Species traits and reduced habitat suitability limit efficacy of climate change refugia in streams.

Climate change vulnerability depends on whether organisms can disperse rapidly enough to keep pace with shifting temperatures and find suitable habitat along the way. Here, we develop a method to examine where and for which species shifting isotherms will outpace species dispersal using stream networks of the southern Appalachian Mountains (United States) and their highly speciose and endemic fish fauna as a model system. By exploring alternative tributary and mainstem dispersal pathways, we identify tributaries as slow-climate-velocity pathways along which some fish can successfully disperse and thus keep pace with climate change. Despite accessibility and thermal suitability, non-temperature habitat conditions in tributaries are unsuitable for some dispersing species, thus probably precluding establishment of persistent populations. Our findings demonstrate a trade-off shaping the efficacy of thermal refugia that depends on species-specific habitat associations and reveal individual-level dispersal behaviour, body size and stream network geometry as general correlates of climate change vulnerability.