| Oceania Ecozone |
Article Index for Oceania |
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Information AboutOceania Ecozone |
| CATEGORIES ABOUT OCEANIA ECOZONE | |
| ecozones | |
| oceania | |
| biogeography | |
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GEOLOGY ''Oceania'', is geologically the youngest ecozone. While other ecozones include old continental land masses or fragments of continents, Oceania is composed mostly of volcanic High Islands and Coral Atoll s 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 Arc s pushed upward by the collision and Subduction of Tectonic Plate s. The islands range from tiny islets, sea stacks and coral Atoll s to large mountainous islands, like Hawaii and Fiji . CLIMATE 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 Seamount s 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 Honeycreeper s (Family ''Drepanididae'') are a classic example. Other adaptations to island ecologies include giantism, 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 Ecoregion s having one of the highest percentages of endemic plants in the world. Flora Land Plant s 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 noteably '' Metrosideros '' trees from New Zealand spread on the wind across Oceania. Other plants, notably Coconut Palm s 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. Bird s 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 Malesia n 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 . Fauna Dispersal across the ocean is difficult for most land Animal s, and Oceania has relatively few indigenous land animals compared to other ecozones. Certain types of animals that are ecologically important on the continental ecozones, like large land Predators and grazing mammals, were entirely absent from the islands of Oceania until humans brought them. Bird s are relatively common, including many Sea Bird s 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 Lizard s, including Gecko es and Skink s, whose ancestors probably arrived on floating rafts of vegetation washed out to sea by storms. With the exception of Bat s, 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 Pig s, Dog s, Chicken s and Polynesian Rat s 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 Cat s, Cattle , Horses , Mongoose , Sheep , Goat s, and the Norway 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 a snake, ''Boiga irregularis'', in the 1940's. OCEANIA TERRESTRIAL ECOREGIONS EXTERNAL LINK |
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