Colonizing Cane Toads cause population declines in native predators: reliable anecdotal information and management implications

Abstract

This paper presents compelling, anecdotal evidence of severe population declines in five predator species, Dasyurus hallucatus, Varanus gouldii, V. mertensi, V. panoptes, and V. timorensis similis, in almost immediate response to Cane Toad colonization of their habitat in three widely distributed areas of northern Queensland. Furthermore, risk assessment of all quoll and monitor taxa whose distributions overlap the potential distribution of the Cane Toad in Australia (Sutherst et al. 1996), indicates that at the continental scale, three of the four quoll taxa and eight of the 20 monitor species examined are at high risk of severe population declines following Cane Toad colonization. One quoll taxon and seven monitor species are at moderate risk and five monitor species are at low risk. The definition of the threat which Cane Toads pose to native predators has received very little research attention, and fundamental questions including; which predator species are most at risk (testing of the risk assessment hypotheses presented here), the extent of these risks (is there a need to manage Cane Toad impacts upon predators?), and the contexts of intraspecific variation in relative extinction risk (for example, interactions of extinction risk with predator and Cane Toad population demography, climate, landscape, and land use), need to be assessed. Assuming that Cane Toads are found to have an impact across a range of taxa and landscapes (which I propose to be likely), management of the impact of this species on predators can be approached from two not necessarily exclusive directions; management of Cane Toad populations and management of predator populations, through both population and habitat management. At this stage, however, management from either viewpoint is constrained by a lack of published information relevant to autecology and fine scale distribution of predators.