Indiscriminate feeding by an alien population of the carnivorous spotted-thighed frog – could severely affect the native biodiversity of southernAustralia according to a new study by the University of South Australia.

The invasive amphibian – Litoria cyclorhyncha – which has hitchhiked acrossthe Nullarbor from Western Australia – has now established a community of1000-plus in Streaky Bay, South Australia, with sightings also confirmed onthe Eyre Peninsula and at the Adelaide airport.

This is the first study of the spotted-thighed frog’s diet in its invadedrange with the findings providing important biological information about theimpact of the alien species on natural ecosystems.

Ecology experts, UniSA’s Associate Professor Gunnar Keppel and ChristineTaylor, say the potential of the spotted-thighed frog spreading to other partsof Australia is very concerning given its destructive eating patterns.

“This frog is an indiscriminate eating machine that will devour just aboutanything it can fit into its mouth,” Taylor says.

“We’re talking about a relatively large, predatory tree frog that, as aspecies is alien to South Australia, and it could have devastating impact oninvaded habitats.

“As it eats away at local species, it’s impacting the natural ecosystem, whichcan displace or destroy local food webs, outcompete native birds, reptiles andmammals for resources, and potentially change natural biodiversity.”

Biodiversity is the theme of this year’s United Nations World Environment Day.

Published in the Australian Journal of Zoology, the study examined the stomachcontents of 76 spotted-thighed frogs across three habitats – an artificialwetland, seminatural bushland and an urban setting.

On average, each frog had at least six prey items in its stomach, with preyestimated to include 200 different species, 60 per cent of which were beetles,spiders and insects. Native geckos, young frogs and mice were also identifiedas prey.

Introduced species can have terrible outcomes for Australia, if not understoodwell. The infamous introduction of the cane toad in the 1930s as a mechanismto control sugar cane beetles, is just one example. The failure of thatinitiative continues to ravage Australia’s ecology, with the cane toad nowlisted as a threatening pest under the Environment Protection and BiodiversityConservation Act.

Assoc Prof Keppel says it is important that people understand how detrimentalintroduced species can be for whole environments. He warns that if the spreadof the spotted-thighed frog is not kept under control they could dominate manyecosystems in south-east Australia, at the expense of the local flora andfauna.

“The spotted-thighed frog is obviously very mobile. Already it’s managed totravel more than 2000 kilometres and set up a colony in Streaky Bay. But itsconsiderable tolerance of salinity and potential ability to withstand hightemperatures could lead to further geographic spread, and if not controlled,it could extend further eastward into the Murray-Darling Basin,” Assoc ProfKeppel says.

“It’s vital that we continue to protect Australia’s biodiversity. Preventingfurther dispersal of the spotted-thighed frog is a high conservation priority.

“The state government should consider managing the invasive population ofspotted-thighed frogs at Streaky Bay. This should include education programsto inform people about what to do if they find a frog, as well as thefeasibility of exterminating the population in South Australia.

“Importantly, if you do see one of these critters in your travels – leave itbe. We don’t want it hitchhiking any further.”

Image: credit UniSA / Christine Taylor

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