We have all heard about food chain, food chain, food chain o trophic web, now we are going to learn much more about them. Organisms of different species can interact in many ways. They can compete, or they can be symbiotes: long-term partners with a close partnership. Or, of course, they can do what we see so often on nature shows: one of them can eat the other! That is, they can form one of the links in a food chain.

In ecology, a food chain is a series of organisms that eat each other so that energy and nutrients flow from one to another. For example, if you eat a hamburger for lunch, you are part of a food chain that looks like this:

Grass → Cow → Human.

What if you had lettuce on your burger? In that case, you are also part of a food chain that looks like this:

Lettuce → Human.

As these examples illustrate, we cannot always fully describe what an organism, such as a human, eats with a line. For situations like the one above, we may want to use a food web that consists of many intersecting food chains that represents the different things that an organism can eat and by which it can be eaten.

On this page, we will take a closer look at food chains and webs to see how they represent the flow of energy and nutrients through ecosystems.

Autotrophos vs. Heterotropos

What basic strategies do organisms use to obtain food? Some organisms, called autotrophs, also known as self-feeders, can make their own food, that is, their own organic compounds, from simple molecules like carbon dioxide. There are two basic types of autotrophs:

  • The photoautotrophsLike plants, they use the energy from sunlight to make organic compounds, sugars, from carbon dioxide in photosynthesis. Other examples of photoautotrophs are algae and cyanobacteria.
  • The chemoautotrophs They use the energy of chemists to build organic compounds from carbon dioxide or similar molecules. This is called chemosynthesis. For example, there are hydrogen sulfide oxidizing chemoautotrophic bacteria found in subsea venting communities where light cannot reach.

The autotrophs they are the basis of all the ecosystems of the planet. That may sound dramatic, but it is not an exaggeration. Autotrophs form the basis of the food chain and food webs, and the energy they capture from light or chemicals sustains all other organisms in the community. When we talk about its role in food chains, we can call autotrophs as producers.

The heterotropic, also known as other feeders, cannot capture chemical or light energy to make their own food from carbon dioxide. Humans are heterotropic. Instead, heterotropes obtain organic molecules by eating other organisms or their by-products. Animals, fungi, and many bacteria are heterotropic. When we talk about the role of heterotropes in food chains, we can call them consumers. As we will see shortly, there are many different types of consumers with different ecological roles, from plant-eating insects and carnivorous animals even fungi that feed on garbage and waste.

What is a food chain?

Now, we can see how energy and nutrients move through an ecological community. Let's start by considering just a few relationships of who eats what, looking at a food chain.

We can say that a food chain is a linear sequence of organisms through which nutrients and energy pass when one organism benefits from another. Let's look at the parts of a typical food chain, starting at the bottom (the producers) and working your way up.

At the base of the food chain are the primary producers. The primary producers are autotrophs and are most often photosynthetic organisms such as plants, algae, or cyanobacteria.

  • The organisms that eat the primary producers are called primary consumers. Primary consumers are generally herbivores, plant eaters, although they may be consumers of algae or bacteria.
  • The organisms that eat the primary consumers are called secondary consumers. Secondary consumers are generally meat eaters and carnivores.
  • The organisms that eat secondary consumers are called tertiary consumers. These are carnivorous carnivores, such as eagles or large fish.

Some food chains have additional tiers, such as quaternary consumers, carnivores that feed on tertiary consumers. Organisms that are at the top of the food chain are called apex consumers.

We can see examples of these levels in the following diagram. Green algae are the primary producers that are consumed by mollusks, the primary consumers. The mollusks then become the lunch of the slimy scorpion fish, a secondary consumer, which in turn is consumed by a larger fish, salmon, a tertiary consumer.

Food chain example

Food chain example

Each of the above categories is called trophic level and reflects how much energy and nutrient transfer, or consumption stages, separates an organism from the original energy source of the food chain, such as light. As we will see later, the assignment of organisms to trophic levels is not always well defined. For example, humans are omnivores that can eat both plants and animals.


Another group of consumers deserves to be mentioned, although it does not always appear in drawings of food chains. This group is made up of decomposers, organisms that break down dead organic matter and waste.

Decomposers are sometimes considered their own trophic level. As a group, they eat dead matter and waste products that come from organisms at other trophic levels; for example, they would gladly consume decomposing plant matter, the body of a half-eaten squirrel, or the remains of a dead eagle. In a way, the level of decomposition parallels the standard hierarchy of primary, secondary, and tertiary consumers.

Fungi and bacteria are the main decomposers in many ecosystems; They use chemical energy from dead matter and waste to fuel their metabolic processes. Other decomposers are detritivores: those that eat debris or those that eat waste and garbage. They are generally multicellular animals such as earthworms, crabs, slugs, or vultures. Not only do they feed on dead organic matter, they often break it up as well, making it more accessible to bacterial or fungal decomposers.

Example of a decomposing fungus, important in the food chain.

Example of a decomposing fungus, important in the food chain.

Decomposers as a group play a critical role in maintaining the health of ecosystems. When they break down dead material and waste, they release nutrients that can be recycled and used as building blocks by primary producers.

Food webs

Food chains give us a clear picture of who is eating whom. However, some problems arise when we try to use them to describe entire ecological communities.

For example, an organism can sometimes eat multiple types of prey or be eaten by multiple predators, even at different trophic levels. The cow is a primary consumer, and the lettuce leaf in the burger is a primary producer.

To represent these relationships more precisely, we can use a food web, a graph that shows all trophic-eater-related interactions between various species in an ecosystem. The diagram below shows an example of a food web. Primary producers are marked in green, primary consumers in orange, secondary consumers in blue, and tertiary consumers in purple:

Example of food web

Example of food web

In food webs, arrows point from an organism that eats it to an organism that eats it. As the food web above shows, some species can eat organisms from more than one trophic level. For example, prawns are eaten by both primary producers and primary consumers.

This food web contains the food chain that we saw earlier in the article:

Seaweed → Mollusks → Chickfish → Salmon.