C4.2.11 Construction of energy pyramids Notes

Construction of Energy Pyramids

1. Energy pyramids are powerful visual tools that illustrate how energy flows through an ecosystem, transferring from one trophic level to the next.
2. They provide insights into energy efficiency and ecosystem sustainability.

1. Each bar’s width represents the energy available at that level, measured in kilojoules per square meter per year (kJ m⁻² yr⁻¹).
2. Energy pyramids visually demonstrate energy loss at each trophic level, emphasizing the inefficiency of energy transfer in ecosystems.

Why Does Energy Decrease at Higher Trophic Levels?

1. Energy transfer between trophic levels is inherently inefficient, with only 10% of the energy from one level passed to the next.
2. This phenomenon occurs due to:
   1. Heat Loss: Energy is lost as heat during metabolic processes.
   2. Incomplete Consumption: Some parts of organisms, like bones or bark, are not eaten.
   3. Incomplete Digestion: Some consumed material is not fully digested and is expelled as waste.

Constructing an Energy Pyramid

1. Follow these steps to accurately build an energy pyramid:
   1. Identify Trophic Levels: Categorize organisms into producers, primary consumers, secondary consumers, and tertiary consumers.
   2. Measure Energy: Calculate the energy at each trophic level using available data, often derived from biomass measurements.
   3. Draw the Pyramid:
      1. Use a stepped design with the widest bar at the base for producers.
      2. Label each bar with the trophic level and corresponding energy value.
      3. Scale the bar lengths proportionally to the energy values.

For A Grassland Ecosystem

1. Producers: Grass, 50,000 kJ m⁻² yr⁻¹
2. Primary Consumers: Herbivores like rabbits, 7,000 kJ m⁻² yr⁻¹
3. Secondary Consumers: Predators like foxes, 3,000 kJ m⁻² yr⁻¹

Practical Applications of Energy Pyramids

1. Ecosystem Efficiency: Highlighting how energy diminishes with each trophic level.
2. Trophic Level Limits: Explaining why ecosystems typically support only four to five trophic levels.
3. Conservation Strategies: Informing sustainable practices, such as protecting primary producers to ensure energy availability for higher levels.