‘Gene drives’ could wipe out whole populations of pests in one fell swoop



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Gene drives aim to deliberately spread bad genes when invasive species such as mice reproduce.
Colin Robert Varndell/shutterstock.com

Thomas Prowse, University of Adelaide; Joshua Ross, University of Adelaide; Paul Thomas, University of Adelaide, and Phill Cassey, University of Adelaide

What if there was a humane, targeted way to wipe out alien pest species such as mice, rats and rabbits, by turning their own genes on themselves so they can no longer reproduce and their population collapses?

Gene drives – a technique that involves deliberately spreading a faulty gene throughout a population – promises to do exactly that.

Conservationists are understandably excited about the possibility of using gene drives to clear islands of invasive species and allow native species to flourish.


Read more: Gene drives may cause a revolution, but safeguards and public engagement are needed.


Hype surrounding the technique continues to build, despite serious biosecurity, regulatory and ethical questions surrounding this emerging technology.

Our study, published today in the journal Proceedings of the Royal Society B, suggests that under certain circumstances, genome editing could work.

The penguins on Antipodes Island currently live alongside a 200,000-strong invasive mouse population.
Wikimedia Commons, CC BY

Good and bad genes

The simplest way to construct a gene drive aimed at suppressing a pest population is to identify a gene that is essential for the pest species’ reproduction or embryonic development. A new DNA sequence – the gene-drive “cassette” – is then inserted into that gene to disrupt its function, creating a faulty version (or “allele”) of that gene.

Typically, faulty alleles would not spread through populations, because the evolutionary fitness of individuals carrying them is reduced, meaning they will be less likely than non-faulty alleles to be passed on to the next generation. But the newly developed CRISPR gene-editing technology can cheat natural selection by creating gene-drive sequences that are much more likely to be passed on to the next generation.


Read more: Now we can edit life itself, we need to ask how we should use such technology.


Here’s how the trick works. The gene-drive cassette contains the genetic information to make two new products: an enzyme that cuts DNA, and a molecule called a guide RNA. These products act together as a tiny pair of molecular scissors that cuts the second (normal) copy of the target gene.

To fix the cut, the cell uses the gene drive sequence as a repair template. This results in a copy of the gene drive (and therefore the faulty gene) on both chromosomes.

This process is called “homing” and, when switched on in the egg- or sperm-producing cells of an animal, it should guarantee that almost all of their offspring inherit the gene-drive sequence.

As the gene-drive sequence spreads, mating between carriers becomes more likely, producing offspring that possess two faulty alleles and are therefore sterile or fail to develop past the embryonic stage.

Will it work?

Initial attempts to develop suppression drives will likely focus on invasive species with rapid life cycles that allow gene drives to spread rapidly. House mice are an obvious candidate because they have lots of offspring, they have been studied in great detail by biologists, and have colonised vast areas of the world, including islands.

In our study we developed a mathematical model to predict whether gene drives can realistically be used to eradicate invasive mice from islands.

Our results show that this strategy can work. We predict that a single introduction of just 100 mice carrying a gene drive could eradicate a population of 50,000 mice within four to five years.

But it will only work if the process of genetic homing – which acts to overcome natural selection – functions as planned.

Evolution fights back

Just as European rabbits in Australia have developed resistance to the viruses introduced to control them, evolution could thwart attempts to use gene drives for biocontrol.

Experiments with non-vertebrate species show that homing can fail in some circumstances. For example, the DNA break can be repaired by an alternative mechanism that stitches the broken DNA sequence back together without copying the gene-drive template. This also destroys the DNA sequence targeted by the guide RNA, producing a “resistance allele” that can never receive the gene drive.

A recent study in mosquitos estimated that resistance alleles were formed in at least 2% of homing attempts. Our simulation experiments for mice confirm this presents a serious problem.

After accounting for low failure rates during homing, the creation and spread of resistance alleles allowed the modelled populations to rebound after an initial decline in abundance. Imperfect homing therefore threatens the ability of gene drives to eradicate or even suppress pest populations.

One potential solution to this problem is to encode multiple guide RNAs within the gene-drive cassette, each targeting a different DNA sequence. This should reduce homing failure rates by allowing “multiple shots on goal”, and avoiding the creation of resistance alleles in more cases.

To wipe out a population of 200,000 mice living on an island, we calculate that the gene-drive sequences would need to contain at least three different guide RNA sequences, to avoid the mice ultimately getting the better of our attempts to eradicate them.

From hype to reality

Are gene drives a hyperdrive to pest control, or just hype? Part of the answer will come from experiments with gene drives on laboratory mice (with appropriate containment). That will help to provide crucial data to inform the debate about their possible deployment.

The ConversationWe also need more sophisticated computer modelling to predict the impacts on non-target populations if introduced gene drives were to spread beyond the populations targeted for management. Using simulation, it will be possible to test the performance and safety of different gene-drive strategies, including strategies that involve multiple drives operating on multiple genes.

Thomas Prowse, Postdoctoral research fellow, School of Mathematical Sciences, University of Adelaide; Joshua Ross, Associate Professor in Applied Mathematics, University of Adelaide; Paul Thomas, , University of Adelaide, and Phill Cassey, Assoc Prof in Invasion Biogeography and Biosecurity, University of Adelaide

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

Are Australia’s native pigeons sitting ducks?



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These migratory pied imperial-pigeons in Far North Queensland, like many of Australia’s 22 species of native pigeons and doves, play an important role in our ecosystems but may be at risk from emerging viruses in domestic pigeons.
Dejan Stojanovic, CC BY-SA

Andrew Peters, Charles Sturt University

The word “pigeon” evokes thoughts of gentle cooing, fluttering in rafters, and poo-encrusted statues. The species responsible for the encrustation is deeply familiar to us, having ridden waves of European expansionism to inhabit every continent, including Australia. First domesticated thousands of years ago, urban pigeons have turned feral again.

Less familiar are the native species that are not your stereotypical pigeons: a posse of pointy-headed crested pigeons in a suburban park, or a flock of topknot pigeons feeding in a camphor laurel.

Crested pigeons (left), brush bronzewings (centre) and pied imperial-pigeons (right) are amongst the 22 species of native pigeons and doves in Australia. Their charm and beauty belies the important functions they play in ecosystems.
Author provided

Australia and its neighbouring islands are the global epicentre of pigeon and dove (or “columbid”) diversity with the highest density of different columbids – an impressive 134 species – found in the region. Twenty-two of these native species are found in Australia alone, in just about every habitat.

These native species play an important role in ecosystem functioning: they forage for and disperse seeds, concentrate nutrients in the environment, and are a source of food for predators. Fruit doves for example, are zealous fruitarians, and the region’s tropical rainforests depend on them for tree diversity. Where fruit-doves have disappeared in the South Pacific, numerous plant species have lost an effective dispersal mechanism.

The rose-crowned fruit-dove is not only beautiful but also plays an important role in dispersing seeds in Australian rainforests.
Author provided

The future of Australia’s native pigeons however, may depend on our domestic pigeons. Australia’s domestic pigeon population — both feral and captive – is large and interconnected by frequent local and interstate movements. Pigeon racing, for example, involves releasing captive birds hundreds of kilometres from their homes only so they may find their way back. While most birds do navigate home, up to 20% will not return, of which some will join feral pigeon populations. Birds are also traded across the country and illegally from overseas. These movements, together with poor biosecurity practices, mean that captive pigeons can and do mingle with feral domestic pigeons.

And here’s a paradox. Could Australia’s feral domestic pigeons become the vector for a dramatic decline of columbids – native species on which Australian ecosystems rely?

Emerging viral epidemics

In recent years, two notable infectious diseases have been found to affect our captive domestic pigeons: the pigeon paramyxovirus type 1 (PPMV1) and a new strain of the pigeon rotavirus (G18P). These diseases are notable because in captive domestic flocks they are both spectacularly lethal and difficult to control.

PPMV1, although likely to have originated overseas, is now endemic in Australia. This virus has jumped from captive to feral domestic pigeon populations on several occasions, but fortunately has yet to establish in feral populations.

Domestic pigeons suffer high mortality rates after being infected with either pigeon paramyxovirus ‘PPMV1’ or pigeon rotavirus ‘G18P’.
Dr Colin Walker

G18P is thought to have spread to Victoria and South Australia from a bird auction in Perth in 2016. PPMV1 also spread rapidly to multiple states following its first appearance in Melbourne in 2011.

The movements of captive pigeons, and their contact with their feral counterparts, can be the route through which virulent and lethal diseases – such as the PPMV1 and the G18P – may spread to Australia’s native columbids.

Pigeon paramyxovirus and pigeon rotavirus are known to have escaped from captive domestic pigeons into feral domestic pigeons (black arrow). The risk is that these viruses will establish in feral pigeon populations and cause epidemics in our diverse and ecologically important wild native columbids (red arrow).
Author provided

What have we got to lose?

Fortunately, neither PPMV1 nor G18P has crossed over to Australia’s native columbids. We can’t say how likely this is, or how serious the consequences would be, because we have not previously observed such viral infections among our native pigeons.

If the viruses prove equally lethal to native columbids as they are to domestic pigeons, we could see catastrophic population declines across numerous columbid species in Australia over a short period of time.

Should these viruses spread (via feral domestic pigeons), the control and containment of losses among our native pigeon species would be near impossible. Such a nightmare scenario can only be avoided by predicting if and how these viruses might “spill over” into wild columbids so that we can prevent this in the first place.

Maps of Australia showing the overlapping distribution of our 22 native pigeon and dove species (left) and the distribution (in orange) and verified individual records (red dots) of introduced feral domestic pigeons (right).
Atlas of Living Australia, Birdlife International

Protecting our pigeons

Agricultural poultry is routinely screened to check their vulnerability to threats like the PPMV1 and G18P. Such screening is an appropriate response to protect our agricultural industry.

For our native pigeons and doves however, no such similar testing is planned. Based on progress in veterinary vaccine development and advancements in understanding of feral pigeon control, the knowledge and technology required to mitigate this threat should be relatively inexpensive. The threat for these species can be actively managed, now, by improving our biosecurity and vaccination programs for captive domestic pigeons, and eradicating feral domestic pigeons.

The ConversationThe protection of our native columbids however, ultimately relies on valuing their ecosystem functions in the first place.

Andrew Peters, Senior Lecturer in Veterinary Pathology, Charles Sturt University

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

Widespread invasive species control is a risky business



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Partula snails were driven to extinction in the wild by introduced predators.
Wikimedia Commons

R. Keller Kopf, Charles Sturt University; Dale Nimmo, Charles Sturt University, and Paul Humphries, Charles Sturt University

In 1977, on the islands of French Polynesia, government authorities released a predatory snail. They hoped this introduction would effectively control another species of invasive snail, previously introduced to supply escargot.

Instead, by the early 1980s, scientists reported alarming declines of native snail populations. Within ten years, 48 native snail species (genus Partula) had been driven to extinction in the wild.

The extinction of the Partula is notorious partially because these snails were, before going extinct, the study subjects of the first test in nature of Darwin’s theory of evolution by natural selection.

In the decades since, attempts to control and eradicate invasive species have become common, generally with far better results.

However, our paper, published today in Nature Ecology and Evolution, highlights the importance of scientific evidence and independent assessments when deciding whether to control or eradicate invasive species.

From islands to continents

Increasingly, large-scale invasive species control initiatives are being proposed worldwide. As early as 2018, a herpes virus will be released in Australia’s largest river system, targeting invasive common carp. As part of its Threatened Species Strategy, Australia is also planning to kill two million feral cats.

Across the Tasman Sea, New Zealand has made a bold commitment to remove three groups of invasive predators entirely by 2050.

New Zealand looks to eradicate three groups of invasive predators: rodents, mustelids, and the common brushtail possum.
Geoff Whalan/Flickr, CC BY-NC-SA

It’s not just Australians and Kiwis making ambitious invasive species control proposals: bounties are being paid to catch invasive fish in the United States. The European Union has blacklisted 37 species of plants and animals within 4 million square kilometres, many of which are well-established and will be targeted by control (not preventative) measures.

Meanwhile, new gene editing technology has made the continental-scale eradication of invasive species a real possibility, for example by implementing gene drives that reduce breeding success. If you haven’t heard of it, CRISPR is a startling new biotechnology that makes genetic modification of plants and animals much easier. It offers new potential solutions to some of the world’s worst environmental, agricultural and human health problems.

These schemes will be implemented across large and complex social-ecological systems, and some options – like releasing a virus or genetically engineered species – may be irreversible.

Managing risk

While these projects may yield great benefits, we must be aware of the potential risk of unexpected and undesirable outcomes.

A prime example is the project to remove invasive carp from a million square kilometres of Australia’s rivers. Some scientists have expressed concern about the potential for the virus to jump species, and the effects of having hundreds of tonnes of dead fish fouling waterways and sapping oxygen from the water. The CSIRO and those planning the release of the virus suggest it is safe and effective.

Despite extensive media reporting giving the impression that the plan is approved to go ahead, the National Carp Control Plan has yet to publish a risk assessment, and is planning to deliver a report in 2018.

Removing well-established invasive species can create unforeseen consequences. These species can play significant roles in food webs, provide shelter for native animals, support ecosystem services, and their sudden death can disrupt ecological processes that are important to native species.

For example, a large amount of time and effort was spent in removing the non-native tamarix (or “salt cedar”) in the southwestern United States, because of the belief it was harming the water table.

Yet, subsequent research has indicated that the negative effects of tamarix have been exaggerated. In some areas, the plant is actually used by large numbers of endangered flycatchers to nest and fledge their young.

A corn bunting perches on a blooming tamarix.
Georgios Alexandris/shutterstock

A science-based solution

In our paper, we highlight a series of considerations that should be addressed before plunging into large-scale invasive species control.

Fundamentally, there must be a demonstrable ecological and social benefit from control or eradication, above and beyond the purely ideological. At first this might seem facile, but invasive species control initiatives are often highly politicised, with science taking a back seat. Given scarce funding for conservation, it is crucial that resources are not squandered on programmes that may not deliver – or could cause environmental damage.

We must avoid assuming that attempting to control invasive species will, by default, solve our environmental problems. This means addressing the full range of human pressures which negatively affect biodiversity. We must also consider how removing an influential invasive species could benefit other invasive species, harm native species through increased predation and competition, or alter ecological processes or habitat.

Comprehensive risk-benefit assessment of invasive species control programs allow decision-makers to proactively avoid, manage or accept these risks.

For example, tonnes of decomposing carp post-virus may cause short-term water quality issues, or the death of native species. Ultimately, however, these risks could be acceptable if the virus is effective, and allows native species a window of opportunity to recover.

The ConversationLarge-scale invasive species control demands careful investigation of the risks and rewards. We hope our paper can provide policy-makers with better guidelines for science-based decision-making.

R. Keller Kopf, Research fellow, Charles Sturt University; Dale Nimmo, ARC DECRA Fellow, Charles Sturt University, and Paul Humphries, Senior lecturer in Ecology, Charles Sturt University

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

The bark side: domestic dogs threaten endangered species worldwide



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A feral dog chasing a wild boar, Banni grasslands, India.
Chetan Misher/Facebook

Tim Doherty, Deakin University; Aaron J. Wirsing, University of Washington; Chris Dickman, University of Sydney; Dale Nimmo, Charles Sturt University; Euan Ritchie, Deakin University, and Thomas Newsome, Deakin University

Humans and their canine companions share many close bonds. Wolves (Canis lupus) were the first animal domesticated by people, some time between 15,000 and 50,000 years ago. The Conversation

There are now an estimated 1 billion domestic dogs across their near-global distribution.

Domestic dogs include feral and free-ranging animals (such as village and camp dogs), as well as those that are owned by and completely dependent on humans (pet dogs).

Our latest research reveals that the ecological “pawprint” of domestic dogs is much greater than previously realised.

Using the IUCN Red List of Threatened Species, we counted how many species are negatively affected by dogs, assessed the prevalence of different types of impacts, and identified regions with the greatest number of affected species.

A dog with a black-naped hare, Maharashtra, India.
Hari Somashekhar/Facebook

Dogs are third-most-damaging mammal

We found that dogs are implicated in the extinction of at least 11 species, including the Hawaiian Rail and the Tonga Ground Skink. Dogs are also a known or potential threat to 188 threatened species worldwide: 96 mammal, 78 bird, 22 reptile and three amphibian species. This includes 30 critically endangered species, two of which are classed as “possibly extinct”.

These numbers place dogs in the number three spot after cats and rodents as the world’s most damaging invasive mammalian predators.

Even though dogs have an almost global distribution, the threatened species they are known to affect are concentrated in certain parts of the globe. South-East Asia, South America, Central America and the Caribbean each contain 28 to 30 threatened species impacted by dogs. Other hotspots include Australia, Micro/Mela/Polynesia and the remainder of Asia.

Lethal and non-lethal impacts

Predation was the most commonly reported impact of dogs on wildlife. The typically omnivorous diet of dogs means they have strong potential to affect a diversity of species. For instance, dogs killed at least 19 endangered Kagu (a ground-dwelling bird) in New Caledonia in 14 weeks. Threatened species with small population sizes are particularly vulnerable to such intense bouts of predation.

The frequency of different types of dog impact on threatened species.
https://authors.elsevier.com/a/1Uxs~1R~e71Xl

Aside from simply killing animals, dogs can harm wildlife in other ways, such as by spreading disease, interbreeding with other canids, competing for resources such as food or shelter, and causing disturbances by chasing or harassment. For example, contact with domestic dogs increases disease risk for endangered African Wild Dogs in Kenya.

Part of the problem is that when wild animals perceive dogs as a threat, they may change their behaviour to avoid them. One study near Sydney found that dog walking in parklands and national parks reduced the abundance and species richness of birds, even when dogs were restrained on leads.

None of the Red List assessments mentioned such indirect risk effects, which suggests that their frequency is likely to be much higher than reported.

Feral dogs chasing Indian wild ass at Little Rann of Kutch, India.
Kalyan Varma/Facebook

Friend and foe

Despite their widespread and sometimes severe impacts on biodiversity, dogs can also benefit some species and ecosystems.

For example, in Australia, the closely related dingo (Canis dingo) can suppress populations of introduced predators such as red foxes (Vulpes vulpes), and in doing so can benefit smaller native prey. It is possible that domestic dogs could perform similar ecological roles in some situations.

In some regions, dogs and their keen noses have been trained to help scientists find threatened species such as Tiger Quolls. Elsewhere they are helping to flush out and control feral cats.

An emerging and exciting conservation role for dogs is their growing use as “guardian animals” for wildlife, with the remarkable story of Oddball being the most well known.

Managing the problem

Dogs not only interact with wildlife, but can also attack and spread disease to humans, livestock and other domestic animals. As such, managing the problem requires looking at ecological, cultural and social perspectives.

Some of the regions with high numbers of species threatened by dogs are also hotspots for urbanisation and road building, which make it easier for dogs to access the habitats of threatened species. Urban development increases food waste, which feeds higher numbers of dogs. As dogs expand into new areas, the number of species they impact is likely to grow.

Street dogs scavenging food waste in India.
Achat1234/wikimedia

We can protect wildlife by integrating human health and animal welfare objectives into dog management. Vaccination and desexing campaigns can reduce disease risk and overpopulation problems. We should also focus on responsible dog ownership, removing dogs without owners, and reducing access to food waste.

Given the close relationship between humans and dogs, community engagement should form the basis of any management program. More research is needed to get a better picture of the scale of the problem, and of how dogs interact with other threats such as habitat loss. Such actions are critically important for ensuring the conservation of wildlife threatened by dogs around the world.


This article was co-authored by Dr Al Glen from Landcare Research, New Zealand and Dr Abi Vanak from the Ashoka Trust for Research in Ecology and the Environment, India. These institutions had no role in the design or funding of this research.

Tim Doherty, Research Fellow, Deakin University; Aaron J. Wirsing, Assistant Professor, School of Environmental and Forest Sciences, University of Washington; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Dale Nimmo, ARC DECRA Fellow, Charles Sturt University; Euan Ritchie, Senior Lecturer in Ecology, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University, and Thomas Newsome, Fulbright Scholar and Postdoctoral Research Fellow, Deakin University

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

Tipping the scales on Christmas Island: wasps and bugs use other species, so why can’t we?


Susan Lawler, La Trobe University

A couple of days ago I published an article with Peter Green about the imminent release of a tiny wasp that will be used for biological control of a bug that feeds the crazy ants that kill red crabs on Christmas Island.

It is understandable that people are nervous about the introduction of exotic species to manage wildlife in a natural setting. It turns out that ecologists are even more nervous than the public about this, so if they have decided to do it anyway, then there is a remarkably good reason.

Parasitoid wasps use scale insects

The release of the wasp has concerned some readers because they imagine swarms of biting insects setting up their nests in the back garden. The truth is that the wasps that will be released are tiny and unlikely to be noticed at all.

First of all, Tachardiaephagus somervillei are only 2 mm long and cannot sting humans or other animals. They do not form colonies, they do not swarm, and they do not build nests. In fact, they won’t be at all interested in hanging around human habitations unless there is a tree nearby containing a colony of the yellow lac scale insect (Tachardina aurantiaca).

This is because these wasps are parasitoids – a type of parasitic organism that kills its host species. They don’t need a nest or a colony because the scale insects they target are both their food source and their home.

The specificity of the wasp for this particular type of scale insect can be seen in the first part of their Latin names: Tachardiaephagus literally means “eater of Tachardina”.

Scale insects use ants

Scale insects are a type of true bug (in the Order Hemiptera) that line up along tree branches like barnacles, sucking sap from the tree and in their mature form, releasing a sweet liquid known as honeydew from their backsides for the benefit of ants. They don’t do this for nothing. Their strategy is to use the ants as body guards.

In a situation where scale insects are relatively rare this increases the number of the ants who will in turn protect the scale insects. On Christmas Island, where the introduced yellow lac scale insects have become common because they do not have any natural predators, the invasive crazy ants have access to large quantities of honeydew. In this case, the crazy ants are using the yellow lac scale insects as a super abundant food source.

The super colonies that have formed as a result have instigated an environmental disaster. The crazy ants kill red crabs and other species mostly due to their extremely high densities driven by the abundance of honeydew.

Any detractors concerned about the dangers of yet another invasive species have not fully grasped the consequences of doing nothing. Chemical baiting of the ants is ongoing but has consequences for other animals and is not environmentally desirable or sustainable.

People using wasps

If the scale insects can use the ants as bodyguards and the ants can use the scale insects as a free food source, why can’t we use a tiny wasp as a biological control?

Unlike birds, lizards or other predators that may be deterred by ants crawling all over the scale insects, the tiny parasitoid wasps can slip through and lay their eggs in a scale insect without being noticed by the ants. Their eggs hatch and develop inside the scale insect, emerging as adult wasps that are ready to lay their eggs in another scale insect nearby.

In essence, the wasp uses the scale insect as a one-stop nursery, food source and conveniently located launching pad for the next generation. Inside a scale insect colony, they are likely to find another scale insect less than a centimetre from where they were born.

Consider how this will allow the wasp population to quickly grow and, perhaps, reduce the scale insect colony density so that the wasps will eventually have to fly further and further to find another scale insect. At some point the effort to find more scale insects will balance the benefit of finding an insect, and the two populations (wasp and scale insect) will reach a new equilibrium at a lower density.

How will the crazy ants respond?

The wasp will not run out of food, nor will the scale insects become extinct, but the ants will find themselves deprived of excess honeydew and will have to adjust their populations accordingly.

How do you empirically test the response of the ants to the removal of excess honeydew from their environment? Well, you can’t remove the scale insects but you can prevent the ants from getting into the trees where the scale insects live, even though it wasn’t easy. Apparently, doing this involves Glad wrap, Mr Sheen furniture polish, and daily vigilance by a research student.

The result was a 95% decrease in crazy ant activity in a few weeks, an outcome that suggests this approach has every chance of reducing the impacts of crazy ants on Christmas Island.

What happens next?

I understand that the team is gathering in Malaysia today to pack up some wasps and fly them to Christmas Island. The release will not happen right away, as the wasps will be acclimatised and grown up in large numbers in a dedicated facility. Monitoring programs are planned to observe the impacts, both short and long term, on the scale insects, the ants, the crabs and the forest structure.

The research to understand the ecology of Christmas Island sufficiently to identify a biological control agent started decades ago, and many scientists were involved along the way. It is not possible to provide links to all the research articles produced thus far, but here is a link to the final risk report.

I am not involved with the research but am familiar with it and in my view there are two things that could happen next. Either the wasp will fail to reduce the scale insect populations and nothing changes, or they will reduce the scale insect populations which could kick start a cascade of beneficial environmental outcomes for Christmas Island.

We are all really hoping that it is the latter.

The Conversation

Susan Lawler, Senior Lecturer, Department of Ecology, Environment and Evolution, La Trobe University

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

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


Tim Doherty, Deakin University; Chris Dickman, University of Sydney; Dale Nimmo, Charles Sturt University, and Euan Ritchie, Deakin University

Invasive species are a threat to wildlife across the globe – and invasive, predatory mammals are particularly damaging.

Our research, recently published in Proceedings of the National Academy of Sciences, shows that these predators – cats, rats and foxes, but also house mice, possums and many others – have contributed to around 60% of bird, mammal and reptile extinctions. The worst offenders are feral cats, contributing to over 60 extinctions.

So how can we stop these mammals eating away at our threatened wildlife?

Counting the cost

Our study revealed that invasive predators are implicated in 87 bird, 45 mammal and 10 reptile extinctions — 58% of these groups’ contemporary extinctions worldwide.

Invasive predators also threaten 596 species classed as vulnerable, endangered or critically endangered on the International Union for the Conservation of Nature Red List. Combined, the affected species include 400 birds, 189 mammals and 149 reptiles.

Twenty-three of the critically endangered species are classed as “possibly extinct”, so the number of extinctions above is likely to be an underestimate.

Until now, these shocking statistics have been unknown, and the heavy toll of invasive predators on native biodiversity grossly underappreciated. Species extinctions attributed to invasive predators include the Hawaiian rail (Zapornia sandwichensis) and Australia’s lesser bilby (Macrotis leucura).

Australia’s lesser bilby, now extinct.

Who are the worst offenders?

We found that three canids (including the red fox and feral dogs), seven members of the weasel family or mustelids (such as stoats), five rodents, two primates, two mongooses, two marsupials and nine species from other families negatively impact threatened species. Some of these species, such as hedgehogs and brushtail possums, don’t immediately spring to mind as predators, yet they are known to prey on many threatened species.

Feral cats threaten the most species overall (430), including 63 that have become extinct. This equates to one-quarter of all bird, mammal and reptile extinctions – making the feral cat arguably the most damaging invasive species for animal biodiversity worldwide.

Five species of introduced rodent collectively threaten 420 species, including 75 extinctions. While we didn’t separate out the impacts of individual rodent species, previous work shows that black rats (Rattus rattus) threaten the greatest number of species, followed by brown rats (R. norvegicus) and Pacific rats (R. exulans).

The humble house mouse (Mus musculus) is another interesting case. Despite their small size, house mice have been recorded eating live chicks of albatrosses, petrels and shearwaters.

Other predators that threaten large numbers of species are the domestic dog (Canis familiaris), pig (Sus scrofa), small Indian mongoose (Herpestes auropunctatus), red fox (Vulpes vulpes) and stoat (Mustela erminea).

Invasive mammalian predators (clockwise from top left): feral dog, house mouse, stoat, feral pig, feral cat, brushtail possum, black rat, small Indian mongoose and red fox (centre).
Clockwise from top-left: Andrey flickr CC BY 2.0 https://flic.kr/p/4M2E7y; Richard Adams flickr CC BY 2.0 https://flic.kr/p/7U19v9; Mark Kilner flickr CC BY-NC-SA 2.0 https://flic.kr/p/4D6LPe; CSIRO CC BY 3.0 http://www.scienceimage.csiro.au/image/1515; T. Doherty; Toby Hudson CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:BrushtailPossum.jpg; CSIRO CC BY 3.0 http://www.scienceimage.csiro.au/image/10564; J.M.Garg CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:Herpestes_edwardsii_at_Hyderaba.jpg; Harley Kingston CC BY 2.0 https://flic.kr/p/ceWFr7 (centre).

Island species most at risk

Species found only on islands (insular endemics) account for 81% of the threatened species at risk from predators.

The isolation of many islands and a lack of natural predators mean that insular species are often naive about new predators and lack appropriate defensive responses. This makes them highly vulnerable to being eaten and in turn suffering rapid population decline or, worse, extinction. The high extinction rates of ground-dwelling birds in Hawaii and New Zealand — both of which lack native mammalian predators — are well-known examples.

Accordingly, the regions where the predators threatened the greatest number of species were all dominated by islands – Central America and the Caribbean, islands of the Pacific, the Madagascar region, New Zealand and Hawaii.

Conversely, the continental regions of North and South America, Europe, Africa and Asia contain comparatively few species threatened by invasive predators. While Australia is a continent, it is also an island, where large numbers of native birds and mammals are threatened by cats and foxes.

Along with feral cats, red foxes have devastated native mammals in Australia.
Tom Rayner

Managing menacing mammals

Understanding and mitigating the impact of invasive mammal predators is essential for reducing the rate of global biodiversity loss.

Because most of the threatened species studied here live on islands, managing invasive predators on islands should be a global conservation priority. Invasive predators occur on hundreds of islands and predator control and eradication are costly exercises. Thus, it is important to prioritise island eradications based on feasibility, cost, likelihood of success and potential benefits.

On continents or large islands where eradications are difficult, other approaches are needed. This includes predator-proof fencing, top-predator restoration and conservation, lethal control, and maintenance of habitat structure.

Despite the shocking statistics we have revealed, there remain many unknowns. For example, only around 40% of reptile species have been assessed for the Red List, compared to 99% for birds and mammals. Very little is known about the impact of invasive predators on invertebrate species.

We expect that the number of species affected by invasive predators will climb as more knowledge becomes available.


This article was co-authored by Al Glen from Landcare Research, New Zealand.

The Conversation

Tim Doherty, Research Fellow, Deakin University; Chris Dickman, Professor in Terrestrial Ecology, University of Sydney; Dale Nimmo, Lecturer in Ecology, Charles Sturt University, and Euan Ritchie, Senior Lecturer in Ecology, Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University

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

Feral animals are running amok on Australia’s islands – here’s how to stop them


Chris Wilcox, CSIRO and Erin McCreless, University of California, Santa Cruz

Australia has some 8,300 islands, many of them home to threatened species. But humans have introduced rodents and predators such as feral cats and foxes to many of these islands, devastating native wildlife and changing entire island ecosystems. Removing invasive mammals has proven to be a very effective tool for protecting island species.

As a result, the federal government has made it a priority to remove invasive vertebrates from islands where they pose the most severe threats to native plants and animals.

But choosing where to remove those invasives is difficult. We don’t have complete information about the distribution of native species and threats across the nation’s 8,300 islands, and we haven’t been able to predict where eradication will have the most benefit.

However, in a recent study published in Nature Communications, our global team of scientists looked at islands around the world to consider where we can get the biggest bang for our buck.

Eradicating cats, rats and pigs from Flinders Island in Tasmania would help save forty-spotted pardalotes.
Francesco Veronesi, CC BY-SA

It costs money to save species

The total cost of the recently completed rat and rabbit eradication on Macquarie Island was A$27 million. The proposed removal of rats from Lord Howe Island off New South Wales is expected to cost A$9 million.

Federal Environment Minister Josh Frydenberg has just announced funding to remove feral cats from five islands: Christmas Island, Dirk Hartog Island and the French Islands in Western Australia; and Bruny and King Islands in Tasmania.

Conservation dollars are limited, so it is important that these pricey interventions be focused on the islands where they will go the furthest toward conserving native island biodiversity.

Conversely, it is essential that we identify places where they won’t provide much benefit, either because a threatened species is likely to go extinct regardless of such interventions, or because the invasive species actually poses little threat.

It cost A$24 million to eradicate rats and rabbits from Macquarie Island.
Macquarie Island image from http://www.shutterstock.com

Island life

We analysed the effects of invasive mammals on 1,200 globally threatened species across more than 1,000 islands to develop a model for where eradicating invasive wildlife will provide the greatest benefits to island species.

We estimate nearly half of threatened species populations on islands could disappear without conservation efforts. But targeted eradication could prevent 40-75% of these losses.

We found that just a few types of invasive mammals – rats, cats, pigs, mongooses and weasels – are most strongly associated with the disappearance of native species from islands.

Importantly, our study shows that the impacts of invasive mammals vary widely across the type of native species (native amphibians, birds, reptiles or mammals) and the conditions of the islands on which they live.

For example, we found that removing invasive mammals from small, dry islands could halve the extirpation risk for threatened native birds and mammals, but doing so on large, wet islands would have less benefit.

Australia’s most important islands

Our study included thirty-three Australian islands, home to 17 species of globally threatened birds, mammals and amphibians including the woylie (or brush-tailed bettong), Tasmania devils, black-browed albatross and Cooloola sedgefrog.

Eighteen of these islands are also home to introduced rats, cats or pigs, which potentially threaten native species with extinction.

Traditionally, we might assume that eradicating cats and rats would always reduce bird extinctions. However, our study suggests otherwise.

Eradicating cats and rats could help northern quolls on some islands.
Quoll image from http://www.shutterstock.com

Rat or cat eradication may have little benefit on some islands. This is either because these invasive species have relatively minor impacts in some island environments, or because the native population is likely to go extinct regardless of conservation interventions.

So our study shows that of these 18 islands, eradicating invasive species on only two would likely prevent extinction of three native species populations. These are the eradication of cats and rats on Groote Eylandt in the Northern Territory, which would avert the extirpation (that is, the island-level extinction) of the northern quoll and northern hopping mouse; and the eradication of cats, rats and pigs on Flinders Island in Tasmania, which would avert the extirpation of the forty-spotted pardalote.

While this sounds like a tiny number, remember we haven’t looked at all of Australia’s islands and the species that live on them. Indeed, we only included species considered threatened at a global level. For the other islands not included in our study, species threatened with extinction at regional or national scales may – or may not – benefit from eradicating invasive species. As more information comes in on these islands, our analysis can suggest which of these we should focus on.

The Conversation

Chris Wilcox, Senior Research Scientist, CSIRO and Erin McCreless, Research scientist, University of California, Santa Cruz

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