Imagine your favorite multiplayer game. Dozens of players, different roles, everyone affecting everyone else. Now replace the players with animals, plants, and tiny microbes, and the game map with a forest, lake, or ocean. That complex network of who eats whom, and how energy and matter move around, is what scientists call a food web.
Food webs are powerful models that help us understand how matter (atoms and molecules) and energy move between producers, consumers, and decomposers in an ecosystem. They also show how nothing is really “thrown away” in nature—dead matter is recycled, and the same atoms are used again and again.
An ecosystem is all the living things (plants, animals, fungi, bacteria) in a certain area, plus the nonliving things (water, air, rocks, soil, sunlight) and all the interactions between them.
Examples of ecosystems include:
In every ecosystem, energy and matter are constantly moving from one part to another as organisms eat, grow, breathe, and die.
To see how these connections work, scientists draw diagrams called food webs. A simple example for a pond ecosystem is shown in [Figure 1].
A food chain is a simple, straight line that shows one possible path energy and matter can take through an ecosystem.
Example of a forest food chain:
Sun → grass → grasshopper → frog → snake → hawk
But real ecosystems are not simple straight lines. Most organisms eat more than one type of food, and can be eaten by more than one predator. That is why scientists use food webs, which connect many food chains together.
A food web is a network of food chains that shows the feeding relationships among many organisms in an ecosystem. It looks more like a web than a line, with many branching arrows.
Food webs are important because they show how a change to one species—like overfishing, pollution, or the arrival of an invasive species—can affect many other species, sometimes in surprising ways.
All organisms in a food web can be grouped into three big categories based on how they get their energy and matter.
Producers are organisms that can make their own food from nonliving materials and energy from the environment. Most producers are plants and algae, and they use a process called photosynthesis.
In photosynthesis, plants and algae take in:
They use these to build sugars (a kind of chemical energy) and other molecules they need to grow. These sugars contain energy stored in chemical bonds and matter made of atoms like carbon, hydrogen, and oxygen.
Examples of producers:
Producers are the foundation of every food web because they are the original source of energy for almost all other living things.
Consumers cannot make their own food from sunlight. They must eat other organisms to get energy and matter.
Types of consumers:
Some animals eat both plants and animals. They are omnivores, and depending on what they eat in a particular interaction, they can act as primary or secondary consumers.
When a consumer eats food, it:
What happens to dead leaves, dead animals, and animal wastes? They don’t just pile up forever. Decomposers break them down.
Decomposers are organisms, usually bacteria and fungi, that feed on dead plant and animal matter and waste. They break large molecules into smaller ones and return nutrients to the environment.
Examples of decomposers:
In terrestrial (land) environments, decomposers return nutrients such as nitrogen and phosphorus to the soil. In aquatic (water) environments, decomposers return nutrients to the water. Plants and algae can then absorb these nutrients again. This creates a loop that keeps matter cycling.
The role of decomposers in a forest soil community is shown in [Figure 2].
Food webs show both energy flow and matter cycling, but these two things do not behave the same way.
Energy in most ecosystems starts with the sun:
Because so much energy is lost as heat at each step, only a small fraction of the energy from one level moves up to the next level of the food web. This is why there are usually fewer top predators than herbivores in an ecosystem.
Energy flows in one direction: from the sun → producers → consumers → heat in the environment. It does not cycle back to the sun.
Matter is different. Matter is made of atoms (like carbon, hydrogen, oxygen, nitrogen) that are rearranged into different molecules but are not destroyed.
In an ecosystem:
This means the same atoms can move from the living part of the ecosystem (organisms) to the nonliving part (air, soil, water) and back again many times.
Did you know? 🤔 Some of the oxygen atoms you breathe in right now might once have been part of a dinosaur’s body or a leaf from a tree hundreds of years ago. Atoms are constantly reused.
In food webs, arrows show the direction of energy and matter transfer. The arrow goes from the organism being eaten to the organism that eats it. For example:
Grass → rabbit → fox
The arrow from grass to rabbit means: energy and matter move from the grass to the rabbit when the rabbit eats the grass.
It is important not to think of the arrow as “eats,” but as “is eaten by” or “gives energy to.”
Let’s return to a pond food web like the one in [Figure 1] and add more detail:
Sample food chains inside this web:
When any of these organisms dies, decomposers break down their bodies and release nutrients back into the water and mud. Then algae and aquatic plants take up those nutrients again, restarting the cycle of matter.
At every level of the food web, matter is being transferred into and out of the physical environment:
These transfers keep important elements (like carbon, nitrogen, and phosphorus) circulating between living organisms and the nonliving environment.
The basic job of decomposers is the same everywhere—breaking down dead matter—but where the nutrients go depends on the environment.
On land (terrestrial ecosystems):
In water (aquatic ecosystems):
The two kinds of nutrient recycling are compared in [Figure 3].
Every living thing is made of atoms that once were part of something else. Let’s follow a carbon atom as an example:
This looping path shows how atoms move between the living (plants, animals, decomposers) and the nonliving (air, water, soil) parts of the ecosystem. This is true not only for carbon, but also for other key elements like nitrogen and phosphorus.
Understanding food webs and matter cycling is not just science-class trivia. It affects real-world issues you hear about all the time.
1. Pollution and Toxins in Food Webs
When harmful substances like mercury or certain pesticides enter an ecosystem, they can move through the food web. Producers may absorb them from water or soil, and then consumers eat those producers.
At higher levels of the food web, these toxins can build up, a process called bioaccumulation. This is why large predators (like sharks or eagles) sometimes have the highest levels of toxins. It can also affect humans who eat fish or other animals from polluted environments.
2. Protecting Top Predators and Biodiversity
If humans remove too many top predators (like wolves or sharks), food webs can be thrown out of balance. Herbivore populations may explode, overgrazing plants or algae. This can change entire ecosystems, including the cycling of nutrients and the health of soil or water.
Conservation scientists study food webs to understand which species are most important for keeping ecosystems stable.
3. Farming, Fishing, and Food Supply
Farmers and fishery managers use knowledge of food webs to:
4. Small At-Home Observation
You can see decomposers and nutrient cycling in action with a simple experiment:
You are watching matter move from once-living material back into the soil, where it can eventually feed plants again.
Food webs are models that show how energy and matter move between producers, consumers, and decomposers in an ecosystem.
Producers (like plants and algae) make their own food using energy from the sun and matter from the environment. They form the base of all food webs.
Consumers eat other organisms to get energy and matter. They include herbivores, carnivores, and omnivores at different levels (primary, secondary, tertiary).
Decomposers (like bacteria and fungi) break down dead plant and animal matter and wastes, recycling nutrients back to the soil in terrestrial ecosystems and to the water in aquatic ecosystems.
Energy flows in one direction, mainly from the sun → producers → consumers → environment as heat, and does not cycle back.
Matter (atoms and molecules) cycles repeatedly between the living and nonliving parts of ecosystems. The same atoms are reused many times.
Transfers of matter into and out of the physical environment occur at every level of the food web, from producers to top predators to decomposers.
Understanding food webs helps us make better decisions about pollution, conservation, farming, and fishing, and shows how deeply connected all life on Earth really is. 🌎
