The red fox in Australia—an exotic predator turned biocontrol agent

The most important problem regarding mammal conservation in mainland Australia is the low abundance and limited distributions of many species, a legacy of an unprecedented collapse of the mammal fauna on a continental scale that unfolded following European colonisation. Two major hypotheses (not necessarily always mutually exclusive) have been proposed to account for the collapse (1) niche loss–damage due to a variety of causes and (2) predation by exotics, in particular by the red fox. This paper provides evidence the supporting the latter cause as a major factor. Five case studies in Western Australia demonstrate that the fox is an efficient predator that restricts medium-sized marsupials to refugia at low densities. Removal of the fox by baiting typically produces two prey responses (1) significant population recoveries and (2) the colonisation and exploitation of habitats outside of refugia. To date, 11 medium-sized marsupial species, representing seven families, have responded in a like manner. The impact of the fox on its known marsupial prey mimics a biocontrol agent as it severely limits prey distribution and abundance. Niche denial and population suppression characterise it's actions on a suite of vulnerable species not yet fully documented.