Cane Toads Threatened by Predatory Meat Ants
Poisonous Bufo Marinus Toads Attacked by Scavenging Tropical Ants
Apr 4, 2009
The discovery was made by Honours student Georgia Ward-Fear and other members of Professor Rick Shine’s Team Bufo at Sydney University School of Biological Sciences' Shine Lab.
Meat ants are found in large numbers around tropical waterholes where the cane toads breed. Although basically scavengers, they are large and aggressive, and have frequently been observed eating small toads.
Native frogs and toads are not in danger from the aggressive ants – which are up to 10 mm long – because they hide during the day when the ants are active.
Cane Toads not Suited to Australian Conditions
Unlike the native species, cane toads breed in the dry season, instead of the wet season, and are active by day instead of at night.
Breeding in the dry seasons means that metamorphs (juvenile toads just metamorphosed from tadpoles) have less water to swim in and have to stay close to the edges of waterholes, surrounded by stretches of drying mud.
As temperatures can reach 30 degrees Celsius most days of the dry season and the humidity is very low, the metamorphs are at risk of desiccation if they wander too far from the water’s edge.
On the drying mud they are at greater risk of attack from the meat ants, which don't hesitate to attack weak young toads.
Cane Toads Shorter and Slower than Native Frogs
Ward-Fear also found by measuring the toads and observing them in comparison to specimens of Litoria, Limnodynastes, and Opisthodon species of similar size and age, that the juvenile toads are smaller and slower.
“On average, the metamorph cane toads were smaller (in both mass and length) than all other species tested except O. ornatus and L. bicolor. Toads also had the smallest tibia length, both in absolute terms and relative to their body size ,” Ward-Fear noted in her paper, ‘Maladaptive traits in invasive species: in Australia, cane toads are more vulnerable to predatory ants than are native frogs’, published online in Functional Ecology on March 31, 2009.
“Toads recorded the slowest speeds and had lower average endurance levels than did any native species except O. ornatus,” she wrote.
She also found that the toads seemed not realise the danger from the ant, and as well as hopping more slowly, often tried to hide by 'freezing'.
Cane Toads’ Behaviour Puts Them at Risk from Meat Ants
The combination of these three behavioural factors – daytime activity, a lack of awareness of the threat from the ants, and smaller, slower hops – puts newly metamorphosed cane toads at risk of becoming prey rather than predator, a risk the native frogs have evolved to avoid.
Cane Toads Caught in Evolutionary Trap
Seeing meat ants eating metamorph toads led Prof Shine’s team to suspect that the toads were not adapted for their habitat – “there might be some kind of mismatch between the invader and its newly invaded range, for example, something about the toads' behaviour that makes them vulnerable to a predator that poses little danger to native frogs,” he said.
This is because the cane toads evolved in vastly different conditions in the Americas, with completely different survival challenges.
“The end result of this mismatch between traits of metamorph cane toads, which evolved in the Americas, and the ecological interaction between metamorph toads and meat ants in tropical Australia, is an 'evolutionary trap'," he said.
“The results are interesting not only because they reveal the cane toad's Achilles' heel – a weakness that could be exploited to help control the spread of the toxic toad – but because the same ‘evolutionary trap’ could be used to snare invasive species elsewhere.”
See Also: Cane Toads Deterred by Cold Feet
See Also: Radical Ways to Control Cane Toads
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