It Takes a Beaver.
Why does a leaf beetle need a beaver? Hold that thought and consider: Biologists like to point out that all living things have roles in their ecosystems, and often the evidence for that notion is obvious. But detailed scientific studies of the ways different species indirectly interact in a given system have been far and few between. Now scientists at Northern Arizona University in Flagstaff have chronicled such indirect relationships between beavers, cottonwoods and leaf beetles.
After a beaver chews down a cottonwood, the tree resprouts with an explosion of new growth. The researchers found that the injury from the beaver prompts the tree to inject far more predator-repelling chemicals into the resulting new shoots than it normally does into young growth. That's when leaf beetle larvae get into the act. The little herbivores not only get nourishment from the repellant-loaded food, they get protection themselves from predators such as ants after ingesting the stuff. "Ants literally do back flips to get away from it," says researcher Gregory D. Martinsen. The resprouting growth attracts 15 times more beetles than other nearby growth.
The beavers' influence may go on and on. The mammals' chomping helps cottonwoods regenerate and grow in mixed-age stands that promote biodiversity. In particular, such stands provide critical bird habitat along the West's streamside areas.