Could disease be driving extinctions of Australian mammals?

Across the vast savannas of northern Australia, mammal populations are collapsing.  Areas that once sustained healthy populations of native mammals are now ecological deserts, virtually devoid of life.  Three researchers from James Cook University, Sandra Abell, Penny van Oosterzee, and Noel Preece, believe that deadly pathogens might be partly responsible for this ongoing calamity:

Brush-tailed bettong -- a critter we don't want to lose.

Brush-tailed bettong -- a critter we don't want to lose.

One third of all mammal extinctions worldwide have occurred in Australia.  Here, 24 mammal species have been wiped out since European arrival -- and that number is still rising.

Loss of habitat, altered fire regimes, and predation by feral cats are all implicated in the recent mammal declines. The role of disease, however, is an understudied but likely contributing factor.

Disease can be deadly for wildlife.  For instance, facial tumor disease is rapidly killing off populations of the Tasmanian Devil.  Trypanosomiasis, introduced by black rats brought by sailing ships, drove the demise of two native species of rainforest rats on Christmas Island, in the Indian Ocean.

Tasmanian Devil with facial tumors -- not a pleasant way to go.

Tasmanian Devil with facial tumors -- not a pleasant way to go.

Now key populations of the Northern Bettong, an attractive wallaby-like animal endemic to north Queensland, is crashing possibly to extinction.

And just this week, endangered Saiga antelopes in Uzbekistan in Asia were reported to have suddenly collapsed, due to the combined effects of climate change and normally harmless bacteria that have evidently become lethal pathogens to the stressed animals.

Saiga Antelope -- another victim of catastrophic disease?

Saiga Antelope -- another victim of catastrophic disease?

We and colleagues have formed a multi-disciplinary group to tackle these declines.  We call ourselves the North Australia Wildlife Decline Disease Investigators.  Our acronym, NAWDDI, rhymes with "naughty".

Our group combines top wildlife ecologists and experts in wildlife disease, including one of the world’s leading experts in wildlife pathogens, Dr Peter Daszak, Director of the EcoHealth Alliance.

NAWDDI is being guided by hard-won lessons learned from the front line of the battle to save imperiled species.

One example is the Brush-tailed Bettong.  Thought to be secure in southwestern Australia, 90 percent of its population has vanished alarmingly over the last decade.  Valiant attempts to understand and halt its decline are providing valuable new insights for conservationists.

NAWDDI is working on a variety of fronts -- from advising on global policy to developing field protocols to make disease investigation a standard practice in researching declines of wild populations.

Disease must be considered early as a potential cause of the rapid and severe mammal declines in northern Australia.  We know that virulent pathogens have caused widespread extinctions or declines of many species worldwide -- from frogs, to Hawaiian birds, to African ungulates and apes, to North American bats.

Pathogens such as the chytrid fungus have driven at least 200 frog species to extinction.

Pathogens such as the chytrid fungus have driven at least 200 frog species to extinction.

Early detection saves money and time -- and could help us avoid the anguish of having to watch helplessly as charismatic mammals like the Brush-tailed Bettong follow the path of three of its sister species to extinction.


Australia’s ‘Ecological Axis of Evil’ triggers native mammal collapse

Dr Mark Ziembicki of James Cook University in Australia has spent much of the last several years chasing an environmental mystery -- the cause of the dramatic collapse of mammal populations in northern Australia.  Here he gives us an update on an emerging biodiversity crisis:

Across the world, biodiversity is being battered by familiar foes.  Habitat loss, overexploitation, invasive species, and impacts of human development are leading us to what many believe may be the sixth great extinction.

A northern quoll.  This native marsupial 'cat' is suffering greatly in northern Australia.

A northern quoll.  This native marsupial 'cat' is suffering greatly in northern Australia.

In contrast to the environmental pressures on other continents, large parts of Australia have undergone only limited modification, and are sparsely settled and remote.  Many areas have substantial nature reserves.

Yet, nonetheless, Australia has the world’s worst record for contemporary mammal extinctions.  One in ten species have disappeared in the last 200 years -- and of those that persist, over a third are now threatened or near threatened.  What’s more, recent analyses suggest the problem is even worse than previously thought.

Greater recent recognition of Australia’s ‘extinction calamity’ and its spread to the tropical north (see here, here and here) has provoked intense interest and stimulated a series of research and management initiatives to study the declines, their causes, and what can be done to halt them.

A new paper I published with a team of coauthors summarizes the research efforts, and assesses the effectiveness of recent conservation-management interventions.

In our view, the loss of Australia’s mammals has been driven primarily by what has been dubbed Australia’s Ecological Axis of Evil -- an unholy trinity comprising the feral cat, altered fire regimes, and grazing impacts.

Just ask George... a conceptual model for an 'Ecological Axis of Evil'

Just ask George... a conceptual model for an 'Ecological Axis of Evil'

Alone, these threats do not explain the declines but there is now some compelling evidence that, when operating in concert, predation by feral cats exacerbated by frequent, intense fires, reduced ground cover from overgrazing, and, in some areas, the control of dingoes are driving the declines.

So what’s to be done?  The demonstration of interacting factors gives conservation managers some options for reducing their impacts.  There are now some examples of rapid recovery of species following threat management.

Priority actions include intensively managing fires, reducing feral livestock in conservation reserves, establishing exclosures to keep feral predators out, enhancing biosecurity for important islands where rare species still persist, and acquiring grazing lands in important mammal areas for conservation purposes.

Despite some progress, we still have much to learn and even more to do, to stop and reverse the devastating declines. 

Equally worrying is that Australia's federal and state governments are planning an ambitious expansion of agriculture, grazing, roads, energy, and irrigation projects in northern Australia.  These developments are likely to intensify threats that have so far been limited in the region, but that have caused much biodiversity loss in other parts of the world.

This is a dangerous time for Australia's biodiversity.  Without effective planning and management actions, a significant component of northern Australia’s mammal fauna could collapse -- contributing further to the continent’s already-woeful record for mammal extinctions.

Are Australia's mysterious mammal declines spreading?

ALERT has previously reported on the enigmatic and alarming population declines of mammal species across northern Australia.  Now, it appears the declines could be even more widespread than previously suspected.

Bye-bye beautiful bettong?

Bye-bye beautiful bettong?

To date, the declines of smaller and medium-sized mammals, such as quolls, bandicoots, and native rodents, have been mainly documented in monsoonal forests and woodlands across Australia's top end -- such as those at Kakadu National Park, where the declines have been best studied

Additional research -- including interviews of Aboriginal communities in remote areas of northern Australia -- have shown the declines to be widespread in nature, extending over many thousands of kilometers. 

Now, recent research -- which has yet to be published -- suggests that the declines might even extend to northeastern Australia, to the wet tropical region of far north Queensland. 

In this area, live-trapping and camera-trap studies by Sandra Abell-Davis of James Cook University suggest that the tropical bettong, an endangered wallaby-like marsupial, may also be declining sharply.

Abell-Davis studied three areas that had formerly been live-trapped for the bettongs, using identical trapping methods.  She found that, on average, bettong numbers had fallen by more than 80%.

Abell-Davis emphasizes that her findings, while alarming, are still provisional.  She wants to trap more extensively for the bettong and use novel genetic analyses, to see if its numbers have fallen elsewhere in the region.  In fact, she is looking for volunteers to help with this important field work. 

A number of possible drivers have been suggested for northern Australia's mammal declines, with feral cats and altered fire regimes being among the leading suspects

Other suggested possibilities include foreign pathogens, changing rainfall regimes, overgrazing, foxes, and the introduced cane toad, which produces toxins deadly enough to kill virtually anything that eats it.

Whatever is going on, it raises frightening prospects for an Australian continent that has already suffered massive extinctions of its native mammals.

The mystery of Australia's small mammal declines

Across the top end of Australia, from Cape York to the Kimberly Mountains, populations of smaller marsupials and native rodents are collapsing.  What's going on?

Tapping into traditional knowledge to help solve a mystery (photo by Ian Morris)

Tapping into traditional knowledge to help solve a mystery (photo by Ian Morris)

Several studies in recent years have documented the declines.  A few have shown major changes in a single location, such as Kakadu National Park.  Others have compiled scattered information over a much broader area; one innovative study used interviews with Aboriginal communities to piece together evidence (find study here).

The bottom line: many species that used to be common have become vanishingly rare, or have geographic ranges that are collapsing. 

What is causing all this?  No one is sure.  Some suspect it could be severe overgrazing by livestock, especially during droughts.  During such times the vegetation can become badly damaged--as we're seeing at present in many areas

Others think altered fire regimes are the cause.  And yet others suspect predation by feral cats, with a possible role for lethal cane toads for certain predatory mammals.

Whatever the cause, this might be a new biodiversity crisis for the Land Down Under, which has already lost more native mammal species than any other continent.