Ring species

	Email		Print
	Bookmark		Link

Ring species

In biology

Biology

Biology is a branch of the natural sciences concerned with the study of living organisms and their interaction with each other and their environment ....
, a ring species is a connected series of neighboring populations that can interbreed with relatively closely related populations, but for which there exist at least two "end" populations in the series that are too distantly related to interbreed.

Discussion

Ask a question about 'Ring species'

Start a new discussion about 'Ring species'

Answer questions from other users

Full Discussion Forum

Explanation of the diagram

The coloured bar to the right shows a number of natural populations, each population represented by a different colour, varying along a cline

Cline (population genetics)

In biology, a cline is a gradual change of phenotype in a species over a geographical area, often as a result of environmental heterogeneity. This meaning of "cline" was introduced by Sir Julian Huxley....
(a gradual change in conditions which gives rise to slightly different characteristics predominating in the organisms that live along it). 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 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, as is shown in C, the genetic differences

Genetic diversity

Genetic diversity is a level of biodiversity that refers to the total number of Genetics characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
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.

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 thought to be.

Larus gulls

A classic example of ring species is the Larus
Larus

Larus is a large genus of gulls with worldwide distribution . Many of its species are abundant and well-known birds in their ranges. Until recently, most gulls were placed in this genus, but this arrangement is now known to be polyphyletic, leading to the resurrection of the genera Ichthyaetus, Chroicocephalus, Leucophaeus, an...
gulls circumpolar species "ring". The range of these gulls forms a ring around the North Pole

North Pole

The North Pole, also known as the Geographic North Pole or Terrestrial North Pole is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets the Earth's surface....
. The Herring Gull

Herring Gull

The Herring Gull, Larus argentatus, is a large gull , and is the most abundant and best known of all gulls along the shores of Asia, western Europe, and North America....
, which lives primarily in Great Britain

Great Britain

Great Britain is an island lying to the northwest of Continental Europe. It is the List of islands by area, and the largest in Europe. With a population of 58.9 million people it is List of islands by population....
and Ireland

Ireland

Ireland is the List of islands by area in Europe, and the twentieth-largest island in the world. It lies to the north-west of continental Europe and is surrounded by hundreds of islands and islet....
, can hybridize with the American Herring Gull

American Herring Gull

The American Herring Gull, Larus smithsonianus, is a large gull which breeds in North America. It is often treated as a subspecies of the European Herring Gull but is now regarded as a separate species by some authorities....
(living in North America

North America

North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere....
), which can also hybridize with the Vega or East Siberian Herring Gull, the western subspecies of which, Birula's Gull, can hybridize with Heuglin's gull

Heuglin's Gull

Heuglin's Gull or Siberian Gull, Larus heuglini, is a seabird in the genus Larus. It is closely related to the Lesser Black-backed Gull, Larus fuscus, and is often classified as a subspecies of it....
, which in turn can hybridize with the Siberian Lesser Black-backed Gull (all four of these live across the north of Siberia

Siberia

Siberia , is the name given to the vast region constituting almost all of North Asia and for the most part currently serving as the massive central and eastern portion of the Russian Federation, having served in the same capacity previously for the Soviet Union from its beginning, and the Russian Empire beginning in the 16th century....
). The last is the eastern representative of the Lesser Black-backed Gull

Lesser Black-backed Gull

The Lesser Black-backed Gull is a large gull which breeds on the Atlantic Ocean coasts of Europe. It is bird migration, wintering from the British Isles south to West Africa....
s back in north-western Europe

Europe

Europe is, conventionally, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural , the Caspian Sea, and by the Caucasus Mountains to the southeast....
, including Great Britain. However, the Lesser Black-backed Gulls and Herring Gull are sufficiently different that they do not normally hybridize; 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). This example only speaks of classical Herring Gull - Lesser Black-Backed Gull complex and does not include several other taxonomically unclear examples which belong in the same superspecies

Superspecies

Superspecies is a group of at least two more or less distinctive species with approximately parapatric distributions. Not all cryptic species complexes are superspecies, and vice versa, but many are....
complex, such as Yellow-Legged Gull

Yellow-legged Gull

The Yellow-legged Gull is a large gull of Europe, the Middle East and North Africa. It is sometimes considered to be part of the same species as the Caspian Gull and the combined species is then called Larus cachinnans....
, Glaucous Gull

Glaucous Gull

The Glaucous Gull, Larus hyperboreus is a large gull which breeds in the Arctic regions of the northern hemisphere and the Atlantic Ocean coasts of Europe....
and Caspian Gull

Caspian Gull

Caspian Gull is a English names for organisms applied to the gull taxon Larus cachinnans, a member of the Herring Gull/Lesser Black-backed Gull complex....
.

Other examples

Other examples include:

The Ensatina
Ensatina

Ensatina eschscholtzii is a complex of plethodontid salamanders found in coniferous forests, oak woodland and chaparral from British Columbia, through Washington, Oregon, across California , all the way down to Baja California Peninsula in Mexico....
salamander
Salamander

Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by slender bodies, short noses, and long tails....
s, which form a ring round the Central Valley in California
California

California is a U.S. state on the West Coast of the United States of the United States, along the Pacific Ocean. It is bordered by Oregon to the north, Nevada to the east, Arizona to the southeast, and to the south the Mexico state of Baja California....
The Greenish Warbler
Greenish Warbler

The Greenish Warbler, Phylloscopus trochiloides, is a widespread leaf-warbler throughout its breeding range in northeast Europe and northern Asia....
(Phylloscopus trochiloides), around the Himalayas
Himalayas

The Himalaya Range or Himalayas for short , meaning "abode of snow" ), is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau....
(Alström 2006)

Ring species

Explanation of the diagram

Problem of definition

Larus gulls

Other examples

See also

External links