In the 1960s, a young scientist named Bob Paine manipulated the small ecosystems in tidepools of the Pacific Northwest. Learn how this simple experiment led to a revolutionary discovery with videos from NATURE: The Serengeti Rules. By removing certain species from the tidepools and observing the results, Paine discovered that some species are more important in maintaining a balanced ecosystem than others. He called these species “keystones” because they hold communities of plants and animals together. Support materials include discussion questions, vocabulary, and a “Keystone Web” activity.