‘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.

Who’s afraid of the giant African land snail? Perhaps we shouldn’t be



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Giant African land snails can grow up to 15cm long.
Author provided

Luke S. O’Loughlin, La Trobe University and Peter Green, La Trobe University

The giant African land snail is a poster child of a global epidemic: the threat of invasive species. The snails are native to coastal East Africa, but are now found across Asia, the Pacific and the Americas – in fact, almost all tropical mainlands and islands except mainland Australia.

Yet, despite their fearsome reputation, our research on Christmas Island’s invasive snail population suggests the risk they pose to native ecosystems has been greatly exaggerated.

Giant African land snails certainly have the classic characteristics of a successful invader: they can thrive in lots of different places; survive on a broad diet; reach reproductive age quickly; and produce more than 1,000 eggs in a lifetime. Add it all together and you have a species recognised as among the worst invaders in the world.

The snails can eat hundreds of plant species, including vegetable crops (and even calcium-rich plaster and stucco), and have been described as a major threat to agriculture.

They have been intercepted at Australian ports, and the Department of Primary Industries concurs that the snails are a “serious threat”.

Despite all this, there have been no dedicated studies of their environmental impact. Some researchers suggest the risk to agriculture has been exaggerated from accounts of damage in gardens. There are no accounts of giant African land snails destroying natural ecosystems.

Quietly eating leaf litter

In research recently published in the journal Austral Ecology, we tested these assumptions by investigating giant African land snails living in native rainforest on Christmas Island.

Giant African land snails have spread through Christmas Island with the help of another invasive species: the yellow crazy ant.

Until these ants showed up, abundant native red land crabs ate the giant snails before they could gain a foothold in the rainforest. Unfortunately, yellow crazy ants have completely exterminated the crabs in some parts of the island, allowing the snails to flourish.

We predicted that the snails, which eat a broad range of food, would have a significant impact on leaf litter and seedling survival.

Unexpectedly, the snails we observed on Christmas Island confined themselves to eating small amounts of leaf litter.
Author provided

However, our evidence didn’t support this at all. Using several different approaches – including a field experiment, lab experiment and observational study – we found giant African land snails were pretty much just eating a few dead leaves and little else.

We almost couldn’t distinguish between leaf litter removal by the snails compared to natural decomposition. They were eating leaf litter, but not a lot of it.

We saw almost no impact on seedling survival, and the snails were almost never seen eating live foliage. In one lab trial, we attempted to feed snails an exclusive diet of fresh leaves, but so many of these snails died that we had to cut the experiment short. Perhaps common Christmas Island plants just aren’t palatable.

It’s possible that the giant African land snails are causing other problems on Christmas Island. In Florida, for example, they carry parasites that are a risk to human health. But for the key ecological processes we investigated, the snails do not create the kind of disturbance we would assume from their large numbers.

We effectively excluded snails from an area by lining a fence with copper tape.
Author provided

The assumption that giant African land snails are dangerous to native plants and agriculture comes from an overriding sentiment that invasive species are damaging and must be controlled.

Do we have good data on the ecological impact of all invasive species? Of course not. Should we still try to control all abundant invasive species even if we don’t have evidence they are causing harm? That’s a more difficult question.

The precautionary principle drives much of the thinking behind the management of invasive species, including the giant African land snail. The cost of doing nothing is potentially very high, so it’s safest to assume invasive species are having an effect (especially when they exist in high numbers).

But we should also be working hard to test these assumptions. Proper monitoring and experiments give us a true picture of the risks of action (or inaction).

The ConversationIn reality, the giant African land snail is more the poster child of our own knee-jerk reaction to abundant invaders.

Luke S. O’Loughlin, Research fellow, La Trobe University and Peter Green, Head of Department, Ecology, Environment and Evolution, La Trobe University

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.

Here’s what you need to know about exotic pets in Australia



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Red-eared sliders were once popular pets but are currently banned in Australia. These turtles are still regularly found in the wild and being kept as illegal pets.
Pablo Garcia-Diaz, Author provided

Pablo García-Díaz, University of Adelaide; Miquel Vall-llosera, and Phill Cassey, University of Adelaide

A taste for owning exotic animals can be addictive – the more flamboyant the better. Earlier this month border security agents found 50 live turtles and lizards smuggled in Lego boxes sent from Indonesia. In April customs officials found a parcel marked “2 pair shoes” that turned out to contain venomous vipers, tarantulas and scorpions.

According to the Animals Medicines Australia 2016 survey some two-thirds of Australian households have pets – more than 24 million animals in total. Not surprisingly, dogs and cats are the most popular (38% and 29% of households, respectively), whereas aquarium fish and birds rank somewhere in the middle (both 12%), and reptiles and less common mammals are kept in some households (both less than 5%).

The federal government largely legislates the owning of exotic pets. The law defines “exotic” as “animals that do not occur naturally in the wild in Australia” – which actually includes dogs and cats. However “domesticated mammals”, which also covers cows, sheep and other farm animals, are generally legal to buy and own. Commercial trade in exotic reptiles and amphibians, on the other hand, has been banned since 1999.

Whether an exotic animal is kept legally or not, some will find their way to the Australian wild through escape or release, posing a potential pest risk. There are some simple things governments and pet owners can do to improve the way this risk is handled, to keep animals and humans safe.

We don’t really know how many exotics are in Australia

Most local councils only require dogs (and sometimes cats) to be registered by their owners. Other pets, whether exotic or native, do not need to be registered. Indeed an owner of an exotic animal is not required to report or register the animal in any way. This means there are very little reliable data and it’s difficult to say how many exotic pets are kept in Australia.

We highlight two cases from our own research: birds and reptiles.

Bird-keeping is common in Australia, particularly of parrots and finches. More than half the bird species traded are exotic and mostly originate in South America, Africa and Asia. Rose-ringed Parakeets are one of the most commonly kept exotic pet bird, and the most frequently reported as having escaped. They are seen as a potential threat because they are a serious agricultural pest in its’ native and exotic distribution, and have a very high risk of establishing in Australia.

The Rose-ringed parakeet is a common pet in Australia and presents a potential biosecurity risk.
Dick Danies/Wikimedia

Reptiles – generally skinks, turtles and dragons – are less popular pets than birds. Nonetheless, judging from the posts on public trading webpages, a variety of native reptile species are kept and traded by hobbyists, also including crocodiles and snakes.

Unfortunately, little is known about native reptile trading in Australia and further research is needed. And while native reptiles can be kept legally, illegal exotic reptiles are a serious problem. In a previous article for The Conversation, we reported that 28 alien reptile species were illegally kept in Victoria between 1999 and 2012. More than a third were highly venomous snakes, posing a real risk to human safety.

Responsibly caring for exotic pets

If you own or want to buy an exotic pet, you must be aware of the regulations that apply to you (you can Google “exotic pet regulations” plus the name of your state or territory). Each jurisdiction keeps official lists of those species that may be kept within their borders, with or without a permit. These lists can be found on local government websites or obtained from their relevant departments.

People should also be able to register all of their pets, including exotic ones. Governments need to promote public awareness of the importance of registration (even if it’s not legally required), and ensure the processes are simple, accessible and affordable.

If you lose your exotic pet, it’s important to alert your state or territory biosecurity agency. Each jurisdiction has its own agency, but examples are the Western Australia Department of Agriculture and Food or Agriculture Victoria. If you want to recover your lost pet the best available option is to report your loss to one of the many missing animal websites.

Governments, when facilitating the registration process, will need to establish best practices to collect and analyse information so that the nature and extent of pet ownership may be better known, monitored and managed.

The ConversationUltimately, the burden of safe and responsible pet ownership should be shared. While public awareness is crucial, the key to a sustainable pet trade is mutual partnership between pet owner communities and governments. This is particularly important as pet sales and trade shift further to an online environment.

Pablo García-Díaz, PhD candidate in invasion ecology, University of Adelaide; Miquel Vall-llosera, Assistant Professor in Shinshu University, Japan, 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.

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.

Millions of rotting fish: turtles and crays can save us from Carpageddon


Ricky Spencer, Western Sydney University; Claudia Santori, University of Sydney; James Van Dyke, Western Sydney University, and Michael B. Thompson, University of Sydney

The Australian government plans to target invasive European carp with a herpes virus, leaving hundreds of thousands of tonnes of carp rotting in the river systems that supply our drinking water and irrigate the fruit and vegetables we eat. The Conversation

The aim of “Carpageddon” is to return Australian aquatic ecosystems to their pre-carp state by eliminating or reducing the serious pest species.

Carp currently make up 83% of the fish biomass in the Murray-Darling Basin in New South Wales. They alter river and lake habitats in a way that reduces habitability for native species, including five threatened species. They also have a major impact on inland fisheries, with an estimated annual economic cost of A$22 million.

This all makes a substantial argument for releasing a carp killing herpes virus. However, dealing with the aftermath could cost A$30 million for NSW alone.

Cleanup costs could be reduced by introducing viruses to discrete populations. However, if the virus escapes into the Murray-Darling Catchment, we will lose control of the virus spread and carp death will be rapid and widespread.

Without a dedicated cleanup effort, the sudden influx of millions of dead fish could permanently pollute our waterways. A potential solution is to recruit nature’s cleaners to do our work for us – scavengers like turtles and crayfish. They could save us from carcass-choked rivers and wetlands, but only if we can protect them from endangerment and extinction.

Turtles and crayfish are our unlikely saviours

Carp carcasses are normally eaten by scavengers, a process that’s vital to the food web (the system of what eats what in a given environment). In fact, the majority of dead fish are consumed by scavengers.

As such, simply removing the carp carcasses may reduce the overall amount of nutrients in the ecosystem. This would destabilise the food web, especially for scavengers such as turtles and crayfish who rely on them.

Instead, these scavenging species can provide crucial biocontrol. They would eat any decomposing flesh in our water systems, particularly in areas we can’t easily access with nets, boats and trucks. They would maintain the quality of our waterways in three ways:

  • Slow the spread of bacteria that break down dead fish, keeping water safe to drink and limiting deoxygenation that could devastate native fish species;

  • Digest carp directly into basic nutrients (fertiliser) that is more readily absorbed by plants and primary producers;

  • Semi-permanently store carp nutrients in their slow to decompose shells and exoskeletons, preventing or limiting toxic algal blooms caused by excess nutrients in water.

Our unlikely saviours are also dying

Threats to crayfish include agricultural and urban expansion, recreational fishing, pollution from surface runoff and insecticides, and introduced species such as trout and cane toads.

Consequently, native crayfish are declining, with nearly 80% of Spiny Crayfish recognised as threatened. However, yabbies have expanded their range.

Turtles on the other hand, are in sharp decline throughout the Murray Catchment and elsewhere in Australia. A recent gathering of turtle experts in Canberra discussed major threats to turtles, and ways to protect them.

The meeting addressed major causes behind the 2% annual mortality rate of adult turtles that is leading the species to rapid extinction. Cars and foxes kill a significant number of adult turtles every year, and foxes destroy more than 95% of turtle nests in the Murray-Darling Basin.

Changes to the hydrology of the Murray Catchment may also impact turtles. Some species require permanent wetlands, while others prefer to move between temporarily flooded wetlands and more permanent waters.

Following modern water management, some temporary wetlands are permanently flooded or gone and some permanent wetlands are dry.

All of these threats together may cause turtles to become functionally extinct in the near future, meaning they cannot play their significant role in the ecosystem anymore.

How can we help conserve the turtle population?

Such a sudden decimation of carp has potentially catastrophic consequences. But it may also be an excellent opportunity to recognise the importance of turtles and prioritise their conservation.

In a recent study, headstarting was named as the only management tool that could protect freshwater turtles from the multiple threats throughout their life cycle and eliminate all risks of extinction.

Headstarting involves rearing eggs or newborn animals in captivity, then releasing them into the wild. It has been controversial for decades, but releasing thousands of little turtles throughout the Murray River just might rescue us from the post-apocalyptic effects of Carpageddon.

Ricky Spencer, Associate Professor of Ecology, Western Sydney University; Claudia Santori, PhD candidate, University of Sydney; James Van Dyke, Postdoctoral fellow, Western Sydney University, and Michael B. Thompson, Professor in Zoology, University of Sydney

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