The most impressive aspect of the living world is it’s diversity. Ernst Mayr: "This is Biology"

Australia

Map in PublicDomain by NASA: http://photojournal.jpl.nasa.gov/catalog/PIA06665

Australia has been separated from other landmasses for more than 50 mya. Due to this isolation several species could survive that are now endemic to Australia. The probably most famous examples are the monotremes, marsupialia (which are otherwise only found in South America), and the tree genus Eucalyptus which is native to Australia and Indonesia but has, unfortunately, spread over almost the whole world.
About 50.000 bis 40.000 years ago first man came to Australia. There were about 400 to 500 aboriginal tribes when first white settlers arrived in 1788. The number of tribes decreased drastically after white peoples arrival and also flora and fauna suffered significantly. Especially invasive species introduced, for example, for hunting, agriculture, or gardening caused dramatic changes. New species may still be introduced although authorities try hard to control.

Invasive species

Probably the most prominent invasive species in Australia, which have been caused and are still causing dramatic changes in native flora and fauna, are the omnipresent rabbits (Oryctolagus cuniculus), as well as the red fox (Vulpes vulpes) both of which have been introduced by settlers for hunting reasons. Rabbits are competing with several marsupial species and the red fox may be both, competitor of native Dasyuromorphia and predator of other small marsupials. Also the cain toad (Bufo marinus), which has been introduced in 1935 as “biological control” of agricultural pests became a very important pest itself. It is spreading dramatically fast and causes disappearance of other amphibians, reptiles (paranoid lizards, snakes, and even crocodiles) and more.