Practice question

Primary consumers feed directly on producers and transfer part of primary production into animal or microbial consumer biomass. Herbivores, zooplankton, and many seed eaters occupy this role. Their feeding can regulate producer abundance and species composition, while their waste and mortality route nutrients and energy into detrital pathways. They do not produce energy—organisms transform energy—and they do not generally consume herbivores. Their assimilation and production efficiencies determine how much producer energy becomes available to predators. Thermodynamic constraints set broad patterns, but species traits, defenses, body size, habitat structure, and disturbance determine the efficiencies observed in a particular ecosystem. Real communities are networks rather than isolated chains, so omnivory, detrital links, and changes in interaction strength modify the simplified trophic sequence. 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.