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.

A new Armageddon for amphibians?

Amphibians -- such as frogs, toads, salamanders, newts, and caecilians -- are among the most ancient of all terrestrial vertebrates.  And increasingly, they seem to be among the most imperiled as well.

Biodiversity in retreat...  many frogs are imperiled  (photo by Mike Trenerry)

Biodiversity in retreat...  many frogs are imperiled (photo by Mike Trenerry)

Why?  For one thing, amphibians, more than any other group of terrestrial vertebrates, rely intimately on water.  Their eggs dry out on land, and their larvae (such as tadpoles) are often aquatic.  Across the planet, aquatic ecosystems are being destroyed and degraded -- by pollution, dams, river channelization, introduced predators and competitors, and other maladies -- at a horrific pace.

Beyond this, amphibians seem unusually vulnerable to exotic diseases.  The water that they rely on so intimately is an excellent medium for transmitting pathogens, many of which will quickly die if they dry out. 

Many amphibians need clean water for survival  (photo by William Laurance)

Many amphibians need clean water for survival (photo by William Laurance)

Combine that trait with our hyper-mobile modern society -- where exotic organisms are suddenly being moved across the planet at lightening speed, often by accident -- and you have the makings of environmental Armageddon.

For example, a few decades ago a mysterious chytrid fungus suddenly appeared and swept like a tsunami across Australia, Latin America, and parts of Asia and Europe with deadly effect. 

In total, some 200 species of frogs and salamanders have declined catastrophically or been driven to global extinction by the fungal disease (notably, ALERT director Bill Laurance and colleagues did some of the earliest work on the pathogen's impacts).  

Now, there is a new disease threat.  Exotic viruses have appeared that seem to be targeting a range of amphibian species.  This is frightening, because viruses are usually specific to a particular species

A virus that can attack several species at once could be catastrophic for amphibians.  Normally, a virus dies out when it kills most individuals of its host species, because the host becomes so rare that the virus is no longer transmitted successfully.

But a multi-species virus is different.  One of its host species might be largely wiped out, but the virus can still thrive in a different species.  Because it persists in the environment, even when one of its hosts becomes perilously rare, such a virus can drive a species completely to extinction.

That is exactly what seems to be happening now in Europe.  At least two new types of Ranaviruses are plaguing frogs and salamanders there, causing massive die-offs in several different species of hosts at once. 

The viruses induce hemorrhaging in the frogs, creating open sores and killing their limb tissues.

Alarmingly, even reptiles might be affected; a snake that ate an infected salamander died soon afterward, apparently from the virus. 

Such events suggest that one of the most damaging features of modern humanity might be our proclivity for moving exotic organisms all around the planet.  Species have adapted to ecosystems in which a major new pathogen might come along once every few centuries or millennia.  Now they're arriving at a pace that's blindingly faster than that.

Little wonder that the amphibians -- among the most ancient denizens of the Earth -- are having a hard time surviving the onslaught.

 

Ten ways you can help stop the sixth mass extinction

Anthony Barnosky is a professor at the University of California, Berkeley, and he's one smart dude.  He's just written a brilliant essay entitled "10 ways you can help stop the sixth mass extinction". 

We really can save nature -- if we get moving now.

We really can save nature -- if we get moving now.

As we all know, we are living in an age of biodiversity crisis.  Some believe we could lose up to three-quarters of all species on Earth in the coming century

Others believe the extinctions will be less severe, but even optimistic estimates suggest the age of humans -- the Anthropocene -- could be one of the greatest extinction events in Earth's 4.5-billion year history. 

Barnosky emphasizes that there's still time to avoid the Sixth Mass Extinction, but we need to pull our thumbs out and get moving -- today. 

We briefly summarize his 10 key messages below.  See his original essay for details about each suggestion:

1. Spread the word, to your family, friends, co-workers, and social media circle: the extinction crisis is real.

2. Reduce your carbon footprint.

3. Buy products from companies committed to using sustainably produced palm oil in their products.

4. Eat fish from only healthy fisheries.

5. Eat less meat.

6. Never, ever buy anything made from ivory -- or from any other product derived from threatened species.

7. Enjoy nature.

8. Adopt a species or become a citizen scientist.

9. Vote for and support leaders who recognize the importance of switching from a fossil-fuel energy system to a carbon-neutral one, who see the necessity of growing crops more efficiently, whose economic agenda includes valuing nature, and who promote women's rights to education and healthcare.

10. Don't give up.

Bottom line: We are not doomed to any particular fate, but we will be if we fail to confront the growing extinction crisis. 

A planet that's too hostile to sustain much biodiversity will not be a good place for people to live either.

 

How many species will go extinct?

A longstanding and often heated debate in ecology concerns the number of species on Earth that will eventually disappear forever because their populations are tiny and isolated.  This is a crucial question, because remaining habitats on Earth are being rapidly fragmented.

Two renowned ecologists, Stuart Pimm and Tom Brooks, have stepped into the fray with a short, lively essay on species extinction (Pimm, notably, is a member of ALERT).  It's worth reading if you want to better understand the fate of Earth's biodiversity.

-Bill Laurance

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