A biogeographic unit is an area delineated on biogeographic parameters. A biogeographic region often corresponds to what may be called a "major habitat type", comprising a large ecoregion or set of ecoregions (or groupings of habitats) that (a) experience comparable climatic regimes, (b) have similar vegetation structure, (c) display similar spatial patterns of biodiversity and (d) contain flora and fauna with similar guild structures and life histories.