Melbourne:

With the gold rush largely over by 1860, Melbourne continued to grow on the back of continuing gold mining, as the major port for exporting the agricultural products of Victoria, especially wool, and a developing manufacturing sector protected by high tariffs. An extensive radial railway network centred on Melbourne and spreading out across the suburbs and into the countryside was established from the late 1850s. Further major public buildings were begun in the 1860s and 1870s such as the Supreme Court, Government House, and the Queen Victoria Market. The central city filled up with shops and offices, workshops, and warehouses. Large banks and hotels faced the main streets, with fine townhouses in the east end of Collins Street, contrasting with tiny cottages down laneways within the blocks. The Aboriginal population continued to decline with an estimated 80% total decrease by 1863, due primarily to introduced diseases, particularly smallpox, frontier violence and dispossession from their lands.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". In 1863, why was Aboriginal population declining?
diseases, particularly smallpox, frontier violence and dispossession from their lands.