Published Web Locationhttps://doi.org/10.1016/B978-0-12-800049-6.00077-9
A ring species is a ring of populations in which there is only a single species boundary. Two contacting forms behave as distinct species yet are connected by a long chain of populations through which there is gradual or stepwise change. Such situations provide an illustration of how the process of speciation, by which one species splits into two, can occur. Ring species are rare, but two cases provide good examples of how ring species can teach us about speciation: greenish warblers and Ensatina salamanders.