BIO 2 GO!
Interactions of Organisms in an Ecosystem
3523 - Trophic Level
3524 – Niche
Interrelationships and Interdependencies among different organisms in
an ecosystem are affected by factors in the environment.
These relationships contribute to the stability of an ecosystem.
Upon successful completion of this unit, you should be able to do the
following:
1.
2.
3.
4.
Explain how energy flows through an ecosystem in terms of trophic levels.
Explain how trophic levels and food chains are related.
Explain how the amount of energy changes as the trophic levels increase.
Describe the role of each of the following in a food chain or food web:
a. sun
b. producer
c. consumer
d. decomposer
5. Describe similarities and differences between food chains and food webs.
6. Describe and explain and organisms niche.
7. Distinguish between a niche and habitat.
8. Use the following words in their correct context:
Trophic level
Producer
Consumer
Decomposer
Herbivore
Carnivore
Omnivore
Food chain
Food web
Phytoplankton
Zooplankton
Krill
Niche
Habitat
Trophic Levels
3523
Trophic levels explains how energy flows (moves) through an
ecosystem. As you know from before, plants take the energy from the sun
and turn it into energy that other organisms can use. This process is called
photosynthesis and the energy that is made during photosynthesis is in
the form of glucose (a sugar). Animals can then get this energy by eating
the plants, by eating other organisms that ate the plants, or by eating both!
Every time an organism receives energy from another source, it adds a
trophic level. It goes like this…
Trophic level =
1
2
3
4
Sun--- Producers--Consumer--Consumer--Consumer--Decomposer
(herbivore) (carnivore) (carnivore)
and/or
and/or
(omnivore) (omnivore)
In the above diagram, the sun begins the process because the sun is the
first source of energy. In trophic level 2, a producer (green plant) uses
the sun’s energy during photosynthesis. In trophic level 3, a carnivore (like
a horse) or an omnivore (like a human) eat the plant and receive the plant’s
energy. At trophic level 3 another carnivore eats the organism in trophic
level 2 and receives its energy. In trophic level 4, the organisms, usually
animals, receive the energy from what they consumed from trophic level 3.
Finally, the decomposers complete the process. So, the organism in trophic
level 4 receives energy that started with the sun and photosynthesis. No
photosynthesis, no energy.
Here’s another example:
Trophic Level=
1
2
3
Sun---grass---cow---human---decomposer
Look at this example:
Trophic Level=
1
2
3
4
Sun---corn---grasshopper---mouse---hawk---decomposer
Note that in every example, the sun is always listed first. The sun is the
ultimate source of energy. Also notice that decomposers are always the
last. Decomposers return the energy, in the form of waste, to the
environment. Food chains can vary in length. Each trophic level receives
less of the original amount of energy.
REMEMBER THIS!!!
As trophic levels increase, the amount of energy they receive
decreases.
So that is how energy moves through the trophic levels! We can also call
this a food chain. Let’s look at each piece.
REMEMBER THIS!!!
A food chain is a diagram that shows the flow of energy through an
ecosystem.
1. Producers
Producers are PLANTS. Some bacteria and algae are also producers.
They take the solar energy from the sun and do photosynthesis in
order to turn it into a chemical energy, called glucose! Other
organisms then eat the producers. They are on the first trophic level.
Question 1: The grocery store has a section in it called the Produce section.
What types of things do you find in that section?
Vegetables and fruits
2. Consumers
Consumers are organisms that consume (eat) plants or other
animals. We are consumers! We have to eat in order to live. There
are three different types of consumers: herbivores, carnivores, and
omnivores.
Herbivores eat only plants. Examples are deer, giraffes, cows, and
horses. They are on the second trophic level.
Carnivores eat only meat. They are called secondary consumers
because they eat the herbivores. You would find them on the 3rd
trophic level. Some examples of carnivores are snakes, tigers, and
wolves.
Omnivores eat both plants and meat. You could find them on
different trophic levels depending upon what they are eating. Humans
are omnivores! (Even though some people are vegetarians, we as a
species are classified as omnivores.) Other examples of omnivores are
bears and some fish
Decomposers are a special type of consumer. They break dead
things down so that they can be reused by plants and other organisms.
Scavengers are organisms that eat dead things, but they do not break
down the organism so they are not considered a decomposer. Vultures
are a scavenger.
Can you imagine if we did not have decomposers? ALL the things that
have ever died since the beginning of time would still be lying around
here! You could be stepping on dinosaur bodies every time you walked!
Yuck! So you see, decomposers are very important!! Bacteria and
fungi are decomposers.
Question 2: Below is an example of a terrestrial (land) food chain. Give two
more food chains using different organisms. Make one of them an
aquatic (ocean) food chain!
Ex. Grass—caterpillar—bird—hawk
Food webs are many food chains that are all interconnected. In most
ecosystems animals eat on more than one trophic level- and writing them
down can get really complicated! Food webs show us all the possibilities of
how an organism would eat. You don’t eat the same thing every day, do you?
Here is an example of a terrestrial food web:
Wolf
Eagle
Hawk
Human
Duck
Blue Bird
Cow
Caterpillar
Horses
Deer
Grass
Most ocean food chains begin with very tiny floating plants called
phytoplankton. These are found near the ocean's surface where there is
plenty of sunlight for photosynthesis (food-making).
Phytoplankton is eaten by floating animals called zooplankton. These are
tiny animals or larvae of crabs, jellyfish, corals and worms.
Zooplankton is food for fish. Bigger fish or mammals eat smaller fish.
These bigger fish might include cod, herring, flounder and sharks. Mammals
that eat fish would include seals and various types of toothed whales.
One type of zooplankton is krill. Krill are tiny shrimp-like creatures. They
eat phytoplankton and even other zooplankton.
Here is an example of an ocean food chain:
Sun's Energy -> Phytoplankton -> Krill -> Humpback Whale
Now you try it!!
Question 3: Using the example of the ocean food chain above as a starting
point, draw an ocean food web. Put in organisms that you are familiar
with that live in the ocean.
Student’s answers will vary.
Question 4: In a food chain, where are the producers always found?
At the beginning
Question 5: Why are consumers always listed after producers in a food
chain?
Because they eat the producers.
Niche
3524
As we discussed in the section on Diversity, 351, all organisms have a
place in the ecosystem. From section 3523 we know about the food chain
and food webs and we can see how organisms relate to each other. The
functional role an organism plays in the ecosystem is called its niche
(pronounced nitch). An organism’s niche tells us what it eats, where it
sleeps, and all the things organisms do on a daily basis. A niche also tells
us about the organisms’ home, what it needs to survive, (like food and
water), and how the organisms reacts with other organisms in the area (are
they predator-prey?).
REMEMBER THIS!!!
An organism’s niche refers to its role, (what it needs to survive, what it
eats, what eats it, etc.) in the habitat and the community.
A niche is also easily remembered if you think of a niche as an
organism’s job. It adds more information than an organism’s habitat. A
habitat tells where the organism is likely to be found.
Question 1: Select an animal. Explain the habitat and niche for that animal.
Student’s answers will vary.
Question 2: How would you describe your niche? What things do you do
every day? What do you eat? Where do you sleep? Describe your niche!
Student’s answers will vary.
TEST YOURSELF
True or False
__T_ 1. The lowest trophic level of any ecosystem is occupied by the
producers.
__F__ 2. Omnivores feed only on primary producers.
__F__3. A food chain is made up of interrelated food webs.
__T__4. All organisms in an ecosystem are part of the food web of that
ecosystem.
__T__5. The number of organisms in a trophic level is always directly
proportional to the amount of energy at that level.
__F__ 6. Producers are animals.
__F__ 7. A carnivore eats only plants.
__F__ 8, Zooplankton is food for larger fish.
__T__ 9. Decomposers are a special kind of consumer.
__T__ 10. The sun is the ultimate source of energy for ecosystems.
__F__ 11. A niche is where an organism lives.
__T__ 12. A niche tells us what an organism eats and sleeps, among other
things.
Matching
A. Organisms that get their food
by eating other organisms.
B. Organisms that eat only meat.
C. Breaks down dead organisms in
the environment.
D. Made up of interconnected
food chains.
E. An organism’s role in the
environment.
F. Organisms that make organic
nutrients for an ecosystem
using energy from the sun.
G. Tiny plant-like creatures that
live in the ocean.
H. Organisms that eat both plants
and meat.
I. Where an organism lives.
J. Explains the energy flow
through an ecosystem.
__J__1. Energy pyramid
__H__2. Omnivore
__F__ 3. Producers
__B__ 4. Carnivore
__A__ 5.Consumers
__I__ 6. Habitat
__C__ 7. Decomposer
__D__ 8. Food web
__G__ 9. Phytoplankton
__E__ 10. Niche
Fill in the Blank
decomposers
trophic
food chain
herbivores
food web
energy
1. The term _DECOMPOSERS______ is given to the bacteria that
break down dead tissue.
2. In an ecosystem, __ENERGY____________ decreases at each higher
trophic level.
3. Animals known as _HERBIVORES_________ eat only primary
producers.
4. A path of energy through the trophic levels of an ecosystem is called
a(n) _FOOD CHAIN_________.
5. The interrelated food chains in an ecosystem are called a(n)
____FOOD WEB_______________.
Answer the following:
1. Why are decomposers necessary for the continuation of life on Earth?
To break down dead organisms so that the nutrients can be
returned to the environment.
2. What is the difference between a food chain and a food web?
A food chain shows the relationship of a small amount of
rganisms. A food web is made of interconnected food webs and
ncompasses many more organisms.
3. Explain how a change in the habitat of a species affects the entire
ecosystem.
When a habitat changes, organisms must adapt, move elsewhere,
or die. This will affect the food chain and food web of that
ecosystem.