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AP Biology — Unit 7 — Natural Selection: Types & Fitness — Drill 28

Drill 28 ·

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About This Drill

AP Biology — Unit 7 — Natural Selection: Types & Fitness — Drill 28 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

Practice identifying and interpreting directional natural selection with this AP Biology drill. You will analyze multi-year population data on body mass in a small mammal population, distinguish directional selection from other modes of selection, evaluate evidence against a genetic drift hypothesis, design an experiment to separate genetic change from phenotypic plasticity, and predict long-term outcomes of sustained directional selection.

Passage

Researchers monitored a population of meadow voles (Microtus pennsylvanicus) in a grassland habitat over four consecutive years. The site supported an established population of red-tailed hawks, which are visual predators that preferentially capture smaller, more easily detected prey. Researchers recorded the mean body mass and standard deviation of body mass for adult voles captured at the end of each breeding season. All individuals were weighed, tagged, and released. Sample sizes varied slightly due to natural fluctuation in population size. Observed body mass data (adult voles at end of breeding season): Year 1 — N=120: Mean body mass = 22.4 g, Standard deviation = 3.2 g Year 2 — N=118: Mean body mass = 23.1 g, Standard deviation = 3.0 g Year 3 — N=121: Mean body mass = 23.9 g, Standard deviation = 2.9 g Year 4 — N=119: Mean body mass = 24.8 g, Standard deviation = 2.7 g Body mass in this population is a heritable trait with a heritability estimate of approximately 0.45.

Questions in This Drill

  1. Based on the data, which of the following best describes the pattern of change in body mass across the four years?
  2. The passage states that hawks preferentially capture smaller voles. Which of the following best explains how this predation pattern could produce the observed shift in mean body mass over four years?
  3. A researcher proposes that the observed increase in mean body mass resulted from genetic drift rather than natural selection. Which of the following observations from the data provides the strongest evidence against the genetic drift hypothesis?
  4. A colleague suggests that the shift in mean body mass may reflect phenotypic plasticity — individual voles growing larger in response to reduced competition for food — rather than heritable genetic change. Which of the following experimental designs would best distinguish between heritable genetic change and phenotypic plasticity as explanations for the observed shift?
  5. Assume the increase in mean body mass reflects genuine heritable genetic change driven by directional selection. If hawk predation continues at the same intensity for many additional generations, which of the following best describes the most likely long-term outcome for the vole population?