Native status is a big deal. It affects where conservation dollars are spent, and our inherent reaction to a species. Most people believe that native equals good and alien equals bad, but in some cases, the distinction between a native and an alien species isn’t so clear-cut.
Dingoes, for example, arrived on the Australian mainland some 4-5000 years ago - they were here when Europeans arrived – yet we know that they were introduced by people (albeit a long time ago). How can we decide if they have been here long enough to be considered a native species?
The impacts of new arrivals
When they first arrive in a new ecosystem, alien species (if they establish) can have big impacts. For example, dingoes probably sent the Thylacine, the Tasmanian native hen, and the Tasmanian devil extinct on the Australian mainland soon after they arrived. More recent arrivals include cats and foxes which are thought to have severely affected populations of many native mammals - such as woylies and numbats - as they spread across the country.
Such impacts often happen because a native species fails to recognise a new enemy, and to defend itself effectively. This occurs when introductions mismatch competitors, plants and herbivores, or in this case, native prey and an alien predator, as likely happened when dingoes first arrived in Australia.
But is this still occurring?
Just ask the locals
Given enough time, local species that don’t go extinct will “learn their lesson” and begin to recognise and respond to their new predator. This happens through learning, adaptation, or both. Eventually, local prey should treat the new predator in much the same way as any native predator.
This process has been repeated throughout history, as ecological communities exchanged members through natural means or human trade. Many species considered native in their communities today were in fact simply introduced to those communities a very long time ago.
As an island nation with a very recent history of multiple invasions of alien species, Australia has a distinctive perspective on this. In other countries and cultures, the lines aren’t so clear cut.
How can we tell if enough time has passed for this process to happen, and an alien to become a native species? We can ask the local species that interact with it.
A ready-made study system
We decided to test this idea out on a ready-made experimental system in the northern suburbs of Sydney. In this area, bandicoots (a medium-sized native mammal) love to come out of the bush at night to dig up residential gardens in search of food. The diggings they leave behind in lawns are well known to residents, who are often less-than-pleased with the mess left behind by a foraging bandicoot.
Many residents also own pet dogs or cats, and we thought that bandicoots might choose to avoid these yards when deciding where to forage. If so, it would imply that they recognise the danger posed by these pets.
To find out, we asked people who lived next door to Kuringai Chase and Sydney Harbour national parks to tell us about the quantity and frequency of bandicoot diggings that typically appear in their yards.
Dingoes are old news to bandicoots
We found that bandicoots avoided back yards with resident pet dogs. They showed no such aversion to yards with cats, and dug happily in the lawns of backyards without pets.
So it seems that bandicoots do avoid dogs when looking for food. As domestic dogs are very closely related to dingoes, this suggests that thousands of years experience with dingoes has enabled the bandicoots to recognise the risk of dogs, but not cats, which have only been killing bandicoots for about 150 years.
In short, then, the predation risk of dingoes is old news to a bandicoot.
What does this mean for dingoes?
Before making any important decisions we need to “ask” many more local species about their response to dingoes. Importantly though, simple recognition of a predator is not enough – prey also need to effectively defend themselves.
While it has been suggested that dingoes suppress foxes and cats with a net benefit for native small mammal biodiversity, we believe that the finer scale behavioural interactions between predator and prey are a critical part of this equation.
If most native mammals remain naive towards cats and foxes, but defend themselves against dingoes, it would suggest that dingoes do have an important role to play in Australian ecosystems.