The Global Ecoregions are the results of regional analyses of biodiversity across the continents and oceans of the world, completed in collaboration with hundreds of regional experts worldwide and by conducting extensive literature reviews.
These ecoregions were chosen from outstanding examples of each terrestrial, freshwater, and marine major habitat type. The 26 major habitat types describe different areas of the world that share similar environmental conditions, habitat structure, and patterns of biological complexity, and that contain similar communities and species adaptations.
In order to represent the unique fauna and flora of the world's continents and ocean basins, each major habitat type was further subdivided by 7 biogeographic realms (Afrotropical, Australasia, Indo-Malayan, Nearctic, Neotropical, Oceania, Palearctic).
Finally, ecoregions that represented the most distinctive examples of biodiversity for a given major habitat type were identified within each biogeographic realm. They were chosen based on the following parameters:
- species richness
- higher taxonomic uniqueness (e.g., unique genera or families, relict species or communities, primitive lineages)
- extraordinary ecological or evolutionary phenomena (e.g., extraordinary adaptive radiations, intact large vertebrate assemblages, presence of migrations of large vertebrates)
- global rarity of the major habitat type
Only the biodiversity value of ecoregions sharing the same major habitat type were compared because the relative magnitude of parameters such as richness and endemism varies widelay among them.