Australasian Science: Australia's authority on science since 1938

Exclusive articles for subscribers

By Stephen Luntz

A collection of Browse articles for subscribers only.

Weed Abundance a Myth
Biosecurity authorities base their list of weeds to fear on the belief that invasive species become much more abundant in a new environment than on their home turf. However, an international study has found that this belief is largely a myth.

The lack of animal species adapted to feed on them gives plants an advantage when they invade distant regions of the world, but Dr Jennifer Firn of Queensland University of Technology found that this doesn’t usually translate to higher densities of the introduced plant.

Firn and her colleagues did not set out to study introduced plants. They are part of a global collaboration called the Nutrient Network, which is comparing the biological productivity of similar sites around the world.

Firn believes that because they were looking for something else gave the Nutrient Network an advantage when studying the behaviour of introduced species. “If you’re studying an invasive species you look in the places they’re known to be common,” she says. This gives an exaggerated indication of their abundance. The Nutrient Network, on the other hand, was using sites that were effectively random.

Firn says there are exceptions to the pattern of plants being found at similar frequencies to their native territory, such as several species of the grass Alopecurus, but most follow the pattern. The reasons are not yet clear, but may have something to do with plants existing in an ecosystem where they maintain a common hierarchy. “We found sites in Switzerland where there were 15 species growing together, and in New Zealand maybe 12 of these would be there,” she says.

“We were looking at individual sites, not across a range, so it is possible a species appears more frequently over a wider area,” Firn adds.

The fact that a plant may be no more abundant than at home doesn’t mean it can’t be damaging. Some invasive species are toxic to native animals, while others can have a major effect on water or nutrient cycling without being dominant in the environment.

Firn believes that the spread of a species within its native territory should be added to the list of items that biosecurity authorities consider when assessing whether a plant can be imported. However, given the exceptions that have been observed she says it can’t be the only question that is asked.

Universe Confirms the Power of One
A variety of physical quantities follow a pattern, known as Benford’s Law, whereby 30% of the first digits of these quantities is 1, nearly 18% will start with the number 2 but only 4% will begin with a 9. Perhaps more surprising is that a practical use for this has been found.

Benford’s Law does not depend on the unit. If the heights of mountains are converted from metres to feet, those previously beginning with a 1 will now start with a different number but the total proportions will be the same.

The pattern has previously been put to use detecting fraud. Accounting data usually follows Benford’s Law, and those who fiddle the books often slip and spread their numbers randomly.

However, Prof Malcolm Sambridge of the Australian National University’s Research School of Earth Sciences says the law is not so well-known to physicists, and only a few natural phenomena have been assessed to see if it applies. Using 750,000 values from 18 data sets, Sambridge checked Benford’s law for extra-solar planetary masses, greenhouse gas emissions and the periods between polar magnetic flips, among others.

“Much to our surprise we found that Benford’s law largely holds true in all these areas,” Sambridge says. “The natural world is littered with a surplus of the digit one.” Sambridge even found that it applies to the career total runs that a test cricketer has made.

However, not everything obeys Benford’s Law. Phenomena that have a dynamic range of two orders of magnitude or less, such as cricketers’ batting averages, are exempt. However, even here the law may apply when one processes the numbers. Temperatures do not follow Benford’s Law, Sambridge found, until one looks at the deviation from the mean temperature.

“We expected that earthquakes would not follow Benford’s Law but that seismograph noise would,” Sambridge says. “In fact, we found the exact opposite.” This applies not only to the overall size of the quake, but data taken every few milliseconds during a quake.

“One of the things we are interested in is automated methods of detecting an earthquake,” said Sambridge. “We found Benford’s law can be used for exactly that purpose.” A previously overlooked tremor in Canberra coinciding with the 2004 Indian Ocean tsunami was identified because the data followed Benford’s Law.

Sambridge says that Benford’s Law occurs when numbers follow a log uniform pattern, but in many cases we do not understand why a phenomenon follows that pattern.

Guidance Blimp
A donut-shaped balloon has been put to use guiding guests to meeting rooms at CSIRO’s Queensland Centre for Advanced Technologies (QCAT). The blimp’s designer, fourth-year Queensland University of Technology avionics engineering student Bryan Huang, says that the project has some way to go before it is really practical, but that’s hardly surprising given he’s only been working on it for 12 weeks.

The guidance blimp was Huang’s project while he was on a CSIRO vacation scholarship studying under CSIRO information and communication technologies researcher Phil Valencia. “It’s an application of what’s known as pervasive computing,” Valencia says. “With these tiny, smart, wireless sensors all around the place measuring things, sending data and making decisions, you end up with a kind of embedded intelligence.”

In the long run people hope to put these to use tracking animals and measuring crop conditions, but Huang wanted to see how pervasive computers would work as a guidance mechanism. Although Valencia provided him with the micro-controllers to go on the blimp, Huang had to design the vehicle himself.

While blimps have traditionally been football-shaped, Huang realised that such an object would not be suited to turning around in tight corridors if it was going to be large enough to carry the equipment required. Moreover, a football shape would have the propellers in positions where they could hurt someone if things went wrong.

The slim donut shape he settled on puts the propellers out of harm’s way and enables easy turning through doorways. While he had thought he might have to twist long, thin balloons into shape, Huang was lucky enough to stumble on a gift shop that sold O-shaped balloons to which he attached the propellers and guidance system.

So far Huang has received no interest from hotels seeking a gimmick to welcome their guests, and says he hasn’t given much thought to other applications besides those already considered for pervasive computing.

Breakfast’s Heart Benefits
Exercise before breakfast may help with weight loss (AS, Sept/Oct 2010, p.5), but skipping the meal altogether is not a good idea. A study has found that people who regularly miss breakfast have more risk factors for heart disease and diabetes.

More than 2000 people who had taken part in the 1985 Childhood Determinants of Adult Health (CDAH) study were followed up to test their current health. “Compared to those who ate breakfast both as a child and an adult, those who skipped breakfast on both occasions had a larger waist circumference and had higher fasting insulin, total cholesterol and LDL cholesterol (the bad cholesterol), which are all risk factors for heart disease and diabetes,” says Ms Kylie Smith of the Menzies Research Institute Tasmania.

Smith says that those who skip breakfast may eat more unhealthy foods later in the day. It is also possible that skipping breakfast slows the body’s metabolism.

Participants were asked whether they ate food between 6am and 9am. Smith says that other researchers have defined breakfast as a meal eaten within a certain time of waking, but the CDAH study did not provide information on when people woke up.

Smith says she also has no data on whether people exercised before they ate, so she is unable to say whether her work contradicts the theory that exercise is more effective prior to eating.

The work was published in the American Journal of Clinical Nutrition, where Smith and her colleagues conclude: “Promoting the benefits of eating breakfast could be a simple and important public health message”.

Fish Are Wise in Crowds
Mosquito fish make simple decisions more quickly and astutely when in groups than on their own, a University of Sydney study has found.

James Herbert-Read, a PhD student in the School of Biological Sciences, placed Gambusia holbrooki in a Y-shaped tube. Mosquito fish prefer deeper water so the tube was sloped, encouraging them to travel down one of the arms rather than stay at the end where they were placed. One of the arms had a replica of a predator in it.

“Even though we used a replica predator, the fish couldn’t be certain of that – from a distance it looked like a predator. It’s better to be cautious and avoid something that might represent a threat,” says Herbert-Read’s supervisor, A/Prof Ashley Ward.

When fish were alone they took the right path just 56% of the time, but their performance improved when in pairs. Things got even better when four fish were together, and groups of eight got it right 90% of the time.

More surprisingly, larger groups were not only more likely to make the right decision but they made it more quickly – a puzzling finding for anyone who has been part of a group trying to choose a restaurant. There was a steady increase in speed with increasing numbers of fish, and while the accuracy levelled off between eight and 16 members (the largest grouping studied), speed continued to improve. As Herbert-Read notes, making a decision quickly when faced with a dangerous situation can be just as important as getting it right.

“Once one individual has spotted the threat, the information is transmitted rapidly throughout the group,” Ward observed. “We don’t know exactly how they communicate this. We assume it is to do with their behaviour, which may change once they detect a potential threat.”

Herbert-Read says that the discovery throws light on an old question – why do social animals stick together? “Theories include more efficient foraging and dilution of predators, but this demonstrates that improved decision-making is also a factor.”

While the choices studied were simple once the crucial information was known, Herbert-Read says it would be interesting to see what happens to decision-making speed when the choice involves weighing various factors. However, he says that such experiments are harder to design.

“We haven’t seen any previous studies that examine how decision-making efficiency changes with group size in any animal,” Ward says. However, Herbert-Read says there are extensive studies of group decision-making in humans. These show that poor information can spread rapidly through the population, which is one of the reasons why hierarchical decision-making is often preferred.

Quantum Computing Sees the Light
Tiny lighthouse lenses have been used to overcome a challenge in quantum computing, bringing the highly anticipated technology a step closer.

“The light from a single ion, an electrically charged atom, indicates the result from a computation,” says A/Prof David Kielpinski of Griffith University’s Centre for Quantum Dynamics. However, “its brightness is typically less than a trillionth that of a light bulb”. Capturing such a small amount of light to record the outcome of the computation poses obvious challenges, particularly since it is important to do so quickly.

To solve the problem Kielpinski turned to Fresnel lenses. Although they do not produce as clear an image as conventional lenses, Fresnel lenses are usually much cheaper to make and have found uses far beyond their original purpose of focusing the beam in lighthouses. Originally made of a number of thin lenses joined together, computer-controlled milling equipment has enabled Fresnel lenses to be made through the use of a single piece of glass cut into zones with the same curvature and stepwise discontinuities between them.

Kielpinski says that the lenses would be etched on a glass wafer placed above the ion trap being observed. “The lenses are made with similar methods to computer chips. This means we can use one, 100 or 10,000 lenses with little variation to price,” says Kielpinski’s colleague, Dr Erik Streed.

Aside from cost, microscope lenses have proved problematic for quantum computers because the ions are emitting ultraviolet rather than visible light.

Bird Loss Hurts Plants
Reduced numbers of native birds have led to a decline in the plant Gloxinia, which depends on the birds for pollination in New Zealand.

The findings, published in Science Express, are in keeping with many past examples of ecosystem decline due to the loss of particular species. Nevertheless, they bolster calls for increased efforts to protect New Zealand’s native birds.

Gloxinia is pollinated when tui, bellbirds and stitchbirds seek nectar from the flower. However, all these birds have suffered reduced numbers on the New Zealand mainland as a result of introduced mammals, particularly rats and stoats. “This could have a cascading impact on biodiversity,” says Prof Dave Kelly of the University of Canterbury’s School of Biological Sciences.

Kelly was part of a team that compared Gloxinia populations on the mainland, where bellbirds are rare and stitchbirds locally extinct, with islands and mainland test sites where non-human mammals have been removed. Seed production was 84% lower where the birds were largely absent, and there were 55% fewer juvenile plants per adult in these circumstances. “Such cascading effects have been of concern worldwide, but are rarely properly documented and often hard to prove,” Kelly says.

Another of the researchers, Ms Sandra Anderson of the University of Auckland, says that the loss is largely invisible until it is too late to reverse.

Where other native birds are wiped out, or become less abundant, native silvereyes have often taken their place. However, silvereyes have shorter tongues than the others and can only reach the nectar by pecking a hole into the side of the flower, thus missing the pollen located at the front.

Evolution might favour flowers that are short enough for silvereyes to reach from the front, but Kelly is not aware of sufficient variation in flower size for this to occur.

Projects to reduce the number of introduced mammals have succeeded in partially restoring tui and bellbird populations, but Kelly says that rodents and cats must be removed entirely to allow stitchbird populations to survive, and considerable efforts at fencing are required to ensure that they don’t return.

Only Beg When You’re Hungry
Whitebrow scrubwren chicks can put themselves in danger from predators by calling for food from their parents. Failing to call, however, can leave them hungry. Consequently, the chicks have evolved to take the wisest course and only call when they are genuinely hungry, according to research published in Biology Letters.

The finding is unsurprising but Tonya Haff, a PhD student in the Australian National University’s Research School of Biological Sciences, says it is the first time it has been verified.

“By playing back hungry nestling calls at active nests of scrubwrens, we found that predators – in the Botanic Gardens that means pied currawongs – only approached nests playing calls of hungry nestlings, and not those where the young called more modestly,” Haff says. “So loud begging does attract predators, making begging worthwhile only when the young are really hungry. It’s further proof that there really is no such thing as a free lunch.”

Calling when food is not desired would make no sense, but Haff says that the chicks would still consume, and indeed benefit from, extra food after they have stopped calling. However, once hunger has ceased the value of greater growth from extra food is outweighed by the risk of being attacked by a predator so the calling stops. Discretion only works so well, with Haff estimating that half the chicks are eaten before they leave the nest.

Haff says that scrubwrens seem to have two kinds of calls: one seeking food when parents are at the nest and a quieter one at other times. The reason for the latter call is not known, but in barn owls something similar appears to be a form of negotiation between siblings as to who should get the next feed.

The complex strategies of calling may vary for other species. Adult scrubwrens are in no position to fight off currawongs, with Haff comparing the difference in their size and fierceness to “us versus a T. rex”. However, behaviour may differ for larger birds that are only vulnerable when the adults are not around to protect their young. Haff is keen to do comparative studies.

Haff doesn’t feel able to comment on whether there are any implications for human babies, but describes the issue as “one to think about”.

Murray Floods Repel Invaders
Changes to flood patterns are the single largest factor in the spread of invasive plants along the banks of the Murray River, a study has found.

“We have always thought that the huge problem of weed invasion along the Murray River had something to do with the changes in flow, but this is the first time we have been able to identify what kind of flow alterations have had the most impact,” says Dr Jane Catford of the University of Melbourne’s School of Botany.

“The introduction of alien plants has dramatically changed the structure and function of these wetlands, which provide crucial habitat and food for a range of birds, fish, turtles and other animals and also play a critical role in filtering water.”

Most species introduced into wetlands around the Murray are actually terrestrial species that are unsuited to flood conditions, Catford says. “There are some exceptions, but these are adapted to stable water levels,” she adds. Native plants are used to variable conditions and take advantage of floods to spread their seed.

Catford believes we need to increase the amount of water allocated to environmental flows, but also thinks that this water can be used more effectively to support wetland ecosystems. “Currently they piggyback releases to make spring floods last longer, but I think they also need to release water at the peak to ensure that peak is what it would be under natural conditions,” she says.

The recent floods have probably given the wetlands a few years’ breathing space, but Catford says floods that once occurred every 10 years now arise less than half that often because water is being captured for other uses.

Catford based her research on 24 wetlands between Albury and Echuca. “I also examined the effect of human-mediated weed dispersal, grazing, soil and water characteristics, but flow regulation was clearly the main factor driving weed invasion,” she says.

Pyrolysis for Low Emission Steel
Researchers at CSIRO Minerals Down Under hope that charcoal produced by the process of pyrolysis, where wood is heated to more than 300°C in a low or no-oxygen environment, could cut the greenhouse gas emissions associated with steel production.

“The easiest way to reduce greenhouse gas emissions is to replace the fossil carbon with renewable carbon that can be readily absorbed into metal extraction industries using the same technologies and equipment they have now,” says Dr Alex Deev.

This is not as easy as it might sound. Not all coal is suitable for use as a reducing agent in steel production, and neither is all charcoal. Deev says that “existing large-scale pyrolysis requires high-quality wood” to be used in steel production. Methods exist to use low-grade wood, but these have been unsuccessful at a larger scale.

Deev cannot discuss the details of CSIRO’s work while patent applications are underway, but says the technique can use low-grade woodchips. He is hopeful that a pilot plant producing 250 tonnes of charcoal per year, to be built at CSIRO’s Clayton site in Melbourne, will demonstrate the scalability of the technology. He also hopes that the plant will be able to replace the pulverised coal that is injected into blast furnaces, which accounts for 25% of the steel industry’s carbon consumption. Other coal uses may also be replaced.

Without a high price on carbon, the charcoal will remain more expensive than coal for the foreseeable future. However, CSIRO hopes to offset this difference by selling by-products of the pyrolysis process. These by-products include bio-oils, biogas and pyroligneous acid, which is used as a source for methanol, acetic acid and acetone.

Deev says that CSIRO is seeking industry partners to enable the creation of a larger plant and develop further energy efficiencies if the Clayton pilot proves a success. “The charcoal will be able to be used elsewhere, but we are focused on the steel industry. We would need substantially more than one million tonnes of charcoal a year to replace 30% of the coal used in Australian steel production,” he says.