Cane toads

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Predicting the impact of cane toads on native fauna: a mechanistic approach

Ben Phillips 1, James Smith 2, Matthew Greenlees 1, Greg Brown 1, Rick Shine 1.
1. School of Biological Sciences, A08, University of Sydney, NSW 2006.
Key Centre for Tropical Wildlife Management, Charles Darwin University, Darwin NT 0909.

Logistical difficulties in quantifying the abundance of animals, combined with large yearly and seasonal fluctuations in population size, make the task of quantifying toad impact difficult in the field. Here we use a mechanistic approach to assess the likelihood of an impact from toads on reptile predators, frogs and invertebrates. That is, we identify a mechanism of potential impact and then test it in an experimental setting. Using this approach, we conclude that: 1. 30% of our terrestrial snakes, 59% of the Agamids, 85% of the Varanids 50% of our crocodiles and most of our freshwater turtles are potentially at risk from toad poisoning. 2. Toads prey upon the same invertebrates as native frogs and thus will only have an impact on invertebrates if the arrival of toads increases the total amphibian biomass. 3. Nevertheless, the strong dietary overlap between frogs and toads provides strong evidence for competition between these species. The mechanistic approach we outline here is cheaper than long term mark-recapture studies and, more importantly, allows us to rapidly identify which taxa we should be concerned about.