We wrote this review as an invited contribution to the Encyclopedia of Evolutionary Biology. The full citation:
Irwin, D.E., and D.B. Wake. 2016. Ring species. Vol. 3, Pages 467-475 in Encyclopedia of Evolutionary Biology, edited by R. M. Kliman. Oxford: Academic Press.
To read, you have three options (I recommend number 3):
- Purchase the article from Science Direct for $31.50: http://www.sciencedirect.com/science/article/pii/B9780128000496000779
- Purchase the Encyclopedia from Elsevier for only $1,260.00 😉 http://store.elsevier.com/product.jsp?isbn=9780128000496
- Email me a request to send you the PDF, and I will gladly do so.
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.