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Sep 25, 2013 10:08 AM EDT

Loss of Australian Digging Mammals Caused Due to Declining Ecosystem, Study


In a new study, researchers from the Murdoch University have linked the declining population of Australian digging mammals like bilbies, bandicoots, potoroos, echidnas and woylies to the loss of ecosystem, overpopulation and urbanization.

Referred to as 'biotic engineers,' these species play an important role in keeping a landscape healthy, maintaining soil health, functioning of the ecosystem, increasing nutrient yield, water infiltration in soil and dispersing seeds.

"Most Australian soils are nutrient-poor and are greatly dependant on external processes to support environmental health," said Associate Professor Trish Fleming. "Digging mammals play a vital role, creating disturbances in the form of nose pokes, scratchings, shallow and deep digs, long bull-dozing tracts and complex subterranean burrows.

These mammals are also credited with lowering fire tragedies as they carry garbage and trash underground with them.

"These interactions lead to soil turnover, nutrient mixing, better breakdown of organic materials, seed dispersal and improved infiltration of water, which decreases surface runoff and erosion. For example, water infiltration in foraging pits created by echidnas is approximately twice as great as in undisturbed soils, and the breaking up of the hard soils allows seeds to find suitable sites for germination," Fleming said.

Fleming said a southern brown bandicoot can dig up to 3.9 tonnes of soil per year. Bilbies once covered 70 percent of Australia.

While woylies, a small mouse-like marsupial, are associated with 20 and 100 excavations per night. This mammal is believed to have roamed across 60 percent of the country but now its population has been restricted to a few places in Western Australia. The United Nations, which has listed the mammal as critically endangered, said that the species has 'no clear signs of population recovery.'

Potoroo is considered to be Australia's most endangered mammal, less than 50 estimated exist in the wild.

However, over the past 200 years around half of all the native digging mammal species have been declared either extinct or listed under conservation threat. They have experienced sharp reductions in population ever since European arrival.

As a result, now Australia is considered to be the one of the world's worst countries for mammal extinctions.

"Australian ecosystems have been undergoing a massive loss of ecosystem processes, including higher tree mortality rates, episodic die-offs and general decline in the number and vitality of plant species," Flemming said. "Meanwhile, Australia has had a higher record of extinction of mammal species over the last 200 years than any other part of the world."

The scientists also blame early residents for trapping and murdering the animals to defend crops. These species were also highly affected by the existence of species such as pigs, rabbits and cats.

"When feral pigs dig up soil, they destroy large habitats, rather than the neat, discreet foraging of these other mammals," Fleming said. "The diggings of animals like rabbits involve more weeds and changing the dynamics of ecosystems in ways that aren't beneficial.

"Some animals survive quite well being close to human habitation, such as bandicoots, which are reasonably resilient to dogs and cats."

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