The endangered endemic ground beetle, Carabus nankotaizanus Kano, 1932 (Coleoptera: Carabidae), consists of 4 subspecies distributed across the lowlands to mountain forests of Taiwan. However, continuous morphological variation among the subspecies and large altitudinal range gaps between lowland and mountain populations of C. nankotaizanus raise questions concerning its species boundaries. We assessed the species boundaries between lowland and mountain populations of C. nankotaizanus using an integrative approach combining morphological, molecular, life-history, and ecological traits. Future suitable habitats were predicted using ecological niche models to evaluate the effect of range shifts driven by climate warming. The analyses of morphological and ecological traits indicate that the lowland and mountain populations of C. nankotaizanus are 2 distinct phenetic and ecological species. The molecular phylogeny further supported 4 divergent groups (paraphyletic C. nankotaizanus sp. 1 of the northern lowland + monophyletic C. nankotaizanus sp. 2 of the northern mountain, paraphyletic C. nankotaizanus sp. 3 of the southeastern lowland + monophyletic C. nankotaizanus sp. 4 of the mountain groups). We recommend the designation of the 4 cryptic C. nankotaizanus as candidate species and officially protected evolutionary lineages. Future range shifts of C. nankotaizanus sp. 1 to higher latitudinal lowlands of northern Taiwan may pose significant challenges to its conservation due to urban development and island boundary. By contrast, upcoming range shifts of the mountain C. nankotaizanus species to higher altitudes of protected national parks and forest reserves in the Central Mountain Range may not represent a major threat to its survival.
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