Divergent Climate Responses Among Three Closely Related Headwater Fishes Within the Genus Rhynchocypris in South Korea

Climate change is altering thermal and hydrologic conditions in stream ecosystems, and headwater organisms may be particularly sensitive to these changes. However, little is known about whether closely related headwater fishes within the genus Rhynchocypris show similar responses to climate change. Using fish occurrence data and a maximum entropy model, we estimated current suitable habitat and predicted future changes in distributions for three Rhynchocypris species ( R. oxycephalus , R. steindachneri and R. kumgangensis ) in South Korea under three shared socio‐economic pathway scenarios (SSP1–2.6, SSP2–4.5 and SSP5–8.5) across four future periods (2021–2040 to 2081–2100). Suitable habitat for all three species was associated with smaller upstream watershed areas. Forest cover was also an important non‐climatic predictor, although responses to forest cover differed among species. The relative importance of climatic predictors also differed among species. Climatic predictors were less important for R. oxycephalus than for the other two species, whereas precipitation of the wettest month (BIO13) and maximum temperature of the warmest month (BIO05) were more important for R. steindachneri and R. kumgangensis , respectively. Suitable habitat for R. oxycephalus remained widespread and generally increased under future climates. By contrast, suitable habitat for the two geographically restricted species decreased across future scenarios, with a particularly rapid decline in R. kumgangensis . Our findings suggest that taxonomic relatedness does not necessarily imply similar climate sensitivity and highlight the need for species‐specific conservation of forested headwater habitats under climate change.