Study guide: Food-web energy, cycling matter, and bounded predictions
Combine feeding relationships with quantitative energy models and distinguish matter cycling.
Ideas to explain in your own words
- Follow energy from a food source to its consumer.
- Find a supplied energy-transfer percentage without assuming a universal rate.
- Explain a simplified matter cycle alongside energy flow.
- Separate a plausible pathway effect from a guaranteed population count.
Watch your reasoning
- The arrow tracks energy from the consumed organism to its consumer, so rabbit → hawk fits the stated relationship. The model does not say that hawks eat grasshoppers directly.
- 30/200 = 0.15, or 15%. This is the specified growth-to-growth fraction.
- The arrows track carbon matter. A matter cycle and an energy pathway describe different quantities; population numbers are not supplied.
- The changed grasshopper link reduces one food route. The supplied alternative and missing quantities limit the prediction.
A worked review example
Read the direction of a food web: One route is grass → grasshopper → frog → hawk. Less grasshopper food could reduce the food available to frogs, but the diagram alone cannot tell us exactly how many frogs remain. Calculate a Model Transfer Efficiency: Grass-to-grasshopper efficiency is 15%; grasshopper-to-frog is 20%. Frog growth is 3% of the initial grass-growth energy because 15/500 × 100 = 3%. Use a Carbon-Matter Arrow Key: Air CO₂ → plant carbon compounds → rabbit carbon compounds → air CO₂ is a carbon route in the map. Energy supports the processes and disperses partly as thermal energy; it is not restored by drawing a carbon loop. Make a Conditional Web Prediction: Frogs could have less food if reduced grasshoppers are not replaced by pond insects. That could affect hawks through frogs, but the hawk’s rabbit route remains. No exact population change follows from these arrows alone.
Make a practice plan
- Try the supplied lesson problems without looking at the answers.
- Compare your method with the worked examples and explain any correction.
- Use the new review cases, then complete the transfer task on paper or in your own document.