Energy&ecosystems

• • Most energy enters ecosystems through the sun - light energy 
• • Biomass= total mass of living (organic) material 
• •  3 ways to measure biomass: 
  • fresh weight/fresh biomass- measured in grams - easy to measure some organisms, harder for others- problem: water content will vary between individuals 
  • Dry biomass/dry weight - measured in grams- organism dried in an 80 degree oven for a set period of time, weighed then put back in oven and weighed again until the mass is constant showing all water has been removed 
  • Estimate mass of carbon in a sample 
• How to convert biomass to energy values 

  • Use a calorimeter - combust biomass
  • The chemical energy stored in dry mass can be estimated

  Most common units:

  • Kilojoules per meter squared per year - KJ M-2 Yr-1
  • Kilojoules per meter cubed per year - KJ M-3 Yr-1
• • Primary producer - any photosynthesising organism
• Primary consumer/secondary consumer etc-  an organism that eats plants and provides the energy needed for other types of consumers to use. Secondary consumers are those that predate upon primary consumers
• • Autotroph- an organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide
• Trophic level- The position of an organism in the food chain ranging from the value of one for primary producers and five for mammals and humans
• Decomposer

  • an organism, especially a soil bacteria, fungus, or invertebrate that decomposes organic material.
• • Saprotroph - a type of decomposer that feeds exclusively on dead and decaying plant matter. including fungi, bacteria, and water moulds which are critical to decomposition and nutrient cycling. They're found in soil and sediments and secrete enzymes 
• % efficiency = energy available after transfer (divided by) energy available before transfer X 100
• • Energy budgets - NPP=GPP-RL    most organic molecules used by primary producers as respiratory substrate  - the rest (NPP) is used for growth, available for next trophic level

   
• Reasons for energy loss in ecosystems

  • Respiratory loss
  • Death
  • Faeces and urine 
  • not all of organism is eaten
• The net production of consumers ( N), such as animals, can be calculated as:

  N =I –(F+R)

  where I=energy ingested, F=energy lost from excretion, R=respiratory losses
• Ecological efficiency is the efficiency at which biomass or energy is transferred from one trophic level to the next trophic level as a percentage