The Australasian realm is a biogeographic realm that is coincident with, but not (by some definitions) the same as, the geographical region of Australasia. The realm includes Australia, the island of New Guinea (comprising Papua New Guinea and the Indonesian province of Papua), and the eastern part of the Indonesian archipelago, including the island of Sulawesi, the Moluccan islands (the Indonesian provinces of Maluku and North Maluku), and the islands of Lombok, Sumbawa, Sumba, Flores, and Timor, often known as the Lesser Sundas.
The Australasian realm also includes several Pacific island groups, including the Bismarck Archipelago, Vanuatu, the Solomon Islands, and New Caledonia. New Zealand and its surrounding islands are a distinctive sub-region of the Australasian realm. The rest of Indonesia is part of the Indomalayan realm. In the classification scheme developed by Miklos Udvardy, New Guinea, New Caledonia, Solomon Islands and New Zealand are placed in the Oceanian realm.
From an ecological perspective the Australasian realm is a distinct region, parts of which have a common geologic and evolutionary history. The entire area has experienced a long period of biological isolation from other regions, and thus harbors a great many unique plants and animals. In this context, Australasia is limited to Australia, New Guinea, New Zealand, New Caledonia, and neighbouring islands, including the Indonesian islands from Lombok and Sulawesi eastward.
The Wallace Line to the west divides areas in the Indomalayan realm of tropical Asia which are or have at times been directly connected to the Asian mainland from islands that have never been so connected. Borneo and Bali lie on the western, Asian side. A second biological dividing line is Lydekker's Line, which similarly separates islands isolated by surrounding deep water from those associated with the Sahul Shelf of the Australian continent. Islands between the two lines (e.g. Sulawesi, the Moluccas and Lombok through Timor) form the biogeographical area of Wallacea, a transition zone between the Indomalayan and Australasian realms populated entirely by aerial or oceanic dispersal (although defined here as part of the Australasian realm).
Australia, New Zealand and New Caledonia are all fragments of the ancient supercontinent Gondwana, the marks of which are still visible in the Christmas Island Seamount Province and other geophysical entities. These three land masses have been separated from other continents, and from one another, for tens millions of years. All of Australasia shares the Antarctic flora, although the northern, tropical islands also share many plants with Southeast Asia.
Australia, New Guinea, and Tasmania are separated from one another by shallow continental shelves, and were linked together when the sea level was lower during ice ages. They share a similar fauna which includes marsupial and monotreme mammals and ratite birds. Eucalypts are the predominant trees in much of Australia and New Guinea. New Zealand has no native land mammals, but also had ratite birds, including the kiwi and the moa. The Australasian realm includes some nearby island groups, like Wallacea, the Bismarck Archipelago, Solomon Islands, and Vanuatu, which were not formerly part of Gondwana, but which share many characteristic plants and animals with Australasia.
Note that this zonation is based on flora; animals do not necessarily follow the same biogeographic boundaries. In the present case, many birds occur in both "Indomalayan" and "Australasian" regions, but not across the whole of either. On the other hand, there are few faunistic commonalities shared only by Australia and New Zealand, except some birds. Meanwhile, Australia, Melanesia and the Wallacea are united by a large share of similar animals, but few of these occur farther into the Pacific. On the other hand, much of the Polynesian fauna is related to that of Melanesia.
|Lesser Sundas deciduous forests||Indonesia|
|New Caledonia dry forests||New Caledonia|
|Sumba deciduous forests||Indonesia|
|Timor and Wetar deciduous forests||Indonesia, Timor-Leste|
|Arnhem Land tropical savanna||Australia|
|Brigalow tropical savanna||Australia|
|Cape York Peninsula tropical savanna||Australia|
|Carpentaria tropical savanna||Australia|
|Einasleigh Uplands savanna||Australia|
|Kimberley tropical savanna||Australia|
|Mitchell grass downs||Australia|
|Trans-Fly savanna and grasslands||Indonesia, Papua New Guinea|
|Victoria Plains tropical savanna||Australia|
|Chatham Islands temperate forests||New Zealand|
|Eastern Australian temperate forests||Australia|
|Fiordland temperate forests||New Zealand|
|Nelson Coast temperate forests||New Zealand|
|North Island temperate forests||New Zealand|
|Northland temperate kauri forests||New Zealand|
|Stewart Island / Rakiura temperate forests||New Zealand|
|Richmond temperate forests||New Zealand|
|Southeast Australia temperate forests||Australia|
|Southland temperate forests||New Zealand|
|Tasmanian Central Highland forests||Australia|
|Tasmanian temperate forests||Australia|
|Tasmanian temperate rain forests||Australia|
|Westland temperate forests||New Zealand|
|Canterbury–Otago tussock grasslands||New Zealand|
|Eastern Australia mulga shrublands||Australia|
|Southeast Australia temperate savanna||Australia|
|Australian Alps montane grasslands||Australia|
|Central Range sub-alpine grasslands||Indonesia, Papua New Guinea|
|Southland montane grasslands||New Zealand|
|Eyre and York mallee||Australia|
|Jarrah-Karri forest and shrublands||Australia|
|Swan Coastal Plain scrub and woodlands||Australia|
|Mount Lofty woodlands||Australia|
|Murray-Darling woodlands and mallee||Australia|
|Southwest Australia woodlands||Australia|
|Carnarvon xeric shrublands||Australia|
|Central Ranges xeric scrub||Australia|
|Great Sandy-Tanami desert||Australia|
|Great Victoria Desert||Australia|
|Nullarbor Plain xeric shrublands||Australia|
|Tirari–Sturt stony desert||Australia|
|Western Australian mulga shrublands||Australia|
|Antipodes Subantarctic Islands tundra||Australia, New Zealand|
|Wikimedia Commons has media related to Australasian realm.|
|Wikivoyage has a travel guide for Australasian wildlife.|
- "Australasia ecozone". World Wildlife Fund. Archived from the original on 2006-10-07.
- Udvardy, M. D. F. (1975). A classification of the biogeographical provinces of the world. IUCN Occasional Paper no. 18. Morges, Switzerland: IUCN.
- Udvardy, Miklos D. F. (1975) World Biogeographical Provinces (Map). The CoEvolution Quarterly, Sausalito, California. link.