Primary Production and Energy Flow

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Primary Production and Energy Flow

• Chapter 18

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Outline

• Introduction
• Terrestrial Primary Production
• Evapotranspiration
• Aquatic Primary Production
• Consumer Influences
• Trophic Levels/Dynamics

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Introduction

• The interactions between organisms and their
  environment are fueled by transformations of
  energy.
• The source of that energy in most ecosystems is
  the sun.

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Introduction

• Primary production Fixation of energy by
  autotrophs in an ecosystem.
• Autotroph an organism that can synthesize
  organic molecules using inorganic molecules and
  energy from either sunlight (photosynthesis) or
  from inorganic molecules such as hydrogen sulfide
  (chemosynthesis).

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Introduction

• Rate of primary production Amount of energy
  fixed over a given period of time.
• Gross primary production Total amount of energy
  fixed by autotrophs.
• Net primary production Amount of energy leftover
  after autotrophs have met their metabolic needs.

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Introduction

• Trophic Level Position in a food web determined
  by number of energy transfers from primary
  producers to current level
• Primary producers (autotrophs) occupy first
  level.
• Primary consumers (herbivores detritivores)
  occupy second level.
• Secondary consumers (carnivores) occupy third
  level.
• Tertiary consumers occupy fourth level.

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Patterns of Terrestrial Primary Production

• Terrestrial primary production is limited by
  temperature and moisture.

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Actual Evapotranspiration and Terrestrial Primary
Production

• Rosenzweig estimated influence of moisture and
  temperature on rates of primary production by
  plotting the relationship between annual net
  primary production and annual actual
  evapotranspiration (AET).

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Actual Evapotranspiration and Terrestrial Primary
Production

• AET Annual amount of water that evaporates and
  transpires off a landscape.
• Cold dry ecosystems tend to have low AET.
• Warm moist ecosystems tend to have high AET.
• AET is affected by both temperature and
  precipitation.

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Evapotranspiration and Terrestrial Primary
Production

• Generally, there is a positive relationship
  between net primary production and AET.

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Evapotranspiration and Terrestrial Primary
Production

• Looking at variation within similar ecosystems
• Sala found east-west variation in primary
  production in grassland ecosystems correlated
  with rainfall.

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Soil Fertility and Terrestrial Primary Production

• Significant variation in terrestrial primary
  production can be explained by differences in
  soil fertility.
• Leibigs Law of the Minimum suggests that the
  single most limiting resource controls primary
  production.

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Soil Fertility and Terrestrial Primary Production

• Shaver and Chapin found arctic net primary
  production was twice as high on fertilized plots
  as unfertilized plots.

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Soil Fertility and Terrestrial Primary Production

• Bowman suggested N is main nutrient limiting net
  primary production in a dry tundra meadow, and N
  and P jointly limit production in a wet meadow.

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Patterns of Aquatic Primary Production

• Aquatic primary production is generally limited
  by nutrient availability.

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Patterns of Aquatic Primary Production

• Several studies have found quantitative
  relationship between phosphorus and phytoplankton
  biomass.

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Patterns of Aquatic Primary Production

• Smith examined the relationship between
  phytoplankton biomass and the rate of primary
  production.
• Strong positive correlation between chlorophyll
  concentrations and photosynthetic rates.

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Patterns of Aquatic Primary Production

• Whole lake experiments support the generalization
  that nutrient availability controls rates of
  primary production in freshwater ecosystems.

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Global Patterns of Marine Primary Production

• Highest rates of primary production by marine
  phytoplankton are generally concentrated in areas
  with higher levels of nutrient availability.

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Global Patterns of Marine Primary Production

• Highest rates found along continental margins.
• Nutrient run-off from land.
• Sediment disturbance
• Open ocean tends to be nutrient poor.
• Vertical mixing main nutrient source.

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Global Patterns of Marine Primary Production

• Graneli gathered results suggesting rate of
  primary production in Baltic Sea is nutrient
  limited.
• Increased nutrients led to increased chlorophyll
  concentrations.
• N appears to be limiting nutrient.

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Global Patterns of Marine Primary Production

• Residual Variation Proportion of variation not
  explained by the independent variable.
• Dillon and Rigler suggested environmental factors
  besides nutrient availability significantly
  influence phytoplankton biomass.
• Intensity of predation on zooplankton.

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Consumer Influences

• Consumers can influence rates of primary
  production in aquatic and terrestrial ecosystems.

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Consumer Influences

• Bottom-Up Controls
• Influences of physical and chemical factors of an
  ecosystem.
• Top-Down Controls
• Influences of consumers.

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Lake Primary Production

• Carpenter proposed piscivores and planktivorous
  fish can cause significant deviations in primary
  productivity.
• Top-down

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Lake Primary Production

• Carpenter and Kitchell proposed the influence of
  consumers on lake primary productivity propagate
  through food webs.
• Trophic Cascade Hypothesis

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Lake Primary Production

• Carpenter and Kitchell found that reduction in
  planktivorous fish populations led to reduced
  rates of primary production.
• In presence of abundant, large herbivorous
  zooplankton, phytoplankton biomass and rate of
  primary production declined.

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Lake Primary Production

• In absence of planktivorous minnows, predaceous
  invertebrates became more numerous.
• Feed on small zooplankton.
• Leads to an increase in large zooplankton.

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Primary Production on the Serengeti

• McNaughton estimated Serengeti grazers consume an
  average of 66 of annual primary production.
• Rate of primary production in the Serengeti is
  positively correlated with rainfall quantity.

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Primary Production in the Serengeti

• Found grazers can increase primary production.
• Increased growth rate.
• Compensatory Growth
• Lower respiration rate due to lower biomass.
• Reduced self-shading.
• Improved water balance due to reduced leaf area.

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Primary Production in the Serengeti

• In addition, McNaughton found compensatory growth
  highest at intermediate grazing intensities.
• Light grazing insufficient to produce
  compensatory growth.
• Heavy grazing reduces plants capacity to recover.

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Trophic Levels

• Energy losses limit the number of trophic levels
  in ecosystems.
• With each transfer or conversion of energy, some
  energy is lost.

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Trophic Dynamic View of Ecosystems

• Lindeman concluded the ecosystem concept is
  fundamental to the study of trophic dynamics
  (energy transfer within an ecosystem).
• Suggested grouping organisms within an ecosystem
  into trophic levels.
• Each feeds on level immediately below.

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Trophic Dynamic View of Ecosystems

• As energy is transferred from one trophic level
  to another, energy is degraded
• Limited assimilation
• Consumer respiration
• Heat production

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Trophic Dynamic View of Ecosystems

• Energy quality decreases with each successive
  trophic level.
• Pyramid-shaped energy distribution.

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Energy Flow in A Temperate Deciduous Forest

• Gosz studied solar energy flow in the Hubbard
  Brook Experimental Forest
• 15 reflected
• 41 converted to heat
• 42 absorbed during evapotranspiration
• 2.2 fixed by plants as gross primary production
• 1.2 used in plant respiration
• 1 left for primary production

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Energy Flow in A Temperate Deciduous Forest

• 99 of solar energy unavailable for use by second
  trophic level.
• Of the net primary production eaten by consumers,
  about 96 is lost as consumer respiration.
• As energy losses between trophic levels
  accumulate, eventually there is insufficient
  energy left to support a viable population at a
  higher trophic level.