1. Food chain: linear flow chart of who eats whom and direction of nutrient and energy transfer
  2. Food web: linked group of food chains (animals have more than one food source)

Conservation of Mass

  • Matter, like energy, cannot be created or destroyed.
    • But elements can cycle–be gained or lost by an ecosystem
  • Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products
    • Ecosystems depend on constant input of energy

Ecological/Trophic Efficiency

  • “Proportion of energy represented at one trophic lvl that is transferred to the next lvl”
    • Always less than production efficiency
  • ~1% of the solar energy that reaches the surface of the earth is converted into organic matter
  • Transfer of energy between trophic lvls is inefficient → ~only 10% of the productivity of one trophic lvl is transferred to the next lvl
    • Remaining 90% is used for metabolic activities, passed thru feces, or transferred to detritivores
  • Most energy for respiration and other metabolic activities is ultimately lost as heat
    • Heat is energy that cannot be harnessed by organisms to do work → represents energy lost from the ecosystem
      • So ultimately all energy originally gained through NPP is lost as heart
    • BUT chemicals, nutrients and matter recycled in an ecosystem (unlike heat)
  • Bcuz ecological efficiency is so low, almost all animals used for food/work are herbivores
    • Carnivores require more energy to sustain themselves
  • Changes in energy availability can result in…
    • Changes in population size & density
    • Disruptions to an ecosystem: Species have adaptations that aid survival when energy availability changes
      • Ex: fat as energy, lose/grow leaves, migration, hibernation, lower metabolic rate
      • Exist reproductive strategies in response to energy availability
        • Produce lots of offspring at one
          • Energy efficient when not enough resources
        • Some produce few offspring at one
          • Energy efficient in stable environments
        • Ex: sunlight can affect number and size of trophic levels

Energy Flow and Chemical Cycling                                                                                           

  • Chemical Cycling: plants take chemicals from soil & air → chemicals passed to herbivores → decomposers break down dead matter, releasing chemicals back to the soil
  • Energy Flow: Energy enters most ecosystems as sunlight → converted to chemical energy by autotrophs → passed to heterotrophs in the organic compounds of food → dissipated as heat when energy used for work
  • Both energy and chemicals are transformed in ecosystems through photosynthesis and feeding relationships. But unlike chemicals, energy cannot be recycled.

How do Organisms Regulate Body Temp and Metabolism?

  • Endotherms use thermal energy generated by metabolism
    • Ex: changes in heart rate, fat storage, muscle contractions (shivering)
    • Metabolic Rate/O2 consumption rate increases with decreasing temperature
      • Spend more energy to maintain internal temp
    • Ectotherms lack efficient body temperature regulating mechanisms
      • Rely on behavior: moving in and out sun, eating
      • Metabolic Rate/O2 consumption rate increases with increasing temperature

Primary Productivity

  • Organisms use energy to grow and reproduce
  • Primary productivity: amount of organic matter produced through photosynthetic (or chemosynthetic) activity per unit of time; components of primary productivity…
  1. Gross primary productivity (GPP): rate at which producers acquire chemical energy before any of this energy is used for metabolism
  2. Net primary productivity (NPP): rate at which producers acquire the chemical energy minus the rate at which they consume energy thru respiration
  • NPP represents the biomass available to herbivores

Respiratory/Metabolic Rate (R): rate at which energy is consumed through respiration (and other metabolic activities needed for life) 

  • Most of energy is lost as heat
  • Larger organisms = higher rate
  • NPP = GPP – R
    • Net Gain = energy storage or growth
    • Net Loss = mass loss or death

Regulation of Primary Productivity

  • Aquatic Biomes: Light and nutrients
  • Terrestrial Biomes: Temperature and moisture

Light Limitation

  • Solar energy exposure controls extent of photosynthesis and biomass of primary producers

Nutrient Limitation

  • Limiting nutrient is the element that must be added for production to increase
    • Usually nitrogen and phosphorous
  • If a nutrient’s outputs exceed its inputs, that nutrient will eventually limit production in that ecosystem
  • Adding more of the limiting nutrient will increase production until some other nutrient becomes limiting.
  • Human impact example: fertilizer runoff adds nutrients and promotes growth of primary producers → primary producers die → bodies are broken down by aerobic decomposers. → depletes the water of much or all of its oxygen → kills large numbers of fish