Ecological Amplitude

(also ecological valence), the degree of adaptation of a living organism to changes in its environment. A species trait, ecological amplitude is expressed quantitatively as the range of environmental changes within which a given species is able to carry on its normal vital activities.

Ecological amplitude can be examined as either the reaction of a species to individual environmental factors or to an aggregate of factors. In the first case, species that are able to tolerate a wide range of changes in the strength of an acting factor are designated by a term consisting of the name of the given factor and the prefix “eury,” such as eurythermal (referring to the effects of temperature), euryhaline (salinity), and eurybathic (depth). Species that are adapted to only a narrow range of changes in a given factor are designated by the same term with the prefix “steno,” for example, stenothermal and stenohaline. Species that exhibit broad ecological amplitude with respect to an aggregate of factors are called eurybionts, while species with low adaptability are called stenobionts. Inasmuch as euroky makes it possible for a species to occupy a variety of habitats while stenoky sharply curtails the range of suitable habitats, these two groups are often referred to as eurytopic and stenotopic, respectively.