors. In this study, we disentangle threats from risk factors and show how their interaction can be used to predict extinction risk. We also investigate the sensitivity of rarity classifications to various thresholds, including biologically meaningful ones. We use the 168 species of North American firefly beetles (Coleoptera: Lampyridae) as our focal family to examine rarity classifications, and to illustrate the importance of clearly distinguishing between risk factors and threats in evaluating extinction risk. Our results show that, beyond rarity, fireflies exhibit numerous risk factors, including diet specialization, poor dispersal ability, light-based mating signals, symbiotic associations, and behaviors that can result in Allee effects, that make them susceptible to various global threats. This suggests that, for this group and perhaps other taxa, rarity type cannot be used as a surrogate for extinction risk. By identifying threats and risk factors and clearly distinguishing between them, this study should facilitate future assessments of extinction risk for this family, and the approach could be used for other taxa.