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AP Biology 7.1 Introduction to Natural Selection- Exam Style questions - FRQ- New Syllabus

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Question

Twenty million years ago the Caribbean Sea and Pacific Ocean were connected, and water flowed freely between the two bodies of water. Many of the same marine species were found in both areas. Over millions of years, the land referred to as the Isthmus of Panama formed, eventually closing off the connection between the Caribbean Sea and Pacific Ocean and creating two separate bodies of water. The ecology of these two marine habitats was dramatically altered by this land formation. The warmer Caribbean water could no longer flow west, so the Pacific water cooled and became more nutrient-rich, while the Caribbean water became warmer.
(A) Describe the genetic evidence that evolution is occurring in a population.
(B) Explain how the isolation of marine species by the formation of a land barrier can lead to divergent evolution of those species.
(C) The formation of the Isthmus of Panama connected two continents, North America and South America. Many North American land animal species migrated to South America after the formation of the isthmus and occupied similar niches as South American species. Predict the effect the formation of the isthmus had on resource availability for South American species.
(D) Justify your prediction in part \( \mathrm{C} \).

Most-appropriate topic codes (AP Biology 2025):

• Topic 7.6 — Evidence of Evolution: Genetic evidence such as changes in allele frequencies indicates evolution in populations — part (A)
• Topic 7.10 — Speciation: Geographic isolation, reduced gene flow, and divergent evolution after formation of a land barrier — part (B)
• Topic 7.1 — Introduction to Natural Selection: Competition for limited resources affects survival and resource availability when new species enter similar niches — parts (C), (D)
• Science Practice 6 — Argumentation: Making a prediction and justifying it with ecological and evolutionary reasoning — parts (C), (D)
▶️ Answer/Explanation

(A)
There are changes in allele or gene frequencies.
There are heritable changes in phenotypes.
Summary: if inherited traits or allele frequencies change over generations, evolution is occurring in the population.

(B)
Selective pressures could result in different allele or gene frequencies.
The land barrier results in reproductive isolation, lack of gene flow, or allopatric speciation.
Different environmental conditions or pressures select for different alleles, genotypes, or phenotypes.
Summary: once the populations are separated, they experience different environments and evolve independently.

(C)
Resource availability would have decreased.
Because many North American species moved into South America and occupied similar niches, fewer resources would be available to the original South American species.

(D)
More species would now be competing for the same resources, resulting in fewer resources for each individual.
This increased competition would reduce the amount of food, space, or other resources available to South American species.

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