- The California floristic province is home to several threatened or endangered species and has been the focus of numerous conservation efforts. These conservation efforts have largely ignored the diverse and distinctive arthropod fauna found in this region.
- We investigate the species boundaries of the four tarantula (Araneae: Theraphosidae) species endemic to California's Southern Coast Ranges through molecular phylogenetic analysis using a 680 bp region of the mitochondrial gene cytochrome oxidase subunit 1 from 51 individuals.
- Our analysis resulted in a well-supported phylogeny showing three distinct clades. As a result, we recognise only one species in the Southern Coast Ranges (Aphonopelma brunnius, with A. chamberlini and A. smithi treated as junior synonyms; if the holotype of A. rileyi is located it will likely be a synonym as well). Two additional species were found in the foothills of the Sierra Nevada.
- Although the tarantulas in California's Southern Coast Ranges are not as endemic as was previously thought, their position as top arthropod predators make them ideal sentinel species, suggesting they should be targeted by conservationists. Furthermore, our analyses illustrate the importance in using molecular tools to investigate biodiversity.