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Loss of 'diggers' threaten ecosystem


Digging mammals like this southern brown bandicoot (quenda) are considered 'ecosystem engineers' (Source: Leonie Valentine)

Digger decline The loss of small Australian mammals that dig up soil could be contributing to ecosystem decline, say researchers.

Wildlife biologist Associate Professor Trish Fleming and colleagues from Murdoch University and the University of Western Australia, report their findings in a recent issue of Mammal Review.

From bandicoots, bilbies and boodies to potoroos, echidnas, wombats and woylies, Australia's digging mammals are 'ecosystem engineers'.

"They dig massive amounts of soil," says Fleming. "The quenda (southern brown bandicoot) will turn over about 3.9 tonnes of every year."

She says this activity is called "bioturbation" and plays a key role in soil health.

As the animals dig in search of such things as insects or truffles, they break up the soil and increase water and oxygen penetration, says Fleming. This in turn increases soil moisture and decreases run off and loss of nutrients.

And the digging also helps recycle nutrients by trapping and incorporating leaf litter.

"By incorporating organic matter into soil the animals increase the availability of nutrients for microorganisms and also increase the availability of nutrients for plants," says Fleming.

Removal of leaf litter also has another important function - it reduces bushfire fuel.

"If you have vast numbers of digging mammals present then it's quite likely that your fuel for fire would be much lower," says Fleming.

Digger decline

Unfortunately, says Fleming, Australia's European colonists trapped, poisoned and hunted the animals, sometimes to extinction.

She says around half of digging mammal species are now extinct or under conservation threat, and most have had their ranges restricted.

For example, she says, boodies (also known as bettongs) were once found across 60 per cent of the Australian continent but they were poisoned because they dug up potatoes. They are now extinct from the natural environment on the mainland.

The bilby was once found across 70 odd per cent of Australia but it was hunted for its beautiful soft light grey fur that was used to make bilby coats, says Fleming. Now it's only found across 20 per cent of its former range.

Only the spiky echidna appears to have remained unaffected by European settlement.

In their review of recent field work, Fleming and colleagues make a link between the loss of these animals, soil processes and vegetation health.

She says a loss of soil health due to declining diggers could be leading to reduced seedling recruitment and reduced plant health and vigour.

This in turn could be a contributing factor to the widespread and mysterious death of trees across the Australian continent - such as the Tuart (Eucalyptus gomphocephala) in Western Australia.

"That loss of resilience in plants could be why we're losing the trees across the landscape."

Fleming says the ecological contributions of digging mammals should be considered when planning fire management, and when translocating mammals like bandicoots from new urban developments.

"Those animals are playing really important functions," she says.

"If we recognise they are valuable then we should be making sure that we're putting them into a habitat that needs those [ecological] systems restored."

Tags: ecology, mammals