stuart davies vestigat the world's most diverse ecosystem -- tropical rainforests. through a worldwide tree census, he hopes to discover how such a wide range of species all competing for the same resources can co-exist. 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 rainfores

on barro colorado island an ecological preserve created through the making of the panama canal, stuart davies hopes to uncover somef 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, and insects, with millions more yet to be discovered. and trees play an essential role in the diversity of these intricate ecosystems. dr. davies: one famous ecologist said trees in tropical rainforests are like -- he called them the ecosystem engineers. what he meant by that is that they provide the habitat on which all these other organisms depend. so monkeys that live up in canopies of trees go extinct if you take the trees away. ants and termites -- they're gonna be absent if the trees disapp

stuart davies vestigat the world's most diverse ecosystem -- tropical rainforests.