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Bats, Birds and Lizards Can Fight Climate Change
Tipping Point Not Likely for Arctic Sea Ice
High-Speed Video Shows How Flies Change Direction So Quickly

Bats, Birds and Lizards Can Fight Climate Change

Posted: 09 Apr 2010 04:03 PM PDT

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Birds, bats and lizards may play an important role in Earth's climate by protecting plants from insects that forage on foliage. A new study suggests that preserving these animals could be a low-tech way to fight climate change.

"The presence, abundance and diversity of birds, bats and lizards, the top predators in the insect world, has impacts on the growth of plants," said ecologist Daniel Gruner of the University of Maryland, co-author of the paper published April 5 in Proceedings of the National Academy of Sciences. "If you don't have plants, you don't have organisms that are recapturing carbon."

Because these animals feed on both plant-eating and insect-eating bugs in equal numbers, it was believed they wouldn't have a net effect on plant growth: When the animals gobble up the plant-eating insects, the population of these harmful insects decreases. But, when the animals feed on insect-eating insects, there are fewer predators to eat the herbivores.

The new meta-analysis indicates this is not the case. The presence of insect-eating animals has a positive effect on the growth of plants.

Gruner's team analyzed the results of 113 studies removing birds, bats and lizards from habitats on four continents and quantified the effect of removing the animals on the population levels of insects and on plant growth.

Things like habitat loss, disease and climate change are affecting the future of these insectivore species. Some of them are thought of as vermin and are killed off by humans. Preserving these creatures will be an important part of keeping ecosystems in check, Gruner said. He also stresses the need for larger, more comprehensive studies of these ecosystems to determine the precise mechanism of how these animals play their protective role.

Image: tillwe/flickr.

Posted: 09 Apr 2010 02:01 PM PDT

A late-winter expansion of Arctic sea ice is a good example of ice-forming dynamics that could keep the Arctic from hitting a "tipping point" in the near future.

Some scientists have predicted that rising temperatures could create a runaway feedback loop in the Arctic. Sunlight-reflecting ice sheets would give way to sunlight-absorbing water, driving up temperatures and melting even more ice. The Arctic climate would change so dramatically that winter ice couldn't form again, producing planet-wide ripples in weather patterns.

But some research suggests that other, previously underappreciated forces may stabilize the melt before it's complete. The Arctic will soon be ice-free in summer, and winter ice will decline, but it won't suddenly become permanently ice-free.

"Everyone thought there would be a tipping point," said Dirk Notz, a Max Planck Institute climate scientist. "But that's too simple."

The most recent Arctic sea-ice spurt was caused by a cold snap over the Bering and Barents Seas that allowed ice to form until later than usual in March, nudging total ice cover towards averages seen between 1979 and 2000. But, Notz emphasized, this was just a single data point. Since 1979, the Arctic's maximum winter sea-ice cover, measured before the summer melt, has dropped by about 6 percent.

The spurt does, however, demonstrate the ability of thin ice, such as that at the edge of Arctic ice sheets, to grow very rapidly. That's a big reason why Arctic ice sheets should be able to re-form in winter. Indeed, as Notz described in a review of polar-sea-ice research in December in Proceedings of the National Academy of Sciences, there's no evidence of the Arctic hitting a tipping point in the last several million years, even though temperatures and sea-ice levels have fluctuated widely.

Over the last few years, Arctic sea-ice cover has reached modern historical lows, stoking the tipping-point fears. Though a tipping point isn't out of the question, it would likely happen at greenhouse gas levels beyond what's expected, said Notz.

The same can't be said for ice sheets in western Antarctica and possibly Greenland. The dynamics of that ice, much of which rests atop solid land rather than floating on water, are different. Melting ice could slide off continental shelves and into the ocean faster than it's replaced by fresh snowfall. This may have been what fueled two sudden, massive sea-level rises at the end of the last Ice Age.

Tipping-point evidence is stronger for western Antarctica than Greenland, said Notz. But even the absence of a tipping point wouldn't necessarily be reassuring. "It doesn't mean Greenland won't melt away," he said. "It just means it will happen gradually."

Image: Ice in the Bering Sea/NASA.

See Also:

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.

High-Speed Video Shows How Flies Change Direction So Quickly

Posted: 09 Apr 2010 12:27 PM PDT

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Fruit flies turn in midair with a shrug of their shoulders.

A new analysis shows that the flies' aerial gymnastics are driven by wing joints that act like wind-up toys, letting the bugs whirl around almost automatically.

Insights from the study, which was published online April 5 in Physical Review Letters, could someday help build better flying robots.

Fruit flies beat their wings about once every 4 milliseconds — much faster than their neurons can fire — and can turn 120 degrees in 18 wing beats. This made study co-author Itai Cohen of Cornell University wonder, "How much of the wing motion is being controlled by the insect, and how much is going along for the ride, being controlled by aerodynamics?"

To investigate, Cohen and his colleagues set up three high-speed cameras trained at the center of a box holding about 10 flies (see video below). A fly crossing the center of the box triggered the cameras to start rolling at 8,000 frames per second. At the same time, a disk of LED lights projected a rotating striped pattern on the inside of the box to trick the flies into making a U-turn.

"The flies see this, and it makes them dizzy," says study co-author Attila Bergou of Brown University in Providence, Rhode Island, who helped perform the experiments as a graduate student at Cornell. "It generates very reliable and repeatable turns in these flies."

The physicists analyzed the videos to extract detailed information on the wings' positions with respect to the body.

"I was surprised that they were able to get it to work as well as they did," comments Ty Hedrick of the University of North Carolina in Chapel Hill. "Getting the uncertainty of these measurements low enough that you can see what you need to see is difficult."

The team found that when the fly turns, one wing tilts more than the other, similar to the way a rower pulls one oar harder than the other to make a boat turn. Thanks to aerodynamics, a wing-tilt difference of just 9 degrees is enough to send a fly off in another direction.

"Essentially these insects are swimming through the air, using drag forces to row themselves in whichever direction they want," Cohen says.

Further analysis using computer models of the fly and aerodynamic simulations showed that the fly's wing joint acts like a torsional spring, the kind found in wind-up toys or old clocks. To change its wing tilt and set up a turn, all the fly has to do is twitch the muscle that controls the spring.

"The insects don't have to do any thinking whatsoever," Cohen says. "They have a natural system that provides just the right amount of torque to the wing."

The physicists are planning comparative studies in other flying insects, like bees and dragonflies. Cohen hopes the findings could help design more-maneuverable flying robots that take advantage of insect aerodynamics.

"Really the idea is, how do we start to build more efficient and smaller robots that take advantage of aerodynamics to do the things they do, rather than brute force the way we usually do these things?" Cohen says. "We're in the dark ages as far as building anything like that. We're nowhere in the ballpark."

Image and Video: Attila Bergou/Physical Review Letters.

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