A War Between Ants, Plants, Bears, and Pests

Plants, ants, and bears, oh my! It seems that these three organisms are in an interesting war of influence, so to speak, in Colorado meadows. A war that researchers are calling a prime example of the largely unconsidered roles that top predators play in ecosystems.

Normally, when we think "big predator," we think of gnashing teeth, feral-rumbling growls, and the chasing of prey. Rarely do we look outside the role of the "hunter" to see what else predators are up to.

However, according to a study recently published in the journal Ecology Letters, black bears are playing the roles of pest control and grounds keeper too.

Researcher Joshua Grinath, from Florida State University, first stumbled upon this bear relation when, strangely enough, studying ants and treehoppers on a plant called rabbitbush commonly found in Colorado meadows.

Treehoppers traditionally prey on rabbitbush by sucking the plants dry of their sap. However, this is hard and time consuming work, and treehoppers become easy prey for top-tier insect predators, such a ladybugs.

In order for them to prey on plants in peace, Grinath found that treehoppers recruit help from local ants, drawing the ants into their vicinity by secreting a tasty, sugary liquid. New ant nests then serve as bodyguards for the treehoppers, scaring prospective predators away - but not all predators.

One summer, in the midst of his field study, Grinath observed a bear move into the site and start digging up ant nests. Bears have long been known to eat insects and berries to supplement their diet, but the researcher was curious how this behavior would impact rabbitbush survival.

For the next four years he and his colleagues monitored 35 ant nests in the meadow for bear damage. During that time, bears damaged or destroyed 26 to 86 percent of the nests. Predictably, plants lacking ants quickly grew better and produced more seeds.

"The study really highlights the complexity of effects that a predator can have on a whole community of species that are interacting with each other," Corinna Riginos, an ecologist at Teton Science Schools in Jackson, Wyoming, who was not involved with the work, told Science magazine.

Other experts also weighed in, impressed with such a concrete example of cause-and-effect triggered by largely indirect interactions. This, they say, is why large predators likely have a far larger impact on ecosystems than we think, as predicting these kinds of relations is difficult work.

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