Food webs and energy flow

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Food webs and energy flow
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• All organisms dead or alive are potential food
  sources for other organisms
• There is little natural waste in natural
  ecosystems

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Food Chain

• Sequence of organisms, each a food source for
  next
• determines how energy nutrients move through
  ecosystem
• begins with photosynthesis

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Trophic Levels

• Feeding level
• 1st trophic level-producers
• 2nd trophic level-primary consumers
• 3rd trophic level-secondary consumers
• Detritivores-(decomposers) process detritus from
  all levels

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Food Chain
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Food Webs

• Most species participate in several food chains
• complex network of interconnected chains
• one way flow of energy

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Food Web
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• Grazing food webs-energy nutrients move from
  plants ?herbivores?carnivores?decomposers
• Detrital food webs organic waste material moves
  from producers?decomposers/detritivores

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Biomass

• Dry weight of all organic material in organisms
• represents chemical energy stored at specific
  trophic level

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• Energy stored in biomass transferred through
  trophic levels
• some usable energy degraded
• some lost as fecal waste
• 5-20 of biomass actually transferred
• Ecological efficiency- transferred

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Pyramid of Energy Flow
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• Earth can support more people if they eat at
  lower trophic levels
• grains, fruits, vegetables directly
• Rarely can there be more than 4 or 5 trophic
  levels
• Top carnivores-few in number first to suffer

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Pyramid of numbers

• Estimating organisms at each trophic level
• 1000 metric tons of grass supports 27,000,000
  grasshoppers
• supports 90,000 frogs
• supports 300 trout
• 1 person for 30 days
• eliminate trout-30 people, 30 days eating 100
  frogs a day...