Practice question

Invertebrates commonly show high production efficiency because many are ectotherms and devote relatively little assimilated energy to maintaining a constant body temperature. More energy can therefore become growth, reproduction, or new tissue. Mammals and birds incur large respiratory costs for endothermy, while fish are also ectothermic and can be efficient; consequently, the ranking is a broad textbook generalization rather than an invariant rule. Age, temperature, activity, food quality, and life history can reverse comparisons among particular species. The distinction between gross transformation and net nutrient release is important: simultaneous microbial uptake can conceal substantial biochemical turnover. Environmental effects are often nonlinear; drought suppresses microbial access to substrates, waterlogging restricts oxygen, and extreme heat can reduce activity despite faster kinetics. Substrate stoichiometry links carbon processing to nutrient demand, so identical mass loss can accompany mineralization in one litter type and immobilization in another. Microbial enzymes act outside cells, making surface area and molecular accessibility as important as the nominal energy content of the dead material.