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Trophic Levels
Notes #10
Trophic Level (notes)
• A trophic level is the “level” an organism occupies in a food chain or
food web based on how far away it is from the original source of
energy
Trophic Levels (not notes)
• This concept is easier to see than it
is to explain
• First: where does the food chain
start?
• Second: how many steps does it
take to get from the beginning to
the organism?
Trophic Level Terms (notes)
In order of increasing trophic level, the terms are:
• Primary producer
• Primary consumer
• Secondary consumer
• Tertiary consumer
• Quaternary consumer
…
• Apex predator (trophic number changes, but nothing consumes it)
(Not notes)
Carnivore
Top/Apex Predator
Hawk
Carnivore/Omnivore
Tertiary Consumer
Snake
Carnivore/Omnivore
Secondary Consumer
Lizard
Herbivore/Omnivore
Primary Consumer
Harvester Ant
Primary Producer
Seed-producing
plant
Names of levels
Example food chain
Consumers
Producer
(Sun)
Trophic Practice (not notes)
Which level does each of the
species represent on the food
chain?
• Plant
• Grasshopper
• Bird
• Snake
• Owl
Trophic Practice (not notes)
Which level does each of the
species represent on the food
chain?
• Plant Primary producer
• Grasshopper Primary consumer
• Bird Secondary consumer
• Snake Tertiary consumer
• Owl Quaternary consumer
(apex predator)
What About Food Webs? (not notes)
• What about food webs where it is possible for an organism to have
more than one trophic level?
• In these cases scientists calculate a “fractional trophic level.” This is
based on the trophic levels of the species’ prey as compared to their
overall diet
10% Rule (notes)
• Review: whenever energy is transformed some is lost as waste heat
• On average, only 10% of the energy from each level is transferred to
the next
• This limits how many organisms an ecosystem can support, and is
why there are always more prey than predators
(Not notes)
Apex predator
Tertiary Consumer
Secondary Consumer
Primary Consumer
Primary Producer
As you go up in trophic level, the
mass of each level decreases
because of the limited amount of
energy available.
Example Problem (not notes)
• If there are 100 grams of minnows in a population, about how many
grams of tuna could they support?
Example Problem (not notes)
• If there are 100 grams of minnows in a population, about how many
grams of tuna could they support?
About 10 grams (or 10% of the mass of the minnows)
Example Problem (not notes)
• If there are 100 grams of minnows in a population, about how many
grams of tuna could they support?
About 10 grams (or 10% of the mass of the minnows)
• About how many grams of shark could be supported by this ecosystem?
Example Problem (not notes)
• If there are 100 grams of minnows in a population, about how many
grams of tuna could they support?
About 10 grams (or 10% of the mass of the minnows)
• About how many grams of shark could be supported by this ecosystem?
About 1 gram (10% the mass of the tuna, or 1% the mass of the
minnows)
Woodlands Food Web Continued
• Reminder: neatness is key! Plan before you glue things down
• In addition to what you began yesterday, label each of the organisms
on your web with their trophic level (including apex predators).
• If an organism has multiple levels list all that apply.