Coba jelasin Lihat pula dari Spesies cincin dong

Alström, Per (2006): Species concepts and their application: insights from the genera Seicercus and Phylloscopus. Acta Zoologica Sinica 52(Supplement): 429-434. PDF fulltext

Liebers, Dorit; de Knijff, Peter & Helbig, Andreas J. (2004): The herring gull complex is not a ring species. Proc. Roy. Soc. B 271(1542): 893-901.  PDF fulltext Electronic Appendix

Irwin, D.E., Irwin, J.H., and Price, T.D. (2001): "Ring species as bridges between microevolution and speciation." Genetica. 112-113: 223-243. PubMed

Futuyma, D. (1998) Evolutionary Biology. Third edition. Sunderland, MA, Sinauer Associates.

Moritz, C., C. J. Schneider, et al. (1992) "Evolutionary relationships within the Ensatina eschscholtzii complex confirm the ring species interpretation." Systematic Biology 41: 273-291.

Nova Scotia Museum of Natural History: Birds of Nova Scotia

Adriaens, P. "Hybrid Gulls Breeding in Belgium"