Who Eats Whom?
In any ecosystem, from a forest to a pond, organisms are connected by what they eat. These feeding relationships determine how energy flows through the ecosystem.
Food Chains and Food Webs
A food chain is a simple, linear path that shows how energy is transferred from one living thing to another.
Example: Grass → Rabbit → Fox
This food chain shows that the rabbit gets its energy by eating grass, and the fox gets its energy by eating the rabbit.
A food web is a more realistic model of the feeding relationships in an ecosystem. It is made of many interconnected food chains. A fox might also eat mice, and rabbits might be eaten by hawks. A food web shows all these complex connections.
Roles in the Ecosystem (Trophic Levels)
Each step in a food chain or food web is called a trophic level.
1.Producers (Autotrophs): These are organisms that make their own food, usually through photosynthesis using energy from the sun. They form the base of every food web.
Examples: Plants, algae, phytoplankton.
2.Consumers (Heterotrophs): These are organisms that get their energy by eating other organisms.
Primary Consumers (Herbivores): Eat producers. (e.g., deer, grasshoppers).
Secondary Consumers (Carnivores/Omnivores): Eat primary consumers. (e.g., snakes that eat mice).
Tertiary Consumers (Carnivores/Omnivores): Eat secondary consumers. (e.g., owls that eat snakes).
3.Decomposers: These are the clean-up crew of the ecosystem. They get their energy by breaking down dead organic matter, like dead plants and animals. This process returns essential nutrients to the soil.
Examples: Bacteria, fungi (mushrooms).
The Energy Pyramid
When one organism eats another, the energy stored in the eaten organism is transferred. However, this transfer is not very efficient. An energy pyramid is a diagram that shows how much energy is available at each trophic level.
Shape: The pyramid has a wide base and gets narrower as you go up. The producers are at the bottom, followed by primary consumers, secondary consumers, and so on.
The 10% Rule: Only about 10% of the energy from one trophic level is actually stored in the bodies of the organisms at the next level.
Where does the other 90% go? It is used by the organisms for their own life processes (like moving, breathing, and keeping warm) and is lost to the environment as heat.
Example:
If the producers (grass) in an ecosystem have 10,000 units of energy...
...the primary consumers (rabbits) that eat the grass will only get about 1,000 units of energy (10% of 10,000).
...the secondary consumers (foxes) that eat the rabbits will only get about 100 units of energy (10% of 1,000).
This is why there are many more producers than top carnivores in an ecosystem. There simply isn't enough energy at the top of the pyramid to support a large population.