Climate Change Affects Predator-Prey Balance, Study


Rising temperatures and shifting precipitation patterns affect predator-prey balance, according to a University of Wisconsin-Madison study. This is the first study to determine the consequence of "global stilling" on predator-prey relationships.

"There are all sorts of other things that are changing in the environment that affect animals and plants and their interactions," said Brandon Barton, a UW-Madison postdoctoral researcher, in a press release. "My students and I were standing out in a cornfield one day as big gusts of wind came by, and the corn stalks were bending almost double. From the perspective of an animal living in the corn, we thought, 'That's got to have a big effect.'"

The researchers said that wind speeds in the Midwest are estimated to drop by 15 percent in the 21st century. Earth's poles are warming at a faster rate than the equator, depriving the atmosphere of some of the temperature differential that creates wind. The American landscape usually follows the trend of using buildings and natural structures as barriers to the wind.

"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.

Lady beetles consume a major soybean pest, the soybean aphid. For the study, the researchers grew soybeans in alfalfa fields, protecting some of the plots with wind blocks and leaving others in the open.

The researchers found two-thirds more lady beetles in the plots hidden from the wind that is twice as many soybean aphids on the plants growing in the open. Wind does not have a direct effect on the aphids, tiny insects that anchor themselves on the plants.

"The aphids appear on the plants whether it's windy or not, and we showed that in lab experiments," Barton said. "But when you add the predators, with the wind block, the beetles eat something like twice as many aphids."

In the lab trials with simulating wind with fans and windless movement, a still soybean plant represented a smorgasbord for the lady beetle.

"How do you do your duty as a predator if you're entire world is moving around?" said Barton. "If the plant is moving, it takes four times as long for the predator to start eating, and it eats less than half as many aphids in an hour."

The researchers said that slower and natural wind speeds could lower the amounts of pesticide used to prevent soybean aphids from destroying harvests.

"By growing trees or not harvesting them around a field, you may be able to have an indirect effect on the number of aphids on your soybean plants," said Barton. "The mechanism may be different for other predators, but it's not hard to start thinking about effects. Think of a wolf or coyote. Larger predators hunting by scent -- and the prey trying to detect their predators -- may be affected by less wind moving scents around."

The finding is published in the journal Ecology.

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