Pyramids of Biomass

Definition

• Biomass: The mass of living organisms in a given area or ecosystem.
• Pyramids of Biomass: Represent the biomass at each trophic level in a food chain.

Example Food Chain

• Grass (Producer)
• Rabbits (Primary Consumer)
• Snakes (Secondary Consumer)
• Hawks (Tertiary Consumer)

Structure of Biomass Pyramid

• Bars represent total biomass at each trophic level.
• Lower trophic levels have larger biomass bars than higher levels.
• Decreasing size of bars indicates loss of biomass and energy at each level.

Biomass Transfer

• Only ~10% of biomass is transferred to the next trophic level.
• Reasons for biomass and energy loss:
  1. Organisms do not consume every part of their prey (e.g., hawks don’t eat snake skeletons).
  2. Not all consumed parts are absorbed (indigestible parts are excreted).
  3. Most absorbed nutrients are used for respiration, not growth.

Calculation of Biomass Transfer Efficiency

• Formula:

  [ \text{Efficiency} (%) = \left( \frac{\text{Biomass Transferred to Next Level}}{\text{Biomass Available at Previous Level}} \right) \times 100 ]

• Example Calculations:

  • Efficiency between snakes and rabbits:
    • Biomass transferred: 15 kg
    • Biomass available: 144 kg
    • Efficiency: [ (\frac{15}{144}) \times 100 = 10.4% ]
  • Efficiency between snakes and hawks:
    • Biomass transferred: 1.6 kg
    • Biomass available: 15 kg
    • Efficiency: [ (\frac{1.6}{15}) \times 100 = 10.7% ]

Conclusion

• Understanding pyramids of biomass helps explain energy transfer and efficiency in ecosystems.
• Essential for comprehending how energy and biomass flow through food chains.