Plant Population Dying, Ant-Eating Bears to the Rescue

Populations of yellow rabbitbrush, a plant species unique to Rocky Mountain meadows, is dying, but fear not, for ant-eating black bears are to the rescue.

A new study published in the journal Ecology Letters found that over a period of four years, black bears feasted on 26 to 86 percent of the 35 ant nests in the meadow research plot at the Rocky Mountain Biological Laboratory in Colorado. And while that's bad news for these defenseless ants, it's good news for yellow rabbitbrush that is under attack in the area.

According to researchers at Florida State University, ants and treehoppers - tiny insects that excrete sweet honeydew juice - are the culprits of this dying plant population. Ants ward off predators that eat treehoppers, and in return, they gorge on delicious honeydew juice. Meanwhile, these protected treehoppers enjoy munching on rabbitbrush.

Rabbitbrush is important for this ecosystem by providing a hideout for sage grouse and food for nearby deer and elk. But since treehopper numbers are not kept in check, they continue to indulge on the plant, causing rabbitbrush to produce fewer seeds and struggle to survive.

"When you look at a real ecosystem, it's not just predator-prey interactions," biologist Josh Grinath told Live Science. "There are many different kinds of interactions, and they all influence each other."

So to further test this system, the researchers completely removed insect predators, such as lady beetles, so the treehopper population thrived, and on other plants they scattered treehopper predators that would feed on the insects.

And as predicted, the plants with the most predators responded with the most growth. This shows that predators like bears are immensely beneficial to these plants by removing ants that would otherwise keep harmful treehoppers alive.

"Because the bears are targeting this one highly connected species, they have the potential to influence all of the organisms in this meadow," Grinath added.

Black bears, rabbitbrush, ants and treehoppers aren't just confined to this one area. All four species are widespread across the Rocky Mountains, so this predator-prey relationship is one that exists in a variety of places.

This study shows researchers the complex relationships that exist in a food web, and highlights the need to conserve certain predators in order to maintain species diversity in an ecosystem.

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