Native meat ants to diminish cane toad population
18 February 2010
With cat food as bait, scientists from The University of Sydney's School of Biological Sciences have succeeded in showing that native meat ants can assist in controlling the spread of cane toads.
In March last year Professor Rick Shine and colleagues Georgia Ward-Fear and Greg Brown found encouraging evidence of the deadly effect of native meat ants on young cane toads.
Now they have further proven their thesis by luring ants to cane toads with cat food.
Professor Shine and his colleagues observed ant-toad interactions on the Adelaide River floodplain 60km east of Darwin, Northern Territory, in the Australian wet-dry tropics during last year's dry season.
Ant densities and toad mortalities increased "more than fourfold" with the addition of cat food baits.
"We can look at an interaction that's already happening, meat ants are already killing millions of cane toads," Professor Shine explains. "We're just looking to make it a bit easier for them."
The research, funded by the Australian Research Council and published in the February edition of the Journal of Applied Ecology, reveals that meat ants can be used with low risk of collateral damage to native wildlife. The approach is also logistically feasible, low technology and inexpensive.
Unlike many previous efforts at pest control in Australia, like the cane toad itself, the use of meat ants promises to be "a useful component of a broadly-based ecological approach," says Professor Shine.
"If we understand the vulnerability of the cane toad we can develop a number of combined tactics to combat this deadly invader," he says.
The team observed the effect of native meat ants on cane toad metamorphs (the first stage of the toad's terrestrial development) near bodies of water, and explored the cane toad's vulnerability to the native predator as a potential means of controlling cane toad numbers.
When cat food was introduced as bait, ant numbers grew and cane toad numbers declined more quickly.
"The end result," the study explains, "is that higher ant densities kill more toads, and kill toads of a wider range of body sizes."
The research continues from a study published by the team last year, which revealed an ecological and behavioural 'mismatch' between cane toads and meat ants. While meat ants posed little enduring threat to native frog and toad species, cane toads were found to be poorly-equipped to escape them.
Cane toads are easy targets for meat ants because unlike their native counterparts they do not try to avoid them at great speed. In addition, cane toads are likely to use the ineffective tactic of crypsis, or immobility, instead of more active escape tactics.
The study found 98 per cent of metamorph toads were encountered by meat ants and 84 per cent were attacked within a very brief (two minute) period. Over 50 per cent of attacks were immediately fatal, while 88 per cent of 'escapee' toads died within 24 hours.
It is hoped the technology will form part of a multi-pronged attack on cane toads.
"No single control will be a silver bullet to eradicate the cane toad from the Australian landscape," says Professor Shine.
However, "if we understand the biology of cane toads and their interactions with Australian fauna we'll be in a much better position to control them."
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