Mountain ecosystems may be more resilient to climate change than previously believed, according to a new study, which reports little empirical support for the widely recognized "escalator to extinction." The findings challenge long-standing assumptions about range shift-driven extinction and instead introduce biotic homogenization as a more immediate concern facing mountain plants and animals. Mountain ecosystems worldwide are undergoing profound change due to rapid climate change. As temperatures increase, species are expected to shift their ranges upslope to take advantage of cooler habitats. However, while mountains offer vertical refuge for species adapting to climate change, their steep and confined topography limits how far some species can move, suggesting that climate warming may disproportionately threaten mountain biodiversity, especially species restricted to high elevations, narrow ranges, or tropical lowlands. This is sometimes described as the "escalator to extinction." While some studies support this prediction, evidence remains inconclusive, especially for range shift gaps and lowland attrition. As such, the ecological consequences of climate warming in mountain regions are likely far more intricate than a uniform upward migration.
Using data from 8,800 records of historical and modern elevational range limits for over 2,000 animal and plant species across five continents, and a sophisticated Bayesian modeling approach, Chen et al. found little empirical support for predicted threats. Instead, the authors found that, despite ongoing climate warming, widespread range shift-driven extinctions in mountain ecosystems have not yet materialized. According to the findings, most species' elevational range shifts remain consistent with expectations shaped by the topographical constraints of mountain landscapes. Narrow-range species are expanding upslope without the hypothesized corresponding losses at their lower limits, countering previous assumed concerns about range shift gaps. Moreover, Chen et al. show that many lowland species are moving upslope without retreating from their lower boundaries, further challenging the prevailing view that tropical lowland species are confined to narrow thermal niches. One notable ecological signal the study revealed was growing biotic homogenization, wherein species communities across different elevations have become increasingly similar. This pattern, observed in several mountain regions, is likely driven by the upslope expansion of widespread lowland species alongside the decline of specialized, range-restricted taxa. According to the authors, this homogenization may foreshadow broader biodiversity losses and could disrupt ecological interactions in ways that reverberate through entire mountain ecosystems.
