Patterns, drivers, and consequences of narrow-ranged species loss for angiosperm functional diversity across East Eurasia

Functional diversity links species traits to ecosystem functioning, yet its large-scale patterns and vulnerability to species loss remain poorly understood. Here, we assembled a comprehensive distribution and trait dataset of all angiosperms across East Eurasia and investigated geographic patterns of functional diversity represented by the richness (FR) and structure (standardized effect size of FR, sesFR) of functional traits, the environmental drivers underlying these patterns, and the potential consequences of losing narrow-ranged species. FR exhibited a strong latitudinal gradient, peaking in tropical and subtropical regions, whereas sesFR declined from southeast to northwest, indicating a transition from functional overdispersion to clustering. These contrasting spatial patterns were associated with different drivers: historical climate stability since the Last Glacial Maximum was the strongest predictor of FR, while contemporary productivity best accounted for the southeast-to-northwest variation in sesFR. Simulated loss of narrow-ranged species from local floras led to only minor reductions in functional diversity across most areas, with moderate losses confined to a few functional richness hotspots. In most grid cells, these effects did not differ significantly from those expected under random species loss or equivalent wide-ranged species loss, suggesting that narrow-ranged species loss does not generally produce disproportionate functional erosion in local floras. Our findings reveal a mismatch between the potential vulnerability of narrow-ranged species and the functional consequences of their simulated loss in local floras, highlighting that future conservation strategies should explicitly assess functional uniqueness alongside species range size to better sustain ecosystem functioning under climate change.