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AP Biology 7.2: Natural Selection and Fitness

Practise AP Biology 7.2 questions by linking phenotypic and molecular variation with environmental selection pressures, fitness and population change.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • explain why natural selection acts on phenotypic and genetic variation within populations
  • connect molecular or enzyme variation with organismal performance, survival and reproductive success
  • predict directional, stabilizing or disruptive changes in trait distributions under altered selection pressures
  • interpret controls, null hypotheses, means, SEM and confidence intervals in fitness and selection experiments

Covered syllabus points

7.2.A—Describe the importance of phenotypic variation in a population7.2.B—Explain how variation in molecules within cells connects to the fitness of an organism

7.2 Natural Selection question 1

[Maximum number: 2]

In 1981 a single immature male Geospiza conirostris finch flew more than 100 kilometers from the Galápagos island of Española to the Galápagos island of Daphne Major, where no G. conirostris finches were living. The immigrant finch bred with a female G. fortis, a species of finch common on Daphne Major. The F1\mathrm{F}_{1} finches and later generations interbred only within their lineage. By 2012 scientists counted 23 individuals, including eight breeding pairs, within this hybrid lineage on Daphne Major. The hybrid lineage became known as Big Bird.

Birds with different beak shapes and sizes eat different types of food. The dimensions of the Big Bird beaks relative to the beaks of the major competitor finch species on Daphne Major are shown in Figure 1.

Figure 1. The dimensions of the beaks of the Big Bird lineage and of its major competitor species in 2012 on Daphne Major. Each symbol represents the beak dimensions of a single bird.

Figure 1. The dimensions of the beaks of the Big Bird lineage and of its major competitor species in 2012 on Daphne Major. Each symbol represents the beak dimensions of a single bird.

Question (a)

(a)

Based on the data in Figure 1, explain why the Big Bird population has been able to survive and reproduce on Daphne Major.

[ 1 ]

Question (b)

(b)

A virus infects and kills all G. magnirostris on Daphne Major but does not affect the other finch species. Assuming food type and availability stay the same, predict the most likely change in the beak phenotype of the Big Bird population after six more generations.

[ 1 ]

7.2 Natural Selection question 2

[Maximum number: 1]

Butterflies of the genus Colias live in the
Rocky Mountains, where they experience a wide
range of temperatures. Different variants of a
particular glycolytic enzyme in the flight muscles
are optimally active at different temperatures.
Within the same population, some individual
butterflies fly most effectively at 29°C, while
others fly most effectively at 40°C. Still others
can be equally active at both temperatures.
Which of the following claims is most consistent
with the observed butterfly behavior?

A

Butterflies that express two variants of the
enzyme are active over a greater range of
temperature.

B

Butterflies that are active over a wide range
of temperatures produce greater amounts of
the enzyme.

C

Temperature has little effect on the activity of
butterflies.

D

Butterflies that are active at warmer
temperatures produce more offspring.

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