 Cane toads pose a serious threat to native species when introduced to a new ecosystem . Classified as an invasive species in over 20 countries , there are multiple reports of the cane toad moving into a new area to be followed by a decline in the biodiversity in that region . The most documented region of the cane toad 's invasion and subsequent effect on native species is Australia , where multiple surveys and observations of the toad 's conquest have been completed . The best way to illustrate this effect is through the plight of the northern quoll , as well as Mertens ' water monitor , a large lizard native to South and Southeast Asia . 
