Forest Food Web

Once students understand how plants capture the sun’s energy and turn it into usable energy, students analyze the phenomena of how energy moves through a forest food web as organisms eat one another. 

• The energy captured by plants through photosynthesis flows through ecosystems. The energy stored in glucose gets passed along from one organism to another when organisms eat each other. 
• All of the energy that organisms need to survive comes from the sun and then moves to producers.
• Ecosystems are communities of different species that depend on interacting with each other and their physical environment for survival.
• Any event that changes conditions in an ecosystem is called a disturbance. These changes can impact the rest of the forest and can disrupt the flow of energy.
  
  

• Why is a forest an ecosystem?
• Why are water, sunlight, and carbon dioxide important in all ecosystems?
• Why is the first trophic level of every food web made up of producers—organisms that capture energy directly from the sun to make their own food?
• How are producers different from consumers?
• How are consumers related to predators?
• What is the difference between primary, secondary, and tertiary consumers?
• How are decomposers different from either producers or consumers?
• How is a food chain different from a food web?
• How do food webs provide evidence that energy is transferred within an ecosystem?
• Why will a change to one part of an ecosystem have a ripple effect throughout the ecosystem?
• Why would a drought likely affect a forest ecosystem?
  
  

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

Fact:  Arrows show the flow of energy.

Misconception: Healthy ecosystems do not change.

Fact: Healthy ecosystems are dynamic and constantly changing.

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 chain: primary, secondary, and tertiary

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

Disturbance : an event that changes conditions in an ecosystem

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

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

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

Producer : an organism that captures energy directly from the sun to make its 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

Storing Food

Eastern gray squirrels love acorns. Acorns are the seeds of oak trees. Right before a squirrel eats an acorn, it shakes it.

The shaking happens so quickly it can be hard to see. But Michael Steele has videoed squirrels eating. When he watched the videos in slow-motion, he saw squirrels shaking the acorns.

Michael is a researcher who has studied squirrel behaviors. He says there is a simple explanation for why the squirrels shake acorns. They want to know if the quality of the seed is good. Depending on what they sense, they will either eat the seed right away or bury it to eat later.

Why Squirrels Bury Seeds

Squirrels bury seeds so they will have enough food to last them through the winter. Squirrels need to eat acorns and other plant materials because they are animals. They cannot make their own food, as plants can. Instead, they have to eat other organisms for energy and nutrients. When squirrels eat acorns, they access some of the energy that the oak tree has produced through photosynthesis and stored in glucose molecules.

Ecosystem Relationships

Michael is particularly interested in relationships between squirrels and the trees that produce squirrels’ food. Both the squirrels and the trees are part of 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 a forest or as small as an oak tree. Regardless of its size, all the parts of an ecosystem work together to make a balanced system.

Mutually Beneficial Relationships

Michael has found that squirrels and oak trees have a mutually beneficial relationship. The squirrels benefit because they need the seeds’ energy and nutrients. They also need oxygen to breathe in. The oak trees benefit because acorns don’t grow well if they are right beneath the parent tree. The branches of the parent tree will block the sun.

The squirrels move acorns to bury them. Gray squirrels are known as scatter hoarders. This is because they bury acorns and other seeds in many places. Researchers have found that gray squirrels have a system when they bury acorns from an oak tree. They bury less-desirable acorns closest to the tree. They bury more-desirable acorns farther away from the tree.

If the squirrel doesn’t make it back to its acorns, those acorns might grow into new trees. This benefits the oak tree because it has passed along its genes. It also benefits the squirrels because it means more food sources.

Squirrels have a competitive relationship with one another. Competition between organisms occurs whenever two or more organisms require the same limited resource. Water and food are both resources. Shelter is another resource. Squirrels will often take another squirrel’s supply of buried seeds if they find them. Because of this, gray squirrels will bury thousands of seeds each season.

There are competitive interactions in every ecosystem. There are also mutually beneficial interactions in every ecosystem.

There are also predatory interactions in every ecosystem. Predation is an interaction that occurs when one organism (a predator) eats another organism (prey). Organisms can be both predators and prey. For example, squirrels are prey to hawks and foxes. Squirrels are also predators of acorns and other plants.

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.

Food Chains and Food Webs

Oak trees, squirrels, and hawks are all connected together in a food web. A food web is a visual that shows the network of food chains in an ecosystem. Food chains show specific paths that energy travels as one organism eats another. Each level of a food web or food chain is called a trophic level.

Scientists study how energy flows through ecosystems to better understand how different organisms are connected together. They group organisms within an ecosystem according to how they obtain energy in a food web.

In this lesson students develop models to analyze the impact of drought phenomena on temperate deciduous forest food webs in Massachusetts. Students use their food web models to figure out how the flow of energy in the phenomena of a forest food web changes during a period of severe drought, causing a ripple effect in the populations of other organisms as a result.