Inferring ancestral climatic niches in a world without clear-cut climatic boundaries

The world’s diverse and complex climates pose significant challenges in ecological and evolutionary studies, frequently resulting in climatic characterizations that overlook the significance of transitional climates. This study examines the nature and distribution of the transitions between climatic regions worldwide and evaluates their impact for inferring the past and present climatic preferences of the Asian Palmates, a highly diverse and climatically complex lineage of Araliaceae. We find consistent geographic patterns of transitions worldwide and extraordinarily heterogeneous climates in the transitions between the temperate and tropical climates in Eurasia. Notably, many current genera of the Asian Palmates and their early ancestors have strong affinities for transitional zones, suggesting an initial diversification under such climates. Such results emphasize the significance of transitional climates in understanding niche diversity and evolutionary patterns and calls for a (re)evaluation of the role of transitional areas in promoting biodiversity across the Tree of Life.