Removing one species from a habitat does not always change it by one species' worth. When sea ott were hun almost t extinction al the Pac coast, t sea urc they h eaten multi without ch and grazed the kelp forests down to bare rock. Dozens of animals that depended on the kelp went with it. Ecologists call such a species a keystone, after the stone that holds an arch together.

Type only the missing letters. Each box is one letter, and the number of boxes matches the letters that are missing.