Question 1
Multiple choiceHard1 markA record for one region covers four consecutive intervals, each 1 million years long. In each interval, the record identifies the ecosystem type and 10 species groups. The final column shows how many groups are also recorded in the immediately preceding interval. Which conclusion is supported by the complete record?
| Time interval (million years ago) | Ecosystem type | Species groups shared with preceding interval |
|---|---|---|
| 4–3 | Forest | — |
| 3–2 | Forest | 8 |
| 2–1 | Forest | 3 |
| 1–0 | Forest | 6 |
Show answer and explanation
Answer: A. All four consecutive intervals are identified as forest, spanning four million years. Fewer than 10 groups are shared at each transition, so species-group composition changed while the ecosystem type remained forest.
B: Confuses the same number of groups in each interval with the same groups; the overlap values are below 10.
C: Uses species-group turnover to infer ecosystem-type change, although every interval is identified as forest.
D: Stops at the most recent two intervals and overlooks the forest classifications in the earlier intervals.
Remember: continuity of ecosystem type does not require identical species composition.