The system of biogeographic realms (or regions) integrates information on the (1) distribution of species and (2) distribution of ecosystem units. Each biogeographic region is subdivided into a subset of biogeographical provinces. Each province is characterized by a dominant ecosystem (also called a major biome or biome-complex). Provincial boundaries can subdivide the area of a biome where significant faunal or floral differences occur. Also large areas of relatively uniform faunas and/or floras are subdivided on the basis of changes in the structure of vegetation.