Last class
• Some expressed apathy – not sure if people
can change
• Some weren’t sure change should happen,
perhaps the earth would be better without us.
• Energy sources
• Information = power
Energy in Ecosystems
How does the energy received from the
sun move through living things on our
Earth?
Energy in Ecosystems
In order to understand how energy flows
in an ecosystem, we must first organize
living things in a certain way. The term
trophic level refers to a way of
categorizing living things according to
how they gain their
energy.
Solar Energy
We have already learned
in the Weather Unit that
about 30 % of the sun’s
energy that reaches
Earth is reflected by the air, clouds and
surface of the planet. 70% of this energy
is absorbed. This energy can be used by
living things.
Autotrophs
Some organisms can make
their own food from
sunlight and nutrients in
the air and soil. The
bunchgrass and algae
are examples of these kinds of
organisms. Some types of bacteria can
also do this. These types of organisms
are called autotrophs (or producers).
Primary Consumers
The second trophic level
contains organisms that
feed on the producers.
These organisms are
referred to as
primary consumers (also called
herbivores).
Grasshoppers and krill are examples of
these types of consumers. They rely on
autotrophs for their source of energy.
Secondary Consumers
At the third trophic level
we find animals that rely
on the primary consumers
as their source of energy.
Consumers at the third
trophic level are referred to as secondary
consumers (also called carnivores) The
spotted frog and crab are examples of
secondary consumers.
Tertiary Consumers
The fourth trophic level
is made up of animals
that eat secondary
consumers to obtain their
energy. The red-tailed
hawk might eat the spotted frog and the
sea otter could eat the crab. These
animals at the fourth trophic level are
called tertiary consumers (also
carnivores).
Detrivores
Detrivores (also
called decomposers)
Are consumers. They
obtain their energy
by eating detritus
which is the bodies of small dead animals,
dead plant matter, and animal wastes.
Detrivores feed at every trophic level and
make up their own important food chains.
Detrivores such as earthworms and beetles
are also an important energy source for
consumers such as birds.
Food Chain
In our example we
can see how energy
flows from one living
thing to another.
A food chain is a step by step sequence
linking organisms that feed on each other,
starting with a food source, such as a
producer or detritus, and continuing with a
sequence of consumers.
Food Web
In nature, many
animals are part
of more than one
food chain and eat
more than one kind
of food to meet their energy requirements.
A food web is a model of the feeding
relationships among organisms in an
ecosystem.
An Example: The Grouse
Look at the grouse in
the model at the
right. The grouse may
is seeds. In this case,
the grouse would be
a primary consumer.
But the grouse can
also eat a butterfly.
In that case it would be secondary consumer.
There are only two examples of the possible food
chains that the grouse could belong to.
Time to Practice
Checklist
1. Define and use correctly the following
terms: trophic level, autotrophs
(producers), primary consumers
(herbivores), secondary consumers
(carnivores), tertiary consumers
(carnivores), detrivores, food chain,
food web
2. State how much of solar energy is
absorbed by Earth.
Practice
1.
a)
b)
c)
d)
e)
f)
g)
Fill in the blanks with the appropriate words.
The term used to categorize living things according to how
they gain their energy is trophic level.
Of all the energy that falls on Earth from the sun, the
percentage that reaches the surface is 70%.
The name given to green plants, bacteria, and all living things
that can make their own food from sunlight, and nutrients
found in the soil and air is autotrophs (producers).
These living things are found at the second trophic level. The
obtain their energy from green plants. The general name given
to them is primary consumers (herbivores).
Another term for carnivores is secondary consumers.
Carnivores are found at the third trophic level.
Those consumers that eat secondary consumers and are also
carnivores are the tertiary consumers and they are found at
the fourth trophic level.
Practice
1. Fill in the blanks with the appropriate
words.
h) Another word for decomposers is
detrivores. Two examples of these living
things are earthworms and beetles.
i) The name given to a step by step
sequence linking organisms that feed on
each other is food chain.
j) A more accurate model of feeding
relationships in a food chain is the food web.
Practice
2. The diagram shows a simple food chain.
For each of the living things you see in this diagram, give the
ecology term that could be applied to it.
Grass: autotroph (producer).
Insect: primary consumer (herbivore).
Frog: secondary consumer (carnivore).
Snake: tertiary consumer (carnivore).
Practice
3. The diagram shows a
food web.
a) If the trout was to
serve as a primary
consumer, what would be
its food?
b) For example a), what type of consumer would the
hawk be and at what trophic level would it be?
c) If the trout aced as a secondary consumer, what
would be its food?
d) For example c), what type of consumer would the
eagle be and what would be its trophic level?
Practice
3. The diagram shows a food web.
a) If the trout was to serve as a primary
consumer, what would be its food?
Phytoplankton
Practice
3. The diagram shows a food web.
b) For example a), what type of consumer
would the hawk be and at what trophic level
would it be?
The hawk would be a secondary
consumer and it would be at the third
trophic level.
Practice
3. The diagram shows a food web.
c) If the trout aced as a secondary
consumer, what would be its food?
Mayfly or dragonfly.
Practice
3. The diagram shows a food web.
d) For example c), what type of consumer
would the hawk be and what would be its
trophic level?
The hawk would be a tertiary consumer
and it would be at the fourth trophic level.