Ecosystems and Their Interactions
LT: Food Webs & Energy Flow in Ecosystems
All living things ultimately get their energy
from the SUN (some directly and some
indirectly).
One exception to the rule:
Chemoautotrophs!!
- Use chemicals to make energy
- Example: Bacteria found in the deepest
parts of the ocean feed off of hydrogen
sulfide released from deep sea vents.
Plants, algae and some bacteria can
capture solar energy and store it as food.
What is this process called?
Photosynthesis
Producers are organisms that produce their
own energy through photosynthesis. They are
also known as autotrophs. Examples?
Consumers are
organisms that get
their energy by
eating other
organisms.
They are also known
as heterotrophs.
Examples?
Consumers can be identified more specifically:
Primary Consumer (1 consumer) – eats producers
Secondary Consumer (2consumer) – eats primary (1)
consumers
Tertiary Consumer (3 consumer) – eats secondary (2)
consumers
Quarternary Consumer (4°consumer) – eats secondary (2) &
tertiary (3) consumers
Let’s plug some organisms into these names to make
more sense of this:
Grass is a producer because it makes its energy from the
sun.
A lady bug is a primary consumer (or 1 consumer)
because it eats the grass which is a producer.
A frog would be a secondary consumer (or 2 consumer)
because it eats the lady bug which is a primary consumer.
A snake would be a tertiary consumer (or 3 consumer)
because it eats the frog which is a secondary consumer.
And so on…
(We will come back to these examples later!)
There are four types of consumers (not
1, 2, 3, etc.).
Can you guess what they are?
Herbivore – only eats plants
Carnivore – only eats animals
Omnivore – eats both plants and animals
Decomposer – breaks down dead organic material
How do you show the energy transferred
through (in) ecosystems?
food chains and food webs
Food chains show the path in which
energy is transferred from one
organism to the next as one eats the
other.
Marine Food Chain
So how do you make a food chain?!?!
3 rules for making a food chain…
1. Choose an ecosystem that you want to focus on.
(You wouldn’t want to put together a rattlesnake, a penguin
and a black bear because they obviously don’t live together
in the same ecosystem!)
2. Choose an organism at each level (producer, primary
consumer, secondary consumer, tertiary consumer, etc.) that
would actually eat the one before it.
3. Place your arrows correctly. Arrows ALWAYS point
towards where the energy is GOING (towards who is doing
the eating).
We actually already made a food chain earlier!
Remember this?
Grass is a producer because it makes its energy from the sun.
A lady bug is a primary consumer (or 1 consumer) because it eats the
grass which is a producer.
A frog would be a secondary consumer (or 2 consumer) because it eats
the lady bug which is a primary consumer.
A snake would be a tertiary consumer (or 3 consumer) because it eats
the frog which is a secondary consumer.
Well it’s a food chain!
Sun  Grass  Lady Bug  Frog  Snake
***Notice that the arrows are pointing to where the energy is going (not what is
eating what)!!
FOOD CHAIN CHALLENGE:
Can you think of a food chain? Do you think you can draw it (with pictures or
words)? Do you think you could draw it with the arrows going in the right direction?
***Remember, describe the direction the arrows are pointing by saying “producer to
primary consumer” or “secondary consumer to tertiary consumer.” NOT “left to
right” because food chains/webs can be drawn in any direction.
Check it out:
Sun  Grass  Lady Bug  Frog  Snake
Snake  Frog  Lady Bug  Grass  Sun
They both mean the same thing!
You could even draw them from top to bottom or bottom to top! Just make sure the
arrows are pointing in the right direction (towards where the energy is GOING).
Now try drawing your food chain (WITH NEW EXAMPLES!)
on your graphic organizer!
Food webs show us the complicated
flow of energy in an ecosystem.
Food webs are really a whole bunch of food
chains. They show us that organisms eat
more than just one thing, and the feeding
relationships between organisms in the
ecosystem.
Marine Food Web
Compare Food Webs & Food
Chains
a. Food webs are made of many food chains
b. Food webs show the transfer of energy in the
ENTIRE ecosystem
TROPHIC LEVEL PYRAMID
(trophic=energy)
Each step in the transfer of energy through an ecosystem
is known as a Trophic Level.
Tertiary
Consumer
Secondary
Consumers
Primary
Consumers
Producers
(photosynthesis)
There is a 90%
energy loss
between trophic
levels.
Tertiary
Consumers
Meaning…
only 10% of
the energy is
transferred.
0.1%
Secondary Consumers
1%
Primary Consumers
10%
Producers (Plants)
100%
Read these questions, then look at your Trophic Level
Pyramid and see if you can answer them.
Why do you think there are so many organisms on
the bottom of the pyramid?
What does this mean?
They provide all of the energy for the entire
ecosystem; they are the basis of the ecosystem
Why are there so few at the top?
What does this mean?
There is not enough energy to support lots
of top consumers.
Read these questions, then look at your trophic level pyramid
and see if you can answer them.
Is there one level that is more important than the
others? Why?
Producers are the most important because
they provide energy for the entire ecosystem.
Energy Transfer – how much is passed on? How
much is lost?
10% is passed on between trophic levels
90% is lost between trophic levels