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Blue-tongue
A true-blue battler

Dingo
Unfairly judged?

Koala control
What to do about the "koala plague" on Kangaroo Island

The Kangaroo industry
Should we eat skippy?

Feral cat
Apex predator in Australia. Confined to urban areas in America.

Tasmanian Devil
The solution to mainland extinctions?

Tasmanian Tiger
A sad tale

Rabbits
Perhaps not so adapted to Australia

Wombat
Keg of muscle


 

 

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Cane Toad Snake

Cane Toad

In the North, Australians are encouraged to kill cane toads and do so by spraying them with dettol, putting them in freezers or hitting them with golf clubs. Thus far, the methods have done with little to reduce the estimated two billion cane toads in Australia.

Even though the attempts at eradication via the golf club or freezer are futile, many Australians persevere anyway because they have been sold a number of myths that propose that cane toads have no natural predators and that they are destroying the ecosystem. Both are false.  At worst, the biggest threat of cane toads is that it looks unsightly to have ugly creatures hoping around in pristine waterways.

In regards to the myth that humans are the toads only enemy, in truth, the toad has so many natural predators that only three in every 10,000 tadpoles grow into adults. These predators include dragonfly nymphs, water beetles, saw-shelled turtles, keelback snakes, wolf spiders, and freshwater crayfish. In addition, water rats and birds have learnt to eat only parts of the toad, such as tongue, internal organs or legs which contain little poison. Chickens can usually eat cane toads without ill effect as can many water birds that migrate back and forth with Asia (where toads have always existed).

As for the myth that the cane toad is pushing native fauna to extinction, in truth, when toads enter a new ecosystem, populations of predators rapidly collapse before they either learn how to eat toads or develop some kind of immunity to the toad's toxins. As predator populations collapse, populations of things eaten by predators, such as frogs, actually increase. As yet, not a single species has gone extinct as a result of the toad. Admittedly, animals like the northern quoll have suffered rapid declines in populations when toads have entered but given time they would probably adapt.

The danger of the myths is that they are being used to justify the CSIRO developing a virus to decimate toad populations much like the CSIRO's myxomatosis virus decimated rabbit populations. If a virus is developed and released, then Australia will really suffer an environmental catastrophe. If the virus causes a rapid crash in toad numbers, predators that had been eating them will have to hunt native fauna instead, before suffering a decline in populations as well. Toads will eventually develop immunity to the virus and recover. They will then re-enter ecosystems where predator numbers are lower than before, and where they will be even less competitors than before. Although the virus will be a short-term decline in toad numbers, in the long-term, there will be a decline in biodiversity and an increase in toad numbers.

Similar problems were seen with the CSIRO's myxomatosis virus. Rabbit numbers crashed and predators started hunting native fauna before declining in numbers as well.  Rabbits eventually developed immunity to the virus, recovered, and repopulated ecosystems with less predators, less competitors and less biodiversity than there had been before.

Despite being a disaster for natural fauna and flora, the release of the myxomatosis virus could at least be justified on short-term economic grounds. By reducing rabbit numbers on farmland, the virus saved farmers billions in lost agricultural output. The release of a cane toad virus can not be justified on economic grounds because the toad is not harming agricultural output.

Reason for optimism

In more ways than one, the keelback snake offers reason to be optimistic that if left to its own devices, the Australian ecosystem will not only reduce toad numbers of its own accord, but may even eliminate them completely. The keelback snake is non-venomous freshwater snake that is immune to the toad's toxins. It has this immunity because its distant ancestor evolved eating toads somewhere in Asia. This begs the question, if a freshwater toad-eating snake was able to migrate to Australia from Asia in the distant past, why wasn't an Asian toad able to do the same?

Perhaps one did, but it went extinct because it was unsuited to Australian conditions. Just because the Australian ecosystem was completely free of toads in 1788 doesn’t mean there were not toads in a previous time. If there were toads, it would be understandable as to why they died out. The synthesis of toxins requires a great deal of energy. If predators develop an ability to either eat around the toxins, or detoxify them, then the synthesis of the toxins puts the toads at a significant disadvantage compared to frogs that may instead devote excess energy to synthesising fat for the kind of tough times that have always occurred in Australia. A strength becomes a weakness.

Wallace Line

The Wallace Line - A stretch of deep water that separates the zoological regions of Asia from those of Australia and Papua New Guinea. In prehistoric times, the Australian continent extended right up to the line. The ancestor of the keelback snake probably crossed the line to enter Australia. Toads might have also crossed the line and entered Australia, but died out.

For toads, their fast breeding is another strength today that may become a weakness in the future. Toads can produce between 7000 to 30,000 eggs each breeding season. This is a very good characteristic for filling environmental voids and rapidly populating ecosystems not adapted to their presence. However, if the ecosystem is adapted, it becomes a weakness. Producing eggs takes a lot of energy. The more eggs that are produced, the more energy that is required. If conditions are tough, this is energy that is not utilised wisely. In addition, the more toads there are in an ecosystem, the more predators can adapt to them, and specifically target them over alternative prey that keeps out of sight.

At present, many Australians are uncomfortable with the idea of letting the ecosystem resolve the toad problem itself. They see themselves as environmental wardens that must correct the mistakes of environmental criminals who released the toad in 1935. Consequently, they take to toads with golf clubs, traps, and sprays. Although these control techniques are generally done for symbolic value and don’t do much harm, the release of a virus would do a lot of harm.

Cane Toads in Oz

 

Environmental Issues

Environmental problems
The cultural basis of defining environmental problems

Indigenous environmentalism
Differences between Indigenous and non-indigenous land management

Sustainability
The dark side of sustainable environmental policies

Native pets
Why no pet wombats?

Bush fire prevention
To go native or exotic?