Cane toads are invasive frogs which threaten the survival of several Australian wildlife species. Scientists and conservation managers have long wondered how to stop the toad’s march across the continent.
This is where our new research comes in. paper just published describes a computer simulation program we have developed to help test cane toad management in the virtual world before strategies are deployed in real life.
The program, structured like a video game, answers questions such as: should toads be caught by hand or trapped? When is the best time in a toad’s life cycle to eradicate it? And how do you best balance effort and cost versus reward?
We hope the program will help scientists and conservation managers get the edge on their poisonous enemy of amphibians.
The Cane Toad Disaster
The cane toad is the ultimate invader, spreading up to 50 kilometers per year and reproducing explosively.
What makes the Cane Toad truly devastating are its weapons of environmental destruction – poison contained in specialized skin glands on its shoulders. This weapon can quickly kill native predators that bite, such as goannas, quolls, snakes and even crocodiles.
The cane toad was brought from Hawaii to Australia in 1935 to control beetles that were damaging sugar cane plantations. While the toads had little impact on the beetles, they thrived in the wild.
There, artificial water bodies for cattle grazing are likely to provide cane toads with safe passage through the arid landscapes and into the Pilbara region – an important refuge for many native species.
Managing Cane Toad Invasions
The Kimberley-Pilbara Corridor is now a crucial battleground between cane toads and conservation managers. But cane toads should also be suppressed in landscapes where the species is already established. And stop the toads from invading Australia offshore islandsor eradicating them once there is also imperative.
Achieving all of this with limited resources is a struggle. We developed virToad to guide scientists and conservation managers in their decisions. virToad is a free and open source program that builds on existing literature and models.
Unlike previous models, virToad simulates the vulnerabilities of cane toads at different stages of their life cycle, and the management strategies that can exploit them. These nuances make virToad’s predictions more useful than previous models.
For example, cane toads need water to breed and rehydrate, so virToad simulates management strategies along freshwater shorelines. These include traps that attract tadpoles, juveniles, and adults, by releasing chemical signals, mimicking toad calls, or attracting insects (a food source) with UV lights.
virToad also simulates a promising new strategy of releasing chemical pheromones to suppress tadpole development.
virToad players can test various management strategies, in any Australian landscape and over time scales ranging from days to years. Each can be done alone or in combination:
By playing around with different strategies and understanding the effort required to implement them, virToad helps conservation managers calculate whether they have the human resources and budget to deploy a plan on the ground.
Read more: What is a waterless barrier and how might it slow down cane toads?
So what worked best?
Our simulations showed that some actions worked better than others in managing cane toad invasions.
In the tropics of the Northern Territory, for example, the manual collection and trapping of juveniles and adults has made the most significant and lasting difference. In fact, a daily effort for a year eradicated the toads. But this strategy is expensive and labor intensive.
The simulation showed that similar results could be obtained when adults and juveniles were hand-caught or trapped once a week, for a year, representing 85% less cost and effort than the daily strategy. .
Unfortunately, the manual collection of toads one day a year – as is the case with community led toad control activities – had no noticeable impact.
Similarly, fencing off water bodies and trapping or chemically removing tadpoles had no lasting impact in the NT tropics simulation. But these strategies may be more effective in other environments. For example, fencing off water bodies can be effective in the arid Kimberley-Pilbara corridor, where other water sources are scarce.
In perhaps our most important finding, small-scale interventions had negligible long-term benefits. Our simulations showed that local toad populations recovered one year after any localized strategy was implemented, regardless of its initial success or effort.
This clearly indicates that a landscape-scale approach is needed to manage cane toad invasions. And virToad is uniquely suited to guide managers in this endeavor.
Of course, our discoveries are only virtual. Although we have taken steps to validate the realism of our model, real data on the impact of various management strategies is needed to confirm our simulated results.
Read more: How Indigenous Expertise Improves Science: The Curious Case of Shy Lizards and Deadly Cane Toads
A new arsenal
We hope that virToad will give scientists and conservation managers a new armory in the fight against cane toads, ensuring that their decisions are both science-based and cost-effective.
Although the design is based on Australian conditions, it can potentially be used in other parts of the world. And as the biodiversity crisis worsens globally, we hope virToad will inspire research into ways to manage other harmful invasive species.
We also plan to further develop virToad into a computer simulation “game” that the general public can play. Through this, we hope to spread the message that effectively controlling cane toads is essential to saving endangered wildlife.
Read more: Pest plants and animals cost Australia around $25bn a year – and it will get worse