Biomass transfer through an ecosystem

Trophic levels

• Each stage of a food chain is a trophic level
• First trophic level = producers aka plants
• The subsequent trophic levels are consumers 
• Decomposers are also important in food webs as they break down dead material

Measuring biomass

• Biomass = mass of living material present in an area or organism
• To calculate biomass at each trophic level, biomass present in each organism * total number of organisms
• Easy way to measure biomass is to weigh fresh material but the water content is too variable for this to be accurate so the material is burned and then the ashed are weighed --> may not be representative of the population as a whole
• Measured in grams per cubic metre for water or grams per square metre for land areas

Efficiency of biomass and energy transfer between trophic levels

• Biomass of each trophic level is generally less than the trophic level below it
• This is because it consists of all the cells and tissues including the carbohydrates and other carbon compounds that the organisms contain
• As carbon compounds contain energy biomass = energy content
• Small proportion of the food eaten by animals is converted to new tissue which is all that is passed onto the next trophic level
• Energy available for each trophic level is measured in kilojoules per metre squared per year 
• As biomass is transferred between trophic levels the energy contained is passed on
• The efficiency with which the biomass or energy is transferred = ecological efficiency

Efficiency at producer level

• Producers convert 1-3% of sunlight to chemical energy aka biomass
  • not all solar energy available is used for photosynthesis (90% is reflected)
  • other factors limit photosynthesis 
  • a proportion of the energy is "lost"
• Plants 20-50% of chemical energy in respiration so the rest is converted to biomass
• Energy available to next trophic level = gross production - respiratory losses
  • gross production = total energy they convert to chemical energy

Efficiency at consumer level

• They at most convert 10% of consumed biomass to their own tissue because
  • not all of the biomass is eaten
  • some energy is transferred to environment as heat due to movement or respiration
  • some parts that are eaten are indigestible and are egested as faeces
  • some energy is lost from the animal in excretory materials like urine
• Only 0.001% of total energy present in sunlight is embidies as biomass in a tertiary consumer
• Efficiency of energy transfer = ecological efficiency
  • ecological efficiency = (energy or biomass available after the transfer / energy or biomass available before the transfer) * 100

Human activities can manipulate biomass through ecosystems

• In agriculture, plants and animals are provided with abiotic conditions they need to thrive like water and warmth and competition from other species is removed as well as the threat of predators
• Agriculture creates simple food chains where only 3 trophic levels are present (farming)
  • producers --> animal feed
  • primary consumers --> livestock
  • secondary consumers --> humans
• This means minimum energy is lost along the way since there are fewer trophic levels
• Highest energy and biomass transfer possible to humans