PCB 3044 | PCB3044 Final Exam: Principles of
Ecology - University of Central Florida Updated
and Latest Questions and Correct Answers with
Rationale
1. Two species of seed-eating finches exhibit identical beak sizes when living on separate
islands, but significantly different beak sizes when they coexist on the same island. What
ecological phenomenon does this illustrate?
A. Batesian mimicry
B. Competitive exclusion
C. Character displacement
D. Commensalism
Correct Answer: C
Expert Explanation: The correct answer is character displacement because it involves
morphological divergence in sympatric populations. This evolutionary process reduces
niche overlap and lessens competition between two species living together. Batesian
mimicry is incorrect because it involves a palatable species imitating a toxic one for
protection. Competitive exclusion is wrong as it implies one species would be entirely
driven to extinction by the other. This scenario illustrates how natural selection drives
phenotypic variation to facilitate coexistence in shared habitats.
2. The reintroduction of wolves to Yellowstone National Park led to a reduction in elk
populations, which subsequently allowed willow and aspen trees to recover. This is an
example of:
A. Bottom-up control
B. Trophic cascade
C. Eutrophication
D. Successional climax
Correct Answer: B
Expert Explanation: The correct answer is a trophic cascade because the presence of
wolves indirectly benefits plants by controlling herbivore populations. This top-down
regulation impacts multiple levels of the food web within an ecosystem. Bottom-up control
is incorrect because it implies primary producers limit the consumer population levels.
Eutrophication is wrong because it describes nutrient enrichment in water bodies rather
than predator-prey dynamics. Understanding these interactions helps ecologists manage
entire ecosystems effectively by recognizing the importance of apex predators.
,3. According to the Theory of Island Biogeography, which of the following islands would likely
have the highest species richness?
A. A small island far from the mainland
B. A large island near the mainland
C. A small island near the mainland
D. A large island far from the mainland
Correct Answer: B
Expert Explanation: The correct answer is a large island near the mainland because size
and proximity maximize immigration while minimizing extinction. Larger islands provide
more niches and resources, which significantly reduces the probability of species
extinction. Proximity to the mainland increases the rate of new species arriving via
immigration. A small island far from the mainland is incorrect because it suffers from both
low immigration and high extinction rates. This theory is fundamental for designing
wildlife corridors and protected areas in conservation biology.
4. A forest ecosystem has a Gross Primary Production (GPP) of 2000 g/m²/yr and the plants
lose 1200 g/m²/yr through autotrophic respiration (Ra). What is the Net Primary Production
(NPP)?
A. 3200 g/m²/yr
B. 2000 g/m²/yr
C. 800 g/m²/yr
D. 8000 g/m²/yr
Correct Answer: C
Expert Explanation: The correct answer is 800 g/m²/yr, calculated by subtracting
autotrophic respiration from the Gross Primary Production. NPP represents the actual
energy available to the heterotrophs in the ecosystem. Adding the values is incorrect
because respiration represents energy lost to the system’s biomass. Gross Primary
Production alone is wrong as it does not account for the metabolic needs of the plants
themselves. This calculation is crucial for understanding the energy budget and carbon
sequestration capacity of various biomes.
5. A population of rare orchids exhibits a decrease in per capita growth rate as the population
density drops to very low levels. This phenomenon is known as:
A. Logistic growth
B. Intraspecific competition
C. The Allee effect
D. The rescue effect
, Correct Answer: C
Expert Explanation: The correct answer is the Allee effect because it describes a positive
correlation between population density and individual fitness at low numbers. This often
occurs due to difficulties in finding mates or a breakdown of social structures in small
groups. Intraspecific competition is incorrect because it usually reduces growth rates as
density increases, not decreases. Logistic growth is wrong because it assumes the growth
rate declines as the population approaches the carrying capacity. Recognizing this effect is
vital for the conservation of endangered species with very small remaining populations.
6. A marine invertebrate produces thousands of eggs but provides no parental care, resulting
in extremely high mortality among larvae. Which type of survivorship curve does this
represent?
A. Type I
B. Type II
C. Type IV
D. Type III
Correct Answer: D
Expert Explanation: The correct answer is Type III because it represents species with
very high early-life mortality followed by high survival for the few that reach adulthood.
These species typically follow an r-selection strategy, producing many offspring to ensure
some survive. Type I is incorrect because it describes species like humans with high
survival throughout most of their life span. Type II is wrong as it implies a constant
mortality rate regardless of the age of the individuals. This curve helps ecologists predict
how populations will respond to environmental changes affecting specific age classes.
7. In the nitrogen cycle, which process converts nitrate (NO₃⁻) back into atmospheric nitrogen
gas (N₂)?
A. Nitrogen fixation
B. Denitrification
C. Nitrification
D. Ammonification
Correct Answer: B
Expert Explanation: The correct answer is denitrification, a process typically performed
by bacteria in anaerobic environments like wetlands or deep soils. This step is essential for
returning nitrogen to the atmosphere and completing the global nitrogen cycle. Nitrogen
fixation is incorrect because it converts N2 gas into reactive ammonia for plant use.
Nitrification is wrong because it converts ammonium into nitrites and then into nitrates.
Ecology - University of Central Florida Updated
and Latest Questions and Correct Answers with
Rationale
1. Two species of seed-eating finches exhibit identical beak sizes when living on separate
islands, but significantly different beak sizes when they coexist on the same island. What
ecological phenomenon does this illustrate?
A. Batesian mimicry
B. Competitive exclusion
C. Character displacement
D. Commensalism
Correct Answer: C
Expert Explanation: The correct answer is character displacement because it involves
morphological divergence in sympatric populations. This evolutionary process reduces
niche overlap and lessens competition between two species living together. Batesian
mimicry is incorrect because it involves a palatable species imitating a toxic one for
protection. Competitive exclusion is wrong as it implies one species would be entirely
driven to extinction by the other. This scenario illustrates how natural selection drives
phenotypic variation to facilitate coexistence in shared habitats.
2. The reintroduction of wolves to Yellowstone National Park led to a reduction in elk
populations, which subsequently allowed willow and aspen trees to recover. This is an
example of:
A. Bottom-up control
B. Trophic cascade
C. Eutrophication
D. Successional climax
Correct Answer: B
Expert Explanation: The correct answer is a trophic cascade because the presence of
wolves indirectly benefits plants by controlling herbivore populations. This top-down
regulation impacts multiple levels of the food web within an ecosystem. Bottom-up control
is incorrect because it implies primary producers limit the consumer population levels.
Eutrophication is wrong because it describes nutrient enrichment in water bodies rather
than predator-prey dynamics. Understanding these interactions helps ecologists manage
entire ecosystems effectively by recognizing the importance of apex predators.
,3. According to the Theory of Island Biogeography, which of the following islands would likely
have the highest species richness?
A. A small island far from the mainland
B. A large island near the mainland
C. A small island near the mainland
D. A large island far from the mainland
Correct Answer: B
Expert Explanation: The correct answer is a large island near the mainland because size
and proximity maximize immigration while minimizing extinction. Larger islands provide
more niches and resources, which significantly reduces the probability of species
extinction. Proximity to the mainland increases the rate of new species arriving via
immigration. A small island far from the mainland is incorrect because it suffers from both
low immigration and high extinction rates. This theory is fundamental for designing
wildlife corridors and protected areas in conservation biology.
4. A forest ecosystem has a Gross Primary Production (GPP) of 2000 g/m²/yr and the plants
lose 1200 g/m²/yr through autotrophic respiration (Ra). What is the Net Primary Production
(NPP)?
A. 3200 g/m²/yr
B. 2000 g/m²/yr
C. 800 g/m²/yr
D. 8000 g/m²/yr
Correct Answer: C
Expert Explanation: The correct answer is 800 g/m²/yr, calculated by subtracting
autotrophic respiration from the Gross Primary Production. NPP represents the actual
energy available to the heterotrophs in the ecosystem. Adding the values is incorrect
because respiration represents energy lost to the system’s biomass. Gross Primary
Production alone is wrong as it does not account for the metabolic needs of the plants
themselves. This calculation is crucial for understanding the energy budget and carbon
sequestration capacity of various biomes.
5. A population of rare orchids exhibits a decrease in per capita growth rate as the population
density drops to very low levels. This phenomenon is known as:
A. Logistic growth
B. Intraspecific competition
C. The Allee effect
D. The rescue effect
, Correct Answer: C
Expert Explanation: The correct answer is the Allee effect because it describes a positive
correlation between population density and individual fitness at low numbers. This often
occurs due to difficulties in finding mates or a breakdown of social structures in small
groups. Intraspecific competition is incorrect because it usually reduces growth rates as
density increases, not decreases. Logistic growth is wrong because it assumes the growth
rate declines as the population approaches the carrying capacity. Recognizing this effect is
vital for the conservation of endangered species with very small remaining populations.
6. A marine invertebrate produces thousands of eggs but provides no parental care, resulting
in extremely high mortality among larvae. Which type of survivorship curve does this
represent?
A. Type I
B. Type II
C. Type IV
D. Type III
Correct Answer: D
Expert Explanation: The correct answer is Type III because it represents species with
very high early-life mortality followed by high survival for the few that reach adulthood.
These species typically follow an r-selection strategy, producing many offspring to ensure
some survive. Type I is incorrect because it describes species like humans with high
survival throughout most of their life span. Type II is wrong as it implies a constant
mortality rate regardless of the age of the individuals. This curve helps ecologists predict
how populations will respond to environmental changes affecting specific age classes.
7. In the nitrogen cycle, which process converts nitrate (NO₃⁻) back into atmospheric nitrogen
gas (N₂)?
A. Nitrogen fixation
B. Denitrification
C. Nitrification
D. Ammonification
Correct Answer: B
Expert Explanation: The correct answer is denitrification, a process typically performed
by bacteria in anaerobic environments like wetlands or deep soils. This step is essential for
returning nitrogen to the atmosphere and completing the global nitrogen cycle. Nitrogen
fixation is incorrect because it converts N2 gas into reactive ammonia for plant use.
Nitrification is wrong because it converts ammonium into nitrites and then into nitrates.
