Ecosystems Ch 54, U117PP

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Ecosystems- Ch 54, U117PP
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Primary Production in Marine and Freshwater
Ecosystems

• In marine and freshwater ecosystems
• Both light and nutrients are important in
  controlling primary production

• The depth of light penetration
• Affects primary production throughout the photic
  zone of an ocean or lake

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Nutrient Limitation

• More than light, though, nutrients limit primary
  production
• Both in different geographic regions of the ocean
  and in lakes

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• A limiting nutrient is the element that must be
  added
• In order for production to increase in a
  particular area
• Nitrogen and phosphorus
• Are typically the nutrients that most often limit
  marine production

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• Experiments in another ocean region
• Showed that iron limited primary production

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• The addition of large amounts of nutrients to
  lakes
• Has a wide range of ecological impacts

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• In some areas, sewage runoff or excessive
  nutrient inputs
• Have caused eutrophication of lakes and rivers,
  which can lead to the eventual loss of most fish
  species from the lakes and dangerous algal blooms
  in rivers

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Primary Production in Terrestrial and Wetland
Ecosystems

• In terrestrial and wetland ecosystems climatic
  factors
• Such as temperature and moisture, affect primary
  production on a large geographic scale

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• The contrast between wet and dry climates
• Can be represented by a measure called actual
  evapotranspiration

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• Actual evapotranspiration
• Is the amount of water annually transpired by
  plants and evaporated from a landscape
• Is related to net primary production

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• On a more local scale
• A soil nutrient is often the limiting factor in
  primary production

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• Concept 54.3 Energy transfer between trophic
  levels is usually less than 20 efficient
• The secondary production of an ecosystem
• Is the amount of chemical energy in consumers
  food that is converted to their own new biomass
  during a given period of time

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Production Efficiency

• When a caterpillar feeds on a plant leaf
• Only about one-sixth of the energy in the leaf is
  used for secondary production

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• The production efficiency of an organism
• Is the fraction of energy stored in food that is
  not used for respiration

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Trophic Efficiency and Ecological Pyramids

• Trophic efficiency
• Is the percentage of production transferred from
  one trophic level to the next
• Usually ranges from 5 to 20

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Pyramids of Production

• This loss of energy with each transfer in a food
  chain
• Can be represented by a pyramid of net production

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Pyramids of Biomass

• One important ecological consequence of low
  trophic efficiencies
• Can be represented in a biomass pyramid

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• Most biomass pyramids
• Show a sharp decrease at successively higher
  trophic levels

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• Certain aquatic ecosystems
• Have inverted biomass pyramids

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Pyramids of Numbers

• A pyramid of numbers
• Represents the number of individual organisms in
  each trophic level

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• The dynamics of energy flow through ecosystems
• Have important implications for the human
  population
• Eating meat
• Is a relatively inefficient way of tapping
  photosynthetic production

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• Worldwide agriculture could successfully feed
  many more people
• If humans all fed more efficiently, eating only
  plant material

Figure 54.14