Feral cats kill a wide range of native wildlife and spread disease and parasites, and for this reason are thought to reduce the distribution and abundance of many native species.
The Problem with Feral Cats
Feral cats are medium-sized predators and a highly successful invasive pest species in Australia. They are also considered the most threatening invasive species worldwide. Cats arrived in Australia as pets of European settlers and were later introduced to help control rabbits and rodents.
References
Department of Climate Change, Energy, the Environment & Water fact sheet