In evolutionary ecology, an ecotype,[note 1] sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within species (or among closely related), which is adapted to specific environmental conditions. Typically, ecotypes exhibit phenotypic differences (such as in morphology or physiology) stemming from environmental heterogeneity and are capable of interbreeding with other geographically adjacent ecotypes without loss of fertility or vigor. 
Range and distribution
Experiments indicate that sometimes ecotypes manifest only when separated by great spatial distances (of the order of 1000 km). This is due to hybridization whereby different but adjacent varieties of the same species (or generally of the same taxonomic rank) interbreed, thus overcoming local selection. However other studies reveal that the opposite may happen, i.e. ecotypes revealing at very small scales (of the order of 10 m), within populations, and despite hybridization.
In ecotypes, it is common for continuous, gradual geographic variation to impose analogous phenotypic and/or genetic variation. This situation is called cline. A well-known example of cline is the skin color gradation in indigenous human populations worldwide, which is related to latitude and amounts of sunlight. But often the distribution of ecotypes is bimodal or multimodal. This means that ecotypes may display two or more distinct and discontinuous phenotypes even within the same population. Such phenomenon may lead to speciation and can occur if conditions in a local environment change dramatically through space or time.
- Earthworms fall into four different ecotypes. Compost earthworm prefer warm and moist environments with a ready supply of fresh compost material. Epigeic earthworms live on the surface of the soil in leaf litter and tend not to make burrows but live in and feed on the leaf litter. Endogeic earthworms live in and feed on the soil, making horizontal burrows through the soil to move around and to feed and they will reuse these burrows to a certain extent. Anecic earthworms make permanent vertical burrows in soil, feeding on leaves on the soil surface that they drag into their burrows.
- Tundra reindeer and forest (or woodland) reindeer are two ecotypes of reindeer. The first migrate (travelling 5,000 km) annually between the two environments in large numbers whereas the other (who are much fewer) remain in the forest for the summer. Currently, and since 1961 classification, tundra reindeer comprise five subspecies and woodland reindeer two.
- Arabis fecunda, a herb endemic to some calcareous soils of Montana, USA, can be divided into two ecotypes. The one "low elevation" group lives near the ground in an arid, warm environment and has thus developed a significantly greater tolerance against drought than the "high elevation" group. The two ecotypes are separated by a horizontal distance of about 100 km.
- It is commonly accepted that the Tucuxi dolphin has two ecotypes - the riverine ecotype found in some South American rivers and the pelagic ecotype found in the South Atlantic Ocean.  Similarly, it is accepted that the Common Bottlenose Dolphin has two ecotypes in the Western North Atlantic.
- The Warbler finch and the Cocos Island Finch are viewed as separate ecotypes.[verification needed][clarification needed]
- The Scots Pine (Pinus sylvestris) has 20 different ecotypes in an area from Scotland to Siberia, all capable of interbreeding.
- A very subtle case of ecotype is the following: It has been observed that two populations of the same Helix snail species separated by only a few hundred kilometers prefer not to cross-mate, i.e. they reject one another as mates. This event probably occurs during the process of courtship, which may last for hours.
Ecotypes have no main taxonomic rank in modern biological classification. However some scientists consider them "taxonomically equivalent to subspecies". This is true in the sense that ecotypes can be sometimes classified as subspecies and the opposite.
Ecotypes are closely related to morphs. In the context of evolutionary biology, genetic polymorphism is the occurrence in equilibrium of two or more distinctly different phenotypes within a population of a species, in other words, the occurrence of more than one form or morph. The frequency of these discontinuous forms (even that of the rarest) is too high to be explained by mutation. In order to be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population (whose all members can potentially interbreed). Polymorphism is actively and steadily maintained in populations of species by natural selection (most famously sexual dimorphism in humans) in contrast to transient polymorphisms where conditions in a habitat change in such a way that a "form" is being replaced completely by another.
In fact, Begon, Townsend and Harper assert that
|“||There is not always clear distinction between local ecotypes and genetic polymorphisms.||”|
The notions "form" and "ecotype" may appear to correspond to a static phenomenon, however this is not always the case. Evolution occurs continuously both in time and space, so that two ecotypes or forms may qualify as distinct species in only a few generations. Begon, Townsend and Harper use an illuminating analogy on this:
|“||… the origin of a species, whether allopatric or sympatric, is a process, not an event. For the formation of a new species, like the boiling of an egg, there is some freedom to argue about when it is completed.||”|
Thus ecotypes and morphs can be thought of as precursory steps of potential speciation.
- Greek: οίκος = home and τύπος = type, coined by Göte Turesson in 1922
- Biological classification
- Cline (biology)
- Polymorphism (biology)
- Ring species
- Species problem
- Ecology: From individuals to ecosystems by Begon, Townsend, Harper, Blackwell Publishing 4th ed. (2006), p.5,6,7,8
- Turesson, Turesson G. (1992). The genotypical response of the plant species to the habitat. Hereditas 3. pp. 211–350.
- Molles, Manuel C., Jr. (2005). Ecology: Concepts and Applications (3rd edition ed.). New York: The McGraw-Hill Companies, Inc. p. 201. ISBN 0-07-243969-6.
- Environmental Encyclopedia by Bortman, Brimblecombe, Mary Ann Cunningham, William P. Cunningham, Freedman - 3rd ed., p.435, "Ecotype"
- race. (2009). Encyclopædia Britannica. Ultimate Reference Suite. Chicago: Encyclopædia Britannica.
- Earthworm ecotypes, information from the Earthworm Society of Britain about the different ecotypes of British earthworms.
- "reindeer (Rangifer tarandus)" Encyclopædia Britannica. Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2009
- "Riverine and marine ecotypes of Sotalia dolphins are different species".
- Common Bottlenose Dolphin
- Encyclopedia of life sciences, 2007, John Wiley & Sons, "Darwin’s Finches"
- Introduction to Ecology (1983), J.C. Emberlin, chapter 8