Wolves changing Yellowstone

Biologists call it a "trophic cascade".  Wolves, a top predator, were re-introduced into Yellowstone National Park in the mid-90's and we are now seeing reverberations all the way down the food chain.

Here's how it works.  Because the wolves prey on elk, the elk population has dropped from nearly 20,000 in 1994 to about 6,100 in 2010.

Because elk have a taste for aspen, willow, and other trees, their populations have shot up.  Here are two photos showing the change in the aspen population in just the last five years and the aspen saplings that would never have survived grazing by a massive population of elk. (Photo credit: Ripple and Beschta, 2011)

And there's more.  The beaver populations benefit from more willows.  The streams will benefit from more beavers.  The songbirds benefit from more aspens.  The bison poplations are increasing because they don't have to compete with a massive population of elk anymore...you get the idea.

We are getting a first glimse of historical Yellowstone.  All this from less than 100 wolves.   Phenomenal.

(Source; pdf)