Feeding Relationships

Energy is contained within organic molecules produced by autotrophs (organisms that make their own food) – such as plants. These energy rich organic molecules are made by autotrophs through the process of photosynthesis. Because these autotrophs are able to make their own food, they are called producers. These producers provide food (material and energy) to heterotrophic organisms (organisms that cannot make their own food), such as animals. These animals may then be eaten by other animals transferring their energy to the next.

This chain continues as each preceding animal is eaten. This chain is called a food chain. A food chain may be defined as a simple diagram that shows the flow of energy from one organism to another in the form of food. Each stage of the food chain or each feeding level of the chain is called the trophic level.

The first level of the food chain is known as the (primary) producer and is in most cases a plant e.g. grass, cabbage etc. Animals (consumers) that eat plants (feed on the primary producer) are called primary consumers. Organisms that feed on the primary consumers are secondary consumers. Those that feed on secondary consumers are called tertiary consumers. Quaternary consumers then feed on tertiary consumers.

Examples of food chains:

Animals that feed on plants ONLY are known as herbivores.

Animals that feed on meat (animals) ONLY are known as carnivores.

Animals that feed on both plants and animals are called omnivores.

Organisms called saprophytes are also found within the food chain, and they serve as decomposers of living organism. A decomposer is an organism that breaks down dead or decaying organisms. In breaking down dead organisms, decomposers recycle nutrients found in dead organisms as well as help with the eradication of waste material. The two most common examples are bacteria and fungi.

Bacteria mostly decompose meat and waste from carnivores, while fungi preferentially break down the remains of fruits and vegetables. Decomposition of dead organisms is important to other members of an ecosystem, as the decomposer often releases substances that are useful to the organisms that are still alive.

NOTE:

1. Food chains are diagrams so they should be constructed with a pencil.

2. The arrows in a food chain always go across (left to right), never up and never down.