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READING MATERIAL
Read About Food Webs
FOOD WEB DEFINITION
To understand how plants and animals interact, scientists make diagrams called food chains. A food chain shows a sequence of living things in which one organism eats the one below it. Most animals eat more than one thing, so to show ALL the feeding relationships, we use food webs which are made of many intersecting food chains.
To better understand the food web definition….
LET’S BREAK IT DOWN!
Energy in food can be traced back to the sun.
Living things need a constant supply
of energy. The sun provides that
energy, which is transformed into
food by plants through
photosynthesis.
Herbivores (plant-eating animals)
eat the plants and receive energy.
When the herbivore is eaten by a
carnivore (an animal that eats herbivores), the energy from the herbivore is transferred to the
carnivore. The transfer of energy from one organism to another makes up a food chain.
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Animals eat to get energy and building blocks.
All living things need food to provide
materials for growth. Food chains
start with organisms that make their
own food, called producers. Plants
are the most common producers.
Animals are called consumers
because they do not make their own
food -- they eat, or consume, other
organisms.
A food chain typically only has a few steps (usually 4 at the most). This is because each time
one organism eats another, some of that energy is used up and released as heat.
In fact, you are releasing heat energy right now as you read this because your body is burning
food to keep warm! Since some energy gets used up in each step of the food chain, there can
only be a few steps, otherwise there is not enough energy left for the organism at the top.
A food web is a model of intersecting food chains.
Most organisms can eat, and be
eaten, by many different animals. A
food chain wouldn't be able to show
this. Food webs show all these
connections. They are more
complicated but more accurate.
In the African savannah food web
shown here, we can see multiple
arrows pointing to different animals. The arrows show the direction the energy is transferred. For
example, we can see that zebras eat trees and grasses, so arrows from trees and grasses are
pointing to a zebra.
The arrows pointing from the zebra to cheetahs, hyenas, and lions tell us that the zebra is eaten
by these animals.
FOOD WEB EXAMPLES
The great horned owl is an apex predator. They eat mice, rats, frogs, snakes, and rabbits. That keeps the prey populations from getting too high and overgrazing the ecosystem.
Overhunting can make an ecosystem out of balance. If wolf populations are reduced, the population of deer would increase dramatically. This causes areas to be overgrazed, meaning there is not enough grass for other animals. Everything needs to be in balance.
Common soil creatures, such as earthworms, are decomposers. They recycle nutrients in the ecosystem through decomposition.
FOOD CHAIN AND FOOD WEB VOCABULARY
Food Chain A sequence of living things in which each one feeds on the living thing below it.
Food Web A food web is a model made of intersecting food chains.
Photosynthesis A process by which plants use sunlight to make sugar from carbon dioxide and water.
Producer
A living thing (almost always a plant) that takes energy from the sun and make its own food. They are found in the first level of a food web.
Apex Predator An animal found at the top of a food web and is not eaten by any other animals. Examples include sharks, owls and lions.
Decomposer Living things that break down dead and decaying organisms. The most common decomposers are bacteria and fungi.
DISCUSSION QUESTIONS ON FOOD CHAINS AND FOOD WEBS
Why do animals eat other animals?
Animals eat other animals to obtain energy and building blocks (nutrients) in order to grow and repair.
What are producers and consumers and how do they get their names?
Plants are producers because they produce their own food through photosynthesis. Animals are consumers because they consume plants or other animals.
What role in the food web does the eagle play?
An eagle is an apex predator, meaning it is at the top of the food web. Nothing else will attack and eat an eagle. Eagles will eat things like birds, snakes, mice and other animals.
What is an apex predator and why are they critical for the health of the
ecosystem?
An apex predator is an animal that feeds on other animals but is at the top of the food web, meaning that it has no predators. Apex predators help control the balance of an ecosystem by keeping the populations of other animals in check.
What do zebras eat and what eats zebras?
Zebras eat grass and they are eaten by predators like hyenas and lions.
What is the role of worms, bacteria and fungi in a food web?
These living things are decomposers. They recycle matter, by breaking down dead and decaying matter. They turn it into nutrients in the soil, which plants use. If ecosystems didn’t have decomposers, dead plants and animals would just pile up.
