Bears Munching on Ants Indirectly Help Plants

A link uncovered by a graduate student shows that plants have bears to thank for trimming them of ants — and another pesky species

Black Bear Eating Plants
Black bears, like this one in Minnesota, which lick ants from leaves are providing an important benefit to the plant. Radius Images/Corbis

Ants may seem like poor sustenance for a black bear, but the protein-packed treats work wonders for their burly physique. And nearby plants benefit just as much when bears eject their sticky tongues to pluck ants from their foliage. Joshua Grinath, a graduate student in ecology at Florida State University, looked closely at the relationship between bears, ants and rabbitbrush — a yellow-flecked shrub which thrives in the alpine meadows of Colorado and serves as a popular shelter for sage grouse — to make the connection, as Science reports.  

The hungry bears in his study destroyed up to 86 percent of ant nests in the vicinity. While that’s bad news for the ants, it was great news for shrubs which the ants would have otherwise overrun. Ants aren’t a direct threat to these plants, but swarms of them can make some insects wary of flitting down on their leaves. As these other insects steer clear, leaf-munchers like the treehopper are only too happy to take their place and chow down, devoid of all competition. “The ants are providing an enemy-free space for all these herbivores,” Grinath says to Elizabeth Pennisi in Science.

By eating the ants, bear remove the deterrent that keeps many insects off the plants in the first place. Once the ants are gone, these insects move right in — and treehoppers have a harder time getting a bite. Grinath found that plants that had their ants removed were better able to grow and produce seeds.

As Grinath points out in his abstract, the ants and treehopper are mutualists — formidable foes for a defenseless plant, unless there is a black bear nearby to lend a tongue.

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