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, 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 abs