The layered structure of a tropical rainforest includes the forest floor, understory, canopy and emergent layer. Each layer contains different flora and fauna unique to its environment. The fundamental difference between these layers is the amount of sunlight they receive. According to the BBC, the upper layers are bathed in sunlight, but the forest floor is almost completely dark.
The rainforest floor has scant vegetation because it is an extremely dark environment. This attracts certain large land mammals that cannot fly, burrow or climb trees. Human cultures that live in the rainforest also dwell on the forest floor.
The BBC explains that the second layer of a rainforest is the understory, a shady zone packed with shade-loving trees, shrubs and vines. Its denizens include hundreds of bird species, insects, snakes, arachnids and rodents. Larger animals such as leopards also live in the understory.
The canopy layer receives much more sunlight than the understory and the forest floor. Some of its plants have roots in the understory. The canopy is extremely dense and only permits a small portion of the sunlight to pass into the bottom layers of the rainforest.
The emergent layer vaults above the canopy and contains the tallest trees in the rainforest. The animals living in it include large birds and tiny rodents.