The cane toad, Rhinella marina, is one of Australia’s most threatening invasive species, so much so that it was listed on the country’s Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). It has been identified as being a threat to the survival, abundance or evolutionary development of native species or ecological communities, according to the act.
Not only is this invasive species toxic to many animals, but they are a prolific bunch of amphibians, too. Introduced from Hawaii in 1935 to control cane beetles, the cane toads bred immediately in captivity. In August of 1935, 102 cane toads were released in several areas in Northern Queensland. They did so well that today, there are over 200 million of the nasty critters, spreading disease and altering the local biodiversity wherever they move.
In arid Australia, many farmers and ranchers construct small dams to hold water for livestock. UNSW Associate Professor Mike Letnic, the lead author of the study says these man-made dams are actually “invasive hubs” for the invasive species, in this case, the cane toad. In other words, the dams provide a refuge for the toads during Australia’s hot, dry summers. The toads, in turn, use the dams as “stepping-stone habitats.” moving on to new territory when the rainy season starts.
Reasoning that if the dams were used as an “environmental trap” by erecting a toad-proof fence around them, theoretically, they would achieve targeted control of the cane toads, as they would congregate at the fences and die, effectively suppressing the populations. To prove the assumption, three dams had fences constructed around the periphery in the Victoria River area while other dams were left unfenced as controls. The study lasted a year.
Around the fenced dams, the toads were still attracted to the water, but because they could not go over or under the fencing, they piled up, dying en masse. Their numbers remained suppressed for an additional year. However, at the dams used as controls, there were 10 to 100 times more toads. “By excluding toads from dams, we converted their invasion refuges into ecological traps and thwarted their spread,” said Letnic.
The researchers say either fencing can be erected around man-made dams or water can be supplied in tanks to help control the spread of this invasive species. “If conducted strategically, excluding toads from man-made water sources could effectively control their populations across large areas of Australia and relieve the impacts that cane toads are having on native predators and dung beetles,” says Associate Professor Letnic.
This study was published in the Journal of Applied Ecology, Feb. 3, 2015. The title of the article is: “Restricting access to invasion hubs enables sustained control of an invasive vertebrate.”
