Scientists believe that more frequent contact between predator and prey populations in contiguous continents such as Eurasia, Africa and the Americas has made prey populations less nave to alien predators by exposing them to similar predator "archetypes".
In contrast, Australias unique marsupial fauna have never had predatory species like feral foxes and cats until recently. Such alien predators were shown to have worse negative impacts than some classic predators, including large carnivores such as wolves.
Case study: foxes and the brush-tailed bettong
In the early 1800s, Australias brush-tailed bettong - a medium-sized kangaroo-like marsupial - was commonplace in central New South Wales, South Australia and the southern regions of the Northern Territory and Western Australia.
However, the population and range of bettongs began shrinking during the 1900s following the release and spread of foxes and rabbits across the continent. Many other species up to two dozen -- are thought to have become extinct during this initial wave of invading alien species.
By the 1970s, the bettong was considered as an endangered species with the only surviving mainland populations found in small pockets of forest in Western Australia. However, even these remnant populations were still being preyed upon by foxes and by the late 70s the species was threatened with extinction.
Following an intensive program of fox-control initiatives, bettong numbers eventually rebounded by more than 20-fold, demonstrating that fox predation had continued to have a devastating impact on bettongs after more than 150 yeas. No native predator anywhere on earth has had such a profound negative impact on their prey.