27.4:
Production Efficiency
The efficiency by which organisms incorporate received energy into biomass for the next trophic level is called Net Production Efficiency, or NPE.
Energy can be lost during metabolic processes like respiration and digestion, as waste and also as unconsumed biomass. For instance, when a fox consumes only part of a rabbit, leaving energy rich resources unutilized.
Ectothermic animals, like reptiles, use less energy for metabolic activities, especially respiration and maintenance of body temperature and therefore have an NPE that is about 10 times higher than endotherms, mammals or birds which must generate more heat to maintain metabolic processes. In the case of the fox and the snake, the discrepancy in NPE means that the fox must consume 10 times as much rabbit as the snake to receive the same amount of energy for building biomass.
27.4:
Production Efficiency
Net production efficiency (NPE) is the efficiency at which organisms assimilate energy into biomass for the next trophic level. Due to low metabolic rates and less energy spent on thermoregulatory processes, the NPE of ectotherms (cold-blooded animals) is 10 times higher than endotherms (warm-blooded animals).
Net Production Efficiency
Energy flows through ecosystems, from one organism to the next. However, only the energy stored in an organism as biomass is available as food for the next trophic level. The rest of the energy is lost over time as heat as a byproduct of metabolic processes and excreted wastes. The efficiency with which organisms assimilate this usable energy into biomass is called net production efficiency (NPE), or the percentage of energy stored in biomass that is not used for respiration. For example, in a study of a desert scrub ecosystem, it was found that only 0.016% of the energy produced by primary producers was then assimilated into small herbivore mammal tissue and available for carnivores in this system.
Endotherm vs Ectotherm
Endotherms like birds and mammals typically have low production efficiencies due to the larger quantities of energy spent maintaining constant high body temperatures, and high metabolic rates. On the other hand, the NPE for ectotherms is an order of magnitude higher due to their lower metabolic rates and thermoregulatory behaviors. Therefore, a mammal must consume more energy to assimilate the same amount of biomass that a reptile would.
Suggested Reading
Shurin, Jonathan B, Daniel S Gruner, and Helmut Hillebrand. “All Wet or Dried up? Real Differences between Aquatic and Terrestrial Food Webs.” Proceedings of the Royal Society B: Biological Sciences 273, no. 1582 (January 7, 2006): 1–9. [Source]