An ecoregion (ecological region) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are relatively large areas of land or water where the probability of encountering different species and communities at any given point remains relatively constant, within an acceptable range of variation (largely undefined at this point). Ecoregions are also known as “ecozones” (“ecological zones”), although that term may also refer to biogeographic realms.
Ecosystems are controlled by external and internal factors. External factors such as climate, parent material which forms the soil and topography, control the overall structure of an ecosystem but are not themselves influenced by the ecosystem. Internal factors are controlled, for example, by decomposition, root competition, shading, disturbance, succession, and the types of species present.
A biome (/ˈbaɪ.oʊm/) is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate.
Biomes may span more than one continent. Biome is a broader term than habitat and can comprise a variety of habitats.
In ecology, habitat refers to the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species.
A species habitat can be seen as the physical manifestation of its ecological niche. Thus “habitat” is a species-specific term, fundamentally different from concepts such as environment or vegetation assemblages, for which the term “habitat-type” is more appropriate.