An ecoregion (ecological region), sometimes calle a bioregion, is an ecologically and geographically defined area smaller than a "realm" or "ecozone". Ecoregions cover relatively large area of land or water, and contain characteristic, geographically distinct assemblage of natural communities and species. The biodiversity of flora, fauna and ecosystems that characterise an ecoregion tend to be distinct from that of other ecoregions.