When my former honours student, Christine Taylor, first noticed the frogs in the artificial wetlands in her hometown of Streaky Bay on the Eyre Peninsula many questions came to mind. How did it get there? How does it move around? Where is it likely to spread to? What does it eat? What will its likely impacts be? She set out to find out more about the strange visitor as part of her studies and some of the findings were worrying for the biodiversity of south-eastern Australia.
The visitor was the spotted-thighed frog, Litoria cyclorhyncha, which is native to south-west Western Australia and hence had to have crossed the dry Nullabor Plain. She learned that the frog had been transported and released in an artificial pond at Eucla in the 1990s. The species must also somehow gotten across from WA to Streaky Bay more recently – maybe as a hitch-hiker in luggage or a camper van or by being collected by kids (as tadpoles or adults) during a road trip and then released into the Streaky Bay Wetlands. Little was known about the frog’s diet in its home range.
Regardless of how it got there, the species was now doing well in Streaky Bay with more than 1000 adult individuals occurring there. The spotted-thighed frog had also been seen elsewhere in the Eyre Peninsula and even at the Adelaide airport. Luckily, Christine was not able to find any other established populations in the Eyre Peninsula but the sightings illustrated the propensity of the species to move around. This prompted Christine to use species distribution modelling to investigate where the species could get to. She found that considerable areas in southern and south-eastern Australia are climatically suitable and hence potential habitat for the spotted-thighed frog. This highlighted the potential of the species to become a widespread invasive.
Next Christine wanted to know what the frogs at Streaky Bay are eating. The answer was almost every living creature that they encounter and can fit in their mouths, as prey items included over 100 species (likely ‘around 200 species’ in total). While beetles and spiders (arthropods) were the most common dietary items, Christine also found low numbers of conspecific young frogs, geckos and a juvenile house mouse in frog stomachs. This indicated that the frog could potentially have considerable impact on ecosystems where it establishes.
So what does this all mean? Obviously, the spotted-thighed frog is very mobile and can be transported great distances by humans. If not controlled, the species will likely get to Adelaide and the Murray River sooner or later. Christine’s diet analyses suggest that this generalist predator would then start feeding indiscriminately, affecting food webs and potentially outcompeting and eating other, native frog species. Therefore, further spread of this species needs to be prevented to protect native biodiversity and ecosystem processes.
Further Reading:
Biodiversity in Oceania 