| Oceania Ecozone |
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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 . 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. 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. Land Plant s dispersed 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. 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. 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 filled with seeds that can pass through the digestive tracts of birds. 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. '' Metrosideros '', '' Pandanus '' and '' Coco '' are tree genera with a fairly ubiquitous distribution across Oceania. Dispersal across the ocean is difficult for most land settlers brought Pig s, Dog s, and, inadvertently, Rat s to the islands; European settlers brought other animals, including Cat s, 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. 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 also caused the human population to implode. 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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