The biodiversity of Tasmania is of exceptional biological and paleoecological interest. A state of Australia, it is a large South Pacific archipelago of one large main island and a range of smaller islands. The terrain includes a variety of reefs, atolls, many small islands, and a variety of topographical and edaphic regions on the largest island, all of which promote the development of unusually concentrated biodiversity. During long periods geographically and genetically isolated, it is known for its unique flora and fauna. The region's climate is oceanic.
Overview
The marine fauna of the period, separate from that of the southwest Pacific, was distinguished as the "Maori province". Gondwana began its fragmentation in the middle and upper Jurassic, and the arrival of benthic invertebrate fauna is visible in fossil deposits. The Cretaceous marked the appearance of marine invertebrate fauna of southern origin. It was then that angiosperm flora such as Nothofagus and Proteaceae colonized New Zealand and New Caledonia, from South America, along the Antarctic margin of Gondwana: Antarctica, mainland Australia and Tasmania. At the beginning of the Tertiary the area moved to north to a warmer climate.
This led to long periods of evolution in near complete isolation. The isolation of the island was not absolute, given the rise and fall of sea level caused by the ebb and flow of ice ages. Land bridges or islands formed between Tasmania and its neighbour, mainland Australia. Thus new species came to Tasmania while Gondwanan species were able to penetrate the Pacific Islands region. Plants have limited seed dispersal mobility away from the parent plant and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant individually or collectively, as well as dispersed in both space and time. Birds and bats swallow seeds, then regurgitate them or pass them in their faeces. Such seed dispersal has been a major mechanism of seed dispersal across ocean barriers. Other seeds may stick to the feet or feathers of birds, particularly migratory or aquatic birds, and in this way may travel long distances. Seeds of grasses, spores of algae, and the eggs of molluscs and other invertebrates commonly establish in remote areas after long journeys of such types.
Flora
The most ancient communities in Tasmania have an ancestry that extend back to a time when the Earth's continents were all joined as single landmass known as Pangea which existed beyond 200 million years ago. Pangea split from east to west into Laurasia, comprising North America and Eurasia, and Gondwana, the two remaining connected at Gibraltar with the Tethys Sea separating them. The presence of closely related organisms in both the Northern and Southern Hemispheres cannot be accounted for by migration.
The Antarctic flora is a distinct community of vascular plants which evolved millions of years ago on the supercontinent of Gondwana, and is now found on several separate areas of the Southern Hemisphere, including southern South America, southernmost Africa, New Zealand, Australia and New Caledonia. Based on the similarities in their flora, botanist Ronald Good identified a separate Antarctic Floristic Kingdom that included southern South America, New Zealand, and some southern island groups. Good identified Australia as its own floristic kingdom, and included New Guinea and New Caledonia in the Paleotropical floristic kingdom, because of the influx of tropical Eurasian flora that had mostly supplanted the Antarctic flora.
Millions of years ago, Antarctica was warmer and much wetter, and supported the Antarctic flora, including forests of podocarps and southern beech. Antarctica was also part of the ancient supercontinent of Gondwanaland, which gradually broke up by continental drift starting 110 million years ago. The separation of South America from Antarctica 30-35 million years ago allowed the Antarctic Circumpolar Current to form, which isolated Antarctica climatically and caused it to become much colder. The Antarctic flora subsequently died out in Antarctica, but is still an important component of the flora of southern Neotropic (South America) and Australasia, which were also former parts of Gondwana.
Some genera that originated in Antarctic Flora are still a recognised major component of New Caledonia, Tasmania, mainland Australia, Madagascar, India, New Zealand, and southern South America.