Hot Topic

Ecological impacts of invasive cane toads

Friday, 20 October 2017  | 

 

Cane toads (Rhinella marina) were brought to Australia in 1935, and released in northeastern Queensland. They have since spread westwards (through Queensland, the Northern Territory, and into Western Australia) and southwards (into NSW). Concern about the toads’ impacts on wildlife spawned predictions that most native species encountering toads would be severely affected, and thus decline in abundance. Recent research is revealing a more complex picture. Toads do indeed cause precipitous population declines (of >80%) in some large-bodied predator species, due to lethal poisoning when predators attempt to eat toads. However, populations of smaller predator species are unaffected; some individuals are fatally poisoned, but most survive (because small toads contain far less toxin than large adult toads) and learn to avoid toads thereafter. Most Australian birds and rodents have inherited a tolerance of toad poison from Asian ancestors, and thus are not affected. Even for heavily impacted predators, populations might eventually recover. Simplistic predictions on the ecological impact of cane toads in Australia have not been supported by field studies – indirect impacts of toads often outweigh direct effects. For example, the abundance of native frogs appears to be unaffected by cane toads, because negative impacts (e.g. frogs being eaten by toads, poisoned by toads, competing with toads) are balanced by positive impacts (e.g. toads reducing abundance of frog-predators). Some native snake species predicted to be vulnerable to toads, have become more common since toad invasion – presumably because of the disappearance of predatory goannas. In summary, the impacts of invaders may be complex, and difficult to predict. Any disruption to one native species is likely to have indirect effects on others. Some native species are winners not losers as the toad invasion rolls across the landscape.

Supporting Research

Title
Aims
Beckmann C. & Shine R. (2009) Are Australia's birds at risk due to the invasive cane toad? Conserv. Biol. 23, 1544–9.
To determine which bird species are potentially at risk of consuming toxic toads and whether the predicted impact is real, or due to a dearth of empirical evidence
Brown G. P., Phillips B. L. & Shine R. (2011a) The ecological impact of invasive cane toads on tropical snakes: field data do not support predictions from laboratory studies. Ecology 92, 422–31.
To evaluate the accuracy of our a priori predictions of the impacts of toads on an assemblage of 12 reptile species in tropical Australia.
Caller G. & Brown C. (2013) Evolutionary responses to invasion: cane toad sympatric fish show enhanced avoidance learning. PLoS ONE 8, e54909.
To determine whether aversion learning is occurring in aquatic ecosystems by comparing cane toad naïve and sympatric populations of crimson spotted rainbow fish
Doody J. S., Green B., Sims R., Rhind D., West P. & Steer D. (2006) Indirect impacts of invasive cane toads (Bufo marinus) on nest predation in pig-nosed turtles (Carettochelys insculpta). Wildl. Res. 33, 349–54.
To quantify and understand the indirect or secondary impacts of the decline in the yellow-spotted monitor lizard (Varanus panoptes) associated with the arrival of cane toads, and the predicted simultaneous impact on pig-nosed turtle nest predation by yellow-spotted monitors
Letnic M., Webb J. K. & Shine R. (2008) Invasive cane toads (Bufo marinus) cause mass mortality of freshwater crocodiles (Crocodylus johnstoni) in tropical Australia. Biol. Conserv. 141, 1773–82.
To quantify the impact of this massive mortality event on the freshwater crocodile population from the Victoria River.
Lettoof D. C., Greenlees M. J., Stockwell M. & Shine R. (2013) Do invasive cane toads affect the parasite burdens of native Australian frogs? Int. J. Parasitol.: Parasite. Wildl. 2, 155–65.
To determine if the cane toad invasion influences rates of parasitism in native frogs
O'Donnell S., Webb J. K. & Shine R. (2010) Conditioned taste aversion enhances the survival of an endangered predator imperiled by a toxic invader. J. Appl. Ecol. 47, 558–65.
To investigate whether conditioned taste aversion (CTA) could be used to mitigate toad impacts by modifying quoll predatorybehaviour and enhance survival
Phillips B. L. & Shine R. (2006) An invasive species induces rapid adaptive change in a native predator: cane toads and black snakes in Australia. Proc. R. Soc. B 273, 1545–50.
To examine the possibility that red-belly blacksnakes display an adaptive response to the presence of cane toads
Pizzatto L. & Shine R. (2011) Ecological impacts of invading species: do parasites of the cane toad imperil Australian frogs? Austral Ecol. 36, 954–63.
To explore the risk posed by Rhabdias pseudosphaerocephala lungworms to native frogs, and to assess the effects of Rhabdias exposure on anuran survival, growth and locomotor performance
Shine R. (2010) The ecological impact of invasive cane toads (Bufo marinus) in Australia. Q. Rev. Biol. 85, 253–91.
To review the ecological impacts of cane toads in Australia
Shine R. (2014) A review of ecological interactions between native frogs and invasive cane toads in Australia. Austral Ecol. 39:1-16.
To review current information on ecological interactions between cane toads and Australian anurans
Shine R. & Doody J. S. (2011) Invasive-species control: understanding conflicts between researchers and the general community. Frontiers Ecol. Environ. 9, 400–6.
To better understand the reasons for disagreements between scientists and community groups about the nature and magnitude of conservation efforts aimed at the invasive cane toad
Ward-Fear G., Brown G. P., Greenlees M. & Shine R. (2009) Maladaptive traits in invasive species: in Australia, cane toads are more vulnerable to predatory ants than are native frogs. Funct. Ecol. 23, 559–68.
To determine how cane toad phenotypes differ from native frogs and then to explore the possibility that any differences might render cane toads more vulnerable to a predator (meat ant) that poses little threat to native anurans