Which trophic level has the least available energy (in kilojoules) in a typical food web?

• A. Tertiary consumers (top predators)
• B. Secondary consumers (carnivores that eat herbivores)
• C. Primary consumers (herbivores)
• D. Producers (e.g., plants and algae)

Answer: (A)

Verified step by step guidance

1. Understand the concept of energy transfer in a food web: Energy flows through trophic levels in an ecosystem, starting with producers and moving up to primary consumers, secondary consumers, and tertiary consumers. At each level, energy is lost primarily as heat due to metabolic processes.
2. Recall the 10% rule: Typically, only about 10% of the energy at one trophic level is transferred to the next level. This means that as you move up the trophic levels, the amount of available energy decreases significantly.
3. Identify the trophic levels: Producers (plants and algae) are at the base of the food web, followed by primary consumers (herbivores), secondary consumers (carnivores that eat herbivores), and tertiary consumers (top predators).
4. Determine which trophic level has the least energy: Since energy decreases as you move up the food web, tertiary consumers (top predators) have the least available energy compared to other trophic levels.
5. Conclude the reasoning: The tertiary consumers have the least available energy because they are at the top of the food web, and energy diminishes significantly at each successive trophic level due to the inefficiency of energy transfer.