in yellowstone national park, robert crabtree and his team of scientists seek to untangle the cascading effects in the ecosystem when the top predator the wolf is removed and years later returned to the park. by looking at the delicate balance between different species, both scientists hope to learn how to manage and preserve these ecosystems and others worldwide. in panama, on barro colorado island, an ecological preserve created through the making of the panama canal, stuart davies hopes to uncover some of the mysteries of a complex ecosystem the rainforest. man: i m the director of the center for tropical forest science, which is a group who study the rainforests of the world. and we work together as one very large network to try to understand how rainforests function and how they re gonna change in the future. narrator: tropical rainforests are believed to be the oldest terrestrial ecosystems on earth. they are home to over 5 million known species of plants, animals