Human Impacts on island ecosystems. (Australia)
There are few paleovegetation records in Australia before 18,000 years ago. To find out the history of the Australian fauna scientists used stable carbon isotopes from the emu eggshell (a flightless bird native to Australia). The samples were largely taken from Lake Eyre. The carbon composition of the eggshell tells us the composition of the bird's diet (over 3-5 days). The emus are mixed feeders herbivores, eating leaves, shoots, fruits, flowers, shrubs and grasses. The variation of the carbon values reflect the changes in the birds diet and hence the composition of the flora. There are 2 different types of plants in Australia, defined by their different photosynthetic pathways. One uses the C4 pathway and the other C3. The photosynthetic pathways depend firstly on the season of rainfall and on the geographical position i.e. north to south variations. C3 grasses grow best in areas affected by the winter monsoons (southern Australia). Whereas C4 grasses dominate areas that are affected by the summer monsoon (central and northern Australia). The majority of trees and shrubs across Australia are C3 plants. Emu normally lay their eggs in the winter so their preferred diet is C3 plants. The relative abundance of C4 grasses has varied over the past 65,000 years.
The fauna found in Australia prior to human arrival was very different to the animals living there now. Over 85% of all animals that exceeded body mass of 44kilos are now extinct. They became extinct in the Late Pleistocene period. These very large animals were mostly marsupials but also included a flightless bird Genyornis newtoni and 3 large reptiles. Two other birds, the emu (Dromaius novaehollandiae) and cassowart (Casuarius casuarius) survived. These large, extinct species are called the Australian megafauna. The extinction of these species was once thought to be the effect of climate change and human predators. It is now believed to be from...
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