The accelerating invader: super-speedy cane toads on the frontline

Associate   Rick Shine:
Associate Rick Shine: "The research has implications for how we assess the impact of invasive species."

Studies that only track established populations of invasive species can underestimate the rate at which they can spread into new territory, researchers from the University of Sydney have concluded.

"Animals at the vanguard of an invasion can move twice as far as the animals already in a region," said Associate Professor Rick Shine , from the University’s School of Biological Sciences.

"The research has implications for how we assess the impact of invasive species and the rate at which native animals move into new habitat because of climate change."

The findings are published in Proceedings of the National Academy of Science on 30 July. The School of Biological Science’s Thomas Lindstrom is lead author and Dr Gregory Brown and Professor Shine are contributing authors to the paper.

The researchers radio-tracked cane toads for eight years on a flood plain near Darwin, as they arrived at a new site and colonised it. They discovered very different movement patterns between ’pioneering’ toads at the forefront of an invasion and those at the same site a few years after the invasion.

"Pioneering toads spend a larger proportion of their time covering long distances in a consistent direction, whereas post-invasion toads are much less mobile," said Professor Shine.

"Toads at the invasion front had more than twice the overall yearly displacement of cane toads tracked a few years later at the same site. So, studies that only look at dispersal rates of animals in established populations may underestimate the rate that they can spread into new territory."

Invasive species are spreading rapidly worldwide, often threatening native species in the process. At the same time, native animals are shifting where they live in response to climate change and human-degraded environments.

"Our research suggests that current modelling, by concentrating on established populations, is routinely underestimating the rate at which such populations can move into a new area," Professor Shine said.

"To predict the influence these animals will have on ecosystems, and how quickly they can spread, we need to study what is happening at the invasion front."