Biogeographic Realms [Ecozones]

Biogeographic realms or ecozones divide global biota into large zones representing distinct climates, evolutionary histories, and ecological communities. Classification systems categorize regional flora and fauna to aid biographic analyses in fields like paleontology, conservation biology, and ecology. Understanding these realms helps identify unique species assemblages and endemic organisms.

Realm Classifications

Influential systems categorizing terrestrial biomes into biogeographic realms include:

  • Paleontologist Joseph Andersson’s system identifying Holarctic, Neotropical, Ethiopian, Oriental, and Australian realms
  • Miklos Udvardy’s system outlining Nearctic, Palearctic, Afrotropics, Indomalaya, Australasia, Oceania, plus Antarctica
  • The WWF system defining up to 14 terrestrial and aquatic realms

These classification frameworks facilitate quantitative analyses of biodiversity patterns, rates of endemism, and species distribution histories across regions.

Major Terrestrial Realms

Key continental ecological zones include:

Nearctic Realm

Extending over North America, including temperate and arctic zones. Characterized by mixed and deciduous forests, grasslands, tundra and deserts. Hosts mammals like deer, wolves, bears; birds like bald eagles, wild turkey; and trees like oak, fir, spruce, cedars,etc.

Neotropical Realm

Encompassing Central and South America, including the Amazon and Andes mountains. Noted for high endemism – 30% of plants and 24% of terrestrial vertebrates exist only here. Diverse landscapes range from rainforests to deserts, hosting jaguars, sloths, armadillos, hummingbirds, anacondas, early lineages of butterflies and ants, etc.


This realm spans Sub-Saharan Africa where early hominid ancestors arose. It encompasses tropical rainforests, acacia savannas teeming with herds of zebra, wildebeest and antelopes, arid deserts, volcanic mountains, and sweeping grassland ecosystems. Over 1,100 mammal species inhabit Africa including gorillas, lions, rhinos, giraffes, chimpanzees and African wild dogs.

Indomalayan Realm

Covering South and Southeast Asian tropical zones, this realm nurtured distinctive Asian flora and fauna like vibrant birds, the prehistoric Meghalayan cloud forests, steamy mangrove forests, etc. It hosts tigers, Komodo dragons, orangutans, Assam macaques, Gharial crocodiles, Javan rhinos, Asiatic cheetahs, etc.

Australasia Realm

Australia, together with New Zealand and New Guinea, maintains evolutionary distinct marsupials and birds. It encompasses iconic species like koalas, kangaroos, wallabies, lyrebirds, kiwis, platypuses, emus and cassowaries across habitats ranging from tropical and temperate rainforests to desert scrublands.

Aquatic and Island Realms

Additional realms categorize marine species and oceanic islands, like the Palearctic for temperate Eurasia, Oceania spanning the tropical Pacific islands, and Antarctica’s simple icy ecosystems. Analyzing biogeography by ecological zone provides insight on biodiversity patterns, endemic species clusters, and flora-fauna histories over geological timescales.

Endemism and Conservation

Understanding bioregional realms helps identify restricted-range endemic species and guide conservation priorities. Targeting reserves toward distinct ecosystem zones better ensures full species representation. As climate shifts accelerate, tracking biome boundaries and range shifts will grow increasingly vital for managing global biodiversity. Integrating biogeographic realm data can strengthen international conservation planning and target protection for highly endemic ecological regions.

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