Food Chain/Food Webs
• Learning Target
• #5, #6, #13
All food chains start with
ENERGY from the sun
Feeding Relationships
• A food chain shows a simple feeding
relationship.
Sun →
•Plants are producers. They turn energy from
the sun into sugars that animals can use
Through Photosynthesis
Because plants produce their own food,
they are called ‘Producers’
Primary consumers eat plants.
They are herbivores.
Insects and other animals eat plants for energy.
Secondary consumers are animals that eat
other animals for energy. They are called
carnivores or omnivores
Decomposers are organisms that eat dead
things for energy.
Food Chains are connected to Food
Webs
• Combined food chains make food webs.
• Food webs start with the sun
• Food webs contain producers, consumers,
and decomposers.
• Are you part of food webs?
Feeding Relationships
• A food chain shows a simple feeding
relationship.
Sun → grass →
Feeding Relationships
• A food chain shows a simple feeding
relationship.
Sun → grass → rabbit →
Feeding Relationships
• A food chain shows a simple feeding
relationship.
Sun → grass → rabbit → fox
The energy is then passed on to animals when
they eat the plant.
Animals of all shapes…
…and sizes!
Because these animals
are the first to take
the food energy
from the plants,
They are called
primary consumers
Some of these primary
consumers have predators.
Other animals that feed on them
Aphids are eaten by….
Ladybugs
Animals that eat primary
consumers are called
secondary consumers
• So far this is a straightforward food chain
• Sun → leaf
aphid → ladybug
But in reality it is more complicated than that
This bird eats
ladybugs and
aphids
This bird eats smaller
birds, mice, and
rabbits
Mice and rabbits have other
predators
What will eat the
frog?
What do you
think the frog
eats?
Sometimes it’s not
entirely clear who
eats who!
We can show what goes on with the help of a
Food Web
What would happen if a disease killed off many of the
hawks?
There will be nothing
to eat the snakes, so
their numbers will
increase.
Many of
the frogs
get eaten
No frogs.
More
crickets
Most of the
cattail gets
eaten by the
crickets
Now the crickets
don’t have enough
food so their
numbers go down
..and so on. Numbers of each species have an effect on the
numbers of the other species in the web.
• Use the food web worksheet to predict
what might happen in the following
situations:
• A) There is very little rain and much of the
Marsh Grass and Cattail die off.
• B) Humans nearby bring cats into the area.
• C) The frogs eats some poisoned slugs
from a garden
Transfer of Energy
• When a zebra eats the grass, it does not
obtain all of the energy the grass has (much
of it is not eaten)
• When a lion eats a zebra, it does not get all
of the energy from the zebra (much of it is
lost as heat)
• No organism EVER receives all of the
energy from the organism they just ate
• Only 10% of the energy from one trophic
level is transferred to the next – this is
called the 10% law
• Key Points to Remember…
• Energy moves from one organisms to another
when it is eaten
• Each step in this transfer of energy is known as a
trophic level
– The main trophic levels are producers, consumers, and
decomposers
DDT affect on Food Webs
http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ec/m3/s4/ecm3s4_2.htm
DDT: Used in the 40’s and 50’s as a pesticide .
Outlawed in 70’s: collects in fats of
organisms and cannot be broken down.
Marine microorganisms greatly affected
collected in plankton and green algae
slows photosynthesis – not death
Mostly noted in birds eggs
thinning of eggshells
Brown Pelican: 1970-550 nests
only 1 chick survived
Food Web
Biomass
• The total mass of the organic matter at each
trophic level is called biomass
• Biomass is just another term for potential energy –
energy that is to be eaten and used.
• The transfer of energy from one level to another is
very inefficient (10% Law)
Biomass
Ecological Pyramid
• An ecological pyramid shows the relationship
between consumers and producers at different
trophic levels in an ecosystem
• Shows the relative amounts of energy or matter
contained at each trophic level
• The Pyramid shows which level has the most
energy and the highest number of organisms
Ecological Pyramid
Ecological Pyramid
Ecological Pyramid
• Which level has the most energy?
• Which level has the most organisms?
• Which level has the least organisms?
• Which level has the least energy?
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