How do wolves affect the food web and change rivers? Video

This is an excellent video about how the absence and reintroduction of wolves in Yellowstone affected the Yellowstone food web and even change the behavior of rivers.  Now you might be wondering as I did, how in the heck can wolves change the behavior or the Yellowstone rivers.   The images in this video are very beautiful and your students will enjoy this short video.  If you are teaching some ecology in your science classroom then this video is for you.