The rainforest is generally divided into four layers. Each layer has different set of environmental conditions tath lead to different kinds of ecosystems.

The Emergent Layer:

• tallest trees  
• 200 feet (60 m) above the forest floor  
• trunks measure up to 16 feet (5 m) around
• usually supported by buttress roots
• greater fluctuations of temperature
• winged seeds or  fruits that are dispersed by wind
• lots of sunlight
• animals: eagles, monkeys, butterflies, insect-eating bats and snakes inhabit this layer, some never venturing below it

 
The Canopy:

• primary layer of the rainforest
• rising to 150 feet (45m).
• oval leaves that come to a point
• filters out 80% of the light
• stops the rain from reaching the plants below
• flowers and fruits abound
• epiphytes, some 28,000 species worldwide, use every tree surface  as a place to live

       
The Under story:

• this area gets only 2-5% of the sunlight available to the canopy
• solar-collecting dark green leaves
• 12 feet (3.5 m) in height
• understory plants have a more difficult time with pollination because of the lack of  air movement, rely on insects
• animals: snakes, frogs, parakeets, leopards, jaguars and the largest concentration of insects
• a large number of plants from this level make up common house plants
• very little direct sunlight or rainfall
• these plants also have had to adapt to poor soil with few nutrients

 

The Forest Floor:

• almost no plants
• 0-2%  light and 100% humidity
• there is heavy competition for nutrients
• lowest  level in the forest
• very little sunlight filters through to this area
• mosses,  herbs and fungi grow here

 
References:
http://www.perspective.com/nature/
http://library.thinkquest.org/27257/rainintro.html