Practice question

Food chains are relatively short because transfer between trophic levels is inefficient. Only part of a level’s production is eaten; only part of what is eaten is assimilated; and much assimilated energy is respired rather than converted into new biomass. Multiplying these efficiencies produces a steep decline in energy available to successive predators. Eventually, production cannot support a viable population at another level. Disturbance, ecosystem area, prey size, and dynamic stability modify chain length, but all operate within this energetic ceiling. Energy budgets must distinguish stocks from rates: standing biomass can remain high or low even when production and transfer through that compartment are rapid. Matter can cycle repeatedly through producers, consumers, and decomposers, whereas usable energy requires continuous external input because respiration degrades it to heat. The amount reaching a consumer level depends jointly on resource production, the fraction consumed, assimilation efficiency, and conversion of assimilates into new biomass.