Australasian realm: geography, biodiversity, and biogeographic history

Geographic extent and boundaries

The core of the Australasian realm includes the Australian continent, the large island of New Guinea (politically divided between Papua New Guinea and the Indonesian provinces), and many smaller island groups. It also embraces parts of eastern Indonesia such as Sulawesi and the Moluccas, the Lesser Sunda islands, and Pacific archipelagos including the Solomon Islands, Vanuatu, New Caledonia and the Bismarck Archipelago. New Zealand and its offshore islands form a distinct sub-region within this realm. The transition to the adjacent Indomalayan realm is often marked by biogeographic dividing lines such as the Wallace Line, which highlights the change in species composition between islands on either side.

Geological origins and historical development

The distinctive biota of the Australasian realm reflects its deep geological history. Much of the region once formed part of the southern supercontinent Gondwana, whose breakup and long isolation shaped plant and animal evolution. Australia slowly drifted northward after separating from Antarctica and experienced climatic shifts and changing connections to neighboring landmasses. These tectonic and sea-level changes created opportunities for both in situ evolution and intermittent dispersal from nearby regions, yielding a complex mixture of ancient Gondwanan lineages and more recent arrivals.

Characteristic flora and fauna

High levels of endemism characterize the Australasian realm. Plants include ancient families and many unique genera adapted to arid and sclerophyll environments as well as moist tropical forests of New Guinea. Animal life shows some of the clearest examples of evolutionary divergence: the only living monotremes (egg-laying mammals) are native here, and the majority of native terrestrial mammals are marsupials, with a wide variety of forms from carnivores to arboreal and burrowing species. Birds, reptiles and insects also show large numbers of endemic species. New Zealand and many Pacific islands display their own distinctive faunas and floras, often with few native mammals and unique bird radiations.

Human influences, colonization and species introductions

Humans have affected the Australasian realm in stages: prehistoric human arrivals altered island ecosystems, introducing domesticates and predators such as the dingo in Australia, and later, European exploration and colonization brought a broader suite of introduced species and substantial habitat change. Introduced mammals, altered fire regimes, land conversion and other disturbances have reshaped native communities and increased extinction risk for many endemic species. In some islands, absence of native terrestrial predators made bird species particularly vulnerable to introduced mammals.

Conservation importance and challenges

Because of its unique evolutionary history and many endemic taxa, the Australasian realm is of high conservation priority. Threats include habitat loss, invasive species, climate change and unsustainable resource use. Conservation strategies combine habitat protection, invasive species control, species recovery programs and indigenous land stewardship. Many protected areas, research programs and transnational conservation efforts focus on preserving representative ecosystems and preventing further extinctions.

Selected links and resources

• Biogeographic definitions and concepts
• Geographic outlines of the realm
• Australasia: regional overview
• Australasia as a cultural and natural region
• Australia: continent and ecosystems
• New Guinea: biodiversity hotspot
• Wallace Line and biogeographic boundaries
• Papua New Guinea: natural history
• Indonesian provinces of New Guinea
• Sulawesi and island biogeography
• Lombok and the Lesser Sundas
• Sumbawa and regional ecosystems
• Sumba: island biodiversity
• Flores and endemic species
• Timor and surrounding islands
• Bismarck Archipelago
• Vanuatu: islands and habitats
• Solomon Islands biodiversity
• New Caledonia: unique flora
• New Zealand: natural heritage
• Antarctic connections in deep time
• Gondwana and continental breakup
• Supercontinents and biogeography
• Characteristic plant lineages
• Faunal distinctiveness
• Monotremes: egg-laying mammals
• Eutherian (placental) mammals in the region
• Marsupial diversity and distribution
• Miocene fossil record and migration events
• Bats and early arrivals
• Rodent colonization history
• Late arrivals and human-mediated introductions
• Fossil evidence and paleontology
• The dingo and prehistoric introductions
• Bali–Lombok transition and Wallace’s work