The canopy shelters the Earth's richest and most diverse ecosystem. Competition and millions of years of evolution help explain why there are so many highly adapted species in the rainforest canopy. The most intricate relationships in the rainforest are between animals and trees. In this competitive market, leaves are the most common currency. In each leaf is sunlight trapped by the forest and turned into energy-filled matter. This self-sufficient system supports not only the trees themselves but also the countless herbivores of the canopy.