European settlement of Australia, and the exotic predators and herbivores they brought with them, caused rapid widespread biodiversity loss. As a result, for the past 200 years Australia has had the highest mammal extinction rate in the world.
Some extinct species were deliberately persecuted, such as the Tasmanian Tiger, Thylacinus cynocephalus, and some were neglected, such as the recently extinct Bramble Cay Mosaic-tailed Rat, Melomys rubicola.
Others, such as Gilbert’s Potoroo, Potorous gilbertii, appear to have simply been in the wrong place at the wrong time. Not yet extinct, but considered the most endangered marsupial in the world, it lost 90% of its natural habitat to a bushfire in late 2015.
When a species is lost from a community, the processes and functions it performed are also lost. All species contribute to the maintenance of their community ecology, but few contribute more than fossorial (digging) species such as bettongs, potoroos and bandicoots.
Part of the cycle
Bettongs are particularly important because most species mainly eat hypogeal fungi (truffles) and spread fungal spores wherever they dig.
As all Eucalyptus plants form a symbiotic relationship with hypogeal fungus during at least part of their life, spreading spores is one of the most important ecosystem services a mammal can perform.
Bettongs also facilitate seedling germination and establishment, soil aeration, incorporate organic matter and improvement moisture infiltration.
Before European settlement, at least five species of bettongs lived on mainland Australia, now (excluding the Rufous Bettong, Aepyprymnus rufescens, a similar beast but not of the genus Bettongia) only Bettongia tropica remains, and it’s listed as endangered.
The almost total loss of these ecosystem engineers from mainland Australia has far-reaching implications that may ultimately lead to vegetation succession, the gradual replacement of one plant community by another. In this case, it will be an impoverished one.
Last year, I published a description of the Desert Bettong (Bettongia anhydra) in the Journal of Mammalogy based on the skull and jaws of an animal that was collected alive near the southwestern corner of the Northern Territory in 1933.
Until now, it has been considered synonymous with its morphologically similar cousin the Burrowing Bettong, Bettongia lesueur. Sadly, the newly-identified Desert Bettong has never been encountered alive since. How many other native mammals have been lost without being recognised or have their remains resting in museum cabinets just waiting for the right person to look at them?
Recent breakthroughs in DNA research have shown that what were once considered wide-ranging species are in many cases species complexes. For example, molecular research on the Dusky Antechinus, Antechinus swainsonii, has revealed a complex of five species.
The good and the bad news
The good news is Australia’s biodiversity is richer than we thought. But the bad news is we’re still losing species at an alarming rate. So what can we do to reduce further loss of our unique mammals beyond protecting pristine areas?
Before attempting a restoration project, we really need to know what it is we want to restore. Many native mammals became locally extinct before historical records were compiled. As a result, Holocene (<10,000 year old) fossils provide better evidence of species distribution and habitat preferences than historical records.
Unfortunately, conservation and natural resource managers rarely consult the fossil record. If they did, they’d see that the modern distributions of many species poorly reflect their fossil distributions.
For example the Broad-toothed rat, Mastacomys fuscus, presently lives in alpine regions, but the fossil record shows that less than 1,000 years ago, it lived near sea level on the Fleurieu Peninsula and the Coorong.
The Mulligans Flat restoration project, in north-eastern ACT, is a great example where Holocene fossils were used to make evidence-based conservation decisions.
The research team used fossil and other evidence to identify species that once lived in their study area. Then, they prioritised the order of species reintroduction based on the range of ecological services each species performed.
Releasing Eastern or Tasmanian Bettongs, Bettongia gaimardi, was their first priority. Their reintroduction appears to be improving soil quality profoundly. I believe the practices used at Mulligans Flat should be applied to all future restoration projects.
The Eastern Bettong is considered secure on Tasmania and the Northern Bettong, Bettongia tropica, still persists naturally on mainland Australia.
All other surviving bettongs live on small islands. This affords protection from predators but limits population size, genetic diversity and reintroduction potential.
If we can’t restore original faunas, I think we have to seriously consider building novel, self-sustaining communities even if they lack present or past analogues. They may even need to include exotic species. Though it sounds extreme, it may be the only way to achieve lasting protection against extinction for what remains of Australia’s unique fauna.