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Are mountain species on the brink? They may be more resilient than we thought

As global temperatures continue to rise, scientists have long worried that mountain species are on an "extinction elevator"—forced to move uphill for cooler temperatures, ultimately accelerating extinction as they run out of space. However, a new study led by Professor I-Ching Chen from National Cheng Kung University, Taiwan, has challenged this idea by analyzing global data.

Their research, in Science, shows that actual evidence for this scenario is weaker than previously thought, offering a fresh perspective on how species are coping with climate change.

The study finds that, despite species moving to higher elevations, those already living near mountain tops haven't lost much of their elevation range, showing resilience to climate change.

Meanwhile, narrow-range and low-elevation species expanded their habitats upward, particularly birds and insects, indicating that organisms are filling suitable climate niches. These patterns help ease some of the scientists' earlier worries, while also showing how complex species movements can be.

The team analyzed global elevation distribution data—both historical and modern—for 440 animal species and 1,629 plant species across 23 mountain regions, totaling 8,800 data points.

Their goal was to revisit key concerns raised in the early 2000s about mountain biodiversity: summit species might disappear because they have nowhere higher to migrate; narrow-range species might fail to keep pace with climate change and lose their preferred climate conditions; and lower-elevation areas experiencing biodiversity decline as species move upward without new species replenishment.

First author Dr. Yi-Hsiu Chen explains that this study uses open data and advanced statistical models to explore global biological responses that thoroughly account for noise from geographic constraints in mountainous regions.

The team used two Bayesian multivariate models to analyze species' upper and lower elevation limits, habitat range, and midpoint changes, rigorously capturing the interactions between various factors—an achievement previous studies had not accomplished and a key reason why Science recognized this work.

Co-author Dr. Jonathan Lenoir cautions that the situation is not risk-free, as delayed biological responses will accumulate an "extinction debt" that may significantly impact biodiversity in the future. For example, the delayed migration of plant communities observed in European mountains suggests that high-elevation ecosystems may currently be in a temporarily stable transition period that will eventually face change.

Additionally, the expansion of many species' distribution ranges has led to greater overlap along elevation gradients, resulting in more homogenized community compositions that reshape mountain biodiversity.

Professor I-Ching Chen pointed out that the expansion of many species' distributions suggests that climate niches in many mountain regions are not fully occupied, possibly due to constraints from biological interactions or other factors.

Climate warming is altering these constraints, highlighting the need for greater focus on how biological interactions mediate species' climate adaptation. From a conservation perspective, mitigating climate warming remains the most fundamental approach, while preserving natural habitats and spatial connectivity ensures species can migrate and adapt to rapidly changing climate conditions.

Q&A with Professor Tzung-Su Ding from the School of Forestry and Resource Conservation at National Taiwan University

What do you think is the most important finding of this study?

I believe the key takeaway is that this study highlights the ecological resilience of living organisms. Unlike inanimate matter, living organisms can respond to environmental stress through physiological, behavioral, and even physical adaptations. These changes can lead to population-level evolution, helping reduce the impact of environmental change. This is one of the biggest differences between biology and fields like physics or chemistry.

The core finding of the study challenges the widely held assumption that mountain species will face rapid extinction due to climate warming—the so-called "extinction elevator" hypothesis. By analyzing large datasets from mountainous regions around the world, the researchers found that mountaintop species have not experienced a widespread or significant shrinkage in their range.

Even more interestingly, many species—especially those with small ranges or living at lower elevations—are actually expanding their vertical range upward.

This is likely because the geometric shape of mountains offers available space at higher elevations. Combined with the species' existing ability to tolerate a range of environmental conditions, this allows them to move upward rather than simply being pushed into extinction.

Overall, the study shows that many species have a higher potential for adaptation to climate warming than previously thought.

Based on your own research and observations in Taiwan, have you seen similar trends?

Yes. With support from Yushan National Park in Taiwan, I conducted bird surveys at elevations between 1,400 and 3,700 meters on Yushan's main peak in 1992, 2014, and 2024, using the same methods and team.

Between 1992 and 2024, air temperatures in the breeding season in the high mountain area increased by 0.8°C. During this period, the breeding ranges of 50 bird species shifted upward by an average of 155 meters. Among them, 69% of the species significantly increased their elevational distribution, while only 11% significantly decreased.

Interestingly, the rate of increase over the last 10 years was even higher than during the previous 22 years.

For example, Alpine Accentor (Prunella collaris), a bird species found only at the highest elevations in Taiwan, has experienced a slight contraction in its elevational range. However, it has not faced the extreme extinction risk once predicted, and has maintained a stable population and range. This observation is consistent with the findings of the study.

How might this research affect Taiwan? What conservation policy adjustments might be needed?

This study offers a global perspective on how mountain species are responding to climate change. It challenges earlier, more pessimistic predictions and highlights the importance of mountain geometry and species' adaptive potential.

It also suggests that "biotic homogenization"—where biological communities in different regions become more similar—might be one of the more visible ecological consequences.

That said, the study does not directly examine the effects on specific regions or species in Taiwan. Our mountains have unique geography, species composition, ecological interactions, and face additional non-climatic threats like habitat destruction and invasive species.

These differences mean we need local data to properly assess how the study's findings apply to Taiwan and whether policy adjustments are needed.

Still, the analytical framework used in this study—including the emphasis on mountain geometry and biotic homogenization—can serve as an important reference for future research and conservation planning in Taiwan.