1. 1.11: Food Chains and Food Webs

2. Food Chains
In order to understand how one organism can affect other organisms, ecologists use the idea of food chains and food webs
Food Chain – a feeding order in which each kind of organism eats the one below it
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3. Example of a Food Chain Grass Mouse Snake Fox Wolf Producer/
Autotrophs
Primary
Consumer
Secondary
Consumer
Tertiary
Consumer
Quaternary
Consumer
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Herbivore
Carnivores
Top Carnivore
(not eaten by any
other organism)

4. Trophic Levels
Scientists also use another naming method to classify where organisms are on food chains called trophic levels
Trophic Level – a way of categorizing living things according to how they gain their energy
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5. Example of a Food Chain 1st Trophic Level 2nd Trophic Level
3rd Trophic Level
4th Trophic Level
5th Trophic Level
Grass
Mouse
Snake
Fox
Wolf
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Producer/
Autotrophs
Primary
Consumer
Secondary
Consumer
Tertiary
Consumer
Quaternary
Consumer
Top Carnivore
(not eaten by any
other organism)
Herbivore
Carnivores

6. Some Things to Keep In Mind…
The producer/autotroph is always at the 1st trophic level, the primary consumer is always at the 2nd trophic level, the secondary consumer is always at the 3rd trophic level, and so on.
The primary consumer eat autotrophs, secondary consumers eat the primary consumers, and so on.
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7. Some Things to Keep In Mind…
Producer = Autotroph (something that can produce its own food from sunlight or basic nutrients)
Consumer = Heterotroph (something that has to get its food by eating other organisms)
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8. Label the Following Food Chains!
secondary
consumer
3rd trophic
level
secondary
consumer
3rd trophic
level
fox
wolf
primary
consumer
primary
consumer
2nd trophic
level
2nd trophic
level
deer
rabbit
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producer/
autotroph
1st trophic
level
producer/
autotroph
1st trophic
level
grass
shrub

9. Any Changes at One Level Affect All Other Levels of a Food Chain
Hypothesize! If the number of deer suddenly goes down, then:
1) The number of wolves will go down because they will have no food
2) There will be more shrubs, since no deer are available to eat them
wolf
deer
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shrub

10. Food Webs
In any one ecosystem, there can be many types of producers, primary consumers, secondary consumers, etc. Any individual organism is involved in many food chains.
Food Web – two or more food chains inter-connected
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11. A Food Web
fox
wolf
deer
grasshopper
rabbit
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grass
grass
shrub

12. Time to Think! True or False: There are 3 food chains in the food web
False: There are many food chains in the food web
Which animal is the top carnivore in this food web?
The wolf
Which organisms are the primary consumers?
Grasshopper, rabbit, deer
On the web, which organism is on the 3rd trophic level in most of the food chains, but on the 4th trophic level on one of the food chains?
The wolf (it consumes the fox in one of the food chains)
Sarah

13. One Last Thing…
Decomposers (organisms that break down and feed on dead organisms) are usually not included on food chain diagrams
Some organisms that are omnivores (eat both plants and animals) might be on a different trophic level depending on what food chain you are looking at
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14. Case Study: The Cane Toad
Cane Toad was introduced to Australia in 1935 from Hawaii to combat the Cane Beetle population that was destroying their Sugar Cane crops.
Toads could not reach the beetles which live high up on the sugar cane
They started to eat everything small enough to fit in their mouths
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15. Case Study: The Cane Toad
There is no natural predator for the toad in Australia
They poison anything that tries to eat them
The introduction of a species to control another species is called biological control. In every single case the outcome is never one we expect
Cane Toad
Sarah

16. Homework!
Read Pg
Do questions #1-7 (Pg. 39)
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