Australia now has copious amounts of Red Fox, Rabbits, Deer.
Other Mammals were brought here for various reasons.
The Donkey was used as a pack animal 150 years ago. With the advent of the motor vehicle, the Donkeys were released into the wild and there are over 5 million Donkeys roaming inland Australia.
Brumby Horses came to Australia with the first fleet and now there are more than 400,000 feral Brumbies roaming the Australian bush.
Camels were introduced as Pack animals over 180 years ago.
Early explorers utilised their sturdiness to explore inland Australia.
Today there are well over 1 million roaming the deserts of Australia and the prediction is that this number will double every 9 years.
Feral Pigs also arrived on the first fleet and there are an estimated 24 million Feral Pigs across Australia
Another to arrive with the first fleet are Goats.
There are well over 2.5 million Feral Goats across Australia.
Buffalos were brought to Australia from Indonesia almost 200 years ago as a food source on Melville Island. There are over 150,000 wild Buffalos in Australia.
All of these introduced animals are devastating the natural environment and contributing to the extinction of some of Australia’s unique Fauna.
A very sad state of affairs
I had no idea , so many were roaming round Australia , Camels especially ,
Theres been an interesting story in the news over the last couple of weeks here , someone illegally released Lynx back into Scotland they had been extinct for the last 500 hundred to a Thousand years .
Fortunately they were recaptured , 4 in total , but one as died .
I wonder at some point in Australia , these animals will be culled , like you say too many can be distructive.
Kangaroo bare back riding I understand is a popular sport in Australia. Australians get a great kick out of it. 
Must ask Bruce sometime.
Doing things contrary to Mother Nature’s plans has as many consequences as doing things contrary to one’s mother’s plans.
Better to let both run the show.
The interesting thing about the camels is that they are much sought after from the Middle East where camels are bred for sport.
The Australian camels have not been selectively bred so are how camels were 150 years ago.
However all this ignores the worst import of them all - the cat which kills millions of native animals every single night.
https://www.dcceew.gov.au/environment/invasive-species/feral-animals-australia
While that is true, yours are not completely alien to their new environment. I mean you already had squirrels and crustations
Most of the feral animals here lack natural predictors to keep their numbers in check. For example prior to European settlement there were no native cats, hoofed animals or poisonous toads so there was nothing to prey on them and they flourished.