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.