A numbers game: killing rabbits to conserve native mammals



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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.




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


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.




Read more:
Mourn our lost mammals, while helping the survivors battle back


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.

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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.




Read more:
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.




Read more:
Controlling rabbits: let’s not get addicted to viral solutions


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.




Read more:
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.

Australia: Macquarie Island – Pest Free


The link below is to an article that reports on the pest free status of Macquarie Island, Tasmania.

For more visit:
http://www.abc.net.au/radionational/programs/bushtelegraph/macquarie-island/5377622

Australia: Western Australia – Rabbit Proof Fence


The link below is to an article concerning Western Australia’s plan to extend the rabbit proof fence.

For more visit:
http://www.australiangeographic.com.au/journal/controversy-over-western-australia-plans-to-extend-rabbit-proof-fence.htm