Functional trait modules link climatic niche geometry to projected range change in global butterflies

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Abstract Climate warming is redistributing insects, but species‐level projections alone rarely show which functional strategies are most exposed or how traits are linked to climatic niche structure. We developed a trait‐anchored framework connecting projected range change, functional trait‐space occupancy and climatic niche geometry in global butterflies. We compiled functional traits and georeferenced occurrences for 12,448 butterfly species across six families. Species distribution models estimated current suitable area (A now ) and mid‐century suitable area under SSP5‐8.5 (A 2050 ), from which we derived an expansion index, E = (A 2050 − A now )/A now . Current suitable cells were projected into a two‐axis climatic harshness space to quantify climatic niche breadth and niche position. We then constructed a global functional trait space, estimated family‐level trait‐space occupancy with trait probability density surfaces, mapped the SDM‐derived expansion index with generalised additive models and tested trait–niche associations with structural equation models. Butterfly functional strategies formed a pronounced core–edge structure. Family core fractions (A50/A99) ranged from 17% to 33%, and standardised total trait‐space extent (A99) varied from 0.12 to 0.85. Projected range change formed a nonlinear, contraction‐dominated trait‐space response surface: mean predicted expansion rates were negative in both functional cores and edges across all families, although contraction intensity and the probability of weakly positive fitted values differed among families. In the pooled SEM, Seasonality was negatively associated with climatic niche breadth ( β = −0.14), whereas Environmental affinity ( β = 0.21) and Diapause timing ( β = 0.13) were positively associated with niche position. Projected climate‐change responses were structured across combinations of functional traits rather than along single traits alone. By linking SDM‐derived range change to functional trait‐space occupancy and climatic niche geometry, this framework shifts vulnerability assessment from species counts toward functional strategy coverage and identifies trait–niche pathways that warrant targeted validation. Read the free Plain Language Summary for this article on the Journal blog.

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