Predator Loss and Ecosystem Effects

Question 1

A patch of phytoplankton holds 12,000 kilocalories of energy. Zooplankton eat the phytoplankton, and small fish eat the zooplankton. Using the 10% rule for each trophic transfer, how many kilocalories of energy are available to the small fish?

Accepted Answer

120 kcal

Answer

1,200 kcal

Answer

12 kcal

Answer

240 kcal

Question 2

Scientists compared two management plans for a coastal fishery that catches sardines, sharks, and also supports a resident humpback whale population. Plan A: Sets a catch limit only for sardines and allows unlimited shark harvest. Plan B: Sets catch limits for sardines, reduces shark harvest by 80%, and protects key feeding areas for the whales. After five years, the fishery using Plan B shows a 25% increase in sardine biomass and better overall ecosystem health, while the fishery using Plan A shows a 15% decline in sardine biomass and a 70% drop in shark numbers. Which statement best explains why Plan B (the ecosystem‑based plan) is more effective?

Accepted Answer

Protecting sharks and whales helps keep the natural food‑web balance, allowing sardine populations to rebound; this shows that managing the whole ecosystem works better than focusing only on sardines.

Answer

Limiting shark catch directly increases the amount of sardines fishermen can harvest, so the plan is better because it yields more fish.

Answer

The plan works because it reduces competition among fishermen for sardines, not because of any ecological effect.

Answer

Plan B is more effective simply because it reduces overall fishing effort, regardless of which species are protected.

Question 3

Which of the following sequences best describes what happens in a kelp forest when sea otters are removed from the ecosystem?

Accepted Answer

Sea otters disappear → sea urchin numbers rise because fewer are eaten → many urchins eat kelp → kelp forest disappears.

Answer

Sea otters disappear → kelp grows rapidly because otters no longer eat kelp → more fish hide in kelp → kelp forest thrives.

Answer

Sea otters disappear → sea urchin numbers drop because they compete with otters → kelp is protected → kelp forest expands.

Answer

Sea otters disappear → sharks increase because they have fewer prey → sharks eat fish that protect kelp → kelp forest shrinks.

Try three questions

A patch of phytoplankton holds 12,000 kilocalories of energy. Zooplankton eat the phytoplankton, and small fish eat the zooplankton. Using the 10% rule for each trophic transfer, how many kilocalories of energy are available to the small fish?

Which of the following sequences best describes what happens in a kelp forest when sea otters are removed from the ecosystem?

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