A food chain is a model that shows the relationships between all organisms in a forest ecosystem based on how they exchange energy with one another.
- Models are pictorial or metaphorical representations of very complex systems that make those systems easier to understand and visualize
Food chains are an important model because it would be impossible to create a diagram of every single energy exchange that takes place in a forest ecosystem. The food chain model allows us to visualize the energy exchanges taking place to make the relationships in an ecosystem easier to understand.
Now let’s describe each “section” of the food chain starting from the bottom and working our way up to the top. Remember, the “bottom” of the food chain is not literally at the bottom, rather, this refers to the fact that all energy works its way up from the base level.
We can also refer to the food chain in terms of trophic levels. A trophic level is the energy category occupied by a group of organisms based on how far away they are from the source of the energy (the sun).
From bottom to top, here is how the forest ecosystem is arranged:
So, tertiary consumers sit at the top of the food chain, in the highest trophic level. (Decomposers aren’t necessarily at the top, we’ll get into that later.) The sun makes up the base of the chain, and the producers occupy the lowest trophic level.
The Foundation of the Food Chain: The Sun
A food chain relies on the exchange of energy between parts of a forest ecosystem. But we know that energy can’t be created, as the energy of the universe is a constant. So where does all the energy needed by a forest come from?
- All energy cycled through a forest ecosystem originates from the sun
The sun is the most important abiotic (non-living) feature of a forest ecosystem, and all living things in the forest rely on the sun in one way or another. But how does the sun transmit energy to the forest ecosystem?
The sun emits tons of energy in the form of light that producers can uptake and turn into their form of energy (sugars) through photosynthesis.
Producers: Harnessing the Sun’s Energy
Producers are any living organism that produces its own energy by using the sun’s energy. This is pretty much any green organism in a forest. These are also called autotrophs because they produce their own food.
Producers are unique in that they do not have to “eat” anything to produce energy for themselves. Rather, they create energy through photosynthesis. The basic equation for photosynthesis is:
Carbon dioxide + Energy from the sun + Water → Oxygen + Sugars
Producers absorb carbon dioxide, water, and the sun’s energy and produce oxygen and glucose (sugar). This means that the role of producers is to produce an energy supply for consumers. Producers form the first trophic level because they take energy from the sun and turn it into energy that is available to be uptaken by consumers.
Consumers: Eating to Produce Energy
Consumers are any organism that must ingest another organism to produce energy. Consumers are also called heterotrophs because they rely on other organisms for food.
There are three main types of consumers:
- Primary consumers
- Secondary consumers
- Tertiary consumers
In terms of a food chain or trophic levels, primary consumers are situated above producers, secondary consumers are situated above primary consumers, and tertiary consumers are situated above secondary consumers.
We can now talk more specifically about each of the three types of consumers and give examples of them.
Primary Consumers
Primary consumers gain energy by ingesting producers. Any organism whose diet is made up of green things is a primary consumer. In this energy exchange, energy travels from the sun to a producer, to a primary consumer.
Here are some examples of primary consumers in a forest ecosystem, we can also think of these as the herbivores:
- Mice
- Squirrels
- Deer
- Rabbits
- Grasshoppers
Each one of these organisms eats plants like grasses, shrubs, berries, or trees and turns the glucose created by that plant into energy for themselves.
Secondary Consumers
Secondary consumers are any organism that ingests primary consumers, but they may also eat producers, making them omnivores or carnivores.
Here are some examples of important secondary consumers in a forest ecosystem:
- Snakes
- Frogs
- Fish
The “Top” of the Food Chain Tertiary Consumers
Tertiary consumers are organisms that eat secondary consumers. These are the major predators of the forest ecosystem. They may also eat primary consumers and are almost always carnivores.
Here are some examples of some tertiary consumers in a forest:
- Hawks
- Grizzly Bears
- Wolves
They occupy the highest trophic level because they are the furthest removed from the initial source of energy (the sun).
Where it All Ends Up: Decomposers
Decomposers are any organism that ingests something that was once alive. The decomposers are not necessarily at the top or the bottom of the food chain, but they are incredibly essential for the food chain. Without decomposers, none of the organisms in a forest ecosystem would be able to live.
This is because decomposers transform dead animals into important nutrients that support the growth of producers. Here are some important decomposers in a forest:
- Fungi
- Worms
- Bacteria
- Some insects
- Snails
- Slugs
Decomposers ensure the health of the soils. Without them, plants would not be able to grow. Decomposers may fit better into the idea of a food chain as a cycle, rather than a pyramid, where the cycle goes from the sun, to producers, to consumers, to decomposers, and then back to producers.
Key Takeaways
- Food chains model energy exchange between the parts of a forest ecosystem including abiotic features (like the sun), and producers, consumers, and decomposers.
- The energy for a food chain is supplied by the sun, making the sun the energetic foundation of a food chain.
- Producers are at the bottom of the food chain in the lowest trophic level because they create energy from the sun’s energy.
- Consumers ingest producers, tertiary consumers are at the “top” of a food chain.
Decomposers don’t necessarily sit at the top or bottom of a food chain, but they are essential for replenishing nutrients in the soil so new producers can grow.