The center of Australia, is a dry, hot, unforgiving landscape, but the edges of the continent are more diverse, with beautiful wooded mountains, lush rainforests and thriving cities. And farms. Lots of farms. About half of Australia is, in fact, covered in land used for grazing livestock (though I should note that some of that grazing does take place in rather harsh areas of the interior as well as nicer bits closer to the coasts). Like many lands around the world, Australia has been incredibly altered by humans.
Altering landscapes often facilitates the spread of non-native species, letting them become invasive pests. The phenomenon is best known among invasive plants, like purple loosestrife, but it seems to hold true for some animals as well, like the cane toad in Australia.
Cane toads, natives of South America, are a big problem in Australia. They first arrived in Queensland in 1935, deliberately brought to the country to help keep beetles in control to improve sugar yields. That plan didn’t pan out, and the toads quickly began to spread across the country. One more amphibian in the landscape might not seem like a huge problem, but cane toads secrete a toxic poison that kills most anything that eats them, even crocodiles. As cane toads have spread, they’ve devastated populations of many native Australian animals.
I first got interested in the cane toad when I blogged about a study in which scientists successfully taught cute critters called quolls to not eat the toads by feeding young quolls young toads (not yet poisonous) laced with a chemical that made the toads taste bad. And then last year, I got a chance to meet the mastermind behind the study, University of Sydney herpetologist Rick Shine, who I profiled in Science magazine. Shine became one of the leading cane toad researchers in Australia after the toads invaded his long-term research site outside Darwin.
In one of his more recent studies, published last November in PLOS ONE, Shine’s group looked at how cow patties might help cane toads survive the hot, dry Australian summer. Members of the group had noticed that toads could often be found on or near cow patties, and they wondered whether the amphibians were indeed more likely to hang out there.
The researchers walked transects set up on a farm located near their research site, recording the locations of both cane toads and cow patties during the dry season. Seventeen of the 26 toads they found were sitting on cow patties, and the remaining nine were fairly close to the piles of poo.
“Toads were found on cowpats more often than expected by chance, and toads that were not on cowpats were closer to them than would be expected by chance,” they write in their paper.
The cow patties, the researchers surmise, provide both a moist environment and food, in the form of dung beetles, which helps the cane toad survive the harsh Australian dry season.
Cane toads are already known to take advantage of water sources, like ponds, set up to supply livestock. Add in the continent’s 300 million cow patties deposited each day — that’s 28.5 million cattle each producing 12 cow patties per 24 hours — and livestock grazing has obviously provided the cane toads with a friendly environment that has helped them spread. Humans have tamed much of Australia to make it more liveable for themselves, but they also made it more liveable for cane toads.
Cane toad image courtesy of flickr user blundershot