Pyramids of Biomass

Pyramids of Biomass

  • Definition and Purpose

    • Pyramids of biomass illustrate the biomass at each trophic level within a food chain.

    • Example food chain:

      • Grass as producer

      • Rabbits as primary consumers

      • Snakes as secondary consumers

      • Hawks as tertiary consumers

  • Understanding Biomass

    • Definition of Biomass:

      • The mass of living organisms within a particular trophic level.

    • Representation in Pyramid:

      • Bottom bar represents total mass of all grass (producer).

      • Next bar for rabbits (primary consumers).

      • Following bar for snakes (secondary consumers).

      • Top bar for hawks (tertiary consumers).

  • Trends in Biomass Across Trophic Levels

    • Observational trend: Bars decrease in size as you ascend trophic levels.

    • Implication of decreasing size: Total mass of organisms diminishes at higher levels.

    • Example: While individual snakes may weigh more than individual rabbits, there are significantly fewer snakes, resulting in lower total biomass of snakes compared to rabbits.

  • Energy Transfer and Biomass Loss

    • Important concept: Not all biomass or energy from one level is transferred to the next.

    • Only approximately 10% of biomass gets transferred up to the next level.

    • Example:

      • Total biomass of grass → 10% transferred to rabbits.

      • Total biomass of rabbits → 10% transferred to snakes, and so forth.

  • Reasons for Limited Biomass Transfer

    • Three main reasons explaining why only about 10% is passed on:

    1. Incomplete Consumption:

      • Consumers do not eat every part of the organism.

        • Example: Hawks do not consume snake skeletons or teeth.

    2. Inefficient Absorption:

      • Not all consumed parts can be absorbed, leading to excretion.

        • Example: Scales or indigestible material may be expelled as feces.

    3. Energy Usage for Respiration:

      • A significant portion of absorbed nutrients is used in respiration, not stored for growth.

      • Waste Products:

        • Released as carbon dioxide and urea, reducing available biomass for transfer.

  • Calculation of Biomass Transfer Efficiency

    • Definition: Efficiency of biomass transfer is the percentage of biomass retained as it moves up each trophic level.

    • Formula for Efficiency:

    • \text{Efficiency} = \left( \frac{\text{Biomass transferred to next level}}{\text{Biomass available at previous level}} \right) \times 100

    • Example Calculation: Efficiency between a pair of trophic levels:

    • Efficiency from rabbits to snakes:

      • Biomass of snakes = 15 kg

      • Biomass of rabbits = 144 kg

      • Calculation:

      • \text{Efficiency} = \left( \frac{15}{144} \right) \times 100 = 10.4\%

    • Interpretation: 10.4% of rabbit biomass is transferred to the snakes.

    • Efficiency from snakes to hawks:

      • Biomass of hawks = 1.6 kg

      • Biomass of snakes = 15 kg

      • Calculation:

      • \text{Efficiency} = \left( \frac{1.6}{15} \right) \times 100 = 10.7\%

  • Conclusion

    • Pyramids of biomass provide a clear visual and quantitative representation of energy flow and biomass in ecosystems across different trophic levels.

    • Significant importance of understanding these concepts in ecology and environmental science.