Niche divergence of evolutionarily significant units with implications for repopulation programs of the world's largest amphibians

Abstract

The niche divergence and potential climate change-induced loss of evolutionarily significant units (ESUs) of flagship amphibian species in China, the Chinese giant salamander clade, were investigated. We tested niche-related ecological hypotheses and identified suitable habitats that are essential for the conservation of ESUs in response to future climate change according to ecological niche models (ENMs). We predicted the localized habitat loss crisis of ESUs induced by global climate heating using the predicted climate derived from two representative concentration pathway (RCP) scenarios 2.6 and 8.5, respectively. In our study, a niche conservatism pattern was found between the two distinctive northern and southern ESUs with sufficient distributional records, but their niches were not equivalent. Furthermore, there was neither abrupt environmental change in nor remarkable biogeographic barriers between the suitable habitats of the species, as indicated by random linear, blob and ribbon range-breaking tests. Under the low-emission scenario RCP2.6, the northern ESU had a moderate loss of suitable range, while the southern ESU had range expansion in the 2070s. The climatic velocities were low in the ranges of both ESUs. However, under the high-emission scenario RCP8.5, the climatic velocities were found to become larger in the suitable ranges of both ESUs. Moreover, the northern ESU had severe habitat loss, bringing it to the edge of extinction, while the southern ESU also had intensified range loss. Considering this, climatic velocity can be an effective indicator of range loss. We argued conclusively that conservation prioritization of ESUs should effectively take into account the underlying geographic and ecological mechanisms driving the speciation process. The conservation of ESUs should consider the conservation of both evolutionary potential and ecological adaptation capacity of each lineage. The present study provided practical guidelines for repopulation programs for endangered species and the conservation of evolutionary diversity.