Question

The graph below shows how the lower limits of the elevational ranges of bird species on a tropical mountain have changed over 20 years (2000 to 2020) because of climate change. Each point below represents a bird species. Points would cluster on the dashed line if species had the same lower elevational range limits in 2000 and 2020. Given that the mountain summit is at an elevation of 3500 m (solid horizontal line), and assuming that the trend shown by the graph continues over the next 20 years, what would you expect in 2040? 

• A. Low-elevation species will become locally extinct.
• B. Mid-elevation species will become locally extinct.
• C. High-elevation species will become locally extinct.
• D. All species will return to their original elevational ranges.

Hint:

Species living at higher elevations are more vulnerable to extinction in the face of climate change, as they have limited options for upward migration.

Answer 1

The Correct Option is C

The graph shows how the lower elevational range limits of bird species have shifted upward between 2000 and 2020 due to climate change. The points of species in 2020 are above the dashed line, indicating an upward shift in their lower elevational range. If this trend continues over the next 20 years, as suggested in the question, the bird species' lower elevational limits will continue to rise, pushing them closer to the summit of the mountain.
Given that the summit is at 3500 m, species that are currently living at high elevations (near the summit) will likely become locally extinct as their range limits shift upwards, without suitable habitat left to support them. High-elevation species are particularly vulnerable because they have fewer opportunities to move upwards, especially if they are already near the summit.
[6pt] - Low-elevation species are less likely to be impacted, as they have more room to move upward. Therefore, (A) is incorrect.
- Mid-elevation species are at a moderate risk of local extinction, but the primary impact will be on species at the highest elevations. Thus, (B) is incorrect.
- High-elevation species are most at risk, as their range limits are already approaching the summit, making them highly vulnerable to local extinction if the trend continues. Therefore, (C) is the correct answer.
- All species returning to their original elevational ranges is not supported by the upward trend observed in the graph, so (D) is incorrect.