Food Webs

Earth’s surface is covered in connected ecosystems, which interact with and depend on one another for survival. An ecosystem phenomena can be as large as an ocean or as small as a pond. Regardless of its size, all the parts of an ecosystem work together to make a balanced system. In this lesson, students model how the introduction of an invasive species affects the flow of energy through the entire food web.

• Ecosystems are communities of different species that depend on interacting with each other and their physical environment for survival. An ecosystem can be as large as an ocean or as small as a pond.
• Regardless of its size, all the parts of an ecosystem work together to make a balanced system.
• All living needs need food for energy and nutrients, and they access those things in an ecosystem.
• Scientists study how energy and matter flow through ecosystems in order to better understand the complex interactions within ecosystems.
• A change to one species in a food web will impact the entire ecosystem.
• A food web shows the complex set of relationships within an ecosystem that are linked by the flow of energy.

• What is an example of an ecosystem?
• Why is an ecosystem considered a system?
• How can both a tree and a forest be an ecosystem?
• How do predatory interactions help to keep an ecosystem balanced?
• How do the different parts of an ecosystem affect each other?
• How is a food chain different from a food web?
• Where does all energy in food webs come from?
• Why is the first level of every food web made up of producers?
• How are producers different from consumers?
• How are consumers related to predators?
• What is the difference between primary, secondary, and tertiary consumers?
• How would the ecosystem of a forest be affected if the grass died out?
• Why do invasive species have such an effect on food webs?

Misconception: Arrows in a food web show which organisms eat other organisms.

Fact: Arrows show the flow of energy.

Misconception: Species in an ecosystem “get along".

Fact: Species compete with and feed on one another for survival. 

Competition : an interaction between organisms that occurs whenever two or more organisms require the same limited resource

Consumer : an organism that eats other organisms; there are three possible levels of consumer in a food web: primary, secondary, and tertiary

Decomposer : an organism that breaks down organic waste and feeds on the nutrients

Ecosystem : a community of different species that depend on interacting with each other and their physical environment for survival

Food chain : the path that energy travels as one organism eats another

Food web : a visual that shows the network of food chains in an ecosystem

Invasive species : non-native species that disrupt the flow of energy through an ecosystem

Parasitic : an interaction between organisms that occurs when one organism (parasite) is dependent on another living organism (its host) and survives by taking the host’s nutrients

Predation : an interaction between two organisms that occurs when one organism (predator) eats another organism (prey)

Primary consumer : the second level of a food web but the first level of organisms that gets energy by eating producers

Producer : organisms that capture energy directly from the sun to make their own food; trees, grasses, and some microbes do this with photosynthesis; the first level of organisms in all food webs are producers

Secondary consumer : the third level of a food web; an organism that eats primary consumers

Tertiary consumer : the fourth level of a food web; an organism that eats secondary consumers

Using Dogs to Sniff Out Mussels

Popeye is a 7-year-old chocolate Labrador dog. Popeye lives in California, and he has an important job. He has been trained to find mussels attached to the hulls of boats.

Mussels are animals that have an outer shell made up of two hinged parts. Zebra mussels and quagga mussels are two kinds of mussels. They attach themselves to rocks or other hard surfaces like boats. When boats move from one waterway to another, they can carry the mussels with them.

Finding and Removing Mussels

Popeye’s job is to find mussels attached to boats before the boats enter a new waterway. He is part of a growing trend to use dogs that can sniff out zebra and quagga mussels on the surface of boats.

Popeye runs around a boat and sniffs. When he smells mussels, he sits to tell his owner he’s found them.

People can then remove the mussels from the boat. This is important because these mussels can cause a lot of damage to an ecosystem. An ecosystem is a community of different species that depend on interacting with each other and their physical environment for survival. All ecosystems include living things that must eat one another for energy and nutrients. They also include oxygen and carbon dioxide from the atmosphere, water, and energy from the sun.

An ecosystem can be as large as an ocean or as small as a pond. Regardless of its size, all the parts of an ecosystem work together to make a balanced system.

Mussels Harm Ecosystems

Zebra mussels aren’t native to North America. This means their presence in U.S. and Canadian waterways isn’t natural. Human activity brought them here. Zebra mussels were first introduced to the Great Lakes by ocean-going ships that arrived from Europe in the late 1980s. The five Great Lakes, located on the U.S. border with Canada, are the largest source of fresh water on Earth’s surface.

When they first arrived in the Great Lakes, the zebra mussels had no predators. Predation is an interaction that occurs when one organism (a predator) eats another organism (prey). Every ecosystem has predators and prey. In a balanced ecosystem, predators and prey act as checks on one another so that no one population of organisms becomes too large. A population is all of the members of a species within a particular area.

No Natural Predators

With no natural predators, the population of zebra mussels exploded. There are now millions of zebra mussels living in the Great Lakes. They grow in massive colonies, and up to 700,000 zebra mussels have been found in one square yard of surface area.

All of these mussels require food because food provides animals with the energy they need to grow and develop.

In this lesson, students develop a model to analyze the science phenomenon of how energy flows through a food web when invasive species are present. Students use their food web models to analyze how the zebra mussel disrupts the flow of energy in an ecosystem, causing changes in the populations of other organisms as a result.