Within‐Island Diversification Generates Lineage‐Specific Climate Vulnerability: Insights From the Taiwan‐Endemic Formosan Duke

Global climate change disproportionately threatens island endemics because their restricted ranges and limited dispersal opportunities constrain their ability to shift their distributions. Therefore, when developing conservation strategies for species, it is crucial to incorporate population genomics data with ecological information to evaluate resilience and forecast vulnerability. However, genomic case studies that explicitly link these factors in island endemics remain scarce. Here, we examine population genetic differentiation of the Formosan Duke ( Euthalia formosana ), an endemic butterfly in Taiwan, to evaluate its potential vulnerabilities under future climate conditions. Our results reveal that the combined effects of topographic barriers, historical connectivity, and climatic heterogeneity can drive rapid diversification, even in species with strong flight ability. The Central Mountain Range has shaped pronounced genetic structure, separating eastern and western lineages, with diversification stronger in the western lineage. This within‐island diversification appears to be shaped by environmental gradients, enhancing persistence in local habitats while reducing a lineage's niche breadth and resulting in different lineage‐specific climate vulnerability. Thus, we suggest that genomic approaches should be included to assess environmental constraints and to guide conservation planning on the persistence of lowland endemics such as the Formosan Duke. This framework also integrates the concepts of habitat restoration with lineage‐specific connectivity to enhance the species' genetic resilience while preserving its capacity for local adaptation. Moreover, this study provides an evidence‐based framework for insular biodiversity conservation under accelerating climate change.