The Larus gulls interbreed in a ring around the arctic. 1: L. fuscus, 2: Siberian population of Larus fuscus, 3: L. heuglini, 4:L. vegae birulai, 5: L. vegae, 6: L. smithsonianus, 7: L. argentatus.
An area where species have spread in a circular area maintaining the ability to interbreed with those population nearest to them. Where the circle meets at the furthest connection however, the species do not breed.
The Ensatina salamanders as an example of a ring species.
Ring Species Video[]
Here is a good short clip showing some great images as well as good explanation of ring species.
http://www.youtube.com/watch?v=PjcFSy1KCTI
Ring Species picture
Found another example of a ring species, Larus gulls. What is unique about this example is their range, a ring around the North Pole.
http://en.wikipedia.org/wiki/Ring_species#Larus_gulls
References[]
University of California Museum of Paleontology, Berkeley. (2006). Biological speciessConcept. Retrieved from http://evolution.berkeley.edu/evosite/evo101/VA1BioSpeciesConcept.shtml