In an ecosystem, solar energy flows from producers to consumers・decomposers. Let us understand the mechanisms of energy flow and matter cycling.
Basic Knowledge
Components of an ecosystem: producers(plants・photosynthesis)・primary consumers(herbivores)・secondary・tertiary consumers(carnivores)・decomposers(bacteria・fungi convert remains・excreta into inorganic substances).
Energy flow: Of the energy received at each trophic level, only 10〜20% can be passed to the next level(the remainder is lost through respiration・remains・feces and urine). Energy does not cycle and eventually dissipates as heat.
Ecological pyramids: energy pyramid=always an upright triangle(never inverted). Pyramids of numbers and biomass may be inverted depending on the conditions.
Matter cycles: carbon cycle=CO₂(atmosphere)→photosynthesis→organic carbon→respiration・decomposition→CO₂. nitrogen cycle=N₂→nitrogen fixation(root nodule bacteria・Azotobacter・cyanobacteria)→NH₄⁺→nitrification(nitrite bacteria→nitrate bacteria)→NO₃⁻→absorption→organic matter→decomposition→NH₄⁺→denitrification→N₂.
When the energy fixed by producers is 10,000 kJ/m² and the energy efficiency is uniformly 10%, calculate the energy received by primary・secondary・tertiary consumers.
Answer: Primary consumers: 10,000 × 0.10 = 1,000 kJ/m². Secondary consumers: 1,000 × 0.10 = 100 kJ/m². Tertiary consumers: 100 × 0.10 = 10 kJ/m². Available energy decreases rapidly at higher trophic levels.
- Energy efficiency=10〜20%(loss at each trophic level)
- The energy pyramid is always an upright triangle
- Energy does not cycle; it flows in one direction and eventually dissipates as heat
- Carbon cycles between atmospheric CO₂ and living organisms
- Nitrogen fixation=N₂→NH₄⁺(root nodule bacteria・Azotobacter)
- Nitrification=NH₄⁺→NO₂⁻(nitrite bacteria)→NO₃⁻(nitrate bacteria)
- Decomposers=bacteria・fungi return organic matter to inorganic substances
Points to Note
① Energy does not cycle, while matter(carbon・nitrogen, and so on) cycles. This difference is important. ② The energy pyramid is never inverted, but pyramids of numbers and biomass may be inverted depending on the conditions. ③ Nitrogen fixation is performed not only by root nodule bacteria(which live symbiotically in the roots of leguminous plants), but also by Azotobacter・cyanobacteria.
Practice
- Which ecological pyramid in an ecosystem is always an upright triangle(never inverted)?
- Name two or more organisms that perform nitrogen fixation.
- When the energy efficiency is 10%, what percentage of the energy reaches tertiary consumers from producers?