The forgotten part of climate change: slower winds
Temperature and precipitation get all the glory in the discussions surrounding climate change. Ocean acidification has earned itself a seat at the table as well. But nobody has really paid any attention to wind. Maybe that’s because you can’t actually see wind, or that the changes have been more subtle than the triple-digit (Fahrenheit) heat that’s stretching later and later into the autumn.
Thanks to new research by Brandon Barton, a Univiersity of Wisconsin–Madison postdoctoral researcher in the Department of Zoology, wind may finally get its moment in the climate change spotlight.
Wind is created thanks to differences in temperature. And since the poles are warming faster than the equator, there is a smaller global temperature differential, reducing the speed of wind. In his paper, online this month in the journal Ecology, Barton points out that global wind speeds have decreased by some 5 to 15 percent over the last three decades, and are expected to decrease another 15 perfect in the coming century. You’ve heard of global warming? Get ready for “global stilling.”
But it’s not just the warming climate that’s slowing wind – it’s also human architecture. Physical, manmade structures are blocking the flow of wind, at least on a local scale. So are trees. “In North America, we’ve been replanting trees that were lost in the 1800s, after settlers showed up and just leveled places like New England,” Barton said in a statement. Ecologists have long investigated the affects of wind on seed dispersal and pollination, or on the ways that winds modify ocean currents. But the affects of wind on predator-prey dynamics have been largely ignored. Barton set out to change all that by looking at the way that wind altered the dynamics between ladybugs (in particular, the multicolored Asian lady beetle Harmonia axyridis), and their prey, the soybean aphids Aphis glycines, pests who can ravage soy plants.
The experiment was very simple. Barton planted soybeans in alfalfa fields. Some plots he guarded with wind blocks, and others were left unprotected. He found that ladybugs were two-thirds more abundant in the protected plots than in the parts of the field that were wind-blown. As a result, there were twice as many aphids in in the windy plots.
That’s because the ladybugs are more susceptible to wind-related disturbance than are the smaller aphids, who can anchor themselves onto a plant thanks to their needle-like mouth parts. He verified that by doing a second experiment, in a greenhouse, where he found that aphids were equally abundant on potted soybean plants subjected to wind or kept still.
But once you factor the aphids’ predators into the mix, they do a lot better in windy environments. Ladybugs made meals out of almost twice as many aphids in wind-protected plots. And in the greenhouse, Barton found that ladybugs found and consumed their snacks five times faster on still plants than on windy ones.
Together, this study shows that wind doesn’t directly affect aphid abundance, but does affect predator performance. That’s probably because aphids are really small, and benefit from the tiny layer of still air clinging to a leaf’s surface – a stable microclimate – even in wind. The ladybugs’ larger surface area gives the wind a better chance to blow them away.
“The behavioral experiments suggest that ladybeetles avoid windy plots because the physical disturbance makes it difficult for them to move among plants and locate their prey,” writes Barton, But there are other possible explanations as well. For example, “wind may interfere with visual or olfactory cues that ladybeetles use to find their prey,” he adds.
The study not only sheds important light on how our changing climate will affect ecosystems in ways we haven’t yet even begun to consider; it also reveals a useful method for farmers who wish to control aphids. They might consider erecting wind barriers near their soy fields, or – for a more ecologically friendly approach – planting tall trees at the edges of their fields, which could not only buffer the wind, but provide an additional refuge for other wildlife.
And the silver lining to this aspect of climate change, if there is one, is that in a world with slower winds, ladybugs will be more adept at controlling soybean aphids. Which means that farmers could use ladybugs as a more natural form of pest control to preserve their soybean crops, reducing their reliance on pesticides. – Jason G. Goldman | 24 September 2014
Source: Barton B.T. (2014). Reduced wind strengthens top-down control of an insect herbivore, Ecology, 95 (9) 2375-2381. DOI: http://dx.doi.org/10.1890/13-2171.1
Header image: An asian lady beetle rests on a plant in a soybean field, copyright Brandon Barton, used with permission.
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