What is defined as the gain by consumers in energy or biomass per unit area per unit time after respiratory losses?

The correct answer is that the gain by consumers in energy or biomass per unit area per unit time after respiratory losses is defined as net secondary productivity. This concept is vital in ecology as it measures the efficiency of energy transfer from one trophic level to another.

Net secondary productivity reflects the energy that is available for growth and reproduction after accounting for the energy expended on respiration by consumers. It quantifies how much of the energy consumed by heterotrophs contributes to their biomass. This means that when organisms utilize energy for metabolic processes such as respiration, some energy is lost, and net secondary productivity captures the remaining energy that contributes to growth.

The other terms have different meanings: net primary productivity refers to the energy or biomass generated by primary producers (like plants and phytoplankton) after their own respiratory losses. Gross secondary productivity represents the total energy fixed by consumers before respiratory losses occur. Energy yield is a more general term that can refer to the efficiency of energy transfer but does not specifically encapsulate the concept of biomass accumulation after respiration. Understanding these definitions aids in comprehending energy flow in ecosystems.