A sparrow can function as a primary consumer when it feeds on seeds, and as a secondary consumer when it feeds on herbivorous insects. Consider a crop field where the Net Primary Productivity (NPP) is 20,000 J . What will be the energy available to the sparrow when it feeds exclusively on the seeds (Case I) and when it feeds exclusively on the herbivorous insects (Case II), respectively?

Step-by-step solution

In Case I, the sparrow feeds on seeds, acting as a primary consumer (second trophic level, T₂ ). Energy available at T₁ (NPP of crop) = 20,000 J . According to the 10 percent law, energy available to the sparrow = 10 % of 20,000 J = 2,000 J . In Case II, the sparrow feeds on herbivorous insects, acting as a secondary consumer (third trophic level, T₃ ). Energy available to insects ( T₂ ) = 10 % of 20,000 J = 2,000 J . Energy available to the sparrow ( T₃ ) = 10 % of 2,000 J = 200 J . Therefore, the energy available