Digital SATReading and Writing: Information and IdeasHard
A team of ecological researchers is studying the population dynamics of a specific species of migratory bird. They observe that in years with unusually cold springs, the birds' breeding success significantly declines due to a lack of insect prey. However, the overall population size of the migratory bird species does not show a corresponding sharp decline in the subsequent year. Which of the following, if true, would best explain the discrepancy between reduced breeding success and stable population size?
- AThe cold springs also lead to a decrease in the predatory bird populations that prey on the migratory species.
- BThe insect prey species develop resistance to cold temperatures in subsequent generations.
- CThe adult migratory birds have a very long lifespan, allowing them to survive multiple years of poor breeding.
- DThe migratory birds adapt by shifting their breeding grounds to warmer regions in subsequent years.
Show answer & explanationAnswer & explanation
Correct answer: C. The adult migratory birds have a very long lifespan, allowing them to survive multiple years of poor breeding.
The discrepancy is that breeding success drops, but overall population doesn't. If adult birds live a long time, then even if new offspring are fewer, the existing, long-lived adults can maintain the population size for a year or two, thus explaining why a single year of poor breeding doesn't immediately cause a sharp population decline.
Why the other options are wrong
- A. While this would reduce mortality, it doesn't directly address the *lack of new birds* from poor breeding success. It's a plausible factor but less direct than adult longevity.
- B. This might help future breeding success by increasing prey, but it doesn't explain why the population *remains stable* immediately after a year of already-reduced breeding success.
- D. The text states 'in years with unusually cold springs,' implying a recurring event, not a permanent shift. Also, changing breeding grounds might prevent *future* declines but doesn't explain the stability *after* a year of poor breeding.
Explaining Discrepancies
Explaining discrepancies involves identifying an underlying reason or factor that accounts for an apparent contradiction or unexpected outcome between two pieces of information or observations.
- Pinpoint the exact contradiction or unexpected result.
- Look for a missing piece of information or an unstated assumption.
- The explanation should logically bridge the gap between the conflicting observations.
Memory trick: Conflicting Clues Call for Clever Contextual Connections.