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Cane Toads Bufo marinus are a highly successful invasive species, having invaded more than twenty countries in the last 150 years. In Australia, they currently occupy more than 1 million square kilometres. Toads are highly toxic and Australian predators have no evolutionary history with the cardiac toxins in toad skin. As such, toads constitute a novel and extremely toxic prey for Australia's predators. Australia's reptiles are perhaps the largest group likely to be affected by the invasion of the toad. By examining species distributions, we conclude that 59% of agamids, 85% of the varanids and all of Australia's crocodiles and freshwater turtles are potentially at risk from toads. We then assayed eleven species of reptile; one freshwater turtle (Chelidae), two crocodiles (Crocodylidae), two dragons (Agamidae), one python (Pythonidae) and five species of monitor (Varanidae) for resistance to toad toxin. We found a high level of variation between species in resistance to toad toxin but in all cases (except for one species of crocodile) all species were easily capable of eating a toad large enough to kill them. We conclude that toads pose a real and ongoing threat to the majority of Australian reptile species we examined.
Key words: Cane Toad, Bufotoxin, Reptiles, Invasive species, ID50.
INTRODUCTION
THE introduction (intentional and accidental) of new organisms into existing native habitats is potentially one of the most detrimental processes affecting biodiversity conservation (Diamond 1989; Mack et al. 2000; IUCN 2001). New organisms can alter the ecology of invaded habitats in many ways including introducing new diseases, altering the vegetative structure, or preying on native species (Williamson 1996; Sandlund et al. 1999). The outcomes of ecological invasion vary considerably among systems, but potentially one of the most powerful effects involves the invasion of a toxic species into the range of native predators that have had no previous exposure to such toxins (e.g., Brodie and Brodie 1999). In such cases native predators may be unable to tolerate the novel toxin and may die in large numbers as they first encounter the invader.
The Cane Toad Bufo marinas (Bufonidae) is a large (up to 230 mm body length) anuran native to South and Central America (Zug and Zug 1979). The species is a highly effective invader of new ecosystems; its...