Practice question

Kilojoules are a standard SI unit for energy pyramids, usually reported as kJ m⁻² yr⁻¹ or an equivalent spatial and temporal flux. However, kilocalories are also legitimate energy units and have been widely used in ecological studies, so the keyed choice is not scientifically unique. Grams measure mass and individuals measure abundance, but both listed energy units can express the same quantity after conversion. The key should therefore be retained only as a unit-preference convention and flagged as an ambiguous mismatch. A snapshot may differ seasonally, especially in plankton or annual vegetation, whereas integrated production better represents ecosystem functioning across time. The ten-percent heuristic is useful for prediction but not exact; empirical transfer efficiencies vary with food quality, ectothermy, producer defenses, and detrital routing. Higher trophic levels are often vulnerable because low energy supply produces small populations that are sensitive to habitat fragmentation and environmental variability. Ecological pyramids must be interpreted according to what is measured—individuals, standing dry mass, or energy flux—because these variables need not have the same shape.