PCB3044 Principles of Ecology Exam 3 Questions &
Answers | Grade A | 100% Correct - WCU
1. Which model of succession suggests that early colonizers make the
environment less suitable for themselves but more suitable for later species?
A. Facilitation model
B. Tolerance model
C. Inhibition model
D. Random walk model
Answer: A
Explanation: The facilitation model proposes that pioneer species change the environment
in ways that favor the arrival and growth of later successional species.
2. In the context of island biogeography, which type of island is expected to
have the highest species richness?
A. Large and near the mainland
B. Large and far from the mainland
C. Small and near the mainland
D. Small and far from the mainland
Answer: A
Explanation: According to the equilibrium theory of island biogeography, large islands
have lower extinction rates and near islands have higher colonization rates.
,3. What is the term for the total amount of carbon fixed by autotrophs in an
ecosystem?
A. Net Primary Production (NPP)
B. Net Ecosystem Exchange (NEE)
C. Gross Primary Production (GPP)
D. Secondary Production
Answer: C
Explanation: Gross Primary Production represents the total energy captured via
photosynthesis before any is used for respiration.
4. The Intermediate Disturbance Hypothesis suggests that species diversity is
highest when:
A. Disturbances are frequent and intense
B. Disturbances occur at moderate levels
C. Disturbances are rare and low intensity
D. Disturbances are completely eliminated
Answer: B
Explanation: Moderate disturbances prevent competitive exclusion by dominant species
while allowing diverse species to persist.
5. Which process converts atmospheric nitrogen (N2) into a biologically usable
form like ammonia (NH3)?
A. Nitrification
B. Denitrification
C. Ammonification
D. Nitrogen fixation
Answer: D
Explanation: Nitrogen fixation is carried out by specialized bacteria to convert N2 gas into
reactive forms.
, 6. Which of the following is the primary reservoir for phosphorus in the global
phosphorus cycle?
A. The atmosphere
B. Sedimentary rock
C. Ocean water
D. Living biomass
Answer: B
Explanation: Unlike carbon or nitrogen, phosphorus does not have a significant
atmospheric phase; its main reservoir is rock and sediment.
7. In a food web, a ‘keystone species’ is one that:
A. Is the most abundant species in the community
B. Occupies the lowest trophic level
C. Has a disproportionately large effect on its community relative to its abundance
D. Is always a primary producer
Answer: C
Explanation: Keystone species maintain community structure despite having relatively
low biomass or numbers.
8. What happens to the energy that is not transferred from one trophic level to
the next?
A. It is destroyed
B. It is recycled back to the producers
C. It is stored indefinitely in the soil
D. It is lost as heat through metabolic processes
Answer: D
Explanation: Energy transfer is inefficient; most energy is lost as metabolic heat (Second
Law of Thermodynamics).
Answers | Grade A | 100% Correct - WCU
1. Which model of succession suggests that early colonizers make the
environment less suitable for themselves but more suitable for later species?
A. Facilitation model
B. Tolerance model
C. Inhibition model
D. Random walk model
Answer: A
Explanation: The facilitation model proposes that pioneer species change the environment
in ways that favor the arrival and growth of later successional species.
2. In the context of island biogeography, which type of island is expected to
have the highest species richness?
A. Large and near the mainland
B. Large and far from the mainland
C. Small and near the mainland
D. Small and far from the mainland
Answer: A
Explanation: According to the equilibrium theory of island biogeography, large islands
have lower extinction rates and near islands have higher colonization rates.
,3. What is the term for the total amount of carbon fixed by autotrophs in an
ecosystem?
A. Net Primary Production (NPP)
B. Net Ecosystem Exchange (NEE)
C. Gross Primary Production (GPP)
D. Secondary Production
Answer: C
Explanation: Gross Primary Production represents the total energy captured via
photosynthesis before any is used for respiration.
4. The Intermediate Disturbance Hypothesis suggests that species diversity is
highest when:
A. Disturbances are frequent and intense
B. Disturbances occur at moderate levels
C. Disturbances are rare and low intensity
D. Disturbances are completely eliminated
Answer: B
Explanation: Moderate disturbances prevent competitive exclusion by dominant species
while allowing diverse species to persist.
5. Which process converts atmospheric nitrogen (N2) into a biologically usable
form like ammonia (NH3)?
A. Nitrification
B. Denitrification
C. Ammonification
D. Nitrogen fixation
Answer: D
Explanation: Nitrogen fixation is carried out by specialized bacteria to convert N2 gas into
reactive forms.
, 6. Which of the following is the primary reservoir for phosphorus in the global
phosphorus cycle?
A. The atmosphere
B. Sedimentary rock
C. Ocean water
D. Living biomass
Answer: B
Explanation: Unlike carbon or nitrogen, phosphorus does not have a significant
atmospheric phase; its main reservoir is rock and sediment.
7. In a food web, a ‘keystone species’ is one that:
A. Is the most abundant species in the community
B. Occupies the lowest trophic level
C. Has a disproportionately large effect on its community relative to its abundance
D. Is always a primary producer
Answer: C
Explanation: Keystone species maintain community structure despite having relatively
low biomass or numbers.
8. What happens to the energy that is not transferred from one trophic level to
the next?
A. It is destroyed
B. It is recycled back to the producers
C. It is stored indefinitely in the soil
D. It is lost as heat through metabolic processes
Answer: D
Explanation: Energy transfer is inefficient; most energy is lost as metabolic heat (Second
Law of Thermodynamics).
