Detrital pathways in freshwater food webs typically have what energy transfer characteristic compared with grazing pathways?

• A. Higher efficiency
• B. Similar efficiency
• C. Much higher efficiency
• D. Lower efficiency

Answer: (D)

The idea being tested is how energy moves through different pathways in freshwater food webs. Detrital pathways rely on dead organic matter being broken down by microbes and detritivores. A lot of that energy is used for maintenance and released as heat through microbial respiration, and the energy that does accumulate in microbial or detrital biomass is transferred to detritivores with further losses at each step. Because there are many steps and substantial losses at each one, only a small fraction of the original energy makes it up to higher trophic levels via the detrital route. Grazing pathways, by contrast, move energy more directly from primary producers to herbivores with relatively higher assimilation efficiency, so energy transfer to higher levels is more efficient per step. Therefore, detrital pathways have lower energy transfer efficiency than grazing pathways.