The Moving Baseline: Global Biodiversity Redistribution and
the Paradigms It Leaves Behind
More than two centuries ago, Alexander von Humboldt linked the zonation of vegetation on tropical mountains to climate and introduced the concept of isotherms, laying the foundations for the study of climate and species distributions. The world has since changed profoundly. Climate warming is redistributing species across the globe, offering an unprecedented opportunity to examine the mechanisms that determine where species live. The prevailing expectation has been that species track climate: as isotherms shift, ranges follow, carrying mountain species onto an “escalator to extinction”. This view implicitly assumes a close correspondence between distributions and climatic niches, while leaving the role of biotic interactions insufficiently resolved.
Our work challenges the climate-tracking paradigm. Upslope isotherm velocity depends on atmospheric moisture as well as warming, and species keep pace mainly where this velocity is low. A global synthesis of more than 2,000 species finds limited evidence of mountaintop extirpation: species near summits have largely maintained their ranges, while many narrow-range and lowland species are expanding. On Mount Kinabalu, moths moved upslope between 1965 and 2007 but, despite continued warming, did not move further upslope between 2007 and 2025. These findings raise questions about when and why species occupy, track, or persist within shifting climatic space. In parallel, large-scale manipulative experiments along elevational gradients show that biotic interactions constrain both upper and lower range limits. Combined with niche theory, these findings open a way to explore how climate mediates biotic interactions to shape species distributions. Finally, timescales matter. Environmental change is accelerating, yet whether biological responses can accelerate in step—and when accumulating mismatches may lead to extinction debt or abrupt transitions—remains an urgent open question as the baseline itself keeps moving.
I-Ching Chen is a Professor in the Department of Life Sciences at National Cheng Kung University (NCKU), Taiwan. She received her Ph.D. from the University of York, UK, in 2011, joined NCKU in 2012, and was a Fulbright Visiting Scholar at Stanford University in 2022.
Her research examines how climate shapes biodiversity across space and time, linking historical climate, evolutionary adaptation, and ecosystem responses. She and her team combine large-scale field experiments, dendroclimatology, and global data synthesis to understand biological responses to environmental change. Their current research uses generative AI to investigate phenotypic diversity and functional trade-offs, and explores temporal changes in ecological communities and ecosystem functioning worldwide and their implications for resilience.