A food web is a tool that illustrates the feeding relationship among species within a specific habitat. It connects multiple food chains to show the interaction between different organisms in an ecosystem.
When you draw multiple food chains together, you end up with a food web. These represent relationships in ecosystems more accurately and give you a much clearer visualization of how each animal affects others.
What is the Difference Between a Food Chain and a Food Web?
Food chains and webs help us understand how energy transfers through an ecosystem. However, food chains and food webs have some significant differences.
A food chain presents a unique, connected path of energy flow in an ecosystem, whereas a food web explains how food chains overlap. It means a food chain shows a single pathway from the producers to the consumers and how the energy flows in this pathway.
Here is an example of a food chain:
However, many overlapping food chains exist in any ecosystem, and most plants and animals are part of various chains. So in the example above, a shrew isn’t just eaten by foxes, and a fox doesn’t only eat shrews — you can only see part of the whole picture.
Food Web Meaning
The food web definition in biology can be explained as a visual representation of all the food chains connected in a single ecosystem.
An ecosystem contains living things that are all part of multiple food chains. All of these food chains are then connected to create a food web. It helps us to visualize the path of energy and nutrients between different living organisms.
Animals don’t eat the same food every day and like to interact with various prey, so a food chain alone might not be enough to represent the complexity of our ecosystems. It is where food webs come in! By combining multiple food chains, food webs show you how energy travels around a habitat.
Food Web Diagram
Giving students food web examples is essential to demonstrate how a food web diagram works visually.
Within the food web example below, there are several individual food chains.
For example:
- Grass → Rat → Fox → Snake → Hawk
- Grass → Antelope → Cheetah → Hawk
- Tree → Rhino → Lion
- Tree → Giraffe → Lion
You’ll also notice some animals have more than one source of food. It is because it gives them more options for food if one of the others decreases.
The lion, for example, eats both giraffes and rhinos. If one becomes unavailable, it will still have a food source to survive.
The antelope, however, relies on grass for food. Therefore, if the environment changed and the amount of grass was quickly depleted, the antelope would have to adapt and look elsewhere for food.
Every part of the food web is affected by another component. If the population of a predator were to increase, then the prey population would decrease. If the prey population (assuming it’s a herbivore) were to grow, the number of plants and green vegetation would decrease.
What are the different types of food webs?
There are two main types of food webs. These are a grazing food web and a detrital food web.
A grazing food web begins with photosynthetic plants and algae, known as autotrophs. Autotrophs are organisms that can use simple inorganic substances like carbon dioxide in nutritional organic substances.
A detrital food web is based on decomposers. Decomposers are organisms that break down, rot and decay organic material. An example of a decomposer is fungi. Learn more about decomposers below.
What are Trophic Levels?
Trophic levels refer to an organism’s level or feeding position in the food chain or web. There are five primary trophic levels within a food chain, which include the following.
Producers
Plants and algae are called producers. Producers create food and energy using sunlight, water, and carbon dioxide. This process is called photosynthesis. Producers are at the bottom of the food chain and serve as the foundation for all food chains.
Primary Consumers
The organisms which eat the producers are called primary consumers. The animals in this group are herbivores. Herbivores are animals that get their energy and nutrients from a diet consisting exclusively of producers such as plants and algae. Some examples of primary consumer animals include sheep, cows, deer, horses, and some insects. These organisms occupy the second trophic level in the food chain.
Secondary Consumers
Secondary consumers are bacteria that feed on primary consumers. They are usually carnivores and occupy the third trophic level in the food chain.
Tertiary Consumers
Tertiary consumers are at the very top of the food chain and often do not have predators. They can be carnivores that feed on other carnivores or omnivores — organisms that eat other animals or plants.
Decomposers
Decomposers are bacteria and fungi that break down dead or decaying plant and animal matter into chemical nutrients like carbon and nitrogen that are issued back into the soil, air, and water. Then, it is consumed again by green plants. Examples of decomposers include fungi, bacteria, earthworms, flies, and larvae. They occupy the very bottom trophic level of the food chain.
How is Energy Transferred in a Food Web?
When one organism eats another, energy is transferred in a food web between trophic levels. It triggers the transfer of energy-rich molecules from the prey’s body. While these energy transfers work, they are inefficient, limiting the length of food chains.
When energy enters a trophic level, a portion of it is stored as biomass in organisms’ bodies. This energy is then available to the next trophic level, as only energy stored as biomass can be eaten. Generally speaking, only around 10% of the energy stored of biomass in 1 trophic level per unit of time is stored as biomass in the next trophic level per the same unit of time.
Let’s break that down with an example. Suppose the primary producers of an ecosystem store 50,000 kcal/m squared/year of energy as biomass. This power will be available to the primary consumers, who eat the primary producers. The rule of 10% would suggest that the primary consumers would store only 5,000 kcal/m squared/year of energy in their bodies. The secondary consumers make power available to their predators at a significantly lower rate.
This ineffective pattern of energy transfer limits the length of food chains. As the size is limited, after energy has been passed between several trophic levels, typically 3 to 6, the power is too little to support a population at a higher level.
So, why does energy transferred in a food web deplete?
There are many reasons why energy transferred in a food web exists between trophic levels. However, here are the main reasons:
- At each trophic level, energy is lost as heat as organisms carry out cellular respiration.
- Many molecules that different organisms consume cannot be digested. For this reason, they leave the body as feces instead of being used as energy.
- Not all organisms at a trophic level get eaten by organisms at the next level up. Instead, these animals die before they are eaten, meaning no energy is transferred.
- The feces and dead, uneaten organisms ultimately become food for decomposers. Decomposers then metabolize them and convert their energy to heat through cellular respiration. None of the power disappears; instead, it all ends up as heat in the end.
Competition and Interdependence
All habitats have a limited amount of the resources needed by plants and animals to survive. For this reason, plants and animals are forced to compete with one another from time to time for food, water, space, and mates to survive. Often, this competition between animals leads to fights.
Plants can generate their food through photosynthesis, so they do not have to compete for food. However, plants do engage in some competition for resources like water, space, and mineral salts.
Interdependence
Interdependence is when variations in one organism’s population impact other organisms’ populations.
What is the Purpose of a Food Web?
There are several practical applications for food webs; they can provide insight into how nature works. Here are some of the essential functions of a food web:
- Food webs are constructed to describe species interactions
The primary function of a food web is to describe the feeding relationships amongst species in a community. Within a food web, all of the species can be separated into different groups: basal species (autotrophs, like plants), intermediate species (herbivores and intermediate-level carnivores), and top predators (high-level carnivores). These feeding groups are called trophic levels (detailed above in the ‘What are Trophic Levels?’ section).
Grouping all species into different groups or trophic levels makes food webs simpler and, thus, makes it easier for us to understand the relationships between species.
- Food webs are used to illustrate indirect interactions among species
Simply put, indirect interactions happen when two species do not interact with each other directly but influence a 3rd species. There is a range of different ways that species can influence one another.
For instance, the rocky intertidal zone of the Pacific Northwest coast is home to several species of starfish, including starfish, barnacles, limpets, and mussels. A food web of this community was constructed and studied, and the results showed that the starfish preyed on a wide range of invertebrate species. When starfish were removed from this community on the Pacific Northwest coast led to a reduction in the diversity of prey species as there was increased competition.
Some other functions of food webs include:
- To study bottom-up or top-down control of community structure
- To reveal different patterns of energy transferred in terrestrial and aquatic ecosystems.
