Ecophenotypic variation ("ecophenotype") refers to phenotypical variation as a function of life station. In wide-ranging species, the contributions of heredity and environment are not always certain, but their interplay can sometimes be determined by experiment.
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Plants display the most obvious examples of ecophenotypic variation. One example are trees growing in the woods developing long straight trunks, with branching crowns high in the canopy, while the same species growing alone in the open develops a spreading form, branching much lower to the ground. Genotypes often have much flexibility in the modification and expression of phenotypes; in many organisms these phenotypes are very different under varying environmental conditions. The plant Hieracium umbellatum is found growing in two different habitats in Sweden. One habitat is rocky sea-side cliffs, where the plants are bushy with broad leaves and expanded inflorescences; the other is among sand dunes where the plants grow prostrate with narrow leaves and compact inflorescences. These habitats alternate along the coast of Sweden and the habitat that the seeds of H. umbellatum land in determines the phenotype that grows.[1] Invasive plants such as the honeysuckle can thrive by altering their morphology in response to changes in the environment,[2] which gives them a competitive advantage. The more immediate responses shown by vascular plants to their environment, for instance a vine's ability to conform to the wall or tree upon which it grows, are not usually considered ecophenotypic, even though the mechanisms may be related.
Since animals are far less plastic than plants, ecophenotypic variation is noteworthy. When encountered, it can cause confusion in identification if it is not anticipated. The most obvious examples are again common observations, as the dwarfing of aquarium fish living in a restricted environment. More interesting are examples where causation is less clear. Among mollusks, examples include the muricid snail species Nucella lamellosa, which in rough, shallow waters is generally less spiny than in deeper, quiet waters.[3] In unionid freshwater bivalves, there are lake, small river, and large river forms of several species.[4] In vertebrates, experiments on mice show reduced length of ears and tails in response to being reared in a lower temperature, a phenomenon known as Allen's rule.
In humans, environmental differences due to lifestyle choices are a consideration, for instance the differences between someone who spends much time on the sofa before the television, beer in hand, and an individual who spends his time in the gym or the soccer field can be pronounced. Franz Boas found that cephalic index was to some degree dependent on where a child was born, independent of the child's genetic or cultural heritage.