Trophic Levels and Pyramids

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Trophic Levels and Pyramids

• Mrs. A. Kay

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Trophic Levels

• Trophic feeding level
• refers to the organisms position in the food
  chain
• Autotrophs are at the base (first trophic level).
• Organisms that eat autotrophs are called
  herbivores or primary consumers (second trophic
  level).
• An organism that eats herbivores is a carnivore
  and a secondary consumer. (third trophic level)
• A carnivore that eats a carnivore that eats a
  herbivore is a tertiary consumer (forth trophic
  level).

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Pyramids

• Ecological Pyramids represent graphically the
  structure of an ecosystem
• 3 types number, biomass, and energy flow
• Pyramid of numbers shows relative population
  size.

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Why do these pyramids look so different?Hint
Look at how they begin (numbers!)
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Answer

• Since more energy is available along the bottom
  of the food chain, generally there are more
  numbers of producers

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• In our example, there is more energy for
  plankton, than there is for small fish more
  energy for the larger fish than the seabirds.
• Usually an animal eats organisms smaller than
  itself, so it makes sense that there needs to be
  more of the smaller species to support the larger
  ones.

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Not always true!

• Exceptions to the pattern.
• Sometimes one large producer can feed many more
  organisms than itself. Ex Oak tree
• There are more caterpillars than birds, and less
  predator-type birds.

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Science Inquiry Activity

• What Eats What?
• Pg 10 of your textbook

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Pyramid of Biomass

• Using numbers doesnt take into consideration the
  sizes of the organisms.
• Biomass tells us how much of a particular
  organism is there.
• Biomass generally decreases as we rise in trophic
  levels

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Exceptions

• Ocean systems with algae eating zooplankton.
• There can be more zooplankton than algae because
  algae reproduces more quickly .
• They produce enough energy to support the system

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Pyramid of Energy Flow

• shows the total chemical energy that flows
  through each trophic level.
• Always less energy available through each level.
• Explains why food chains rarely have more than 4
  links.
• Think!! You cant support a population on a
  0.000001 of stored energy.

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notice that there is less energy at each higher
level.
increasing energy
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Use the following to create your own pyramid of
numbers, biomass and energy flow. What
assumptions did you make?
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Practice for Homework

• Page 17 1-6

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Answers

• 2nd trophic level can be any primary consumer
  herbivore. Ex rabbit
• Rarely more than 4 links because as you move up a
  food chain there is less energy available. After
  4 links there would only be 0.001 energy left to
  support that population.
• Pyramid of numbers population size Ex 1500
  cows Pyramid of biomass the entire mass of the
  population.
• Ex 20 000kg of cow

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• Must consider the of foxes and their sizes.
• Rabbits more of them (b/c lower on the food
  chain, so more energy), but they weigh less than
  a fox
• Fox less of them (2nd consumer), but weigh more
  than a rabbit
• There is usually significantly more rabbits
  within an ecosystem than foxes, so their
  difference in size would not affect our biomass
  pyramid. Rabbits would have a higher biomass
  than foxes

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• Fleas to dog
• Numbers easier to count the fleas than weigh
  them
• Biomass doesnt show the severity of the
  situation for the dog.
• Ex 100 fleas vs. 1 dog
• If using biomass, ex 20kg of dog vs 0.0001kg of
  fleas

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• Bacteria?Protozoan?Zooplankton?Fish
• Pyramid of numbers
• more bacteria on the
• bottom, less fish on top
• Pyramid of biomass
• bacteria are microscopic and
• have extremely small mass (also reproduce more
  quickly) so will have small biomass, but supports
  the system.

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• Pyramid of energy flow
• Less
• Energy
• More
• energy