The impact of cane-toads on the trophic cascades of freshwater ecosystems in the Northern Territory

A project undertaken at the Institute of Wildlife Research University of Sydney and supervised by Mike Letnic

The cane toad is one of the world’s most successful invasive species. Since they were introduced to Queensland in 1935 they have invaded much of northern Australia and their range is still expanding. Cane toads contain high concententrations of bufotoxin which is poisonous to most Australian vertebrates, including crocodiles. Freshwater crocodiles (Crocodylus johnstoni) prey upon and can be poisoned by cane toads. Consequently populations of freshwater crocodiles are likely to decline with the arrival of cane toads.

If crocodile populations decline in response to the cane toad invasion, it is likely that there will be major flow-on effects within freshwater ecosystems. Studies in both aquatic and terrestrial environments have shown that the disruption or total cessation of interactions between top-order predators and their prey species can have dramatic effects on the organization and function of ecosystems. These effects include the irruption of prey species and an increase in the abundance of smaller predators owing to the absence of competition or predation by larger carnivores and changes in the composition of plant communities owing to altered-plant-herbivore relationships. In this study I will investigate the direct impact of cane toads on crocodile populations in freshwater rivers of Northern Australia and the indirect effects of cane toads on the structure and function of freshwater ecosytems.

Collaborators

Dr Tim Dempster (Sintef Norway), Professor Rick Shine (University of Sydney), Dr Jonathon Webb (University of Sydney), Dr Robyn Delaney (Parks and Wildlife Service of the Northern Territory).