It's worth mentioning that the way this has taken away seats from the two major parties is not mostly through the rise of third parties, but the election of independents unaffiliated with any party. This has invariably occurred in electorates which are so homogeneous they were safe for one or the other major party, usually (but not always) rural.
The most spectacular example of this was the election of three rural independents who then proceeded to install Julia Gillard from Labor as Prime Minister, even though they were conservative. Their stated reasons were Labor's promise to build a fibre-to-the-premises broadband network and their assessment of the conservative leader. Other examples include members in wealthy Sydney suburbs who, while otherwise conservative, wanted action on climate change, and members in farming electorates unhappy with the way the Nationals have been captured by mining and housing development interests and failed to represent farmers.
(The Nationals, formerly the Country Party, always join the conservative Liberals in coalition, apparently having forgotten the purpose of coalitions.)
An exception is the Greens, who usually score one seat based on the central business district of Melbourne. This includes very high density apartment towers, and student accommodation for the University of Melbourne, and is demographically odd.
Many observers believe the rural independents may eventually coalesce into a new party which displaces the Nationals. I see no evidence thay the Liberals' several humiliating losses to independents in "safe" seats is causing them to rethink their policies. This may or may not change once they are unable to rely on whatever replaces the Nationals to form government.