In ecology both seem to show who eats whom, so why do we need two separate terms? When do I use each one?
A food chain is a single, straight-line sequence showing how energy and food pass from one organism to the next, for example grass to grasshopper to frog to snake to eagle. Each step is called a trophic level, and a food chain usually shows only one path. The problem is that in nature animals rarely eat only one type of food. A food web is many interconnected food chains linked together, showing the realistic feeding relationships in a community. For example, the frog might also be eaten by a bird, and the snake might eat other animals too. So a food web gives a more complete and accurate picture of energy flow. In short, use a food chain to show one simple path and a food web to show all the overlapping feeding connections in an ecosystem.
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