Food Chain, Food Web and Food Pyramid

Food Chain:

One of the basic characteristics of living organism is the fact that they can feed. The process of nutrition may be considered as a form of chain that brings different species of organisms into interaction; for instance, a zebra will interact with different plants in the savanna biome for the purpose of food. Similarly, a lion interacts with a zebra for the same purpose (food). This interaction of organisms for food (food chain) will always commence with producers. Producers in food chain refers to organisms that manufacture or produce their own food. These producers also feed from the food they produce while other organisms will always depend on them for ready made food, either directly or indirectly.

You can read on the Savanna and Tropical Rainforest Biomes here.

Organisms that manufacture their own food are referred to as autotrophic organisms or autotrophs. (In food chain, we often refer to them as producers).

Please read on autotrophic mode of nutrition here

Examples of autotrophs or producers are green plants, blue-green algae and chemosynthetic bacteria.

Note: When autotrophs require sunlight to make their food, they are referred to as photoautotrophs and the process involved is termed photosynthesis. Examples of photoautotrophs are all green plants and blue-green algae. On the other hand, when autotrophs utilizes chemicals for making their food, they are referred to as chemoautotrophs and the process is termed chemosynthesis. Chemoautotrophs includes methanogenic archaea, aquificae, and sulfur-oxidizing epsilon proteobacteria.

A Food Chain is a diagram that shows the relationship between plants and animals within a habitat on the basis of how they rely on each other for food.

Think of habitat as a place where organisms live; for instance, it could be terrestrial (land), aquatic (water) and arboreal (treetops).

Image Credit: Dreamstime

Normally, a food chain begins with the producers. These producers are usually consumed by other organisms (herbivores organisms) and are referred to as consumers.

Note: Organisms that directly feed on producers in a food chain are preferably called primary consumers. Examples of primary consumers are zebra, grasshopper, antelope, rabbit and other plant feeding organisms.

Next, the primary consumers are consumed or eaten by another sets of consumers called secondary consumers. Secondary consumers may include animals like rats, lion, cats and snakes. (They can be carnivorous or ominvorous organisms).

Secondary consumers may be consumed by a third set of consumers called tertiary consumers. Vultures and Eagles are examples of a tertiary consumers.

Finally, the tertiary consumers are consumed by the last group of organisms called decomposers. Decomposers in food chain are organisms that feed on dead organisms, bringing about their decomposition in the process. They may also be regarded as saprophytes (in some cases).

Producers begins food chain while decomposers signifies the end of a food chain.

 

Food Web

Food chain can be interlinked in a habitat, giving rise to food web. Consider the diagram below.

From the above diagram, let’s say we have those organisms within a habitat. Recall that organisms need to survive, so they have to feed on one another. Notice that the feeding pattern is interlinked. For instance:

1. Grasshopper feeds on berries. The frog feeds on the grasshopper. A snake feeds on the frog. A titmouse feeds on the snake. The fox eats the titmouse.

Berries >> Grasshopper >> Frog >> Snake >> Titmouse >> Fox.

This is one food chain in the habitat. Notice that the food chain is linked to other food chains as illustrated below.

2. Notice that apart from the grasshopper, the greenfly and butterfly also fed on the berries. The ladybird feeds on the greenfly. Dragonfly feeds on the ladybird. The frog feeds on the dragonfly. The snake eats the frog and the Buzzard eats the snake

This is another food chain but it has some links with the above food chain.

It is this linking of food chains that gives rise to food web.

3. Also, you may have observed that apart from the dragonfly feeding on the ladybird, the titmouse also fed on the lady bird. Also, the butterfly and titmouse fed on the berries along side the greenfly and grasshopper. Similarly, the rabbit, mouse and grasshopper all fed on plantain. The buzzard and fox feeds on the mouse and rabbit. We can go on and on but the point to note is:

A food web shows multiple food chains or multiple feeding relationships or multiple feeding connections all linked together.

Food web always consist of more than one food chain (at least, a minimum of 2 food chains linked together).

 

Food Pyramid

All organism get their energy from the food they eat.

A food chain that shows the movement of energy through it is termed a food pyramid.

Note: The food pyramid is always drawn in a triangular form with the narrow edge at the top. This narrowing at the top (food pyramid) signifies that energy is lost or reduced as we go top of the food pyramid.

From the above diagram, the primary consumers (grasshoppers) fed on the grasses and gained 1,000kcal of energy. Most of this energy would have being used for their metabolic activities like hopping, respiration, movement, reproduction and so on.

All living organism must lose energy in the form of heat to their surroundings. This is as a result of their metabolic activities.

By the time the secondary consumers consumed the grasshoppers, it was only able to get 10kcal of energy simply because the grasshoppers had already lost some energy in the form of heat to it's surroundings. The secondary consumers will also use some of this energy (10kcal) for it’s metabolic activities thus losing some energy in the form of heat.

Finally, the tertiary consumer consumed the secondary consumers and was able to get 1kcal of energy. This is because the secondary consumers had lost 9kcal of energy in the form of heat to its surroundings.

Note: As a student, you should be able to state the second law of thermodynamics because it has everything to do with “the loss of heat to the surroundings”.

2^nd Law of Thermodynamics, with regards to food chain

In the course of energy transformation or transfer, some energy is lost in the form of heat to the surroundings.

Note: Energy is always lost as heat during metabolism.

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