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Overview
Cane Toad Wars chronicles the work of intrepid scientist Rick Shine, who has been documenting the toad’s ecological impact in Australia and seeking to buffer it. Despite predictions of devastation in the wake of advancing toad hordes, the author’s research reveals a more complex and nuanced story. A firsthand account of a perplexing ecological problem and an important exploration of how we measure evolutionary change and ecological resilience, this book makes an effective case for the value of long-term natural history research in informing conservation practice.
Product Details
| ISBN-13: | 9780520967984 |
|---|---|
| Publisher: | University of California Press |
| Publication date: | 03/20/2018 |
| Series: | Organisms and Environments , #15 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 288 |
| File size: | 6 MB |
About the Author
Read an Excerpt
CHAPTER 1
An Ecological Catastrophe
A careful observation of Nature will disclose pleasantries of superb irony. She has for instance placed toads close to flowers.
HONORÉ DE BALZAC,Massimilla Doni, 1837
This book tells a story of warfare, at several levels and among several combatants. It's a tale of an invasive amphibian that has devastated native wildlife in Australia; of how the ecosystem fought back to get the invader under control; of battles between scientists who championed the the toad's introduction and those who opposed it; of claims and counterclaims regarding toad impact and management, fought out in the public arena by scientists and community toad-busting groups; and of how my research team developed a new arsenal of weapons to control the Cane Toad. Ironically, we stole most of those weapons from the toads themselves, by eavesdropping on tricks they use to kill their competitors — the fiercest battles involve Toad against Toad.
But I was blissfully unaware of all those complexities when I became embroiled in the War of the Toad. All I knew was that the toad invasion was rolling westward across tropical Australia and would soon arrive at my doorstep; that the arrival of Cane Toads spelled doom for many native animals; and that vast energy and effort from other scientists, as well as from the general community, had failed to slow the toad's progress.
At its worst, a biological invasion is a nightmare. Suddenly confronted by a new type of enemy, even abundant and widespread species may be faced with ecological Armageddon. We see it most clearly with emerging diseases: plagues like the Black Death wiped out one-third of Europe's human population in the fourteenth century; the Chytrid Fungus is obliterating frogs on every continent; and Chestnut Blight Fungus kills even century-old trees. But larger invaders wreak havoc as well. All around the world, the arrival of rats, cats, and people has eradicated unique wildlife. And in Australia, Cane Toads are writing a new chapter in the dismal history of invader devastation.
Isolated from the other continents for millions of years, Australia evolved its own unique fauna. Instead of deer, squirrels, and beavers, we have Red Kangaroos, Koalas, and Platypuses. Instead of drab little songbirds, my front garden in Sydney is home to raucous Sulphur-crested Cockatoos and ornate Rainbow Lorikeets. And instead of garter snakes, rattlesnakes, and adders, I find Red- bellied Black Snakes and Diamond Pythons. (Species' common names are capitalized throughout, whereas common names that refer to groups of species are uncapitalized. All common names of species are listed in alphabetical order in the appendix, alongside their scientific names.) Geographically inaccessible to the animal groups that dominate other continents, Australia has been a cradle for the development of life-forms and ecological dynamics found nowhere else. But that uniqueness has a downside: a vulnerability to invasion. If introduced to Australia, animals and plants from North America, South America, Europe, and Asia can blindside the native species. Species within an ecosystem evolve side by side, which gives them an opportunity to adapt to each other. Predators, prey, and parasites are locked in evolutionary "arms races," each finely tuned to the threats and opportunities posed by the other species.
Invasion breaks those rules. It exposes an entire fauna and flora to a type of organism they have never encountered before. That newcomer can be devastating. So it was with the Cane Toad. It has no close relatives in Australia — members of its lineage (the "true toads": Family Bufonidae, or "bufonids") never reached our continent, though they occur widely on others. And early in their long evolutionary history, the bufonids developed a powerful defense against predators: a potent poison. In the toads' native range, local predators adapted to that chemical via a gradual arms race; they can eat toads without dying. But Australian predators never had that evolutionary opportunity. Even a drop of toad poison is deadly.
As a result, native wildlife is being massacred across Australia. That slaughter began when toads arrived in 1935, and the wave of death is moving faster and faster. Nobody paid attention to the carnage in the first few decades after toads began to spread. Most of the Cane Toad's victims were animals that people disliked (like crocodiles and snakes) or that were a threat to poultry (like large lizards and predatory marsupials). But as environmental awareness grew, and unreasoning hatred of reptiles receded, the terrible truth became clear. In 1975, two biologists at the Queensland Museum published a landmark paper drawing attention to the catastrophic mortality of wildlife caused by the Cane Toad invasion.
It took another three decades before detailed studies were conducted to measure the impact of Cane Toads on wildlife. In site after site across tropical Australia, that research showed that within a few months of Cane Toads arriving in an area, more than 90 percent of the "top predators" were dead. The rotting bodies of Freshwater Crocodiles floated downstream. The corpses of giant varanid lizards ("goannas") dotted the floodplain. Species once common, like the Northern Quoll and the massive Bluetongue Lizard, could no longer be found. These are apex predators — critically important for ecosystem function. They control the numbers of smaller species. Take the top predators away and everything changes. In North America, the near eradication of Wolves and Mountain Lions was followed by an explosion in deer abundance and massive overbrowsing of vegetation. The ecosystem changed. It is changing in tropical Australia as well, as Cane Toads mow down the top predators, and we still don't know where it will all end.
How could this happen? How could an animal that evolved in the Amazon — in a warm, wet world — survive and flourish in the harsh Australian outback? From the perspective of its victims, the Cane Toad was the wrong animal in the wrong place at the wrong time.
To explain the toad's success in Australia, we have to go back to its origins in South America. Cane Toads belong to a pioneering group of amphibians — the bufonids — whose transcontinental invasions make Genghis Khan and his Mongol hordes look like introverted homebodies. Toads thrive in most parts of the world because they are ecological generalists. Thirty-five million years ago, ancestral toads embarked on a circum global journey that would end with world domination. Beginning in South America, these humble, squat little creatures achieved an extraordinary diaspora from Acapulco to Zanzibar.
Not all toads are created equal. Some kinds of toads were better than others at marching across continents and floating on driftwood over oceans. Across millions of years and the entire circumference of the globe, the pioneering toads were those with land-dwelling adults (so they could move from one pond to the next), large poison glands (that kept them safe from predators), fat-storage organs (to survive the bad times, when food was scarce), opportunistic breeding (so they could make babies whenever the chance arose), and a large number of offspring in every clutch (so at least a few babies survived). Once they had evolved that set of characteristics, the South American toads took off to North America, Africa, Europe, and Asia.
So, toads were Great Invaders long before a supersized species evolved 20 million years ago in the Amazon Basin, at the margins of the great rainforests. This giant species — the Cane Toad — was destined to become the ultimate world traveler, eclipsing all of its relatives. Nonetheless, it was just building on a long family tradition, established eons before pre-humans evolved in the African savannas 2 million years ago. And the final missing element in the Bufonidae's global conquest fell into place in 1935, when thirty-three-year-old Reg Mungomery collected 101 Cane Toads in Hawaii and brought them back to Australia. Reg brought toads to the only toad-habitable continent that they hadn't reached on their own.
The sugarcane growers who invited the Cane Toad to Australia wanted an animal that would eat as many insect pests as possible. And they succeeded: given the opportunity, Cane Toads eat hundreds of prey items in a single night. When you pick up a well-fed Cane Toad, it crackles in your hand from insect exoskeletons rubbing together in the toad's stomach. The cane farmers didn't realize that they had also chosen an awesome invader. Cane Toads inherited a capacity for long-distance dispersal, powerful toxins, a flexible lifestyle, and a prodigious reproductive output. They are the living embodiment of the characteristics that enabled ancestral bufonids to spread around the planet, primarily because they are among the largest toads. Being bigger gives you longer legs (increasing your mobility), bigger poison glands (increasing your toxicity), an ability to eat large as well as small prey (allowing you to adapt your diet to local conditions), and a capacity to produce vast numbers of eggs (there is a lot of room for eggs inside a female Cane Toad). If you tried to design an Amphibian Invasion Machine, you couldn't do much better.
Five characteristics of Cane Toads have made them extraordinarily good invaders. First, they are tough. Their large body size buffers them against unfavorable conditions. The bigger you are, the longer it takes to dry out or overheat; and you can travel a long way to find shelter. And toads tolerate extremes of temperature, salinity, and acidity that would kill a lesser amphibian.
Second, they are flexible. Not in physique, but in behavior and ecology. Toads exploit every opportunity. If a wildfire burns through the forest, Cane Toads flock to the newly formed open clearings to feed. If someone leaves a tap dripping, the toads find it. Take a harsh, inhospitable landscape, but throw in a moist patch with a few bugs — perhaps a pile of poo from a passing cow — and watch the ultimate opportunist hop over to top up his water level, and have dinner as well. As a result of that flexibility, Cane Toads thrive in disturbed areas around towns and cities. The human race has helped the Cane Toad become one of the most abundant amphibians on Earth.
The Cane Toad's flexibility extends to its diet: a toad will eat just about anything it can fit into its mouth. Beetles, bugs, cockroaches, and ants are the staple fare, but Cane Toads will tackle even well-defended creatures like bees, ignoring the powerful sting. After bringing Cane Toads to Hawaii in 1934, Cyril Pemberton wrote that "a toad will, without hesitation, gulp down a bee ... and apparently suffer no discomfort. After swallowing such a fiery creature as a carpenter bee, Bufo was observed to execute a few abdominal motions suggestive of the Hawaiian 'hula dance.'" Insects dominate the menu for most kinds of frogs, so toads resemble other amphibians in this respect. But frogs won't seize an item unless it moves, whereas toads take nonmoving things also — even bizarre "prey" like lighted cigarette butts, human feces, and rotting vegetables. In Hawaiian botanical gardens, toads died after eating the petals falling from strychnine trees.
Nonetheless, Cane Toads aren't simple-minded gluttons. They use sophisticated tricks to get that evening meal. For example, suburban toads soon learn the location of productive foraging spots, like Fido's food bowl. Beneath bug- attracting streetlights, toads space themselves out so that each has enough room around it from which to pick up a fluttering bug. Even in natural areas without artificial lights, Cane Toads in Australia use a similar tactic, an evolutionary precursor to their use of neon lights. The smooth white trunks of gum trees reflect the moonlight, attracting bugs. Cane Toads gather around such a tree, unmoving, staring intently at the gleaming trunk. It looks like a solemn Druid ceremony, the religious observance of a tree-worshipping toad clan.
The third factor that has made the Cane Toad such a devastatingly successful invader is its mobility. No other amphibian on the planet has dispersed as far and as fast as the Cane Toad in Australia. Radio-tracked Cane Toads sometimes move more than 2 kilometers (1.2 miles) in a single night. Most amphibians don't move that far in their lifetimes.
Fourth on my list of Toad Tactics is poison: potent toxins that spell death for almost any predator foolish enough to launch an attack. The eggs are full of poison, as are the young tadpoles. And as soon as they transform into miniature toads, the juveniles grow parotoid (shoulder) glands to manufacture their own deadly arsenal. And they are flexible in how much they invest: a tadpole that has been stressed transforms into a young toad with bigger-than-average parotoid glands. It's worth investing in weapons if you live in dangerous times.
Lastly, the Cane Toad's fifth key to success is its incredible reproductive rate. A well-fed female toad can produce two clutches a year, each containing up to 40,000 eggs. As a result, a few pioneer toads can rapidly populate the area with thousands of progeny.
In short, millions of years of evolution at the margins of the South American rainforest created a supersized, toxic, reproductively prolific, mobile, behaviorally flexible amphibian. A creature that could survive the tough times and exploit the opportunities that arose when humans cleared the land to build farms and cities. The Cane Toad had already colonized a huge area of South and Central America, but it needed help from humans to take up that challenge in far-flung lands. By giving it that help, we doomed millions of Australian native animals to an agonizing death.
The massacre of native wildlife by invasive toads isn't just an intellectual issue. Death By Toad is quick, but it isn't pretty. And so, as soon as people understood what was going on, the wave of toads spreading across Australia was accompanied by a wave of revulsion. If you enjoy wildlife around your home, and recognize the local lizards individually, it's heart-rending to find those animals lying dead in your backyard.
So, Australians set out to stop the toad invasion. Somehow, anyhow. They killed toads whenever they saw them. They designed and deployed traps. They formed community groups to eradicate toads. They organized toad-busting days. They funded scientists to find new ways to eradicate the hated amphibians. Nothing worked. The toads kept coming. Even though people went out every night to destroy the feral amphibians, toads soon outnumbered native frogs. In their frustration, Australians developed a passionate hatred of Cane Toads.
With little reliable information about the Cane Toad or its impacts, myths began to spread: Cane Toads are aggressive, attacking people on sight. Toads grow big enough to swallow your pet dog, and perhaps even your baby. The post- toad-invasion world will be a wasteland full of the corpses of rotting Koalas and Red Kangaroos. If your car won't start in the morning, it's because a Cane Toad has crawled up into the exhaust pipe. Toads poison the drinking water. Your school-age children will abandon their studies to smoke dried toad skins.
As the wave of toads spread across tropical Australia, communities at the invasion front took up the fight. The "toad-busters" were zealous and saw the battle as too important to ignore. But within a few years of toads arriving, the futility of killing them was apparent. The amphibian tsunami kept coming.
And that's where my own involvement with the Cane Toad began. I was faced with a unique opportunity, as the alien amphibians marched toward the site where I had been researching reptiles for twenty years. I could study the enemy on a battlefield that I already knew very well. It was a chance to find out what was really going on during a biological invasion.
I was naive when I began my research on Cane Toads. In truth, I didn't know what I was getting into. I saw Cane Toads as an ecological issue, not a political one. Being a scientist, I saw my role as finding out what toads were doing and how we could stop them from doing it. I didn't realize that Cane Toads were also important to other groups — including community-based "environmental" organizations and politicians at every level, from the local to the federal tier. Or how much passion could be aroused when the conversation turned to Cane Toad control.
Why have Cane Toads become such an iconic animal in Australia? No other amphibian, anywhere in the world, has such a high public profile. Surveys of the Australian public rank Cane Toads as a greater threat to native biodiversity than any other invasive species (including animals like Rabbits and Foxes, which have had far worse ecological impacts). And why do nine out of ten Australians rank Cane Toads as among the worst feral pests? The fundamental answer is simple: Australians love to hate Cane Toads.
(Continues…)
Excerpted from "Cane Toad Wars"
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Table of Contents
Foreword by Harry W. Greene viiPreface xi
1 • An Ecological Catastrophe 1
2 • How the Cane Toad Came to Australia 13
3 • Arrival of Cane Toads at Fogg Dam 36
4 • How Cane Toads Have Adapted and Dispersed 55
5 • The Impact of Cane Toads on Australian Wildlife 79
6 • How the Ecosystem Has Fought Back 108
7 • Citizens Take On the Toad 130
8 • The Quest for a Way to Control the Toad 155
9 • A New Toolkit for Fighting the Toad 178
10 • Toad Control Moves from the Lab to the Field 203
11 • What We’ve Learned 228
Acknowledgments 245
Appendix 247
Bibliography and Suggested Reading 251