Ecological efficiency is the efficiency with which biomass or energy is transferred from one trophic level to the next.Producers
Plants convert only about 1-3% of the light energy falling on them into chemical energy in biomass. The rest is lost because:
• much of the light is the wrong wavelength, is reflected, or misses chlorophyll entirely;
• photosynthesis is limited by other factors, such as low CO2 concentration or temperature;
• energy is lost in the reactions of photosynthesis.The total chemical energy made by plants is gross primary production (GPP). Plants use some of it in their own respiration (R). What remains, stored as new biomass and available to primary consumers, is net primary production (NPP):NPP = GPP − R Worked example: grassland has a GPP of 21 000 kJ m−2 yr−1 and loses 13 000 kJ m−2 yr−1 in respiration.
NPP = 21 000 − 13 000 = 8000 kJ m−2 yr−1.Consumers
Transfers between consumers are typically only around 10%, though they vary widely. Efficiency is lower for:
• herbivores, because plant material contains cellulose and lignin that are hard to digest, so more is lost in faeces;
• endotherms (mammals and birds), because they use much of their energy in respiration to keep a constant body temperature.Carnivores tend to have higher efficiencies than herbivores, because meat is more easily digested. Ectotherms, such as insects and fish, have higher efficiencies than endotherms.
Plants convert only about 1-3% of the light energy falling on them into chemical energy in biomass. The rest is lost because:
• much of the light is the wrong wavelength, is reflected, or misses chlorophyll entirely;
• photosynthesis is limited by other factors, such as low CO2 concentration or temperature;
• energy is lost in the reactions of photosynthesis.The total chemical energy made by plants is gross primary production (GPP). Plants use some of it in their own respiration (R). What remains, stored as new biomass and available to primary consumers, is net primary production (NPP):
NPP = 21 000 − 13 000 = 8000 kJ m−2 yr−1.Consumers
Transfers between consumers are typically only around 10%, though they vary widely. Efficiency is lower for:
• herbivores, because plant material contains cellulose and lignin that are hard to digest, so more is lost in faeces;
• endotherms (mammals and birds), because they use much of their energy in respiration to keep a constant body temperature.Carnivores tend to have higher efficiencies than herbivores, because meat is more easily digested. Ectotherms, such as insects and fish, have higher efficiencies than endotherms.