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Chapter 3 Food Chains and Food Webs
Lesson 1 Food Chains
A food chain is a model that shows the path of energy and nutrients in
an ecosystem.
The arrows on a food chain show the flow of energy from one organism
to another. The arrow points to the animal that eats the other animal.
All food chains start with the Sun. Producers get their energy from the
sun.
Producer
1st level consumer
2nd level consumer
Producers are organisms that use the sun’s energy to make their own
food. Producers are always second to the Sun on a food chain.
Examples: grass, trees, algae
Consumers are organisms that eat plants or other animals because they
cannot make their own food. Examples: deer, lizards, humans
Decomposers break down the dead or decaying plants or animals.
Examples: fungi, bacteria, worms
Herbivores are animals that eat only plants. Examples: deer, squirrels,
grasshoppers. They are also knows as primary consumers because they
are the first consumers in a food chain.
Herbivores have adaptations like flat teeth to help them eat plants.
Herbivores are often prey for other animals.
Prey are organisms that are eaten by predators.
Predators are organisms that hunt and kill other organisms for food.
Predators are important because they limit the size of animal
populations.
Carnivores and omnivores:
Carnivores are animals that eat only other animals. Examples: lions,
owls, hawks. Carnivores are called secondary consumers. They are
often at the top of most food chains.
Omnivores are animals that eat both plants and animals. Examples:
raccoons, humans, mice.
Decomposers:
Decomposers have the important job of cleaning up the environment.
They break down dead organisms into nutrients for the soil.
There are different types of decomposers.
Scavengers are animals that feed on the remains of dead animals they
did not kill or hunt. Examples: jackals, vultures, raccoons
Examples of food chains:
Sun
algae
stonefly
Sun
flower
butterfly
sunfish
heron
robin
bobcat
Lesson 2 Food Webs
A food web is a network of food chains that have some links in
common. Just like with food chains, the arrows show the flow of
energy.
One organism can be a part of several food chains. Animals have to
compete for food, water, sunlight, and space.
Competition is the struggle between organisms for the same resource.
How food webs change:
If one organism is changed in an environment, the whole food web is
affected.
When top carnivores are removed from a food web, prey populations
are no longer controlled and can reproduce without limits. When the
prey population increases in number, they need more producers to
feed them. Soon there would be not enough producers to feed the
organisms.
How new organisms change food webs:
Exotic species are plant and animal species that are not native to an
environment. Example: Elephants are an exotic species for Mississippi
When a new species is introduced to an environment, they threaten
native species. Native species must compete even more for resources
to survive. Sometimes the population of exotic species can get out of
control and cause major problems for native species.
Energy Pyramid:
An energy pyramid is a model that shows how much energy flows
through a food web. Less energy and organisms are available the higher
you go up an energy pyramid.
Consumer
(bob cat)
Consumer
(bird)
Energy
Consumer
(butterfly)
Producer
(flower)