Question 21·Hard·Command of Evidence
Prairie dogs produce rapid alarm calls when they notice a potential threat. Some researchers propose that experience affects how precisely prairie dogs adjust their alarm-calling rate to different kinds of threats: adults, having encountered more threats, may vary their calling more strongly from one threat type to another, whereas juveniles may respond more uniformly.
A student reviewing the data in the graph claims that the data support the researchers’ proposal because ____. Which choice most effectively uses data from the graph to complete the student's claim?
For graph-based command-of-evidence questions, first identify what kind of relationship the claim must support (here, greater variation across threat types for adults). Then do the relevant within-group comparisons (adult bars across categories vs. juvenile bars across categories) and choose the option that states that comparison accurately without switching comparisons or changing what the claim is trying to prove.
Hints
Match the claim to the researchers’ proposal
The blank should provide evidence that adults’ call rates change more across threat types than juveniles’ do.
Use a within-group comparison
For each age group, compare the hawk bar to the coyote bar and see which group shows the bigger change.
Prefer the choice that uses the most relevant comparison
A statement can be true but still not support the proposal about adults being more variable across threat types.
Step-by-step Explanation
Restate what the student is trying to support
The student claims the graph supports the researchers’ proposal that adults vary their alarm-calling more by threat type than juveniles do.
Compare hawks vs. coyotes within each age group
From the graph:
- Adults: about 12 calls/min for hawks and about 8 calls/min for coyotes (a difference of about 4).
- Juveniles: about 9 calls/min for hawks and about 9 calls/min for coyotes (a difference of about 0).
Choose the option that matches that evidence
Therefore, the best completion is: adults vary their calling rate more between hawks and coyotes than juveniles do: adults call about 12 times per minute for hawks but about 8 for coyotes, while juveniles call about 9 for both