CLEP Biology Ecology & Evolutionary Processes 4 — Questions and Answers
Question 1: Which type of selection favors individuals at both extremes of a phenotypic trait and eliminates intermediate phenotypes?
- Stabilizing selection
- Directional selection
- Disruptive selection (Correct answer)
- Sexual selection
Correct answer: Disruptive selection
Disruptive (diversifying) selection favors phenotypic extremes over intermediate forms, potentially splitting a population into two distinct groups.
Question 2: A keystone species is best described as a species that:
- Is the most abundant in its ecosystem
- Has a disproportionately large effect on its ecosystem relative to its biomass (Correct answer)
- Occupies the top trophic level
- Is an invasive species that dominates the community
Correct answer: Has a disproportionately large effect on its ecosystem relative to its biomass
A keystone species has an outsized ecological impact — its removal causes dramatic changes in community structure, far greater than expected from its numbers alone.
Question 3: Which reproductive isolating mechanism prevents two species from mating because they breed at different times of year?
- Mechanical isolation
- Temporal isolation (Correct answer)
- Behavioral isolation
- Gametic isolation
Correct answer: Temporal isolation
Temporal isolation is a prezygotic barrier where species breed at different times (seasons, times of day), preventing interbreeding even if they share the same habitat.
Question 4: The r-selected reproductive strategy is characterized by:
- Few offspring with high parental investment
- Many offspring with little parental investment (Correct answer)
- Long lifespan and slow maturation
- Strong competition for resources
Correct answer: Many offspring with little parental investment
r-selected species (r-strategists) produce large numbers of offspring with minimal parental care, maximizing reproductive rate rather than offspring survival.
Question 5: Carbon is returned from the biotic community to the atmosphere primarily through:
- Nitrogen fixation
- Photosynthesis
- Cellular respiration and decomposition (Correct answer)
- Transpiration
Correct answer: Cellular respiration and decomposition
Cellular respiration by all organisms and decomposition by decomposers release CO₂ back into the atmosphere, completing the carbon cycle.
Question 6: Which type of population growth occurs when resources are unlimited and the population increases at a constant per-capita rate?
- Logistic growth
- Exponential growth (Correct answer)
- Density-dependent growth
- Carrying capacity growth
Correct answer: Exponential growth
Exponential (geometric) growth produces a J-shaped curve and occurs when birth rates exceed death rates with no resource limitations.
Question 7: Homologous structures in different species provide evidence for evolution because they suggest:
- Independent evolution in similar environments
- Descent from a common ancestor (Correct answer)
- Identical functions in all species
- Random mutation in isolated populations
Correct answer: Descent from a common ancestor
Homologous structures share anatomical origin from a common ancestor, indicating shared evolutionary history even if the structures now serve different functions.
CLEP Biology Ecology & Evolutionary Processes 4
Which type of selection favors individuals at both extremes of a phenotypic trait and eliminates intermediate phenotypes?