Meet keystone species—the hidden heroes of the natural world—and learn about the ecosystems they support in this marvelous nonfiction picture book from the author of Crossings: Extraordinary Structures for Extraordinary Animals. Keystone species are plants, animals, or other organisms that have a huge effect on the environments around them. From beavers to elephants, alligators to hummingbirds, keystones help themselves and other species survive. Whether it’s creating habitats for themselves and other animals, leaving behind leftovers that fertilize the soil, or clearing out harmful algae, keystones live up to their name in their essential contribution to the harmony of our natural world.