In evolutionary ecology, an ecotype, sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within a species, which is genotypically adapted to specific environmental conditions. Typically, though ecotypes exhibit phenotypic differences stemming from environmental heterogeneity, they are capable of interbreeding with other geographically adjacent ecotypes without loss of fertility or vigor.
Definition
An ecotype is a variant in which the phenotypic differences are too few or too subtle to warrant being classified as a subspecies. These different variants can occur in the same geographic region where distinct habitats such as meadow, forest, swamp, and sand dunes provide ecological niches. Where similar ecological conditions occur in widely separated places, it is possible for a similar ecotype to occur in the separated locations. An ecotype is different than a subspecies, which may exist across a number of different habitats. In animals, ecotypes owe their differing characteristics to the effects of a very local environment. Therefore, ecotypes have no taxonomic rank.
Terminology
Ecotypes are closely related to morphs. In the context of evolutionary biology, genetic polymorphism is the occurrence in the 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 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. Polymorphism is actively and steadily maintained in populations of species by natural selection 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 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: Thus ecotypes and morphs can be thought of as precursory steps of potential speciation.
Range and distribution
Experiments indicate that sometimes ecotypes manifest only when separated by great spatial distances. This is due to hybridization whereby different but adjacent varieties of the same species interbreed, thus overcoming local selection. However other studies reveal that the opposite may happen, i.e., ecotypes revealing at very small scales, within populations, and despite hybridization. In ecotypes, it is common for continuous, gradual geographic variation to impose analogous phenotypic and genetic variation. This situation is called cline. A well-known example of a 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.
Examples
Tundrareindeer and woodland reindeer are two ecotypes of reindeer. The first migrate annually between the two environments in large numbers whereas the other remain in the forest for the summer. In North America, the species Rangifer tarandus, spacing and migration —the migratory George River Caribou Herd, for example in the Ungava region of Quebec.
Arabis fecunda, a herb endemic to some calcareous soils of Montana, United States, 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.
The Scots pine 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.
