Are feral animals in Australia's north really pests that need to be eradicated, or is the nation automatically pulling the trigger on non-native creatures without thinking?

Is the world being denied the last vestiges of wild creatures that may benefit the environment?

These questions occupy the mind of Dr Arian Wallach, an ecologist originally from Israel who has lived in Australia for the past 10 years.

Dr Wallach, who now works at the University of Technology Sydney's Centre for Compassionate Conservation, says Australia and New Zealand stand out on the world stage when it comes to concentrating conservation actions on killing introduced animals.

Megafauna wild in Australia: Water buffaloes

Water buffaloes Camels

Camels Banteng

Banteng Donkeys

Donkeys Sambar deer

Sambar deer Red deer

Red deer Wild cattle

Wild cattle Brumbies

She says in other parts of the world, conservation has developed to be less concerned with whether an animal is native or not, with introduced species even protected in parts of the world, such as wild horses and wild donkeys in the United States.

Looked at like that, it could be argued that Australia has mishandled its approach to introduced species, as the nation looks at the negatives from the creatures without exploring the upsides.

Dr Wallach recently co-authored a study on introduced herbivorous megafauna, defined as animals larger than 100 kilograms, which number in the hundreds of thousands in Australia.

These include large creatures conventionally thought of as pests that need to be controlled, like camels, water buffaloes and horses.

The Northern Territory has the highest number of introduced megafauna anywhere on earth.

Rewilding Australia to replace extinct animals

Australia used to have all sorts of native megafauna, which included animals like giant kangaroos and wallabies, wombat-like creatures called Diprotodon that may have weighed up to three tonnes, giant lizards known as Megalania and many others.

Diprotodons were large wombat-like creatures that existed in Australia but died out during the Pleistocene. ( Wikimedia Commons: Dmitry Bogdanov )

Although there is some debate over how the large creatures died out, the prime suspect is the arrival of humans to the landscape at least 65,000 years ago, who may have hunted the animals to extinction or at least changed the landscape so much the megafauna died out.

Climate change may have also played a part.

"Australia has been empty of [herbiviorous] megafauna for tens of thousands of years — since the extinctions — and now in the Anthropocene, a time that we think of as essentially somewhat lacklustre from a natural perspective, Australia is wild," Dr Wallach says.

"It is extraordinarily wild and filled with wild camels and wild cattle and wild donkeys and deer and water buffalo and all sorts of creatures."

Dr Wallach says megafauna had big impacts and Australia's loss of such creatures thousands of years ago would have left a huge hole in the country's ecology that introduced megafauna might be helping to fill.

"We have had an extraordinary rewilding of Australia after the megafauna collapse of the past," she says.

'Water buffaloes affect environment, but so do fairy-wrens'

Rewilding is where animals are introduced into areas where they have died out, and this activity has a number of what ecologists call trophic cascades, or run-on impacts down the food chain and on the environment.

The supposed benefits of rewilding have seen bison reintroduced to eastern and northern Europe, lynx returned to Spain and wolves to parts of the USA and Germany.

Tasmanian devils are part of a breeding program in NSW. ( Supplied: Save the Tasmanian Devil )

In Australia, Tasmanian devils, which have not lived on mainland Australia for thousands of years, are now in a breeding program at Barrington Tops in NSW.

Even fairy-wrens affect the environment in some ways, says Dr Wallach. ( Supplied: Jessica McLachlan )

They may also control numbers of feral cats and rabbits.

But are introduced megafauna — relatively newcomers to Australia — having beneficial impacts on the landscape?

"All species provide both costs and benefits to other species in their ecosystem. That is what it means to be alive," Dr Wallach says.

"Those water buffalo for example would have ecological influences that benefit some and harm others, which would also be true of a fairy-wren."

She says some of the lost functional roles once played by Pleistocene megafauna are probably being partly replaced by introduced megafauna.

"Introduced megafauna are probably both replacing old and adding new ecological functions," Dr Wallach says.

Water buffalo endangered, IUCN says

The recent paper she co-authored argues there is "substantial and growing evidence that introduced species can perform significant and desirable ecological roles".

"As large herbivores, these introduced species can consume plant matter indigestible to smaller herbivores, which may reduce fire frequency, accelerate nutrient cycling, and shape plant communities," the paper reads.

Australia's introduced megafauna are also in some cases the last wild vestiges for these large creatures anywhere in the world.

Water buffalo are considered endangered by the IUCN. ( Supplied: Ben Kleinig )

The International Union for Conservation of Nature (IUCN), considered the authority on the status of the world's wildlife, lists wild water buffalo as endangered, and banteng — a species of wild cattle found in large numbers in the Top End — also as endangered.

Australia's camels the last wild herds in the world

Wild dromedaries, which Australia has in huge numbers in the deserts, are not thought to have existed in the wild anywhere else for about 3,000 to 5,000 years.

By killing off wild water buffalo and camels, Australians may be denying the world of the last wild herds of these creatures, to study and learn from or for people to experience.

"If we were to eradicate wild camels from Australia, we would be causing their extinction worldwide," Dr Wallach says.

"Not to mention the severe ethical problems with basing conservation on mass killings.

Camels in Australia are said to be the last wild herds of the creatures anywhere on earth. ( ABC Rural: Caddie Brain )

"The idea that you can kill your way to some glorious tomorrow is a form of fundamentalism."

'Heartbreaking to see damage caused by buffaloes'

Acting manager of the cultural heritage and biodiversity management unit at Kakadu National Park, Anthony Mann, takes a different view, and says the large invasive species cause problems when their numbers get out of hand.

He said before efforts to reduce the number of water buffalo began in the 1970s and 1980s, the impacts were severe.

"It is pretty heartbreaking when you see some of these water bodies where the water buffalo have been in and the pigs have been in and they have really trashed the area," Mr Mann said.

"We are talking about massive fields of mud, with barely any vegetation in sight whatsoever."

He said the aim was not to eradicate the animals completely, because traditional owners of the region had different opinions on how they wanted the large animals dealt with.

"In some areas, traditional owners want certain feral animals eradicated, in other areas traditional owners want some feral animals left on country, mainly for hunting and subsistence purposes," he said.

Director of wildlife use and pest animals at the NT's Department of Environment and Natural Resources, Glenn Edwards, says he has problems with thinking that introduced megafauna could replace the ancient megafauna.

"We don't know a lot about the ecology of our extinct megafauna and for example, how many there were and the impacts that they may have had on the environment and what processes if any were in place to regulate their numbers," he says.

"These newer species that have come in are large hard-hoofed animals, which is something new on the Australian continent.

"Coming from the perspective of being a pest animal manager myself, these introduced species like horses, buffaloes, camels, donkeys and so on, if their populations are not managed, then their impacts can be catastrophic on the environment and we have seen that time and time again in the Northern Territory," Mr Edwards says.

Bringing lions, tigers, Komodo dragons to northern Australia?

In the past other people have considered re-introducing animals such as lions, tigers or Komodo dragons to Australia, to replace extinct animals such as marsupial lions or Megalania, a giant lizard that once roamed northern Australia.

Professor Tim Flannery, chief of counsel at the Australian Climate Council, is a fan of introducing Komodo dragons to the Top End, which he considers a native species.

"It evolved here in Australia as far as we can tell and became extinct around 40,000 or 50,000 years ago," he says.

Some people would like to see Komodo dragons in the wild in Australia. ( ABC News: Xavier La Canna )

"When I think about the Komodo dragon I think of it as a native species that survived on an offshore island, much like the Tasmanian devil survived on Tasmania after becoming extinct on the mainland."

He says the Komodo dragons would likely target introduced species like pigs and other invasive animals like goats.

While native animals evolved for millions of years to cope with the threat of large lizards, feral animals did not, and the introduction of Komodo dragons may help target some invasive species, Professor Flannery says.

"We know from [the island of] Komodo that the other species — the introduced species —really have very little awareness and fall prey to Komodos."