Estimating Distribution Range Shifts of the Japanese Alpine Butterfly <i>Colias palaeno</i> Induced by Historical Climate Fluctuations and the Crucial Role of Its Host Plant

ABSTRACT The glacial relict butterfly Colias palaeno , which inhabits alpine zones in Japan and is designated a protected species, depends strongly on its host plant Vaccinium uliginosum . Recent environmental changes have raised concerns about shifts in its habitat range; therefore, understanding its distributional dynamics is important for future conservation. However, despite its ecological and conservational importance, temporal changes in the distribution of C. palaeno and the roles of environmental and biological factors have not been quantitatively evaluated across time scales. In this study, we used a landscape ecology approach to examine historical distribution changes and key environmental factors and then estimated the potential future habitat range. Field surveys were conducted in mountainous areas between 2020 and 2023. MaxEnt (Maximum Entropy) niche models indicated that temperature and the presence of V. uliginosum were major factors influencing C. palaeno occurrence. Analyses using paleoclimate reconstructions revealed that both species occupied broader ranges at lower elevations during the Last Glacial Maximum and then shifted upward and became fragmented during the Holocene Thermal Maximum. The degree‐day model supported these results by confirming the physiological constraints on the habitat range over time. Based on future projections under the Shared Socioeconomic Pathways (SSPs; SSP2‐4.5, 2041–2060), the distributions of both species are expected to be greatly reduced, with habitat fragmentation in the Northern Japanese Alps range and loss of habitat in the Asama mountain range. These findings clarify the vulnerability of C. palaeno to environmental changes and provide essential baseline information for alpine biodiversity conservation.