Invasive frog threatens ecosystems in South Australia

The tree frog Litoria cyclorhyncha (Image: University of South Australia / Christine Taylor
The tree frog Litoria cyclorhyncha (Image: University of South Australia / Christine Taylor

In southern Australia, an invasive frog species is a major concern for biologists. This tree frog, which is up to eight centimetres in size, continues to spread and eats almost everything that fits into its mouth. In addition, it can withstand heat itself and seems to be superior to many other animal species in its new habitats. Scientists fear that Litoria cyclorhyncha could severely harm South Australia if biodiversity spreads further.

Invasive species are considered to be one of the greatest threats to biodiversity – after humans. Because when animal or plant species spread in areas where they are not originally native, they often have no natural enemies. As a result, they can displace domestic competitors or decimate prey animals to the brink of extinction.

Spotted tree frog conquers South Australia
An example of such an invasive species is now coming from southern Australia. There, biologists observe with concern the advance of the tree frog species Litoria cyclorhyncha. This frog, which is up to eight and a half centimeters long, is brownish on its back with green spots and has striking yellow dots on the inside of its thighs, to which it owes the name “Spotted-thighed Tree Frog” in English. Originally, this frog species only appeared in the far south-west of Australia, but now it has established itself far beyond its old distribution limits.

“This tree frog is very mobile,” explains Gunnar Keppel of the University of South Australia. “He has already managed to hike more than 2000 kilometers and establish a colony in Streaky Bay.” Streaky Bay is a bay on the Eyre Peninsula in South Australia, whose unique nature is protected by several national parks. As the researchers report, there are already more than a thousand of these invasive frogs there. “Its considerable tolerance to salt and heat could cause the frog to expand its area even further and move further east to the Murray-Darling Basin,” Keppel said. This basin, which covers more than a million square kilometers, includes Australia’s largest river system and its most fertile area.

The problem is: “This frog is a real eating machine – it devours almost everything that fits in its mouth,” says Keppel’s colleague Christine Taylor. As part of a study, she and her team examined the stomach contents of 76 of these invasive frogs in three different habitats – an artificial wetland, semi-natural bushland, and urban habitat. This enabled them to determine for the first time how large the food spectrum of Litoria cyclorhyncha is.

On average, each frog studied had at least six semi-digested prey animals in their abdomen, which confirms its greediness. But the diet is also immense: the biologists found prey from 200 different animal species in the digestive tract of the frogs. About 60 percent of them were insects and spiders, but mice, geckos, and young frogs of other species had also devoured the tree frogs. “We’re talking about a relatively large predatory tree frog that could have a devastating impact on the habitats it conquers,” Taylor said. “Because this frog can break or destroy local food webs, feed native birds, reptiles and mammals and displace them.”

If the spread of this invasive frog species is not controlled, it could become a threat to many ecosystems in south-eastern Australia, scientists warn. “It is essential that we protect Australia’s biodiversity. Therefore, preventing the further spread of Litoria cyclorhyncha should be given a high priority in species protection,” says Keppel.

Source: University of South Australia; Professional article: Australian Journal of Zoology, doi: 10.1071 / ZO19042