Question 79·200 Super-Hard SAT Reading Questions·Information and Ideas
Conservation biologist Leila Moreno proposes that chains of small, shallow pools can reconnect tree-frog populations separated by dry farmland. Moreno argues that these pools function mainly as temporary refuges that divide a long overland journey into shorter ones, not as additional breeding sites. She further predicts that this corridor effect should be strongest when surrounding soil is dry, because crossing long stretches then carries greater dehydration risk.
Researchers built outdoor enclosures, each with a deep pond at either end and six shallow pools of equal total area. In some enclosures, the shallow pools were evenly spaced between the deep ponds; in others, they were clustered near one deep pond. The researchers kept the soil damp in half the enclosures and dry in the rest. After releasing tagged adult frogs into one deep pond, they tracked the frogs’ movements and counted juveniles emerging from the shallow pools.
Which finding from the study, if true, would most strongly support Moreno’s hypothesis?
For a command-of-evidence question about a scientific hypothesis, separate the hypothesis into its predicted outcome, mechanism, condition, and rejected alternative. Then compare the choices for evidentiary strength: direct behavioral or causal evidence is generally stronger than a correlation that could result from another feature of the study.
Hints
Break apart the hypothesis
Identify the proposed mechanism, the environmental condition under which the effect should be strongest, and the alternative function the researcher rejects.
Assess evidence strength
Distinguish evidence that directly records the predicted sequence of behavior from an association that could arise because successful frogs travel farther.
Evaluate every component
Prefer the finding that addresses the mechanism, the comparison between soil conditions, and the breeding-site explanation most directly.
Step-by-step Explanation
Identify the hypothesis’s components
Moreno predicts that evenly distributed shallow pools help frogs cross farmland by serving as temporary refuges, that this corridor benefit is strongest on dry soil, and that the pools are not functioning primarily as breeding sites.
Look for direct evidence of the mechanism
Choice D reports that motion records showed frogs pausing in a sequence of evenly spaced pools before reaching the opposite pond. The timing and sequence directly support the proposed mechanism: the pools divide the journey into shorter stages.
Check the environmental and breeding predictions
Choice D also reports that the spacing advantage was larger on dry soil than on damp soil and that juvenile production was low in every condition. These results support both the predicted effect of dehydration risk and the claim that breeding is not the pools’ main function.
Compare the strongest alternative
Choice C reports the predicted soil-dependent spacing advantage and low juvenile production, and it associates greater pool entry with crossing success. However, frogs that travel farther may simply have more opportunities to enter pools, so that association does not establish that sequential refuge use helped them complete the crossing. Choice D supplies more direct behavioral evidence.