The Australasian realm is one of eight biogeographic realms that is coincident with, but not (by some definitions) the same as, the geographical region of

Australasia Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...

. The realm includes

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, the island of

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

(comprising

Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...

and the

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

n province of Papua), and the eastern part of the Indonesian archipelago, including the island of

Sulawesi Sulawesi ( ), also known as Celebes ( ), is an island in Indonesia. One of the four Greater Sunda Islands, and the List of islands by area, world's 11th-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Min ...

, the Moluccas (the Indonesian provinces of Maluku and

North Maluku North Maluku (; ) is a province of Indonesia. It covers the northern part of the Maluku Islands, bordering the Pacific Ocean to the north, the Halmahera Sea to the east, the Molucca Sea to the west, and the Seram Sea to the south. It shares marit ...

), and the islands of Lombok, Sumbawa, Sumba, Flores, and

Timor Timor (, , ) is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is Indonesia–Timor-Leste border, divided between the sovereign states of Timor-Leste in the eastern part and Indonesia in the ...

, often known as the Lesser Sundas. The Australasian realm also includes several Pacific island groups, including the Bismarck Archipelago,

Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (; ), is an island country in Melanesia located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of northern Australia, northeast of New Caledonia, east o ...

, the

Solomon Islands Solomon Islands, also known simply as the Solomons,John Prados, ''Islands of Destiny'', Dutton Caliber, 2012, p,20 and passim is an island country consisting of six major islands and over 1000 smaller islands in Melanesia, part of Oceania, t ...

, and

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and its surrounding islands are a distinctive sub-region of the Australasian realm. The rest of Indonesia is part of the

Indomalayan realm The Indomalayan realm is one of the eight biogeographic realms. It extends across most of South and Southeast Asia and into the southern parts of East Asia. Also called the Oriental realm by biogeographers, Indomalaya spreads all over the Ind ...

. In the classification scheme developed by Miklos Udvardy, New Guinea, New Caledonia, Solomon Islands and New Zealand are placed in the

Oceanian realm The Oceanian realm is one of the eight biogeographic realms and is unique in not including any continental land mass. It has the smallest land area of any of the List of terrestrial ecoregions (WWF), WWF realms. This realm includes the islands ...

.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

Geography

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

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s and

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s. In this context, Australasia is limited to Australia, New Guinea, New Zealand,

, and neighbouring islands, including the

n islands from Lombok and

eastward. The

Wallace Line The Wallace Line or Wallace's Line is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace and named by the English biologist Thomas Henry Huxley. It separates the biogeographic realms of Asia and 'Wallacea', a ...

to the west divides areas in the Indomalayan realm of tropical

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

which are or have at times been directly connected to the Asian mainland from islands that have never been so connected.

Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...

and

Bali Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller o ...

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 Geology, Geologically, the Sahul Shelf () is a part of the continental shelf of the Australia (continent), Australian continent, lying off the northwest coast of mainland Australia. Etymology The name "Sahull" or "Sahoel" appeared on 17th c ...

of the Australian continent. Islands between the two lines (e.g. Sulawesi, the Moluccas and Lombok through Timor) form the biogeographical area of

Wallacea Wallacea is a biogeography, biogeographical designation for a group of mainly list of islands of Indonesia, Indonesian islands separated by deep-water straits from the Asian and Australia (continent), Australian continental shelf, continental ...

, 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).

Geology

Australia, New Zealand and New Caledonia are all fragments of the ancient supercontinent

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

, 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 of millions of years. All of Australasia shares the

Antarctic flora Antarctic flora are a distinct community of vascular plants which evolved millions of years ago on the supercontinent of Gondwana. In 2025, species of Antarctica flora reside on several now separated areas of the Southern Hemisphere, including ...

, 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 age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

s. They share a similar fauna which includes

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

and monotreme mammals and ratite birds.

Eucalypt Eucalypt is any woody plant with Capsule (fruit), capsule fruiting bodies belonging to one of seven closely related genera (of the tribe Eucalypteae) found across Australia: ''Eucalyptus'', ''Corymbia'', ''Angophora'', ''Stockwellia'', ''Allosyn ...

s 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

, the Bismarck Archipelago,

, and

, which were not formerly part of Gondwana, but which share many characteristic plants and animals with Australasia.

Ecology

Note that this zonation is based on flora;

s do not necessarily follow the same biogeographic boundaries. In the present case, many

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s 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

Polynesia Polynesia ( , ) is a subregion of Oceania, made up of more than 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are called Polynesians. They have many things in ...

n fauna is related to that of Melanesia.

Ecoregions

References

External links