PCB3044 Principles of Ecology Exam 3 2026 – UCF
1. Which of the following terms describes the number of species in a
community?
A. Species evenness
B. Species dominance
C. Species diversity
D. Species richness
Answer: D
Rationale: Species richness is the count of the total number of different species present in
a community.
2. In the Shannon-Wiener Diversity Index (H’), what does the ‘pi’ represent?
A. The proportion of the total individuals belonging to the i-th species
B. The biomass of the species
C. The total number of species
D. The log of the species richness
Answer: A
Rationale: In diversity indices, pi represents the relative abundance or proportion of
individuals belonging to a specific species.
,3. Which concept suggests that communities are predictable associations of
species that reach a stable equilibrium?
A. Individualistic concept
B. Neutral theory
C. Organismic concept
D. Stochastic model
Answer: C
Rationale: The organismic concept, championed by Clements, views communities as
integrated units that function like super-organisms reaching a climax state.
4. A ‘keystone species’ is best defined as:
A. A species that is the most abundant in a community
B. A species that has a large effect on community structure despite low abundance
C. A species that provides the most biomass in an ecosystem
D. The first species to colonize a new habitat
Answer: B
Rationale: Keystone species exert a disproportionate influence on their community
relative to their actual population size or biomass.
5. Which type of succession occurs on a site that has never supported a
biological community?
A. Secondary succession
B. Primary succession
C. Cyclic succession
D. Autogenic succession
Answer: B
Rationale: Primary succession begins on substrates that lack soil and have not previously
been inhabited, such as lava flows or retreated glaciers.
, 6. According to the Intermediate Disturbance Hypothesis, diversity is highest
when:
A. Disturbance is at a moderate level
B. Disturbance is very rare
C. Disturbance is very frequent
D. There is no disturbance at all
Answer: A
Rationale: Moderate disturbance prevents competitive exclusion by dominant species
while allowing pioneer species to coexist, maximizing diversity.
7. In a food web, a ‘trophic cascade’ occurs when:
A. Primary producers increase in biomass due to more sunlight
B. Energy is lost as heat at every level
C. Predators limit the density/behavior of their prey, thereby enhancing survival of the next lower trophic
level
D. Nutrients cycle between the biotic and abiotic components
Answer: C
Rationale: A trophic cascade is a top-down effect where changes at the top of the food
chain impact lower levels, often alternating in effect.
8. What is the primary difference between Gross Primary Production (GPP) and
Net Primary Production (NPP)?
A. NPP includes decomposer respiration
B. GPP is only the energy stored in roots
C. NPP is GPP minus the energy used by producers for respiration
D. There is no difference between them
Answer: C
Rationale: NPP represents the energy remaining after plants have met their own
respiratory needs (NPP = GPP - Ra).
1. Which of the following terms describes the number of species in a
community?
A. Species evenness
B. Species dominance
C. Species diversity
D. Species richness
Answer: D
Rationale: Species richness is the count of the total number of different species present in
a community.
2. In the Shannon-Wiener Diversity Index (H’), what does the ‘pi’ represent?
A. The proportion of the total individuals belonging to the i-th species
B. The biomass of the species
C. The total number of species
D. The log of the species richness
Answer: A
Rationale: In diversity indices, pi represents the relative abundance or proportion of
individuals belonging to a specific species.
,3. Which concept suggests that communities are predictable associations of
species that reach a stable equilibrium?
A. Individualistic concept
B. Neutral theory
C. Organismic concept
D. Stochastic model
Answer: C
Rationale: The organismic concept, championed by Clements, views communities as
integrated units that function like super-organisms reaching a climax state.
4. A ‘keystone species’ is best defined as:
A. A species that is the most abundant in a community
B. A species that has a large effect on community structure despite low abundance
C. A species that provides the most biomass in an ecosystem
D. The first species to colonize a new habitat
Answer: B
Rationale: Keystone species exert a disproportionate influence on their community
relative to their actual population size or biomass.
5. Which type of succession occurs on a site that has never supported a
biological community?
A. Secondary succession
B. Primary succession
C. Cyclic succession
D. Autogenic succession
Answer: B
Rationale: Primary succession begins on substrates that lack soil and have not previously
been inhabited, such as lava flows or retreated glaciers.
, 6. According to the Intermediate Disturbance Hypothesis, diversity is highest
when:
A. Disturbance is at a moderate level
B. Disturbance is very rare
C. Disturbance is very frequent
D. There is no disturbance at all
Answer: A
Rationale: Moderate disturbance prevents competitive exclusion by dominant species
while allowing pioneer species to coexist, maximizing diversity.
7. In a food web, a ‘trophic cascade’ occurs when:
A. Primary producers increase in biomass due to more sunlight
B. Energy is lost as heat at every level
C. Predators limit the density/behavior of their prey, thereby enhancing survival of the next lower trophic
level
D. Nutrients cycle between the biotic and abiotic components
Answer: C
Rationale: A trophic cascade is a top-down effect where changes at the top of the food
chain impact lower levels, often alternating in effect.
8. What is the primary difference between Gross Primary Production (GPP) and
Net Primary Production (NPP)?
A. NPP includes decomposer respiration
B. GPP is only the energy stored in roots
C. NPP is GPP minus the energy used by producers for respiration
D. There is no difference between them
Answer: C
Rationale: NPP represents the energy remaining after plants have met their own
respiratory needs (NPP = GPP - Ra).
