5.1 Communities and Ecosystems

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5.1 Communities and Ecosystems

• Outcomes 5.1.6, 5.1.7, 5.1.8

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5.1.6 Define Trophic level

• An organisms trophic level refers to its
  position in a food chain.
• Trophic levels classify organisms by their
  feeding relationships with other organisms in the
  same ecosystem.
• There must be a large number producers and
  decreasing numbers of each subsequent level.

Trophic Levels Trophic Levels
T5 Quaternary consumer
T4 Tertiary consumer
T3 Secondary consumer
T2 Primary consumer
T1 Producer
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5.1.7 Deduce the trophic level of organisms in
a food chain, and a food web

• A food chain begins with a producer.
• For Example algae Mosquito Larva Dragonfly
  Larva Fish Raccoon
• So to determine the trophic level of each
  organism we begin with the producer, which is the
  only organism in the chain which
  photosynthesizes.
• Second Trophic Level, which is occupied by the
  primary consumer, is determined by finding out
  which organism eats the producers from the
  example mosquito larva.
• Next levels are occupied by the secondary then
  tertiary consumers and so on.

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5.1.7 Deduce the trophic level of organisms in
a food chain, and a food web (cont.)

• Highest trophic level in a food chain is occupied
  by a top predator ( For example, it would be the
  raccoon). Other top predators are birds of prey,
  bears, sharks, or humans.
• Some food chains have 6 trophic levels, most
  however have 4.
• Number of levels can be limited by how much
  energy enters the ecosystem. So since so much is
  lost at each level, low energy at the start will
  quickly disperse whereas abundant energy for
  producers can last for several trophic levels

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5.1.7 Deduce the trophic level of organisms in
a food chain, and a food web (cont.)

• Food webs are more complex than food chains
  therefore, determining trophic levels is more
  challenging.
• Best method is to isolate a single food chain
  inside the web and analyse it in the same way as
  above
• For Example
• A river food web which includes the food chain
  Algae Mayfly Larva Juvenile Trout
  Kingfisher
• From this example we should be able to determine
  why the juvenile trout, for example, is a
  secondary consumer ( on the third trophic level)

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5.1.8 Construct a food web containing up to 10
organisms, using appropriate information

• Always begin with the producer at the bottom of
  the diagram.
• After this, include all of the primary consumers.
• Continue until you reach the top predator.

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5.1.8 Construct a food web containing up to 10
organisms, using appropriate information (cont.)

• For example, one could construct a food web from
  these statements.
• Algae is eaten by the mayfly larva
• Leaf debris is eaten by the caddis fly larva and
  blackfly larva.
• The mayfly larva and the blackfly larva are eaten
  by juvenile trout.
• The juvenile trout is eaten by the kingfisher
• The mayfly larva is also eaten by the sculpin and
  the stonefly larva, all of which are eaten by
  adult trout

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5.1.8 Construct a food web containing up to 10
organisms, using appropriate information (cont.)
King Fisher
Sculpin
Adult Trout
Juvenile Trout
Caddis Fly Larva
Mayfly Larva
Blackfly Larva
Stonefly Larva
Leaf Debris
Algae