Food Chain, Food Webs and Trophic Levels

As living and non-living things interact, energy is transferred from one level to the other. The ecosystem actually operates as a movement where all organisms depend on the primary producers, the green plants.

1. Food Chain

Food chain is the transfer of food energy from producers (green plants) to a series of organisms in a habitat. In the arrangement of the food chain, the natural rule is that it must start from a producer or an autotroph. Some examples of food chain are below:

1. Grass     →    Grasshopper       →       Lizard      →      Snake
2. Plankton      →      Tilapia      →     Water snake
3. Dead wood       →      Termite     →      Frog     →      Hawke

Note: that each level of competition in the food chain is called a trophic level. Looking at example 1, it represents the terrestrial habitat.

2. Food Web

Considering food chain energy pathway, you will observe that it is a single energy pathway. In the actual sense, such simple food chains as shown above rarely exist within a community because consumers rarely depend on only one type of food. Often a particular food item is eaten by more than one consumer. Therefore, a network of interrelated food chains forms what is called a food web.

3. Trophic Levels

These are stages at which the energy is found as it moves through the various organisms or levels of transfer in the ecosystem. Hence, trophic level refers to the part of a food chain.

4. Food Pyramid

Food pyramid is a representation of food chain in the food producers from the base and carnivores from the apex.

5. Pyramid of Numbers

This is the progressive drop in the population at each higher or successive trophic level of the food chain or the relative decrease in number or organisms in a food chain as one ascends the higher trophic levels.

6. Pyramid of Biomass

The pyramid of Biomass (or standing crop) indicates, by weight, the total mass of individuals or organisms at each trophic levels.

7. Pyramid of Energy

This is the progressive drop or decrease in the total available energy at each higher trophic level or the progressive diminution of energy in the feeding chain as one ascends the higher trophic levels.

Differences between Pyramid of Numbers and Pyramid of Energy

		Pyramid of Numbers	Pyramid of Energy
	1.	Size of organism is not recognized, only numbers are counted	This is based on a common unit of energy joule
	2.	Shape is not constant, it might be inverted e.g. grasshoppers feeding on a large tree.	Shape is constant