AP® BIOLOGY

AP

®

BIOLOGY

2015 SCORING GUIDELINES

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Question 6

In an

attempt to rescue a small isolated population of snakes from decline, a few male snakes from several

larger populations of the same species were introduced into the population in 1992. The snakes reproduce

sexually, and there are abundant resources in the environment.

The figure below shows the results of a study of the snake population, both before and after the

introduction of the outside males. In the study, the numbers of captured snakes is an indication of the

overall population size.

(a) D

escribe ONE characteristic of the original population that may have led to the population's

decline in size between 1989 and 1993.

Description (1 point)

• Lacked genetic diversity/variation

• Was an aged/post-reproductive population/not enough young snakes

• Had unfavorable sex ratio/too few males

• Possessed a harmful mutation/disease

(b) Propose ONE reason that the introduction of the outside males rescued the snake population

from decline.

Proposal (1 point)

• Increased genetic diversity in the population

• Increased reproductive success

• Established beneficial sex ratio/sufficient proportion of males for reproduction

• Introduced resistance to disease that was affecting the original population

(c) Describe how the data support the statement that there are abundant resources in the

environment.

Description (1 point)

• Population can/does grow

• If resources are limited population would not grow

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AP

®

BIOLOGY

2015 SCORING COMMENTARY

Question 6

Question 6 was written to the following Learning Objectives in the AP

®

Biology Curriculum Framework: 1.5,

3.28, 4.19, and 4.26.

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This question focused on possible evolutionary mechanisms underlying changes in population size. Students

were presented with a graph representing changes in the size of a small, isolated population of snakes before

and after the introduction of outside males. Students were asked to use the data to describe one

characteristic of the original population that led to the population decline. Students were then asked to

propose a reason to explain how the introduction of snakes from an outside population rescued the

population from decline. Finally, students were asked to use the data to support the claim that the snake

population inhabited an area with abundant resources over the entire course of the study.

Sample: 6A

Score: 3

The response earned 1 point in part (a) for describing that limited genetic variation of the original population

may have led to the decline of the population.

The response earned 1 point in part (b) for proposing that the introduced males increased genetic variation

and could have rescued the population from decline.

The response earned 1 point in part (c) for supporting the presence of abundant resources by describing that

the population is growing.

Sample: 6B

Score: 2

The re

sponse earned 1 point in part (a) for describing that the original population may have been very

unbalanced in terms of gender and had significantly fewer males.

The re

sponse earned 1 point in part (b) for proposing that the introduced males balanced out the male-to-

female ratio and could have rescued the population from decline.

Sample: 6C

Score: 1

The r

esponse earned 1 point in part (b) for proposing that the introduction of outside males could have

introduced favorable alleles into the population.

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