Australasian realm

Australasian realm. The Australasian realm is one of the world's eight major biogeographic realms, encompassing a distinct evolutionary arena isolated for millions of years. It is defined by the unique flora and fauna that evolved in relative isolation following the breakup of the supercontinent Gondwana. The realm primarily includes the landmasses of Australia, New Zealand, New Guinea, and the surrounding islands of the eastern Malay Archipelago, with a boundary known as Wallace's Line sharply demarcating it from the Indomalayan realm.

Geography and boundaries

The realm's core consists of the continental mass of Australia and the islands of Tasmania and New Guinea, which sits on the same continental shelf. To the east, it encompasses New Zealand and its outlying islands, including the Chatham Islands. In the northwest, the boundary is famously delineated by Wallace's Line, an abrupt faunal transition running between the islands of Bali and Lombok, and north through the Makassar Strait between Borneo and Sulawesi. This line, identified by the naturalist Alfred Russel Wallace, separates the Australasian realm from the Indomalayan realm. The eastern portion of the Indonesian archipelago, including islands like Sulawesi, the Moluccas, and Timor, falls within the realm, while islands like Sumatra and Java lie to the west of the line. The remote Pacific Islands further east, such as Fiji and New Caledonia, are sometimes included in related classifications like the Oceanian realm.

Flora and fauna

The realm is renowned for its high degree of endemism and distinctive evolutionary lineages. Its fauna is dominated by marsupials, including iconic species like the kangaroo, koala, and Tasmanian devil, alongside monotremes such as the platypus and echidna. Birdlife is exceptionally unique, featuring flightless birds like the kiwi and emu, and a spectacular array of parrots including the kakapo and cockatoo. The flora is equally distinctive, characterized by ancient plant families like the Proteaceae, with genera such as Banksia and Grevillea, and vast forests of Eucalyptus and Acacia. New Guinea hosts incredible biodiversity, including birds-of-paradise and the world's largest pigeon, the Victoria crowned pigeon.

Evolutionary history

The evolutionary history of the Australasian realm is a story of long-term isolation following the fragmentation of Gondwana. Australia began to separate from Antarctica via the opening of the Southern Ocean around 45 million years ago, drifting northwards in isolation. This separation allowed the unique marsupial and monotreme mammals to diversify without competition from placental mammals, which came to dominate other continents. New Zealand's history is even more isolated, having separated from Gondwana approximately 82 million years ago, leading to a fauna dominated by birds, reptiles, and insects, with no native land mammals except bats. The intermittent land connections between Australia and New Guinea via the Sahul Shelf during glacial periods facilitated faunal exchange, explaining shared species like tree kangaroos.

Major ecosystems

The realm contains a vast array of ecosystems shaped by its climatic and geographic diversity. These include the extensive arid and semi-arid deserts of the Australian interior, such as the Great Victoria Desert. Significant temperate and tropical rainforests are found in regions like Queensland's Wet Tropics and the Gondwana Rainforests, as well as across the highlands of New Guinea. Unique Mediterranean-type ecosystems, known as kwongan and mallee, are present in southwestern Australia. New Zealand is famed for its temperate forests dominated by ancient podocarp and southern beech trees, and its extensive alpine habitats in the Southern Alps. Major marine ecosystems include the Great Barrier Reef and the diverse coral systems of the Coral Triangle.

Conservation status

The unique biodiversity of the Australasian realm faces significant threats, leading to a critical conservation status for many species and ecosystems. Major threats include habitat loss due to land clearing for agriculture and urban development, invasive species such as the cane toad, red fox, and brushtail possum in New Zealand, and the impacts of climate change on sensitive habitats like coral reefs and alpine zones. Conservation efforts are spearheaded by organizations like the IUCN and government bodies including Australia's Department of Climate Change, Energy, the Environment and Water. Protected areas such as Kakadu National Park, Fiordland National Park, and the TransFly region of New Guinea are vital refuges. The legacy of human arrival, particularly the Late Quaternary extinctions which saw the loss of megafauna like Diprotodon, underscores the ongoing vulnerability of its endemic species.

Category:Biogeographic realms Category:Ecology of Oceania Category:Australasia