Excluding invasive cane toads from water can provide benefits for ecosystems in semi-arid Australia
The invasion of cane toads (Bufo marinus) across northern Australia has been an ecological tragedy. Cane toads contain toxins that are absent from Australian frogs and as a consequence many native Australian predators die after attacking or consuming toads. Efforts to control cane toad numbers have had little success, and we urgently need methods to mitigate toad impacts on native predators. Unlike native arid-adapted frogs, cane toads require regular access to water to survive the long-dry periods that occur in semi-arid regions in Australia. Consequently, the colonization of these regions has been facilitated by commercial livestock production that provided artificial water sources (bore-fed dams) as an essential resource subsidy in a naturally unsuitable ecosystem. A recent study demonstrated that landholders could eradicate cane toads by replacing their bore-fed dams with above-ground tanks made of plastic or steel that gravity feed into raised cattle troughs. These tanks do not allow toads to access water. We evaluated the effectiveness of this toad control strategy by surveying abundances of large varanid predators and lizard communities in regions where toads can access water in bore-fed dams, with regions where dams have been replaced by above-ground tanks.
We found significantly lower abundances of varanid lizards in areas where cane toads have access to water stored in bore-fed dams in comparison to areas where water tanks have been installed. In contrast, small and medium-sized lizards, among the preferred prey species of varanids in our study, were found in higher abundances in the vicinity of dams in comparison to the vicinity of tanks. Our results suggest that the invasion of cane toads has caused direct and indirect impacts on native species with large predators being negatively affected while the predators’ prey species profited from their disappearance, leading to a disruption of ecosystem structures. Our study provides evidence that reducing the availability of water through the replacement of bore-fed dams with water tanks can limit the impact of cane toads on species communities and thus provide benefits for ecosystems in Australia’s semi-arid regions.