Web of Life

Question 3B: Disruption Scenario: If pesticide runoff kills 95% of the Mayfly Nymphs, describe one direct impact on Bullfrogs and one indirect impact on Phytoplankton:

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Part 4: Energy Pyramid Calculations (10% Rule)

(20 Points)

Ecological Scenario: In an East African savanna grassland, autotrophic grasses capture sunlight to generate \(65,000 \text{ kcal/m}^2/\text{year}\) of net primary productivity.

Fill In Available Energy

Apex: Lion

__________ kcal

2° Cons: Hyena

__________ kcal

1° Cons: Zebra

__________ kcal

Producers: Savanna Grass

65,000 kcal/m²/yr

4A. Calculate energy transferred to Zebras (Level 2):

Show work:

Ans: _______ kcal

4B. Calculate energy transferred to Lions (Level 4):

Show work:

Ans: _______ kcal

4C. Explain where the remaining 90% of energy went:

Task 4D: Ecological Reasoning: Why can an African grassland sustain thousands of herbivore zebras, but only a small pride of apex lions? Use the 10% rule and biomass availability in your explanation.

ECOSYSTEM DYNAMICS • PRACTICE ACTIVITIES PAGE 2 OF 2 • END OF ACTIVITY

Question 3A Key (4 Pts)

Acceptable Identifications:
• Bullfrog: Consumes Mayfly Nymphs (1° consumer) or Pond Snails.
• Largemouth Bass: Consumes Mayfly Nymphs or Minnows.
• Water Snake: Consumes Bullfrogs or Minnows.

Question 3B Key (Cascade) (6 Pts)

• Impact on Bullfrogs (Direct): Population drops due to severe loss of prey, or frogs intensify predation on snails.
• Impact on Phytoplankton (Indirect): Mayflies graze on phytoplankton. With mayflies gone, phytoplankton may experience an algal bloom from reduced grazing pressure.

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Part 4: Energy Pyramid Calculations (10% Rule)

20 Pts Total

Calculated Pyramid Values (5 Pts)

Apex: Lion

65 kcal/m²/yr

2° Cons: Hyena

650 kcal/m²/yr

1° Cons: Zebra

6,500 kcal/m²/yr

Producers: Grasses

65,000 kcal/m²/yr

4A. Work for Zebras (Level 2): (4 Pts)

\(65,000 \times 0.10 = \mathbf{6,500 \text{ kcal/m}^2/\text{yr}}\)

4B. Work for Lions (Level 4): (5 Pts)

\(6,500 \times 0.10 = 650\) (Hyenas) → \(650 \times 0.10 = \mathbf{65 \text{ kcal/m}^2/\text{yr}}\)

4C. Where 90% Energy Goes: (3 Pts)

Lost as thermal metabolic heat via cellular respiration, consumed in daily life processes (movement, foraging), and unabsorbed in waste/feces.

Task 4D Synthesis Rubric & Exemplar (3 Pts)

Exemplar: With 90% of energy dissipating at each level, only 0.1% (\(65 \text{ kcal}\)) of the initial \(65,000 \text{ kcal}\) captured by plants reaches apex lions. Because apex predators require huge caloric intakes to sustain their high metabolic demands, the available energetic biomass at Level 4 can only energetically sustain a tiny population, whereas Level 2 retains 100 times more usable energy (\(6,500 \text{ kcal}\)) to support thousands of zebras.

ECOSYSTEM DYNAMICS • TEACHER ANSWER KEY PAGE 2 OF 2 • END OF KEY