

Bears destroy the nests of ants that help another insect munch on rabbitbrush. The end result is healthier rabbitbrush/FSU Bears destroy the nests of ants that help another insect munch on rabbitbrush. The end result is healthier rabbitbrush/FSU

Whether you believe wolves can have an impact on the course of rivers in Yellowstone National Park or not, there is evidence that bears can impact the vegetation of a landscape, simply by eating.

The question of what impact wolves have on rivers was raised in a provocative piece by Sustainable Man that looked at how Yellowstone's wolves could alter the park's landscape by preying on ungulates that browse on shoreline vegetation. While that video might have lacked a documented scientific foundation, a study by a Florida State University researcher demonstrates how the diet of bears in Colorado helped vegetation flourish. The key? The bears ate ants.

In a paper published this week by Ecology Letters, Florida State researcher Josh Grinath looks at the relationship among bears, ants and rabbitbrush ' a golden-flowered shrub that grows in the meadows of Colorado and often serves as shelter for birds.

'Bears have an effect on everything else because they have an effect on this one important species ' ants,' Grinath said.

As John Muir said long ago, "When we try to pick out anything by itself, we find it hitched to everything else in the Universe." And that certainly seems the case with bears, ants, and rabbitbrush.

Grinath, who finished his doctorate in December working in the labs of Associate Professors Nora Underwood and Brian Inouye, had spent several years monitoring ant nests in a mountain meadow in Almont, Colorado. On one visit, he discovered that bears disturbed the nests, which led him to wonder exactly how this disturbance might affect other plants and animals in the meadow.

From 2009 to 2012, Grinath, Underwood and Inouye collected data on bear damage to ant nests. Simultaneously, the team realized that the nearby rabbitbrush, a dominant plant in the area, was growing better and reproducing more near damaged nests. Eventually, they were able to figure out why. The missing link was an insect called a treehopper, a tiny cicada-like arthropod that sucks sap out of plants.

Grinath had previously studied the relationship between the ant and the treehopper and knew that the two had a mutualistic relationship, meaning they benefitted from one another. So, the research team began a series of controlled field experiments to see what would happen to treehoppers with more ants around, and then with fewer ants.

They found that ants didn't prey on the treehoppers or the rabbitbrush. Rather, the ants scared away other bugs such as beetles that typically prey on treehoppers. In a situation where bears disturbed and ate ants, other bugs were free to prey on the treehoppers and other plant-feeding insects, and thus the rabbitbrush thrived.

Grinath's work was funded by the Rocky Mountain Biological Laboratory and the STAR Fellowship from the Environmental Protection Agency. Additional funding was provided by the National Science Foundation.