Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 55.3 Energy Transfer Between Trophic Levels Is Typically Only 10% Efficient
Energy flow through ecosystems is inefficient. At each trophic level, most energy is lost as heat or waste. Only a small fraction—typically around 10%—is converted into biomass and transferred to the next level. This inefficiency limits the number of trophic levels and affects ecosystem structure and food web stability.
1. Secondary Production and Production Efficiency
- Secondary production: energy in food converted to new biomass in consumers
- Example: A caterpillar eats 200 J of plant energy
- 100 J lost as feces
- 67 J used for respiration
- 33 J used for growth
- Production efficiency = (Net secondary production / Assimilation) × 100%
- Caterpillar: 33%
- Birds and mammals: 1–3%
- Fishes: ~10%
- Insects and microbes: up to 40%+
2. Trophic Efficiency
- Trophic efficiency: % of energy transferred to the next trophic level
- Always less than production efficiency
- Accounts for respiration, feces, and unconsumed biomass
- Typical trophic efficiency ≈ 10%
- Example:
- Plants → herbivores: 10%
- Herbivores → carnivores: 10%
- Only ~0.1% of solar energy reaches tertiary consumers
3. Energy and Biomass Pyramids
- Energy pyramid: shows loss at each trophic level
- Wide base (producers), narrow top (predators)
- Biomass pyramid: total dry mass at each level
- Usually bottom-heavy
- Inverted pyramids can occur in aquatic systems
- Example: phytoplankton → rapid turnover supports more zooplankton
4. Real-World Example: Salt Marsh Energy Flow
- John Teal’s study in Georgia salt marsh
- Solar input: 600,000 kcal/m²/year
- Gross primary production: 34,580 kcal
- Net primary production: 6,585 kcal
- Net insect production: 81 kcal
- Detritus loss to ocean: 3,671 kcal
- Shows low energy efficiency and importance of detritus
5. Implications for Humans
- Eating plants is more energy-efficient than consuming meat
- Plant-based food production uses less energy and land
- Understanding trophic energy flow helps with sustainable resource use
In a Nutshell
Only about 10% of the energy at one trophic level moves to the next, limiting food chain length and the abundance of top predators. Most energy is lost as heat or waste. Energy and biomass pyramids reflect this reality, shaping ecosystem dynamics and offering insight into efficient energy use—both ecologically and agriculturally.