Energy Transfer

Each animal species or link in the food web is a source of energy transfer from one organism to another. Drawings of food webs typically include arrows that show the relationships among the species; by following which way the arrow go, you can see which organisms give and receive energy (who eats who).

Types

The producers in a food web do not eat anything, but get energy from the sun. Primary consumers are the next links; they eat producers, followed by secondary consumers that eat the primary consumers, and tertiary consumers that eat the primary and secondary consumers.

Quantity

Most food webs have only four or five links between the producers and the top consumers. This is because animals expend most of the energy they eat in order to grow and survive, leaving only a small portion of the energy available for the next link to receive.

Significance

The importance of a link in a food web can be seen if you imagine what would happen if that animal were to go extinct. It would impact both the population it consumes, which would grow, and that above it, which would not have as much food as it needs.

Food "chain" vs. "web"

The word "link" was particularly useful when the concept of a food "chain" was used, because organisms were pictured connected in a straight line, with producers linking to consumers above them. However, food chains are incomplete descriptions of an ecosystem, and now we commonly refer to food webs, which recognizes the complex interactions among species.

Source:

Bigelow Laboratory for Ocean Sciences: Fitting Algae Into the Food Web

Virtual Teacher Aide: Food Chains and Food Webs

Geography 4 Kids: Biosphere: Food Chains