Production and Productivity

• Net primary production (NPP)

  The chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
• Net production of consumers (N)

  The total chemical energy consumers store after energy losses to faeces, urine, and respiration have been taken away from the chemical energy store of the ingested plant food
• The percentage efficiency of energy transfer from one trophic level to another can be calculated
• NPP

  Available for plant growth and reproduction
• Gross primary production (GPP)

  The total quantity of chemical energy stored in plant biomass, in a given area or volume
• NPP


  Available for consumers in the food chain such as herbivores and decomposers
• Primary and secondary productivity


  The rate of primary or secondary production, respectively. It is measured as biomass in a given area in a given time e.g. kJ ha–1 year–1
• Farming practices increase the efficiency of energy transfer to increase yields by

  1. Reducing respiratory losses in a human food chain e.g. reduce movement of animals

  2. Simplifying food chains to reduce energy loss to non-human food chains e.g. killing weeds and pests using herbicides and insecticides
• Net production of consumers (N)

  N = I - (F + R) where N is net production, I represents the total chemical energy store in ingested food, F is the energy lost in faeces and urine, and R is energy lost to respiration. All use units (kJ m-2 yr-1)
• Net Efficiency of Energy Transfer:

  (energy transfer after respiratory losses / energy available before) x 100