Food web

All organisms that live together in an ecosystem depend on one another for food. An ecosystem is a community of living and nonliving things that share an environment. These organisms have relationships with each other. A food chain shows the relationships that exist among several organisms in the ecosystem. A typical food chain shows what eats what. A food web gives a more complete picture of the ecosystem by showing all existing food chains. A food web is a useful tool that helps scientists determine the health of an ecosystem.

Overview

All living things need nutrients to survive. Nutrients are substances that provide energy for growth and life. Living things obtain nutrients from each other through their feeding relationships. Food chains show how energy is passed from one group of organisms to another by illustrating the path that nutrients, or energy, follow in the ecosystem. Because feeding relationships are complex and the organisms in the ecosystem play a role in multiple food chains, a food web is used to show a more complete picture of this energy flow. To understand food webs, however, you must first understand food chains.

In any food chain, the sun is the original source of energy. Some organisms in the ecosystem get their energy directly from the sun. Other organisms get their energy from eating this group of organisms, and so on. Living organisms in an ecosystem are grouped by trophic level. A trophic level is the position an organism occupies in the food chain. A trophic level indicates what the organism eats for energy, as well as what eats the organism for energy. Ecosystems have three main trophic levels: producers, consumers, and decomposers.

The Sun

The sun is the original source of energy for Earth. Every food chain on Earth’s surface, as well as many in the upper parts of the ocean, begins with the sun. The sun radiates waves of light energy from space. Because Earth lies in the sun’s path, it receives this light energy. The light energy is absorbed by producers.

Producers

Producers are the plants in an ecosystem that use the light energy from the sun to produce food energy. Producers use a process called photosynthesis to convert light energy into chemical energy that becomes food. The chemical energy is stored within the producers as carbohydrates (sugar). Producers make their own food and are not dependent on other organisms for energy. Another name for producers is autotrophs.

In most ecosystems on land, green plants are the primary producers. However, other organisms can also act as producers. For example, in ocean ecosystems, common producers include algae and phytoplankton (microscopic, plant-like organisms).

Consumers

The next trophic level in the food chain is made up of consumers. Most ecosystems have three levels of consumers: primary, secondary, and tertiary. Some may have an additional level—the quarternary consumer.

Primary consumers are the organisms that eat the plants in an ecosystem. Because these consumers eat only plants, they are known as herbivores, or plant eaters. By eating plants, primary consumers absorb the chemical energy that the plants converted from sunlight. When consumers eat the plants, they obtain some of the energy that has been stored by the plants.

Primary consumers on land include organisms such as deer, grasshoppers, rabbits, mice, squirrels, and even elephants and giraffes. These are all herbivores that survive by eating plants. In water ecosystems, primary consumers include fish, turtles, and zooplankton, such as shrimp and crabs that eat algae and phytoplankton.

Secondary consumers are organisms that eat herbivores, or primary consumers. Secondary consumers are carnivores, or meat eaters. By eating primary consumers, the secondary consumers access the energy that these organisms absorbed from producers.

The third type of consumers are tertiary consumers. These consumers are generally the top predators in an ecosystem. They may eat both primary and secondary consumers. They can be carnivores or omnivores, which are organisms that eat both plants and animals.

Depending on the complexity of the ecosystem, a quarternary consumer may exist, as well. This is a top-level predator. Because energy is generally limited at the higher trophic levels, it is unusual for more than four or five tropic levels to exist in one ecosystem.

Decomposers

The final trophic level in an ecosystem is occupied by decomposers. These are organisms that get energy by feeding on the decaying matter of dead plants and animals. Decaying matter is organic waste. Decomposers convert organic waste into inorganic materials, such as nutrient-rich soil.

What It Looks Like

Food chains use arrows to show the flow of energy in the ecosystem. The arrows show the relationship among the organisms. Each arrow shows how the energy flows upward through the different trophic levels. In other words, in a food chain, an organism is eaten by the organism to which it points.

For example, a food chain in a grassland ecosystem might look like this:

Sun → Grass → Grasshopper → Rat → Snake

In this food chain,

Sun = original source of energy

Grass = producer; uses photosynthesis to convert sun’s energy

Grasshopper = primary consumer; eats grass

Rat = secondary consumer; eats grasshopper

Snake = tertiary consumer; eats rat

A food web is more complex because it includes multiple food chains to represent all the relationships in an ecosystem. In a food web, every organism is connected to at least two other organisms.

Healthy Food Webs

A food web is defined by its level of biomass, or the total amount of energy of the living organisms. A healthy food web has a large amount of biomass and includes many producers (autotrophs), many primary consumers (herbivores), and only a few secondary, tertiary, and quarternary consumers (carnivores and omnivores). A healthy food web shows that an ecosystem is in balance and able to maintain and recycle its biomass.

Bibliography

“Food Web.” National Geographic, 19 Oct. 2023, education.nationalgeographic.org/resource/food-web/. Accessed 15 Nov. 2024.

Sottosanti, Karen. "Food Web." Britannica, 25 Oct. 2024, www.britannica.com/science/food-web. Accessed 15 Nov. 2024.

“Photosynthesis.” University of Cincinnati, Clermont Department of Biology, 13 Apr. 2022, biology.clc.uc.edu/Courses/Bio104/photosyn.htm. Accessed 15 Nov. 2024.