The mystery of the Top End’s vanishing wildlife, and the unexpected culprits



A brush-tailed rabbit-rat, one of the small mammals disappearing in northern Australia.
Cara Penton, Author provided

Alyson Stobo-Wilson, Charles Darwin University; Brett Murphy, Charles Darwin University; Graeme Gillespie, University of Melbourne; Jaana Dielenberg, The University of Queensland, and John Woinarski, Charles Darwin University

Only a few decades ago, encountering a bandicoot or quoll around your campsite in the evening was a common and delightful experience across the Top End. Sadly, our campsites are now far less lively.

Northern Australia’s vast uncleared savannas were once considered a crucial safe haven for many species that have suffered severe declines elsewhere. But over the last 30 years, small native mammals (weighing up to five kilograms) have been mysteriously vanishing across the region.




Read more:
Scientists and national park managers are failing northern Australia’s vanishing mammals


The reason why the Top End’s mammals have declined so severely has long been unknown, leaving scientists and conservation managers at a loss as to how to stop and reverse this tragic trend.

The author smiles at an adorable glider in a little blanket she's holding.
Alyson Stobo-Wilson with a savanna glider. Gliders are among the mammals rapidly declining in northern Australia.
Alyson Stobo-Wilson, Author provided

Our major new study helps unravel this longstanding mystery. We found that the collective influence of feral livestock — such as buffaloes, horses, cattle and donkeys — has been largely underestimated. Even at quite low numbers, feral livestock can have a big impact on our high-value conservation areas and the wildlife they support.

The race for solutions

In 2010, Kakadu National Park conducted a pivotal study on Top End mammals. It found that between 1996 and 2009, the number of native mammal species at survey sites had halved, and the number of individual animals dropped by more than two-thirds. Similar trends have since been observed elsewhere across the Top End.

Given the scale and speed of the mammal declines, the need to find effective solutions is increasingly urgent. It has become a key focus of conservation managers and scientists alike.

The list of potential causes includes inappropriate fire regimes, feral cats, cane toads, feral livestock, and invasive weeds.

Many small and medium-sized mammals are in rapid decline in northern Australia.

With limited resources, it’s essential to know which threats to focus on. This is where our study has delivered a major breakthrough.

We looked for patterns of where species have been lost and where they are hanging on. With the help of helicopters to reach many remote areas, we used more than 1,500 “camera traps” (motion-sensor cameras to record mammals) and almost 7,500 animal traps (such as caged traps) to survey 300 sites across the national parks, private conservation reserves and Indigenous lands of the Top End.

A new spotlight on feral livestock

We found most parts of the Top End have very few native mammals left. The isolated areas where mammals are persisting have retained good-quality habitat, with a greater variety of plant species and dense shrubs and grasses.

This habitat provides more shelter and food for native mammals, and has fewer cats and dingoes, which hunt more efficiently in open areas. In contrast, sites with degraded habitat have much less food and shelter available, and native mammals are more exposed to predators.

Six dark coloured horses roam among sparse trees in the Top End.
Feral horses can overgraze and trample over habitat, making it far less suitable for small native mammals.
Jaana Dielenberg, Author provided

Across northern Australia, habitat quality is primarily driven by two factors: bushfires and introduced livestock, either farmed or feral.

Our surveys revealed that areas with more feral livestock have fewer native mammals. This highlights that the role of feral livestock in the Top End’s mammal declines has previously been underestimated.

Even at relatively low densities, feral livestock are detrimental to small mammals. Through overgrazing and trampling, they degrade habitat and reduce the availability of food and shelter for native mammals.




Read more:
The world’s best fire management system is in northern Australia, and it’s led by Indigenous land managers


Frequent, intense fires also play a big role. Australia’s tropical savannas are among the most fire-prone on Earth, but fires that are too frequent, too hot and too extensive remove critical food and shelter.

Yet, even if land managers can manage fires to protect biodiversity, for example by reducing the occurrence of large, intense fires, the presence of feral livestock will continue to impede native mammal recovery.

A wild buffalo walks over grass, in front of trees.
Even small numbers of feral livestock can play a big role in native mammal declines.
Northern Territory Government, Author provided

A new way to manage cats

Cats have helped drive more than 20 Australian mammals to extinction. So it’s not surprising we found fewer native mammals at our sample sites where there were more cats.

However, our results suggest the best way to manage the impact of cats in this region may not be to simply kill cats, which is notoriously difficult across vast, remote landscapes. Instead, it may be more effective to manage habitat better, tipping the balance in favour of native mammals and away from their predators.

A striped, ginger cat with shining eyes looks at the camera at night.
A feral cat at one of the study sites. Cats have helped cause more than 20 native mammal extinctions.
Northern Territory Government, Author provided

The combination of prescribed burning to protect food and shelter resources, and culling feral livestock, might be all that’s needed to support native mammals and reduce the impact of feral cats.

What about dingoes?

Many scientists have suggested dingoes could also be part of the solution to reducing cat impacts — as cats are believed to avoid dingoes. With this in mind, we explored the relationship between the two predators in this study.

A brownish motion detection camera trap strapped to a tree.
One of more than 1,000 motion detection cameras used in this study.
Jaana Dielenberg, Author provided

We found no evidence dingoes influenced the distribution of feral cats. In fact, survey sites with more dingoes had fewer native small mammals, suggesting a negative impact by dingoes.

But, unlike cats, culling dingoes is not an option because they provide other important ecological roles, and are culturally significant for Indigenous (and non-Indigenous) Australians.

Controlling herbivores, not predators

Our study suggests an effective way to halt and reverse Top End mammal losses is to protect and restore habitat. For example, by improving fire management and controlling feral livestock through culling.




Read more:
EcoCheck: Australia’s vast, majestic northern savannas need more care


It is also very important to conserve the environments that still have high-quality habitat and healthy mammal communities, such as the high-rainfall areas along the northern Australian coast. These areas provide refuge for many of our most vulnerable mammal species.

A photo from a camera trap showing a black-footed tree-rat on its hind legs.
The native black-footed tree-rat has had major declines across northern Australia. It’s vulnerable to cats and is now restricted to areas that still have good quality habitat, fewer herbivores and less frequent fire.
Hugh Davies, Author provided

The tropical savannas of northern Australia are the largest remaining tract of tropical savanna on Earth and new species are still being discovered.

While there’s more research to be done, it’s crucial we start managing habitat better, before we lose more of our precious mammal species.


The authors would like to gratefully acknowledge the support from many Indigenous ranger groups, land managers and Traditional Owners. This includes the Warddeken, Bawinanga, Wardaman and Tiwi rangers, the Traditional Owners and land managers of Kakadu, Garig Gunak Barlu, Judbarra/Gregory, Litchfield and Nitmiluk National Parks, Djelk, Warddeken and Wardaman Indigenous Protected Areas, and Fish River Station and was facilitated by the Northern, Tiwi and Anindilyakwa Land Councils.The Conversation

Alyson Stobo-Wilson, Postdoctoral Research Associate, Charles Darwin University; Brett Murphy, Associate Professor / ARC Future Fellow, Charles Darwin University; Graeme Gillespie, Honorary Research Fellow, University of Melbourne; Jaana Dielenberg, Science Communication Manager, The University of Queensland, and John Woinarski, Professor (conservation biology), Charles Darwin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

When introduced species are cute and loveable, culling them is a tricky proposition



Shutterstock

Lily van Eeden, University of Sydney; Chris Dickman, University of Sydney; Jeremy T. Bruskotter, The Ohio State University; Mathew Crowther, University of Sydney, and Thomas Newsome, University of Sydney

Almost one in five Australians think introduced horses and foxes are native to Australia, and others don’t want “cute” or “charismatic” animals culled, even when they damage the environment. So what are the implications of these attitudes as we help nature recover from bushfires?

Public opposition to culling programs is often at odds with scientists and conservationists.

These tensions came to the fore last month when scientists renewed calls for a horse-culling program to protect native species in Kosciusko National Park – a move strongly opposed by some members of the public.

To manage the environment effectively, including after bushfires, we need to understand the diversity of opinion on what constitutes a native animal, and recognise how these attitudes can change.

Governments are responding

In Australia, native species are usually defined as those present before European settlement in 1788. Lethal pest control usually targets species introduced after this time, such as horses, foxes, deer, rabbits, pigs, and cats.

But fire makes native fauna more vulnerable to introduced predators. Fire removes ground layer vegetation that small wildlife would use as protective cover. When this cover is gone, these animals are easier targets for predators like cats and foxes.




Read more:
Fire almost wiped out rare species in the Australian Alps. Feral horses are finishing the job


State governments have started to respond to this impending crisis. In January, the New South Wales government announced its largest ever program to control feral predators, in an effort to protect native fauna after the fires.

The plan includes 1500-2000 hours of aerial and ground shooting of deer, pigs, and goats and distributing up to a million poison baits targeting foxes, cats, and dingoes over 12 months.

Similarly, the Victorian government announced a A$17.5 million program to protect biodiversity the fires affected, including A$7 million for intensified management of threats like introduced animals.

But will the public be on board? Widespread media coverage of the recent fires and their impacts on wildlife, including the loss of more than a billion animals, might garner support for protecting native wildlife from pests.

On the other hand, efforts to manage animals such as cats and horses might be hampered by a lack of public support for culling charismatic animals that many people value or view as belonging in Australia now.

Different folks, different strokes

The distinctions many Australians draw – native animals are “good” and introduced species are “bad” – shape how people view conservation efforts. A survey we conducted in 2017 found people more likely to disapprove of lethal methods for managing species they perceived to be native.

In the same survey, we found nearly one in five Australians considered horses and foxes to be native to Australia.

This suggests either that a) people lack knowledge of Australia’s natural history or b) people disagree with conservationists’ definition of animal “nativeness”.

Calls to manage horses to prevent environmental degradation in Australian national parks are hugely controversial, with many people arguing the horses belong now.
Shutterstock

Many introduced species, such as horses and foxes, have existed in Australia for more than a century and have established populations across much of the country. It’s unlikely they’ll ever be eradicated.

Some people, including scientists, say we should just accept introduced species as part of Australia’s fauna. They argue current management justifies killing based on moral, not scientific judgements and introduced animals may increase biodiversity.




Read more:
Feral cat cull: why the 2 million target is on scientifically shaky ground


But the issue remains extremely divisive. A central tenet of traditional conservation is that humans have a duty to protect native species and ecosystems from the threat introduced species pose. It’s difficult to do this without culling introduced animals.

Animal welfare concerns may also drive opposition to culling, taking the view that all animals, even non-natives, have intrinsic value and the right to live.

What’s more, non-native culling programs can be controversial when the animal is considered “cute” or “charismatic”, or of cultural value. For example, a plan to cull feral horses in the Kosciusko National Park in 2018 was met with public outrage, prompting the NSW government to overturn the decision.

Yet protecting introduced species in national parks goes against the very reason they were created – to conserve native ecosystems and species.

Some animals are more equal than others

When analysing public attitudes towards various species, we must also consider how attitudes shift over time.

In Australia, non-native animals such as domestic camels and donkeys were considered useful for transport and highly valued. But we ultimately turned them loose and relabelled them as pests when we started using cars.

We asked the Australian public whether they viewed dingoes, horses, and foxes as native or non-native in Australia.
van Eeden et al. (2020)

Interestingly, we’ve already accepted some introduced species as native. Humans brought dingoes to Australia at least 3,500 years ago. They’re described as native under Australian biodiversity legislation, and 85% of our 2017 survey participants considered dingoes to be native.

Perhaps its only a matter of time until more recently arrived species like horses and foxes are counted as native. Some scientists argue this shift should be based on how ecosystems and species adapt to these new arrivals. For example, some small Australian mammals show fear of dingoes or dogs, but they haven’t yet learnt to fear cats.

Native species can be pests too

Native species, such as kangaroos and possums, may also be culled if they’re perceived to be overabundant or damaging economic interests like agriculture.




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From feral camels to ‘cocaine hippos’, large animals are rewilding the world


While the plight of bushfire-affected koalas on Kangaroo Island attracted considerable media interest, and the immediate welfare of any animal affected by fires is always a concern, koalas were actually introduced there.

They’ve been managed as a pest on Kangaroo Island for more than 20 years, and it’s unlikely the rescued koalas will be returned to the island. In this case, public concern transcends the distinction between native and introduced.

Public perception is important

We might never all agree on how best to manage native and non-native species. But effective environmental management, including after bushfires, requires understanding the diversity of opinion.

Doing so can help to develop management plans the public supports and allow effective communication about management that is controversial.

In fact, the NSW Office of Environment and Heritage did undertake an extensive public consultation process in developing their horse management plan for Kosciuszko National Park, but it wasn’t used after the “brumby bill” gave horses protection in 2018.




Read more:
Passing the brumby bill is a backward step for environmental protection in Australia


With human lives and many animal lives lost, response to the bushfires is already highly emotive. Failure to consider public attitudes towards managing animals will lead to backlash, wasted money and time, and continuing decline of the native species whose conservation is the goal of these actions.The Conversation

Lily van Eeden, PhD Candidate in Human-Wildlife Conflict, University of Sydney; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Jeremy T. Bruskotter, Professor, School of Environment and Natural Resources, The Ohio State University; Mathew Crowther, Associate professor, University of Sydney, and Thomas Newsome, Lecturer, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Invasive species are Australia’s number-one extinction threat



Barking Owls are one of Australia’s 1,770 threatened or endangered species.
Navin/Flickr, CC BY-SA

Andy Sheppard, CSIRO and Linda Broadhurst, CSIRO

This week many people across the world stopped and stared as extreme headlines announced that one eighth of the world’s species – more than a million – are threatened with extinction.

According to the UN report from the Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services (IPBES) which brought this situation to public attention, this startling number is a consequence of five direct causes: changes in land and sea use; direct exploitation of organisms; climate change; pollution; and invasion of alien species.




Read more:
‘Revolutionary change’ needed to stop unprecedented global extinction crisis


It’s the last, invasive species, that threatens Australian animals and plants more than any other single factor.

Australia’s number one threat

Australia has an estimated 600,000 species of flora and fauna. Of these, about 100 are known to have gone extinct in the last 200 years. Currently, more than 1,770 are listed as threatened or endangered.

While the IPBES report ranks invasive alien species as the fifth most significant cause of global decline, in Australia it is a very different story.

Australia has the highest rate of vertebrate mammal extinction in the world, and invasive species are our number one threat.

Cats and foxes have driven 22 native mammals to extinction across central Australia and a new wave of decline – largely from cats – is taking place across northern Australia. Research has estimated 270 more threatened and endangered vertebrates are being affected by invasive species.

Introduced vertebrates have also driven several bird species on Norfolk Island extinct.

The effects of invasive species are getting worse

Although Australia’s stringent biosecurity measures have dramatically slowed the number of new invasive species arriving, those already here have continued to spread and their cumulative effect is growing.

Recent research highlights that 1,257 of Australia’s threatened and endangered species are directly affected by 207 invasive plants, 57 animals and three pathogens.

These affect our unique biodiversity, as well as the clean water and oxygen we breath – not to mention our cultural values.

When it comes to biodiversity, Australia is globally quite distinct. More than 70% of our species (69% of mammals, 46% of birds and 93% of reptiles) are found nowhere else on earth. A loss to Australia is therefore a loss to the world.

Some of these are ancient species like the Wollemi Pine, may have inhabited Australia for up to 200 million years, well before the dinosaurs.




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Wollemi pines are dinosaur trees


But invasive species are found in almost every part of Australia, from our rainforests, to our deserts, our farms, to our cities, our national parks and our rivers.

The cost to Australia

The cost of invasive species in Australia continue to grow with every new assessment.

The most recent estimates found the cost of controlling invasive species and economic losses to farmers in 2011-12 was A$13.6 billion. However this doesn’t include harm to biodiversity and the essential role native species play in our ecosystems, which – based on the conclusions of the IPBES report – is likely to cost at least as much, and probably far more.

Rabbits, goats and camels prevent native desert plant community regeneration; rabbits alone impacting over 100 threatened species. Rye grass on its own costs cereal farmers A$93M a year.

Aquaculture diseases have affected oysters and cost the prawn industry $43M.

From island to savannah

Globally, invasive species have a disproportionately higher effect on offshore islands – and in Australia we have more than 8,000 of these. One of the most notable cases is the case of the yellow crazy ants, which killed 15,000,000 red land crabs on Christmas Island.




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A tiny wasp could save Christmas Island’s spectacular red crabs from crazy ants


Nor are our deserts immune. Most native vertebrate extinctions caused by cats have occurred in our dry inland deserts and savannas, while exotic buffel and gamba grass are creating permanent transformation through changing fire regimes.

Australia’s forests, particularly rainforests, are also under siege on a number of fronts. The battle continues to contain Miconia weed in Australia – the same weed responsible for taking over 70% of Tahiti’s native forests. Chytrid fungus, thought to be present in Australia since 1970, has caused the extinction of at least four frog species and dramatic decline of at least ten others in our sensitive rainforest ecosystems.

Myrtle rust is pushing already threatened native Australian Myrtaceae closer to extinction, notably Gossia gonoclada, and Rhodamnia angustifolia and changing species composition of rainforest understories, and Richmond birdwing butterfly numbers are under threat from an invasive flower known as the Dutchman’s pipe.

Australia’s rivers and lakes are also under increasing domination from invasive species. Some 90% of fish biomass in the Murray Darling Basin are European carp, and tilapia are invading many far north Queensland river systems pushing out native species .

Invasive alien species are not only a serious threat to biodiversity and the economy, but also to human health. The Aedes aegypti mosquito found in parts of Queensland is capable of spreading infectious disease such as dengue, zika, chikungunya and yellow fever.

And it’s not just Queensland that is under threat from diseases spread by invasive mosquitoes, with many researchers and authorities planning for when, not if, the disease carrying Aedes albopictus establishes itself in cooler and southern parts of Australia.




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Stowaway mozzies enter Australia from Asian holiday spots – and they’re resistant to insecticides


What solutions do we have?

Despite this grim inventory, it’s not all bad news. Australia actually has a long history of effectively managing invasive species.

Targeting viruses as options for controlling rabbits, carp and tilapia; we have successfully suppressed rabbit populations by 70% in this way for 50 years.

Weeds too are successful targets for weed biological control, with over a 65% success rate controlling more than 25 targets.

The IPBES report calls for “transformative action”. Here too Australia is at the forefront, looking into the potential of gene-technologies to suppress pet hates such as cane toads.




Read more:
We’ve cracked the cane toad genome, and that could help put the brakes on its invasion


Past and current invasive species programs have been supported by governments and industry. This has provided the type of investment we need for long-term solutions and effective policies.

Australia is better placed now, with effective biosecurity policies and strong biosecurity investment, than many countries. We will continue the battle against invasive species to stem biodiversity and ecosystem loss.The Conversation

Andy Sheppard, Research Director CSIRO Health & Biosecurity, CSIRO and Linda Broadhurst, Director, Centre for Australian National Biodiversity Research, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The summer bushfires you didn’t hear about, and the invasive species fuelling them



File 20190311 86707 1ji5xqu.jpg?ixlib=rb 1.1
Fire has burned through a swathe of the Tjoritja National Park.
Author provided

Christine Schlesinger, Charles Darwin University and Barry Judd, Charles Darwin University

In January 2019, fires burned across a 100-kilometre length of the iconic Tjoritja National Park in the West MacDonnell Ranges, from Ormiston Gorge nearly to the edge of Alice Springs.

These fires affected an area comparable to the recent Tasmanian fires, but attracted relatively little national attention. This is partly because the fires in Tasmania were so unusual – but we believe the fires in central Australia were just as unexpected.




Read more:
Dry lightning has set Tasmania ablaze, and climate change makes it more likely to happen again


In the past, fires of this magnitude have tended to come after heavy rain that powers the growth of native grasses, providing fuel for intense and widespread fires. But our research highlights the new danger posed by buffel grass, a highly invasive foreigner sweeping across inland Australia and able to grow fast without much water.

Far from being pristine, Tjoritja and the Western MacDonnell Ranges are now an invaded landscape under serious threat. Our changing climate and this tenacious invader have transformed fire risk in central Australia, meaning once-rare fires may occur far more often.

Buffel grass in Australia

Buffel grass is tough and fast-growing. First introduced to Australia in the 1870s by Afghan cameleers, the grass was extensively planted in central Australia in the 1960s during a prolonged drought.

Introductions of the drought-resistant plant for cattle feed and dust suppression have continued, and in recent decades buffel grass has become a ubiquitous feature of central Australian landscapes, including Tjoritja.

Buffel grass has now invaded extensive areas in the Northern Territory, Queensland, Western Australia and South Australia and is spreading into New South Wales and Victoria. It was legally recognised as a key threat in 2014, but so far only South Australia has prohibited its sale and created statewide zoning to enforce control or destruction.

Buffel grass crowds out other plants, creating effective “monocultures” – landscapes dominated by a single species. In central Australia, where Aboriginal groups retain direct, active and enduring links to Country, buffel grass makes it hard or impossible to carry out important cultural activities like hunt game species, harvest native plant materials or visit significant sites.

Buffel grass impacts on Anangu Pitjantjatjara Yankunytjatjara communities in central Australia.

But buffel grass isn’t only a threat to biodiversity and Indigenous cultural practices. In January the Tjoritja fires spread along dry river beds choked with buffel, incinerating many large old-growth trees. Much like the alpine forests of Tasmania, the flora of inland river systems has not adapted to frequent and intense fires.

We believe the ability of the fires to spread through these systems, and their increased intensity and size, can be directly attributed to buffel grass.

Fire and buffel grass

Because of the low average rainfall, widespread fires in central Australia have been rare in the recorded past, only following unusual and exceptionally high rainfall.

This extreme rain promoted significant growth of native grasses, which then provided fuel for large fires. There could be decades between these flood and fire cycles. However, since the Tjoritja (previously West MacDonnell Ranges) National Park was established in the 1990s, there have been three large-scale fires in 2001, 2011 and 2019.

What has changed? The 2001-02 and 2011-12 fires both came after heavy rainfall years. In fact, 2011 saw one of the biggest La Niña events on record.

Climate change predictions suggest that central Australia will experience longer and more frequent heatwaves. And although total annual rainfall may stay the same, it’s predicted to fall in fewer days. In other words, we’ll see heavy storms and rainfall followed by long heatwaves: perfect conditions for grass to grow and then dry, creating abundant fuel for intense fires.

The remains of a corkwood tree after an unplanned bushfire in an area heavily invaded by buffel grass near Simpsons Gap. Very few large old corkwood trees now remain in this area.
Author provided

If central Australia, and Tjoritja National Park in particular, were still dominated by a wide variety of native grasses and plants, this might not be such a problem. But buffel grass was introduced because it grows quickly, even without heavy rain.

The fires this year were extraordinary because there was no unusually high rainfall in the preceding months. They are a portent of the new future of fire in these ecosystems, as native desert plant communities are being transformed into dense near-monocultures of introduced grass.

The fuel that buffel grass creates is far more than native plant communities, and after the fire buffel grass can regenerate more quickly than many native species.

So we now have a situation in which fuel loads can accumulate over much shorter times. This makes the risk of fire in invaded areas so high that bushfire might now be considered a perpetual threat.

Changing fire threat

In spinifex grasslands, traditional Aboriginal burning regimes have been used for millennia to renew the landscape and promote growth while effectively breaking up the landscape so old growth areas are protected and large fires are prevented. Current fire management within Tjoritja “combines traditional and scientific practices”.

However, these fire management regimes do not easily translate to river environments invaded by buffel grass. These environments have, to our knowledge, never been targeted for burning by Aboriginal peoples. Since the arrival of buffel grass, there is now an extremely high risk that control burns can spread and become out-of-control bushfires.

Even when control burns are successful, the rapid regrowth of buffel grass means firebreaks may only be effective for a short time before risky follow-up burning is required. And there may no longer be a good time of year to burn.




Read more:
How invasive weeds can make wildfires hotter and more frequent


Our research suggests that in areas invaded by buffel grass, slow cool winter burns – typical for control burning – can be just as, or more, damaging for trees than fires in hot, windy conditions that often cause fires to spread.

Without more effective management plans and strategies to manage the changing fire threat in central Australia, we face the prospect of a future Tjoritja in which no old-growth trees will remain. This will have a devastating impact on the unique desert mountain ranges.

We need to acknowledge that invasive buffel grass and a changing climate have changed the face of fire risk in central Australia. We need a coordinated response from Australia’s federal and state governments, or it will be too late to stop the ecological catastrophe unfolding before us.


The authors acknowledge the contribution of Shane Muldoon, Sarah White, Erin Westerhuis, CDU Environmental Science and Management students, and NT Parks and Wildlife staff to the research at experimental sites and ongoing tree monitoring in central Australia.The Conversation

Christine Schlesinger, Senior Lecturer in Environmental Science and Ecology, Charles Darwin University and Barry Judd, Professor, Indigenous Social Research, Charles Darwin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How we wiped out the invasive African big-headed ant from Lord Howe Island



File 20181106 74772 gz1lz8.png?ixlib=rb 1.1
Not welcome: the African big headed ant might be small but it can be a pest if it gets in your home.
CSIRO, Author provided

Ben Hoffman, CSIRO

The invasive African big-headed ant (Pheidole megacephala) was found on Lord Howe Island in 2003 following complaints from residents about large numbers of ants in buildings.

But we’ve managed to eradicate the ant completely from the island using a targeted mapping and baiting technique than can be used against other invasive species.

Up to 15% of Lord Howe Island was thought to be infested with the ant.
CSIRO, Author provided

A major pest

The African big-headed ant is one of the world’s worst invasive species because of its ability to displace some native plants and wildlife, and adversely affect agricultural production.




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In an ant’s world, the smaller you are the harder it is to see obstacles


It’s also a serious domestic nuisance. People can become overwhelmed by the large number of ants living in their buildings – you can’t leave a bit of food lying around, especially pet food, or it will be covered in ants.

It remains unclear how long the ant had been on Lord Howe Island, in the Tasman Sea about 770 km northeast of Sydney, before being found. But it is likely to have been present for at least a decade.

Because of the significant threat this ant posed to the conservation integrity of the island, an eradication program was started. But on-ground work done from 2003 to 2011 had many failings and was not working.

In 2011, I was brought in to oversee the program. The last ant colony was killed in 2016, but it is only now, two years later, that we are declaring Lord Howe Island free from the ants.

No African big-headed ants have been seen on the island for two years.
CSIRO, Author provided

A super colony

The ability to eradicate this ant is largely due to its relatively unique social organisation. The queens don’t fly to new locations to start new nests – instead, they form interconnected colonies that can extend over large areas.

This makes the ant’s distribution easy to map and treat. The ant requires human assistance for long-distance transport, so the ant will only be found in predictable locations where it can be accidentally transported by people.

From 2012 to 2015, all locations on the island where the ant was likely to be present were formally inspected. Priority was given to places where an infestation was previously recorded or considered likely. The populations were mapped, and then treated using a granular bait available at shops.

In the latter years we found 16 populations covering 30 hectares. Limited by poor mapping in the early years, we estimate that the ant originally covered up to 55 hectares, roughly 15% of the island.

Stopping the spread

The widespread distribution of the ant through the populated area of the island is thought to have been aided by the movement of infested mulch and other materials from the island’s Waste Management Facility.

To prevent any more spread of the ant, movement restrictions were imposed in 2003 on the collection of green waste, building materials and other high risk items from the facility.

The baiting program used a product that contains a very low dose of insecticide that has an extremely low toxicity to terrestrial vertebrates such as pet cats and dogs, birds, lizard etc. The toxicant rapidly breaks down into harmless chemicals after exposure to light.

No negative impacts were recorded on any of the native wildlife on the island.

Importantly, the African ant usually kills most other ants and other invertebrates where it is present, so there are few invertebrates present to be affected by the bait.

Ecological recovery of the infested areas was rapid following baiting and the eradication of the African ant.

Another ant invader

One of the main challenges was getting the ground crew to correctly identify the ant.

It turns out there was a second (un-named) big-headed ant species present, also not native to the island, that created a lot of unnecessary work being conducted where the African ant wasn’t present.

CSIRO and Lord Howe Island Board team tackling the African big headed ant problem.
CSIRO, Author provided

Like numerous other exotic ant species present, this second species was of no environmental or social concern, so there are no plans to manage or eradicate it.

The protocols used in this program are essentially the same that are being used in other eradication programs against Electric ant in Cairns and Browsing ant in Darwin and Perth, because those two species also create supercolonies.




Read more:
We’ve got apps and radars – but can ants predict rain?


It is highly likely that those programs will also achieve eradication of their respective species, the first instance where an ant species has been eradicated entirely from Australia.

The fire ant program in Brisbane has many similarities, but there are distinct differences in that the ants there don’t form supercolonies that are so easy to map, and the area involved is far greater.The Conversation

Ben Hoffman, Principal research scientist, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

A numbers game: killing rabbits to conserve native mammals



File 20180709 122262 6ap5ri.jpg?ixlib=rb 1.1
Controlling rabbit populations has a key role in conserving Australia’s native plants and animals
William Booth

Euan Ritchie, Deakin University; Damien Fordham, University of Adelaide, and Miguel Lurgi, Centre national de la recherche scientifique (CNRS)

Invasive species have a devastating effect on biodiversity. In Australia, introduced red foxes and feral cats have been implicated in the majority of the extinctions of the native mammal fauna, which has been decimated since European arrival.

But there’s a herbivore that also causes eco-catastrophe. Rabbits both compete with native animals for food and shelter and act as easy prey for abundant populations of cats and foxes. By over-grazing vegetation and reducing habitat complexity, they make hunting easier for introduced predators.




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Food webs are complex. Because of this, once an invasive species is embedded in a food web, simply eradicating them without considering the potential knock-on effects to other species they interact with, could cause unintended and undesirable consequences. We modelled different rates of rabbit population reduction to assess what level of control might be best for aiding the conservation of native mammals and not causing negative outcomes.

Rabbit numbers boom and crash

Rabbits, famously, reproduce rapidly and can cope with a relatively high predation rate. This can cause “hyper-predation”, where rabbit-inflated cat and fox populations indirectly increase the predation pressure on native mammals. This is especially so when rabbit populations intermittently crash due to, for example, extreme environmental events (like severe and prolonged droughts) or disease. This causes predators to switch their diet and eat more native mammals.

Threatened species such as the greater bilby are likely to benefit from rabbit control.
Jasmine Vink

This logically suggests that reducing rabbit numbers might thus help reduce cat and fox populations, by removing their abundant prey. Collectively this should benefit native plants and animals, including many threatened mammal species. However, ecosystem and pest management is a complex game.

When controlling rabbits we need to look beyond one or two species. We should consider the potential consequences for the entire ecological community, which ultimately depend on how changes in one species percolate through the network of ecological interactions between them.

Our new research, recently published in the Journal of Applied Ecology, set out to examine these questions in more detail. We consider other key players in Australia’s arid regions, such as kangaroos and dingoes, when looking at the effects of rabbit control on small native mammals. Our aim was to provide a better understanding of how changes in rabbit populations might affect other species via the food web.

We developed a multi-species ecological network model to describe and quantify how changing rabbit abundance can affect species on different feeding levels. In addition to rabbits, small native mammals, and mesopredators (cats and foxes), our model also considers apex predators (dingo) and large herbivores (kangaroo) as part of the Australian arid food web. This model allowed us to examine changes in predator-prey interactions (including potential prey switching and hyper-predation) and how these could affect the survival of native prey through time.

Our model of an Australian arid ecosystem food web.
Author provided

We found that removing rabbits at rates between 30-40% appeared to benefit small mammals. This is approximately the rate at which rabbits are currently managed in Australia using biocontrol agents (introduced diseases).

Rabbit control in Australia typically involves a “press and pulse” approach. Rabbit populations are suppressed via biocontrol (press) and periods of warren destruction and poisoning (pulse). Finding that reducing rabbit populations by around 40% seems most beneficial to small mammals is important, as it informs how and when we combine these strategies.

The 40% rate corresponds well with the disease-induced (press) mortality rate in rabbit populations due to rabbit haemorrhagic disease and myxomatosis. These are the primary biocontrol agents used in arid Australia to control rabbit populations.

Our study supports rabbit-reduction strategies that involve sustained “press” control, that kill a moderate portion of a rabbit population, with less frequent removal at higher proportions of the population.

To effectively manage invasive species, it’s important to focus on entire communities. Targeting single species might not be enough – every animal exists within a complex web of interactions.




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There has been much focus by the current government on controlling feral cats, as a way to conserve many of Australia’s unique and threatened mammal species.

The ConversationHowever, more focus could be devoted to protecting habitat cover and complexity, by reducing the land clearing and over-grazing that makes hunting easier. We can also manage rabbits sensibly to reduce competition for resources, and indirectly control cats and foxes.

Euan Ritchie, Associate Professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University; Damien Fordham, , University of Adelaide, and Miguel Lurgi, Postdoctoral research fellow, Centre national de la recherche scientifique (CNRS)

This article was originally published on The Conversation. Read the original article.

Tandem virus cocktail kills pest rabbits more effectively



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Tagged European rabbit kitten infected with myxoma virus, but that died from rabbit haemorrhagic virus disease (RHDV).
Photo by David Peacock, Biosecurity South Australia, CC BY-NC-SA

Corey Bradshaw, Flinders University; Louise Barnett, Flinders University, and Thomas Prowse, University of Adelaide

Farmers, landowners and conservationists across Australia are benefiting from an unexpected, combined effect of two biological controls that target feral populations of European rabbits (Oryctolagus cuniculus), according to our research, published in the Journal of Applied Ecology.




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Explainer: how ‘biocontrol’ fights invasive species


Pest rabbits cost the Australian economy over A$200 million each year in lost production, and millions more in pest control. They compete with livestock for food and cause enormous environmental damage.

Rabbits previously reached plague numbers in much of agricultural and outback Australia, until the introduction of two rabbit-specific viruses and insect vectors.

Myxoma virus was first introduced in 1950, followed by European rabbit fleas in the 1960s to help spread the virus, and then Spanish rabbit fleas in the 1990s to increase spread into arid areas.

Then, in 1995, rabbit haemorrhagic disease virus (RHDV) escaped from quarantine, before an official release in 1996. These biocontrols have reduced rabbit numbers by an estimated 75-80% (see references in our paper) in South Australia alone since the 1950s.

Rabbits around a waterhole at the myxomatosis trial enclosure on Wardang Island in 1938.
National Archives of Australia/Wikimedia Commons

Together, myxoma virus and RHDV saved the Australian economy an estimated A$70 billion by 2011.

But managing rabbits’ growing immunity to these virus biocontrol agents is now presenting new challenges for Australian land managers.




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This is why our new discovery of a positive interaction between the two main viruses is great news for the Australian environment and economy.

Our study represents the first solid evidence that a combination of these two rabbit diseases is more effective in reducing rabbits’ abundance, providing agencies and landowners with more bang for their buck during rabbit control programs.

Our findings were made possible by one of the longest-running monitoring programs in disease ecology: the 21-year (and ongoing) Turretfield Rabbit Research Project north of Adelaide.

Roughly every two months for more than two decades, PIRSA Biosecurity South Australia has counted, tagged, virus-tested, and released rabbits of all ages from the isolated sentinel rabbit population.

Analysing this unrivalled dataset, we discovered that the probability of dying from rabbit haemorrhagic disease was 10% higher than expected when an individual rabbit had previously been exposed to myxoma virus. These means that rabbits that are now immune to the myxoma virus (Australia’s first rabbit biocontrol) are nevertheless more susceptible to RHDV (Australia’s second rabbit biocontrol).

In other words, the two diseases (a poxvirus and a calicivirus) interacted to give a population-level effect that resulted in more rabbit deaths overall.

Such an interaction between biocontrol agents is rare; in fact, it is the first discovery of its kind in the world.

Tagged rabbit from Turretfield (photo taken September 8, 2014). This individual had no antibodies against RHDV or myxoma virus, but was found dead from haemorrhagic disease two hours later.
David Peacock/Biosecurity SA

The knowledge that the two viruses combine as a potent weapon against rabbits has major implications for land owners and farmers around the world who battle pest rabbits. Disease outbreaks could potentially be timed to ensure that the death rate of pest rabbits is as high as possible.

In Australia, rabbits are a dietary mainstay for two other damaging invasive species: feral cats and red foxes. A large rabbit population can keep the two predator species at high densities, thus promoting their high predation rates on native wildlife.




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Invasive predators are eating the world’s animals to extinction – and the worst is close to home


Keeping rabbit numbers low can therefore benefit our environment. In fact, the rate of native vegetation cover has increased since RHDV began to spread in 1995, and there have been documented increases in the numbers of small native mammal species since that time.

Ecologically informed biocontrol is therefore just another smart way to manage invasive species.

Our discovery also has implications right across the world. European rabbits cause environmental and agricultural damage in places as diverse as the United Kingdom, New Zealand, and in parts of South America.

The ConversationOur findings will also help researchers and conservationists to safeguard the rabbit in its natural range in Europe, and support Australia’s search for other biocontrols in the future.

Corey Bradshaw, Matthew Flinders Fellow in Global Ecology, Flinders University; Louise Barnett, Adjunct researcher, Flinders University, and Thomas Prowse, Postdoctoral research fellow, School of Mathematical Sciences, University of Adelaide

This article was originally published on The Conversation. Read the original article.

The future is fenced for Australian animals



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Mala, also known as rufous hare-wallabies, will be protected behind an enormous cat-proof fence.
Donald Hobern/Flickr, CC BY-SA

Michael Bode, The University of Queensland

Many of Australia’s mammals spend their entire lives imprisoned, glimpsing the outside world through tall chain-link fences and high-voltage wires. There are dozens of these enclosures across Australia. Many are remote, standing alone in the endless expanse of inland Australia, but others are on the outskirts of our largest cities – Melbourne, Perth, Canberra.

Every year there are more of them, the imprisoned population growing, while the wild populations outside dwindle. These are Australia’s conservation fences.




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The captives within our conservation fences are adorable – floppy-eared bilbies, tiny hare-wallabies, long-tongued numbats – and they all share an extreme susceptibility to introduced predators. At least 68 native mammal species cannot exist in the wild if either foxes or cats are present. Many of these species once numbered in the millions, ranging from the woodlands of Queensland to the deserts of Western Australia, but predation has driven them to the brink of extinction.

Fences offer these species a future in the wild, and conservation groups have risen to the challenge. Last week, the Australian Wildlife Conservancy completed a new cat-proof fence in their Newhaven Sanctuary, the largest conservation fence ever constructed.

Fences are extraordinarily successful

Make no mistake, these conservation fences work. Species that wilt at the sight of a fox, that have been exterminated from every corner of the Australian mainland, will explode in numbers behind fences. Along with offshore islands, inside these fences are the only places in Australia where these species can prosper – a few hundred square kilometres of safety, surrounded by 7.6 million lethal square kilometres.

Environmentalists have never particularly liked fences. Rather than hide behind walls, they repeatedly took the fight to the cats and foxes on the outside.

Their tactics have been diverse, innovative and brutal. Managers have rained bullets from helicopters and poison baits from planes. They have set cunning snares and traps, mimicked the smell and sound of their enemies, and have turned landscapes to ash with wildfire.

Nothing has worked for the most threatened marsupials. Some of the largest and most expensive management campaigns in Australian conservation history have ended in exhaustion and stalemate, and with a retreat back behind the fences.

Fences were once a source of vehement debate in conservation circles. Should they be permanent? Are fenced populations wild or captive? Should they contribute to species’ conservation status?

These arguments have effectively been abandoned. Scientific studies and painful experience has proven fences and offshore islands to be the only reliable method of protecting predator-threatened species http://www.wildliferesearchmanagement.com.au/Final%20Report_0609.pdf. In place of these debates, conservation organisations and governments have turned to more practical questions of fence height, electric wire voltage and skirt depth.

So now, on average, Australians are building a new fence every year, some of them truly enormous. The just-completed fence at Newhaven encloses a staggering 10,000 hectares of red sand and spinifex. By the time the project is complete, this fence will be home to 11 different threatened mammal species.

And Australia is not alone: around the world, from New Zealand to Hawaii to South Africa, an archipelago of fences is emerging from an ocean of predators. It is one of the great achievements of modern conservation and has already averted the extinction of critically endangered species. Although it’s much smaller than our network of protected areas, it offers refuge to species that are long-gone from our national parks and wilderness areas.

Red foxes have been extraordinarily successful in Australia.
Harley Kingston/Flickr, CC BY

A troubling pattern

However, in recent years a concerning pattern has begun to emerge. While the number and size of fences continue to increase, the number of new species being protected has stalled. In fact, the last five fences haven’t included any new species – they have only offered additional protection to species that were already protected behind existing fences https://www.nature.com/articles/s41559-017-0456-4.

As an example, the first two marsupials planned for introduction behind the Newhaven fence will be the mala (Lagorchestes hirsutus) and the burrowing bettong (Bettongia lesueur). These two species undeniably deserve more protection. Both are highly susceptible to foxes and cats and will derive tremendous benefit from the protection of this enormous fence. However, both species are already found elsewhere behind fences (four different fences for burrowing bettongs). Meanwhile, yet-to-be-published research from the National Environmental Science Program has found 41 other species that are desperately vulnerable to introduced predators are not protected by any fence.

This problem is not new to conservation. In the 1990s, Australian researchers suddenly realised that our national park system was failing to protect the full range of Australian ecosystems. Despite our best efforts, we had created a system of reserves that was biased towards mountainous landscapes and deserts, and away from the fertile valley floors. The solution was to create new national parks using systematic and mathematical methods.

This discovery – the theory of systematic conservation planning – revolutionised global conservation. In 2018, conservation fences need their own systematic revolution.

Unfortunately, the national park system had natural advantages that fences lack. The vast majority of Australia’s protected areas belong to the state and federal governments. The centralised nature of the protected area network is perfect for systematic thinking and top-down optimisation – picture the Soviet Union’s Politburo. In contrast, the conservation fencing sector is diverse and decentralised – picture the third day of Woodstock.




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Fences are built by governments at the state, federal and municipal levels, by multimillion-dollar NGOs like the Australia Wildlife Conservancy, by tiny local environmentalist groups and by profit-making corporations. This diversity is a fundamental strength of the fence network, giving it access to a spectrum of funding and ideas. But it makes it almost impossible to plan in a systematic manner. You can’t tell a small bilby conservation group in western Queensland that they should protect the central Australian rock-rat instead (Zyzomys pedunculatus). It doesn’t necessarily matter to them that bilbies are already protected behind four different fences and the rock-rat has none.

While conservation science tries to work this problem out, new and larger fences will continue to be built at an accelerating rate into the foreseeable future. True, the absence of coordination will make mathematicians break their slide rules, but each fence will do its job. The furry denizens will hop, and scurry, and bounce around, heedless of their precarious safety.

The ConversationAnd for us, from the outside looking in, these fences will help us forget the parlous state of Australian marsupial conservation. It will be possible to forget our record-breaking rate of extinctions, to forget the empty forests and deserts, and to imagine what a bushwalk might have been like before Europeans unleashed foxes and cats onto Australia.

Michael Bode, Associate Professor of Mathematics, The University of Queensland

This article was originally published on The Conversation. Read the original article.

South Africa should sort out the bad from the really bad on its invasive species list



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Managing trout is a contentious issue with conflicting views about whether they pose a risk, or are beneficial.
Shutterstock

Tsungai Zengeya, South African National Biodiversity Institute

This article is the third in a series The Conversation Africa is running on invasive species.

Alien species have been introduced to Africa for a variety of reasons. They provide food, raw materials for industry, ornamental plants, recreation in the form of sport fishing, hunting and pets. Some that are highly valued have been moved around widely. And in some areas they now form prominent components of societies and ecosystems like the domestic cat for example.

Many alien species bring considerable benefits. But some have become invasive, causing a loss of biodiversity, changes to ecosystems, economic losses and, in some cases, even affecting people’s health.

The shrub Prosopis or mesquite is an example. It was introduced to South Africa to provide fodder, firewood and shade in arid parts of the country. But it’s also a major water user. And two trout species (S. trutta and O. mykiss) are used for recreational angling and commercial aquaculture. But they’ve also been implicated in having a negative effect on the environment.

Managing invasive species is therefore critical. In South Africa the movement and use of 552 listed invasive species are managed under the Biodiversity Act and regulations attached to it. But not all the species on the list are equally harmful. Several may in fact be relatively harmless.

All the listed species under these regulations require management. Given that the capacity is limited, regulations should arguably focus on priority species because not all are necessarily harmful to the extent that would justify spending large amounts of time and effort on keeping them under control.

The question then is: are there some species that could be removed from the list? In our recent study we set out to answer this question by classifying species as inconsequential, beneficial, destructive or conflict generating species. This was done by assessing the relative degree of benefit they brought and their negative effects.

Beneficial and harmful species

The classification was done by using a simple scoring system. It had two categories for the negatives (ecological and socio-economic) and two for the benefits (economic and intrinsic).

  1. Inconsequential species: these make up 55% of the species listed under the act and in the regulations. They were associated with relatively low costs and low benefits to society. Species in this group had limited distribution or no known impact and were largely introduced as ornamentals or pets. Some examples include the eastern grey squirrel (Sciurus carolinensis), European perch (Perca fluviatilis), and the Père David’s Deer (Elaphurus davidianus).

  2. Destructive species: these make up 29% of the list. They don’t bring substantial benefits to society or the environment, but they have a highly negative impact. Many were introduced accidentally and are regarded largely as pests and weeds. Examples include invasive rodents like the black rat (Rattus rattus) which causes damage to infrastructure and transmission of zoonotic diseases and pitch canker (Fusarium circinatum) a growing threat to pine plantations and forests worldwide.

The jacaranda is an iconic tree species in the city of Pretoria where it’s regarded as part of the identity.
Shutterstock
  1. Beneficial species: they make up 10% of the list and have clear social or environmental benefits. For example the jacaranda (Jacaranda mimosifolia) is an iconic tree species in the city of Pretoria where the species is regarded as part of the identity and “sense of place” of the city. Active management is not necessary or should only be done in particular cases.

  2. Conflict-generating organisms: these can be either beneficial or destructive, depending on one’s perspective or what value is placed on them. They make up only 6% of the list. There’s huge disagreement about whether these species should be controlled, or how they should be controlled. Examples include woody plants introduced for forestry, erosion control, sand dune stabilisation, agriculture and as ornamentals. Acacias and pines are examples. Animal examples include species like the Himalayan tahr which was introduced to the Table Mountain National Park. The goat has been the focus of eradication attempts, despite strong opposition. It also includes species introduced for aquaculture like maroon and brown trout. Managing trout has been highly contentious with conflicting views about whether they pose a risk, or deliver a benefit. This has led to them being listed and delisted. The trout fraternity refuse to acknowledge that trout are invasive species and highlight the lack of scientific evidence of the risks they pose.

Finding common ground

We need to keep sight of the fact that there is general agreement on 94% of listed species. By identifying the small number that are generating the greatest tension, it’s more likely discussions can be held to reach common ground on regulation.

Most countries in Africa don’t have invasive species regulations. But there’s growing recognition that they’re needed. South Africa offers useful lessons on how this could be done.

The control of species listed under the country’s biodiversity act is compulsory. This means that plans to manage them have to be drawn up and implemented. But this doesn’t seem sensible given that not all are equally harmful and resources are limited. Our study suggests that some of the species currently regulated could be removed from the list.

Countries wanting to set up a system of managing invasive species could start by classifying a prospective list of candidates. Policymakers could then quickly bring out legislation against the most damaging and destructive ones. At the same time, discussions could be had on the ones that generate conflict with the aim of reaching consensus.

The ConversationThis would allow managers and regulators to focus on the most destructive species – as well as those that are at the centre of fierce disagreement.

Tsungai Zengeya, Researcher at the South African National Biodiversity Institute, South African National Biodiversity Institute

This article was originally published on The Conversation. Read the original article.