UNCG 301 Ecology UNIT 4

• Primary productivity


  The rate at which autotrophs convert carbon dioxide (in the atmosphere or water) into organic compounds
• Chemoautotrophs


  Organisms that convert carbon dioxide into organic compounds using energy from chemical compounds (oxidation of electron donating molecules)
• Photoautotrophs


  Organisms that convert carbon dioxide into organic compounds using energy from sunlight (photosynthesis)
• Gross primary productivity (GPP)


  The total rate of photosynthesis (energy assimilated) by autotrophs
• Net primary productivity (NPP)

  The rate of energy storage as organic molecules after energy is expended for cellular respiration (R)
• Productivity


  Usually expressed in units of energy per unit area per unit time (e.g. grams per square meter per year)
• What controls productivity on land?

  • Climate is a primary control on net primary productivity in terrestrial ecosystems
  • Nutrient availability is a primary control on net primary productivity in terrestrial ecosystems
• As mean annual temperature increases

  Net primary productivity increases
• As mean annual precipitation increases


  Net primary productivity increases
• Warm temperatures and adequate water supply

  Give the highest net primary productivity
• Nutrient availability


  Influences the rate of nutrient uptake, photosynthesis, and plant growth
• As nutrient availability increases


  Net primary productivity increases
• What controls productivity under water?

  • Nutrient availability is a primary control on net primary productivity in aquatic ecosystems
  • Light availability is a primary control on net primary productivity in aquatic ecosystems
• As nutrient availability increases in aquatic ecosystems


  Net primary productivity increases
• As light availability increases in aquatic ecosystems

  Net primary productivity increases
• Energy allocation and plant life-form


  Influence primary production
• Primary production varies within an ecosystem with time and age
• Primary production varies seasonally
• Primary production varies annually due to climatic variation
• Primary production varies with ecosystem age and disturbances
• Secondary production


  The net energy allocated to the formation of living heterotroph biomass over a period of time
• As net primary productivity increases


  Secondary productivity of herbivores increases
• As net primary productivity increases

  Herbivore biomass and consumption of primary productivity by herbivores increases
• Primary productivity limits secondary production
• Assimilation efficiency


  The efficiency of extracting energy from food
• Production efficiency


  The efficiency of incorporating assimilated energy into secondary production
• Efficiently assimilated energy is incorporated into secondary production


  1. 100 J of ingested energy is assimilated (A)

  2. 100 J of ingested energy is expelled as waste (W)

  3. 60 J of assimilated energy is used for respiration (R)

  4. 40 J of assimilated energy is used for production (P)

  5. 200 J of plant material ingested (I)
• In the example shown in Figure 20.22, I = 200 J, A = 100 J, W = 100 J, R = 60 J, and P = 40 J.
• Assimilation efficiency (A/I)


  Measures the efficiency of extracting energy from food
• Production efficiency (P/A)


  Measures how efficiently assimilated energy is incorporated into secondary production
• Assimilation efficiencies vary widely

  • Endotherms are much more efficient than ectotherms
  • Carnivores are more efficient than herbivores (carnivores ~80% vs herbivores ~20-50%)
• Ranking of assimilation efficiencies

  • lion
  • giraffe/horse
  • predatory spider
  • grasshopper
• Production Efficiencies in general

  • Invertebrates have higher efficiencies than vertebrates
  • Ecotherms have intermediate production efficiency
  • Endotherms convert a very small amount (1 to 2 percent) of assimilated energy into production
• There are two major food chains in any ecosystem: the grazing food chain and the detrital food chain
• The source of energy for the detrital food chain is the grazing food chain's dead organic material and waste
• Energy flow is unidirectional in the grazing food chain but not unidirectional in the detrital food chain
• Dead organic material and waste from each level return as inputs to the base of the food chain
• At higher levels, carnivores from both food chains feed on herbivores from both food chains
• Consumption efficiency


  The ratio of ingestion to production at the next-lower trophic level, defining the amount of available energy being consumed
• Grazing herbivores play the dominant role in energy flow in some open-water aquatic ecosystems when dominated by aquatic algae (phytoplankton) - median of 79 percent