When I tell friends and acquaintances that I studied the impact of bison on ants, a common first expectation is that the bison are stomping on or eating the tiny gals. This is not really the case (bison actually increase plant diversity, which is expected to indirectly increase ant diversity), but I’ve always thought the image of bison eating ants a rather amusing one:
Grinath came upon another predator-plant connection while studying the partnership between ants and treehoppers on a common plant called rabbitbrush. These tiny sap-sucking insects secrete a sugary liquid the ants eat in return for taking care of the treehoppers. One summer, a bear moved into Grinath’s study site and started digging up the underground ant nests, eating both larvae and adults. So he decided to see what effect the bears had on his study subjects. …
The ants aren’t directly harming the plants, he and colleagues concluded after a series of field experiments. Instead, the presence of the ants scares off predatory insects, in turn enabling treehoppers and other plant-munching insects to thrive and take a serious toll on plant growth. “The ants are providing an enemy-free space for all these herbivores,” Grinath says. Where bears have eaten the ants, predators return and help protect the plants, he and his colleagues reported online ahead of print in Ecology Letters.
Such indirect interaction cascades are part of what makes ecology so interesting, but also rather daunting. Grinath was lucky to have been in the right place at the right time to observe the bears eating ants (the more times I get to write that phrase, the better). Otherwise, who would have proactively investigated the impacts of bears eating ants? Bears eating ants is not something one expects. In fact, even this case of bears eating ants involves a relatively simple system with a limited scope – who knows the full breadth of impacts caused by bears eating ants? Plus, it took four years for the researchers to discover what they did about bears eating ants. Still, it is exciting to know that bears eat ants, and that this consumption is an important factor in the reproductive success of local plants.