Predicting rat plagues in the heart of the continent

They ate the supplies belonging to Burke and Wills, and more recently chewed on the electrical wiring through-out homesteads, and have even disrupted communication networks. An invasion that presumably leaves the Channel Country in western Queensland and spreads out across central Australia, holding siege to some of the remotest and driest regions of Australia.

“…we remained there (Camp 63) until the 5th when we were driven out by the rats…” – Burke 1860

It sounds like a scene from Rommel’s army, moving across the African deserts in World War 2, but it is rare irruption of native rats. One that people rarely see or want to see again. Once every ten years or more conditions change in central Australia and flooding rains fall across the desert. The desert blooms and turns a vivid bright green – such a contrast against the red sand and deep blue sky. A mass seeding event takes place as grasses pour out their life boats in hope of more rain. These are the conditions the long-haired rat, otherwise known as the plague rat (Rattus villosissimus), take advantage of.

long-haired rat

Long-haired rat or plague rat. Photo by Aaron Greenville

The long-haired rat feeds on seeds and vegetation, but also anything else they can get to. If camping in central Australia this rat is known to eat all the paper labels off your tins and even have a go at your swag – it doesn’t matter if you are still trying to sleep in it! Weighing in at up to 280 g they are much bigger than other desert-dwelling rodents and they are not shy in throwing their weight around either. They are aggressive,  quickly monopolising resources, but they do have their enemies; native predators,  including snakes, dingoes, and the nocturnal letter-winged kite. In addition feral cats and foxes take advantage of this abundance in prey.

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A letter-winged kite comes into land. Channel Country, Queensland. Photo by Aaron Greenville

Given the quite conspicuous nature of the rat, it is surprising that we still do not know that much about its biology. Thus we set out to find out more. In our study published in the Greening of arid Australia: new insights from extreme years, a special issue of Austral Ecology, we collated historic, media and anecdotal records to work out if we could predict when this rat may irrupt. We found there was an 80% chance of a rat plague following a large flooding annual rainfall event of 750 mm. To put that in perspective, central Australia has an average annual rainfall of 150-200 mm.

But where do the rats come from in the first place? They are quite rare in the predominantly dry times in central Australia and disappear from much of the desert, persisting in small and localised refugia. The species is not physiologically well adapted to dry conditions, so the refugia are crucial in providing a reliable supply of green food and moist areas for shelter and digging burrows. Are they holding out in one or multiple refugia? Important information to know if we want to conserve, or manage, this species. We don’t want all our rats in one basket, so to speak. Plomley (1972) suggested that the rats irrupt from a single refuge in the Barkly Tablelands, to the north of our study region, and follow drainage lines into the desert. To investigate this we set up live-trapping grids twelve sites across our study region. We assumed if the rats have only one refugia, as suggested by Plomley (1972), then we would predict that they would move in a wave in one direction from the north and if they followed drainage lines, we would get greater captures at trapping grids closer to these features. We did find greater captures at trapping grids closer to drainage lines, but the direction the rats came from was from the south. This suggested that other refugia exist and drainage lines provide important corridors for dispersal.

So what else was happening at the invasion front? For mammals, it is quite common that juveniles, particularly males, are the predominate dispersers, heading out to find their place in the world. However, we found that the larger rats that were at the invasion front and regardless of sex. Presumably, larger individuals could move greater distances and exploit the new food sources. This could be an important finding for understanding dispersal of invading species, like the cane toad.

Even though the long-haired rat can be an inconvenience to some, it has some interesting biology. Perhaps, in other 10 years time we can find out some more.

References:

Burke, R. O. 1860. Robert O’Hara Burke’s dispatch, Cooper’s Creek, 13 December. MS 13071, Box 2082/1a, Item 13. Records of the Burke & Wills Expedition. Australian Manuscripts Collection, State Library of Victoria, Victoria.

Greenville, A.C., Wardle, G.M. and Dickman, C.R. (2013). Extreme rainfall events predict irruptions of rat plagues in central Australia. Austral Ecology, 38: 754–764.

Plomley N.J.B. (1972) Some notes on plagues of small mammals in Australia. J. Nat. Hist. 6, 363–84

*up-date: This article was re-published in Biology News.

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EcoTas 2013: Spatial and temporal synchrony in small mammal populations

Here I give a summary of my talk to EcoTas13. A joint conference of the Ecological Society of Australia and New Zealand Ecological Society, Auckland. A big thanks to my co-authors Chris Dickman and Glenda Wardle.

Determining the factors that influence the spatial dynamics of species’ populations remains a key goal in ecology and is an imperative for managing species that are in decline. Sub-populations across species’ ranges seldom share the same level of resources, and this may lead to different densities and growth rates among them. Dispersal may dampen these differences, but this effect decreases with distance.  Nonetheless, local populations can still behave synchronously across large (>1000 km) spatial scales, suggesting that external drivers are operating.

Prof. Patrick Moran
Patrick Moran was born in Sydney in 1917. He was educated at the University of Sydney and Cambridge. At university, he studied chemistry, zoology, mathematics and physics. He was discouraged to continue with mathematics, but persevered anyway. He studied statistics and in the 1950s wrote a series of influential papers on the population dynamics of the Canadian lynx. One of these papers was published in the first volume of Australian Journal of Zoology. This paper described how populations of lynx could be in synchrony across vast areas of Canada, due to climate. This work is now known as the Moran effect or Moran’s theorem. Prof. Moran continued and contributed significantly to the advancement of population biology and statistics. To learn more about Moran see here.

The Moran effect or theorem provides a theoretical basis for population synchrony across large areas, and states that sub-populations with a common density dependent structure can be synchronised by a spatially correlated density independent factor, such as climate.

In this study we tested five hypotheses concerning the spatial population synchrony of five species of small mammals – two rodents and three dasyurids (the carnivorous or insectivorous marsupials). We then use the best fitting spatial models (based on AICc) to incorporate drivers that may regulate these populations. Using Moran’s theorem, we predicted that species with synchronous spatial dynamics are driven by factors that operate at the landscape scale, such as resource-pulses from large-scale rainfall events or wildfires, whereas species with asynchronous sub-populations will be influenced largely by factors operating at local scales.

study species pic

The spatial and temporal population dynamics was investigated for two rodent and three dasyurid species, Simpson Desert, Australia.

MARSS models
MARSS framework is hierarchical and allows modelling of different spatial population structures and parameters, such as density dependence, while including both process and observation variability. Process variability represents temporal variability in population size due to environmental stochasticity. Observation variability includes sampling error.The process component is a multivariate first-order autoregressive process and is written in log-space:
MARSS process eqnwhere X = matrix of all m sub-populations at time t
B = density dependence
u = mean growth rate of the sub-population
w = process errors, assumed to be independent and to follow a multivariate normal distribution with a mean of 0 and variance-covariance matrix Q.
The observation component, written in log-space:
MARSS obs eqnwhere Y = a matrix of observations of all sub-populations at time t,
a = the mean bias between sites
Z =  a matrix of 0’s and 1’s that assigns observations to a sub-population structure.
v = observation error, assumed to be uncorrelated and follow a multivariate normal. distribution, with a mean of 0 and a variance-covariance matrix R

We used multivariate autoregressive state-space (MARSS) models to investigate the spatial population structures of small mammals using 17 ‑ 22 years of intensive live-trapping data from nine spatially distinct sites in central Australia.

What we found
For rodents and the mulgara, sub-populations were synchronous or had two structures and driven by large-scale processes. Populations of the smaller insectivorous marsupials (S. youngsoni and N. ridei) were asynchronous and driven by local events. Density dependence was detected in all species, but was weakest in insectivorous dasyurid marsupials.

The covariates spinifex seed, spinifex cover and 12 months cumulative rainfall were significant drivers of the population dynamics for both species of rodents. For the mulgara, spinifex cover and rodents were both positively correlated with their population. For the smaller dasyurids: S. youngsoni populations were positively correlated with two month prior mean rainfall event size and negatively correlated with mulgara captures (a predator and/or competitor of this species). For N. ridei population only spinifex cover was positively associated.

Our findings suggest that local environmental stochasticity is more important than intrinsic factors in driving dasyurid population dynamics. In contrast, populations of rodents and a large carnivorous dasyurid were driven by both extrinsic and intrinsic factors that operate at the landscape scale, confirming predictions derived from Moran’s theorem.

Further reading:

Moran, P. (1953) The statistical analysis of the Canadian Lynx cycle. Australian Journal of Zoology, 1, 291-298.

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Conversation: Will we hunt dingoes to the brink like the Tasmanian tiger?

By Aaron Greenville, University of Sydney and Glenda Wardle, University of Sydney

dingoHotTopic pic

A dead dingo in 2013 (left) and a Tasmanian tiger, last seen in the wild in 1932. Dingo photography by Aaron Greenville; a hunted thylacine in 1869, photographer unknown.

The last Tasmanian tiger died a lonely death in the Hobart Zoo in 1936, just 59 days after new state laws aimed at protecting it from extinction were passed in parliament.

But the warning bells about its likely demise had been pealing for several decades before that protection came too late – and today we’re making many of the same deadly mistakes, only now it’s with dingoes.

Earlier this month the Queensland government announced it would make it easier for farmers to put out poison baits for “wild dogs”. In Victoria, similar measures have already been taken.

Lethal methods of control have lethal consequences. It is time to rethink our approach in how we manage our wild predators.

A deadly history lesson

Commonly known as Tasmanian tigers because of their striped backs, thylacines were hunted due to the species alleged damage they were doing to the sheep industry in the state. However, the thylacine’s actual impact on the industry was likely to have been small.

Instead, the species was made a scapegoat for poor management and the harshness of the Tasmanian environment, as early Europeans struggled implementing foreign farming practises to the new world.

The tiger [thylacine]… received a very bad character in the Assembly yesterday; in fact, there appeared not to be one redeeming point in this animal. It was described as cowardly, as stealing down on the sheep in the night and want only killing many more than it could eat… All sheep owners in the House agreed that “something should be done,” as it was asserted that the tigers have largely increased of late years.
– The Mercury, October 1886.

Grainy footage is all we have left of the thylacine.

More than a century later, and it’s now the dingo in the firing line.

Since 1990, the number of sheep shorn in Queensland has crashed 92 per cent, from over 21 million to less than 2 million. Although there have been rises and falls in the wool price and droughts have come and gone, it’s the dingoes that have been the last straw.
ABC Radio National, May 2013

An ancient predator vs modern farmers

Producing sheep is an incredibly tough business, with droughts, international competition and volatile markets for wool and meat – mostly factors that are well beyond the control of an individual farmer.

Dingoes are seen as one of the few threats to livelihood that producers can fight back against. As a result, the dingo has experienced a severe range contraction since European settlement and there is mounting pressure to remove the dingo from the wild, despite dingoes calling Australia home for 4000 years.

Dingoes are now rare or absent across half of Australia due to intense control measures. While they are more common in other areas, we have seen how species populations can collapse quickly. For example, bounty records from Tasmania showed the thylacine population suddenly crashed in 1904-1910 due to hunting pressure from humans.

Will the dingo’s demise be like that of the thylacine? We simply do not know, but the social conditions and a rapidly changing environment mirror the story of the thylacine.

It’s true that dingoes have an impact on livestock. Estimates from industry-funded reports range from A$40 million to A$60 million, which include damage to livestock and cost of control measures.

And the emotional cost to farmers should not be underestimated. As authors, one of us has sheep farmers in the family, and knows the pride people gain from having a happy and healthy flock.

The choice is whether we want to follow the old colonial attitude of trying to conquer our environment, or find new and cheaper methods to live with our environment.

Dingoes and wild dogs

The issue of how to manage one of the few remaining mammalian top predators in Australia is further complicated by the suggestion that dingoes are not distinct from “wild dogs” due to interbreeding.

In eastern Australia dingo purity is low, but it is still high in many regions, such as central Australia.

But whether you call them dingoes or wild dogs, these predators work as unpaid pest species manager that works around the clock, effectively controlling feral cat and red fox numbers.

Even in eastern Australia, there is evidence that dingoes are fulfilling this role by reducing fox numbers.

Dingoes can also control kangaroo numbers, reducing grazing pressure. Reducing pests and grazing pressure are a win for farmers and conservation alike.

Learning to live with dingoes

As CSIRO researchers suggested a decade ago, we need to get better at dealing with genetically ambiguous animals, such as those that could be classified as dingoes or wild dogs. Instead, they argued that better approach to conservation decisions would involve protecting animals based on their role in the environment, as well as their cultural value.

Traditionally, barrier fences and lethal control (such as poisoning) have been used as methods to reduce livestock losses from dingoes.

However, the costs of removing the dingo as our free pest species manager, and the impact of fences as barriers to other wildlife, need to be taken into account when assessing the true cost of maintaining these approaches.

Alternatives to lethal control do exist. Guardian dogs can protect stock from dog attack and have a return on investment between one to three years. Such cost-effective strategies can allow both the dingo and grazing to co-exist.

Over thousands of years, dingoes have played a functional role in the Australian landscape and can provide benefits for farmers, traditional Indigenous owners and to the conservation of native wildlife.

It is time to learn how to live with the dingo. If not, we risk eventually driving dingoes out of the wild and into lonely zoo enclosures, just like the thylacine.

Aaron Greenville receives funding from Australian Postgraduate Award and Paddy Pallin Science Grant funded by Humane Society International, Royal Zoological Society of NSW.

Glenda Wardle receives funding from the Australian Research Council

The Conversation

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

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While Abbott fumbles abroad, at home Australians demand action on climate change.

By day four of the United Nations climate talks in Warsaw, Australia had won its third Fossil Award; the award given by the international Climate Action Network to the country which has done the most to block progress at the climate change negotiations on that day.

At the same time 60 000+ people attended rallies across the nation in support for more action on climate change. In fact, 160 towns and regional centres hosted the rallies organised by Getup. It takes a major sporting event to draw such crowds in Australia! My wife and I attended our local rally in the Blue Mountains, west of Sydney. I was struck with how the issue of climate change was important for not just “greenies”, but for people from all walks of life. Climate change is real and has become a mainstream issue – for scientists, teachers, firefighters and paramedics, to name a few at our rally. So why does the Abbott government insist on scrapping initiatives to combat climate change? The government claim to have a mandate, but do they?

What is a mandate?

After the 1998 election the Howard government claimed they had a mandate to introduce the GST. This debate prompted the Parliamentary Library to produce a research paper on mandates in 1999. It found that a “mandate is a political idea” and are not legally enforceable. Mandates are “political whacking sticks, used to advantage one political position over another”.

“This is an absolutely vital piece of legislation. It is at the heart of the Government’s mandate. The people got to vote on the carbon tax at the election and in the days to come this Parliament will get to vote on the carbon tax and I trust that ‘Electricity’ Bill Shorten will have a light bulb moment and will appreciate that the people’s verdict must be respected,” Tony Abbott 12th November 2013.

So in other words they mean nothing.

Australians want action

During the 2013 Australian federal election the ABC ran Vote Compass. This was a voluntary survey developed by political scientists. It took a snap shot in time of issues surrounding Australian politics and revealed some surprising results.

cathy wilcox climate pray

Australians are calling for more action on climate change, both experts and non-experts alike. Image by Cathy Wilcox

Overall, over 60% of Australians that took part in the survey wanted “more” or “much more” to be done by the federal government to tackle climate change. In fact, no matter how you break the figures down – age, sex, education – the majority of Australians wanted more action. The figures change slightly, with younger people, women and the more highly educated wanting much more action, but overall Australians want to do something about climate change. The exception was when grouped by respondent’s ideology, where around 50% of those on the political right wanted less action on climate change – note that 50% want the same or more action!

So should “the people’s verdict” be respected? Well if Tony Abbott wishes to show some signs of respect to the people, then perhaps he should review the Coalition’s policy on climate change.

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Not another blog?!

I have finally succumbed to the temptation of writing a blog.

Not another blog?! –  I hear you say.

Well yes. I am writing this as helicopters fly over head and sirens scream up the highway, off fighting a bush fire, one of the worst in the Blue Mountains, since 1968. Already 198 homes have been destroyed and over another 100 damaged. But this wildfire is different. Not because it affects me. I grew up near the Australian bush and have been through fires before. I have even had some basic training and been on the fire line for previous work. No – it’s because it is only spring. Fires across summer are a regular occurrence, but the size, intensity and sheer might of this fire before summer is quite a worry.

Within 45 min of starting this bush fire roared down the ridge opposite our home creating a path of distruction not seen since 1968.

Within 45 min of starting this bush fire roared down the ridge opposite our home creating a path of destruction not seen since 1968. Photo by Aaron Greenville.

Our new federal government, following the ultra-conservative ideology, is winding back all policies and initiatives to combat climate change. We have no science minister. That was one of their first moves and recently our environment minister used Wikipedia as defence to dismiss the link between increased bush fire intensity and climate change.

So I have decided to start writing. Some may say ranting, which is quite true. But it is not all bad news. I love science. A logical process to solve problems and discover, well actually wonder, about nature. Hence, it confuses me when faith over-rides fact or ideology overwhelms rational thought. You may argue that science is just another ideology, blinding me to the truth. However, science is a process of rational thought and scepticism. If you or another scientist has an idea you don’t go out to find evidence (= data) for it. You try and find evidence against it. Your idea will be scrutinised by your peers well before it even sees the light of day (gets published) and if it’s a good idea, it will survive centuries of further scepticism i.e. further experimentation to find evidence that it is wrong. I wish to use this evidence based approach for this blog.

I am an ecologist. Basically, studying life and its complexities, particularly with the environment. I have been working in arid ecology for over 10 years, but also dabbled with work in forests. My hobbies follow this interest, from nature and astrophotography to brewing craft beers. I hope you join me on this adventure, as I write about these interests, with a little bit of politics thrown in.

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