In this diagram, interbreeding populations are represented by coloured blocks. Variation along a cline may bend right around forming a ring.

In biology, ring species present an interesting problem for those who seek to divide the living world into discrete species. Image File history File links Ring_species_diagram. ... Image File history File links Ring_species_diagram. ... Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek Βìο meaning life and Λoγος meaning the study of) is the study of life. ... In biology, a species is one of the basic units of biodiversity. ...

Explanation of the diagramme

The coloured bar to the right shows a number of natural populations, each population represented by a different colour, varying along a cline (a gradual change in conditions which gives rise to slightly different characteristics predominating in the organisms that live along it). Interbreeding between two populations is shown by a grey zone. Such variation may occur in a straight line (for example, up a mountain slope) as is shown in A, or may bend right around (for example, around the shores of a lake), as is shown in B. In population genetics, a cline is a gradual change of a character or feature (phenotype) in a species over a geographical area, often as a result of environmental heterogeneity. ...

In the case where the cline bends around, populations next to each other on the cline can interbreed, but at the point that the beginning meets the end again, the genetic differences that have accumulated along the cline are great enough to prevent interbreeding (represented by the gap between pink and green on the diagram). The interbreeding populations in this circular breeding group are then collectively referred to as a ring species. For a non-technical introduction to the topic, please see Introduction to genetics. ...

Problem of definition

The problem, then, is whether to quantify the whole ring as a single species (despite the fact that not all individuals can interbreed) or to classify each population as a distinct species (despite the fact that it can interbreed with its near neighbours). Ring species illustrate that the species concept is not as clear-cut as it is often understood to be.

Larus gulls

The Larus gulls interbreed in a ring around the arctic

A Herring Gull (front) and a Lesser Black-backed Gull (behind) in Poland: two species with clear differences.

A classic example of ring species is the Larus gulls circumpolar species "ring". The range of these gulls forms a ring around the North Pole. The Herring Gull, which lives primarily in Great Britain, can hybridize with the American Herring Gull (living in North America), which can also interbreed with the Vega or East Siberian Herring Gull, the western subspecies of which, Birula's Gull, can hybridize with Heuglin's gull, which in turn can interbreed with the Siberian Lesser Black-backed Gull (all four of these live across the north of Siberia). The last is the eastern representative of the Lesser Black-backed Gulls back in north-western Europe, including Great Britain. However, the Lesser Black-backed Gulls and Herring Gull are sufficiently different that they cannot interbreed; thus the group of gulls forms a continuum except in Europe where the two lineages meet. A recent genetic study has shown that this example is far more complicated than presented here (Liebers et al, 2004). Image File history File links Download high resolution version (505x611, 24 KB)Diagram showing the ring species formed by herring gulls in the arctic, created by Viki Male 13/09/04 File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old... Image File history File links Download high resolution version (505x611, 24 KB)Diagram showing the ring species formed by herring gulls in the arctic, created by Viki Male 13/09/04 File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old... Image File history File linksMetadata PT05_ubt. ... Image File history File linksMetadata PT05_ubt. ... North Pole Scenery When not otherwise qualified, the term North Pole usually refers to the Geographic North Pole – the northernmost point on the surface of the Earth, where the Earths axis of rotation intersects the Earths surface. ... Binomial name Larus argentatus Pontoppidan, 1763 The Herring Gull, Larus argentatus, is a large gull which breeds across North America, Europe and Asia. ... // In biology, hybrid has two meanings. ... World map showing North America A satellite composite image of North America. ... Binomial name Larus argentatus Pontopiddan, 1763 The Herring Gull, Larus argentatus, is a large gull which breeds across North America Europe and Asia. ... Binomial name Larus heuglini Bree, 1876 Heuglins Gull, Larus heuglini, is a seabird in the genus Larus. ... Siberian Federal District (darker red) and the broadest definition of Siberia (red) Udachnaya pipe Siberia (Russian: , Sibir; Tatar: ) is a vast region of Russia constituting almost all of Northern Asia. ... Binomial name Larus fuscus Linnaeus, 1758 The Lesser Black-backed Gull, Larus fuscus is a large gull which breeds on the Atlantic coasts of Europe. ... World map showing Europe A satellite composite image of Europe Europe is one of the seven traditional continents of the Earth. ...

Other examples

Other examples include:

• The Ensatina salamanders, which form a ring round the Central Valley in California
• The Greenish Warbler (Phylloscopus trochiloides), around the Himalayas (Alström 2006)

Ensatina eschscholtzii (commonly known by its genus name, Ensatina) is a species of salamander with a range stretching from British Columbia, through Washington, Oregon, across California (where all seven subspecies variations are located), all the way down to Baja in Mexico. ... Suborders Cryptobranchoidea Salamandroidea Sirenoidea Salamander is the common name applied to approximately 500 amphibians with slender bodies, short legs, and long tails. ... The California Central Valley The California Central Valley dominates the central portion of the state of California. ... Official language(s) English Capital Sacramento Largest city Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... Binomial name Phylloscopus trochiloides (Sundevall, 1837) Subspecies see text The Greenish Warbler, Phylloscopus trochiloides, is a widespread leaf warbler throughout its breeding range in northeast Europe and northern Asia. ... Perspective view of the Himalayas and Mount Everest as seen from space looking south-south-east from over the Tibetan Plateau. ...

References

• 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. DOI:10.1098/rspb.2004.2679 PDF fulltext Electronic Appendix

Cover of Proceedings of the Royal Society is a scientific journal published by the Royal Society of London. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

• Greenish Warbler
• Ensatina Salamander