When is an ecosystem said to have high net primary productivity?

• A. When the rate of energy captured by producers through photosynthesis exceeds the energy lost through respiration by a large margin.
• B. When the total biomass of consumers is greater than that of producers.
• C. When the rate of decomposition is higher than the rate of photosynthesis.
• D. When there is little to no energy transfer between trophic levels.

Answer: (A)

Verified step by step guidance

1. Understand the concept of net primary productivity (NPP): NPP is the amount of energy captured by producers (plants, algae, etc.) through photosynthesis minus the energy they use for their own respiration. It represents the energy available for growth and reproduction, and ultimately for consumers in the ecosystem.
2. Analyze the first option: 'When the rate of energy captured by producers through photosynthesis exceeds the energy lost through respiration by a large margin.' This aligns with the definition of high NPP, as it indicates a significant surplus of energy available for the ecosystem.
3. Evaluate the second option: 'When the total biomass of consumers is greater than that of producers.' This does not directly relate to NPP, as NPP is focused on energy flow rather than biomass comparisons between consumers and producers.
4. Examine the third option: 'When the rate of decomposition is higher than the rate of photosynthesis.' This would indicate a decline in energy availability, as decomposition breaks down organic matter rather than contributing to energy capture, which contradicts the concept of high NPP.
5. Review the fourth option: 'When there is little to no energy transfer between trophic levels.' This suggests inefficiency in energy flow within the ecosystem, which is unrelated to high NPP. High NPP implies abundant energy available for transfer to higher trophic levels.