Ecosystems are constantly changing. In Australia this natural process has been accelerated to a dangerous level by the ravages of European development. White settlement in Australia devastated natural vegetation, polluted rivers, and encroached upon and destroyed the native habitat. This is why 28 species of bird and animal, 100 species of plant and an unknown number of insect species are now extinct in Australia.

None of this is the fault of feral animals. It is human actions which have killed the native animals and human actions which have replaced them with new species and new balances.