This piece is the pre-print of an article first published in The Conversation.
Pest managers’ historic blunders committed a century ago have since spiralled into one of the most well-known environmental catastrophes today — the cane toad’s global invasion. The cane toad stirs environmental havoc wherever it invades, costing world governments millions in ecological damage and management burden.
Over the past decade, cutting-edge strategies have been developed for managing cane toad invasions. But despite this progress, conservation managers still grapple with what, when, and where should they carry out management strategies to make the most of their minimal budget.
In a paper just published in Landscape Ecology, we showcase a state-of-the-art computer program called virToad. Scientists and conservation managers may use virToad to virtually test the efficiency and cost of potential management strategies before carrying them out in the real world.
virToad gives conservation managers an edge over cane toad invaders and may help save remaining threatened wildlife.
The cane toad fiasco
The cane toad is an American frog that attracted the global limelight a century ago. In their admiration of the cane toad’s voracious appetite, pest managers found great promise in using the cane toad to biocontrol pests devastating sugar cane plantations. And so, they set loose cane toads in over a hundred territories globally.
It was a terrible mistake — an ill-informed action unthinkable with today’s scientific standards. The cane toad did not do a good job of clearing out pests. But instead, it became a pest to the environment.
The cane toad is the ultimate invader.
It can spread fast, marching up to 50 km a year. And it can multiply explosively, laying up to 36,000 eggs in one sitting.
But perhaps what makes the cane toad truly devastating is its weapons of environmental destruction — poison packed in specialised skin glands on its shoulders. This weapon can poison and quickly kill a full-grown wildlife predator wanting to take a bite. In Australia alone, the cane toad’s invasion has likely killed millions of native wildlife, such as freshwater crocodiles, goannas, quolls, and snakes. And this wildlife massacre has disrupted entire ecosystems.
Since its release in northern Queensland in the 1930s, the cane toad has invaded almost the entirety of the Australia’s northern regions (~1.4 million square kilometres of land), and it is not done just yet. Its western invasion front is in Fitzroy Crossing in Western Australia’s Kimberley Region and is fastly creeping southwest.
We can expect the cane toad to take a few more years to reach the Kimberley-Pilbara corridor (some 100 km away from the western invasion front). This strip of land provides cane toads with a safe passage through inhospitable arid landscapes and into the Pilbara region — the last refuge for many Australian wildlife impacted by the cane toad’s invasion.
All eyes and resources are focused on stopping the cane toad’s invasion front from alluding through the Kimberley-Pilbara corridor — a critical battleground between the cane toads and conservation managers. But suppressing cane toad numbers in landscapes that have already been invaded is equally essential. More so, preventing or eradicating cane toad invasions on offshore islands is imperative.
Several cutting-edge strategies have been developed for eradicating, suppressing, or stopping cane toad invasions. However, conservation managers still struggle in deciding what management strategy or combination of strategies to use, and where and when to implement them on-the-ground. This is in light of the limited people and budget, as well as the environmental challenges manager’s face in different landscapes. Unfortunately, existing decision support tools are not designed to provide helpful insights on this.
We developed virToad to help scientists and conservation managers in their fight against cane toad invasions. virToad is a state-of-the-art, freely-available, and open-source computer program that can realistically simulate cane toad invasions and management. We designed virToad to be flexible and convenient so users can easily trial management plans in any Australian landscape they want.
virToad is like a computer simulation game where the players’ goal is to develop the most efficient and low-cost management plan against cane toad invasions. Players can trial five types of management strategies individually or in combination:
- Manual hand-capturing of juveniles and adults
- Placing cane toad-proof fences along waterbodies
- Trapping juveniles and adults using light- and advertisement-call baited traps
- Trapping tadpoles using baited funnel traps
- Placing chemical suppressants — a new strategy in the development that uses chemicals to suppress tadpoles from developing into frogs
Players tell virToad where in the landscape to implement the strategies, and at what time scales from days to years.
By playing virToad, scientists and conservation managers can test what management plan is the most effective in either eradicating, suppressing, or stopping cane toad invasions. But more importantly, they can assess whether they have the people and budget to carry out the management plan on the ground.
The silver bullet
There is no silver bullet; the effectiveness of management strategies will vary in different landscapes.
In our simulations in Northern Territory tropics, some strategies worked better than others in managing cane toad invasions. Hand-collecting and trapping juveniles and adults made the most significant and lasting difference. In fact, a daily effort over a year eradicated toads. But this strategy is expensive and labour-intensive.
Remarkably, our simulations showed similar results could be obtained when adults and juveniles were hand-captured or trapped once a week, for a year. That’s 85% less cost and effort than the daily strategy.
Meanwhile, hand-collecting toads for one day a year – as happens with community-led toad-busting activities – had no noticeable impact.
Likewise, fencing waterbodies and trapping or chemically suppressing tadpoles had no lasting impact in the NT tropics simulation. But these strategies may be more effective in other environments. For example, fencing waterbodies may be effective in the arid Kimberley-Pilbara corridor, where other water sources are scarce.
In perhaps our most significant finding, unsustained localised interventions had negligible long-term benefits, regardless of the management strategy or amount of effort. This is because cane toads from neighbouring areas can quickly recolonise.
A landscape-scale approach is needed to manage cane toad invasions. And virToad is uniquely well-suited to guide managers on this undertaking.
Of course, our findings are only virtual. While simulated cane toad population and invasion dynamics were remarkably realistic, real-world data is needed to confirm simulated findings of the effectiveness of management strategies.
A new arsenal
virToad can guide scientists and conservation managers in making science-based and cost-effective management plans, which they can trial virtually before carrying out in the real world. This makes virToad an essential new arsenal, giving scientists and conservation managers an edge in the fight against cane toad invasions. All this is to save the remaining threatened wildlife from the wrath of the cane toad’s invasion.
virToad provides the scientific skeleton of an actual computer simulation game in development that anyone can play. This game aims to make the general public understand and appreciate the importance of the fight against cane toad invasions.
Behind the paper
“Agent-based modelling…” was the first phrase I heard as I woke up from my lull through Manila’s traffic. Who would expect that waking up at the right moment would be so pivotal in the following years of my academic life?
In the front passenger seat of our GrabCab, I overheard my fellow National Geographic explorers, Narod Eco and Din Matias, passionately raging about Manila’s decades-unresolved traffic we found ourselves stuck in circa May 2019.
“… Woah. After all these years, they haven’t fixed this traffic problem in EDSA!” muttered Din, who had just returned from finishing a PhD at the University of Queensland, Australia.
But like classic National Geographic explorers, Din and Narod did not stop at complaining; they brainstormed possible solutions. And I was half-awake absorbing information.
“… they can potentially fix this problem by developing Agent-Based Models! It allows you to simulate vehicles and road users, and find the best solution to ease up the traffic!”
And then I lulled back to sleep, just like a typical Manila commuter.
Some three months later, just a few days into my PhD, my supervisors dropped a real-life problem. Groote Eylandt, an island off the coast of Northern Territory, Australia, is at grave risk of cane toad invasion. Groote Eylandt is the third largest island (excluding Tasmania) in Australia. It is currently cane toad-free, but one or two cane toads have been spotted there in the past decade or so. Groote Eylandt is a refuge for many Australian wildlife threatened by cane toads on the mainland. Thus, keeping the island cane toad free is imperative.
And immediately, I said, “Agent-Based Modelling!”. And my supervisors, albeit having no previous experience making such a model, agreed that agent-based models hold much promise.
Poorly did I know that Agent-Based Modelling, more commonly known in ecology as Individual-Based Modelling, is perhaps the most complex type of model for any biological and ecological system. Developing one requires tremendous ecological knowledge of the system, first-rate creativity and problem-solving skills, and backbreaking perseverance.
Tangent (excerpt from Pili et al. 2022):
“Individual-based modelling (IBM) is a bottom-up computational approach that simulates populations, communities, and/or ecosystems (i.e., macro-level systems) as being comprised of unique, autonomous, and goal-oriented individuals interacting with each other and their environment.
Individual-Based Models can account for spatiotemporally dynamic and fine-scale life-history processes (e.g., interactions with the environment or other organisms) that are impossible to represent in traditional models; and this additional biological nuance is essential when extrapolating local-scale mechanisms and drivers up to populations and landscapes (Buchadas et al. 2017; Cuddington et al. 2013; DeAngelis and Yurek 2016).
Likewise, IBMs have the potential to mechanistically link life-history processes to landscape structures (e.g., habitat fragmentation, landscape connectivity), dynamic environmental conditions (e.g., daily rainfall), and simulated management actions, making it possible to generate forecasts of population dynamics that are responsive to environmental change and to competing management scenarios (DeAngelis and Yurek 2016; McLane et al. 2011).
Together, these attributes make IBMs essential decision support tools for IAS management (Briscoe et al. 2019; Schuwirth et al. 2019).”
Racing to scoop
I was off on a longLong research journey. A rollercoaster ride that, unfortunately, has become a bit political, I lost the fun of it halfway through.
My cane toad IBM, which I called virToad (not my most creative moment), took one-and-a-half years of my PhD program to develop, validate, analyse, and write, and another ten months to publish.
Don’t get me wrong, I enjoyed the challenge of developing virToad.
What took the fun out of it was the race-to-scoop four or more labs in the world who were also making an IBM of the cane toad!
What further exacerbated the horrors of the race was rejections after rejections – three in total.
Wait, there’s more! All my worries were constantly glazed with words of non-affirmation.
(drop me an e-mail for more tea ;) )
I spiralled into medical anxiety with nightly panic attacks that still linger to this day.
All is well
Godsent — I had the privilege of collaborating with THE Dr. Nathan Schumaker. Dr. Nathan is a world expert in developing IBMs and eco-evolutionary models. He developed HexSim – the platform I used to develop virToad. But equally outstanding is his excellent writing and communication skills. He taught me how to communicate complex models, becoming my pseudo-supervisor through the process! His writing style is infectious, and I bring out the set of guiding questions I picked up from him whenever writing papers.
Six months after a complete manuscript overhaul, virToad got published!
Current research and future directions
Using virToad, I am currently running tens of thousands of cane toad invasion and management scenarios, (1) to estimate the probability of establishment of cane toads in Groote Eylandt, and (2) to explore and optimise management strategies to prevent cane toads from establishing on the island.
On the sidelines, I am also developing what I fancy calling a “next-generation quantitative invasion risk assessment framework for species, pathways, and sites.” More on that in the future!
Now that I have a scientific skeleton, I plan to develop virToad into an actual computer simulation game that anyone can play. This game aims to make the general public understand and appreciate the importance of the fight against cane toad invasions. #conservationTechnology #conservationEducation
I am very proud of myself that I pulled off virToad.
But honestly, sometimes, I wish I did not wake up from my slumber through Manila’s traffic.
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