What makes an animal native?
PROTECTING NATIVE SPECIES is high priority for any conservationist, but not all native species are created equal.
While the term ‘native’ conjures thoughts of Australian species such as kangaroos and koalas, the classification of more recent arrivals, like dingoes, is a tricky subject.
Cane toads are viewed as pesky interlopers, but how long do they have to be here before they’re considered Aussie-grown?
The question has sparked a heated debate at times, with some scientists believing that human introduction irrevocably makes a species alien, whilst others name the arbitrary date of 1788 – with the landing of the First Fleet.
“Determining whether species are native or not is actually a worldwide conundrum,” says Associate Professor Peter Banks from the University of Sydney. “Scientists, governments and legislators have struggled with the question of how long it is before you can consider a ‘new’ species to be native.”
The dingo (Canis lupus dingo) is a case in point. Arriving at least 4000 years ago (having originated in China 18,000 years ago), they’re considered native if you go by the pre-1788 cut-off. However, dingoes are said to have arrived with humans – and no one knows if they were domesticated or wild at the time – which leads some scientists to categorise them as introduced.
When invaders become natives
A recent study, published this month in the journal PLoS One by PhD student Alexandra Carthey from the University of Sydney and her supervisor Peter, suggests that observing how native species interact with introduced species could be a radical new way of determining when an alien species become native.
Alexandra says using more objective criteria, such as how foreign species interact with natives, is a better determinant for deciding native status than the arbitrary criteria used currently.
The main idea is that local prey species, like the bandicoot (Perameles nasuta), will have specific survival adaptations against native predators and have little or no adaptations against alien species. The thinking goes that if the native prey responds to a species, then it must have gained native status.
Alexandra’s study uses the dingo as an example species, because of its debated native status and similarity to pet dogs.
“We wanted to see how a vulnerable species [like] the bandicoot reacts to domestic dogs (Canis lupus familiaris), which are the same species as the dingo,” says Alexandra.
The researchers surveyed people who live near national parks in Sydney and asked them whether they had dogs, domestic cats or other pets, and how bandicoots behaved around them.
“We were hoping to see whether bandicoots recognised and avoided yards with cats and dogs,” says Alexandra.
Are dingoes native?
The results showed that even when the dogs were kept inside at night and had no chance to chase bandicoots away, the native animals tended to avoid yards with dogs.
Bandicoot diggings appeared less frequently and in smaller quantities in yards with dogs than in yards with either resident cats or no pets, Alexandra says.
“They must have somehow recognised that dogs posed a threat to them and avoided those yards.”
This points to dingoes’ integration into the ecosystem, suggesting that even after thousands of years, bandicoots recognise dogs – ergo dingoes – as a threat and will avoid them.
“[However], they are yet to recognise the threat cats pose as predators, as bandicoots haven’t been in contact with cats for as long,” Alexandra says.
“Invasive predators often have catastrophic impacts because [native] prey don’t recognize them as a threat,” says Dr Mike Letnic from the University of New South Wales.
But he agrees that these results are important for borderline species like the dingo. “It shows that bandicoots have coevolved with dingoes to the extent that they can perceive dingoes as a threat,” he says. “This lends support to the idea that dingoes should be regarded as native.”