Examining elevation and thermoregulatory trait differences of endemic tropical swallowtail butterflies to assess their vulnerability to climate change

Abstract

Tropical montane insects are vulnerable to climate change if up‐hill range retractions reduce range sizes and increase extinction risk. Endemic species will be particularly at risk if they disproportionately occur at higher elevations, although threats may be ameliorated if they have morphological traits associated with improved thermoregulatory ability. We examine the vulnerability of endemic swallowtail butterflies on Sulawesi (Indonesia) to climate change by quantifying inter‐specific variation in traits associated with thermoregulation (body size and melanism) and whether species' traits are associated with the elevation of species' ranges. We collected data on size, melanism and elevation of 29 swallowtail butterfly species (Lepidoptera: Papilionidae) from 754 specimens at the Natural History Museum (United Kingdom) and the Zoologische Staatssammlung München (Germany). Endemic butterflies were less melanised (16 endemic species, mean = 83% melanised; 13 non‐endemic species = 89% melanised) but similar to non‐endemics in size (endemic, mean = 56 mm; non‐endemic = 53 mm) and elevation (endemic, mean = 345 m.a.s.l.; non‐endemic: 291 m). There was no evidence that species size or melanism patterns were related to elevation in either group. Few differences in elevation of endemic and non‐endemic species imply that endemic swallowtail butterflies are not disproportionately more threatened by climate‐driven mountaintop extirpation than non‐endemic species. Further work is needed to examine whether paler wings alter the ability of endemic species to thermoregulate and adapt to changing climates. In the absence of reductions in anthropogenic global greenhouse gas emissions, on‐going climate warming will continue to threaten tropical montane species.