Keystone Species: How Predators Create Abundance and Stability

Wolves, bears, otters, starfish — these ecosystem engineers affect nature in overt yet surprisingly subtle ways.

Wolves Hunting Elk
Reintroduction of wolves to Yellowstone thinned the excessive population of elk, enabling much-needed regrowth of willow, aspen and cottonwood trees.  
MINDEN PICTURES/DONALD M. JONES