´╗┐Food chains show the main or simple feeding relationships.
However, feeding relationships in an ecosystem are usually more complicated that simple food chains.
The pattern of feeding represented by the interconnected and branching food chains is called a food web.
Some consumers can feed at different trophic levels (this causes more variety).
Food chains and food webs do not usually show the decomposers.

Food chain:
011-food-chain.jpg
Food web:

foodweb.gif