Oceanian realm

The Oceanian realm is one of the World Wildlife Fund (WWF) biogeographic realms, and is unique in not including any continental land mass. It is the smallest in land of an area of the WWF realms.

This realm includes the islands of the Pacific Ocean in: Micronesia, the Fijian Islands, the Hawaiian islands, and Polynesia (with the exception of New Zealand).

New Zealand, Australia, and most of Melanesia including New Guinea, Vanuatu, the Solomon Islands, and New Caledonia are included within the Australasian realm.

Map OC-Oceania
Map of islands of Oceania


Oceania is geologically the youngest realm. While other realms include old continental land masses or fragments of continents, Oceania is composed mostly of volcanic high islands and coral atolls that arose from the sea in geologically recent times, many of them in the Pleistocene. They were created either by hotspot volcanism, or as island arcs pushed upward by the collision and subduction of tectonic plates. The islands range from tiny islets, sea stacks and coral atolls to large mountainous islands, like Hawaii and Fiji.


The climate of Oceania's islands is tropical or subtropical, and range from humid to seasonally dry. Wetter parts of the islands are covered by Tropical and subtropical moist broadleaf forests, while the drier parts of the islands, including the leeward sides of the islands and many of the low coral islands, are covered by Tropical and subtropical dry broadleaf forests and Tropical and subtropical grasslands, savannas, and shrublands. Hawaii's high volcanoes, Mauna Kea and Mauna Loa, are home to some rare tropical Montane grasslands and shrublands.

Flora and fauna

Since the islands of Oceania were never connected by land to a continent, the flora and fauna of the islands originally reached them from across the ocean (though at the height of the last ice age sea levels were much lower than today and many current seamounts were islands, so some now isolated islands were once less isolated). Once they reached the islands, the ancestors of Oceania's present flora and fauna adapted to life on the islands.

Larger islands with diverse ecological niches encouraged floral and faunal adaptive radiation, whereby multiple species evolved from a common ancestor, each species adapted to a different ecological niche; the various species of Hawaiian honeycreepers (Family Drepanididae) are a classic example. Other adaptations to island ecologies include gigantism, dwarfism, and among birds, loss of flight. Oceania has a number of endemic species; Hawaii in particular is considered a global 'center of endemism', with its forest ecoregions having one of the highest percentages of endemic plants in the world.


Land plants disperse by several different means. Many plants, mostly ferns and mosses but also some flowering plants, disperse on the wind, relying on tiny spores or feathery seeds that can remain airborne over long distances notably Metrosideros trees from New Zealand spread on the wind across Oceania. Other plants, notably coconut palms and mangroves, produce seeds that can float in salt water over long distances, eventually washing up on distant beaches, and thus Cocos trees are ubiquitous across Oceania. Birds are also an important means of dispersal; some plants produce sticky seeds that are carried on the feet or feathers of birds, and many plants produce fruits with seeds that can pass through the digestive tracts of birds. Pandanus trees are fairly ubiquitous across Oceania.

Botanists generally agree that much of the flora of Oceania is derived from the Malesian Flora of the Malay Peninsula, Indonesia, the Philippines, and New Guinea, with some plants from Australasia and a few from the Americas, particularly in Hawaii. Easter Island has some plants from South America such as the totora reed.


Kagu Rhynchetos jubatus detail
Kagu (Rhynochetos jubatus), a flightless bird from New Caledonia

Dispersal across the ocean is difficult for most land animals, and Oceania has relatively few indigenous land animals compared to other realms. Certain types of animals that are ecologically important on the continental realms, like large land predators and grazing mammals, were entirely absent from the islands of Oceania until humans brought them. Birds are relatively common, including many seabirds and some species of land birds whose ancestors may have been blown out to sea by storms. Some birds evolved into flightless species after their ancestors arrived, including several species of rails. A number of islands have indigenous lizards, including geckoes and skinks, whose ancestors probably arrived on floating rafts of vegetation washed out to sea by storms. With the exception of bats, which live on most of the island groups, there are few if any indigenous mammal species in Oceania.

Impact of settlement

Many animal and plant species have been introduced by humans in two main waves.

Malayo-Polynesian settlers brought pigs, dogs, chickens and polynesian rats to many islands; and had spread across the whole of Oceania by 1200 CE. From the seventeenth century onwards European settlers brought other animals, including cats, cattle, horses, small Asian mongoose (Herpestes javanicus), sheep, goats, and the brown rat (Rattus norvegicus). These and other introduced species, in addition to overhunting and deforestation, have dramatically altered the ecology of many of Oceania's islands, pushing many species to extinction or near-extinction, or confining them to small islets uninhabited by humans.

The absence of predator species caused many bird species to become 'naive', losing the instinct to flee from predators, and to lay their eggs on the ground, which makes them vulnerable to introduced predators like cats, dogs, mongooses, and rats. The arrival of humans on these island groups often resulted in disruption of the indigenous ecosystems and waves of species extinctions (see Holocene extinction event). Easter Island, the easternmost island in Polynesia, shows evidence of a human-caused ecosystem collapse several hundred years ago, which contributed (along with slave raiding and European diseases) to a 99% decline in the human population of the island. The island, once lushly forested, is now mostly windswept grasslands. More recently, Guam's native bird and lizard species were decimated by the introduction of the brown tree snake (Boiga irregularis) in the 1940s.

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Biogeographic realm

A biogeographic realm or ecozone is the broadest biogeographic division of the Earth's land surface, based on distributional patterns of terrestrial organisms. They are subdivided in ecoregions, which are classified in biomes or habitat types.

The realms delineate large areas of the Earth's surface within which organisms have been evolving in relative isolation over long periods of time, separated from one another by geographic features, such as oceans, broad deserts, or high mountain ranges, that constitute barriers to migration. As such, biogeographic realms designations are used to indicate general groupings of organisms based on their shared biogeography. Biogeographic realms correspond to the floristic kingdoms of botany or zoogeographic regions of zoology.

Biogeographic realms are characterized by the evolutionary history of the organisms they contain. They are distinct from biomes, also known as major habitat types, which are divisions of the Earth's surface based on life form, or the adaptation of animals, fungi, micro-organisms and plants to climatic, soil, and other conditions. Biomes are characterized by similar climax vegetation. Each realm may include a number of different biomes. A tropical moist broadleaf forest in Central America, for example, may be similar to one in New Guinea in its vegetation type and structure, climate, soils, etc., but these forests are inhabited by animals, fungi, micro-organisms and plants with very different evolutionary histories.

The patterns of distribution of living organisms in the world's biogeographic realms were shaped by the process of plate tectonics, which has redistributed the world's land masses over geological history.


Brachyanax is a genus of bee fly in the subfamily Anthracinae. It was circumscribed by Neal Evenhuis in 1981. Thirteen species are recognized, and they are found in Asia and Australasia.

Evolutionary anachronism

Evolutionary anachronism is a concept in evolutionary biology, named by Connie C. Barlow in her book The Ghosts of Evolution (2000), to refer to attributes of living species that are best explained as a result of having been favorably selected in the past due to coevolution with other biological species that have since become extinct. When this context is removed, said attributes appear as unexplained amounts of energy investments on the part of the living organism, with no apparent benefit extracted from them, and can even be prejudicial to the continued reproduction of the surviving species. The general theory was formulated by Costa Rican-based American botanist Daniel Janzen and University of Arizona-based geologist Paul S. Martin (a prominent defender of the overkill hypothesis to explain the Quaternary extinction event) in a Science article published in 1982, titled Neotropical Anachronisms: The fruit the gomphotheres ate. Previously in 1977, Stanley Temple had proposed a similar idea to explain the decline of the Mauritius endemic tree tambalacoque following the extinction of the iconic dodo.Janzen, Martin and Barlow mainly discussed evolutionary anachronisms in the context of seed dispersal and passive defense strategies exhibited by plants that had evolved alongside disappeared megaherbivores. However, some examples have also been described in animal species. John Byers used the name relict behavior for animal behavior examples. Evolutionary anachronisms, as properly understood, should not be confused with examples of vestigiality. Though both concepts refer ultimately to organs that evolved to deal with pressures that are no longer present today, in the anachronisms case, the original function of the organ and the capacity of the organism to use it are still retained intact (e.g. the absence of gomphotheres to eat avocados doesn't make the avocado's pulp in any way vestigial, rudimentary or intrinsically incapable of playing its original function of helping disperse the avocado's seeds through zoochory, were a new suitable ecological partner to appear; while a true vestigial organ like the python's pelvic spurs cannot in any way be used to walk again).

List of biogeographic provinces

Biogeographic Province is a biotic subdivision of realms.

The following list of biogeographic provinces was developed by Miklos Udvardy in 1975, later modified by other authors.

See also
Sovereign states
Dependencies and
other territories

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