Elevated temperatures alter competitive outcomes and body condition in southern Appalachian salamanders

Temperature elevation due to climate change is directly altering organismal performance and distributions, but the mechanisms behind these shifts require additional attention. Because small aquatic ectotherms are proposed to perform better at future climates, it is possible that competitive interactions in size‐structured communities may also shift. To study the interactive effects of climate and competition on species performance, we evaluated body condition of small and large desmognathan salamanders at current and elevated temperatures in stream mesocosms, and characterized habitat use. In situ evaluation of capture locations demonstrated that the widespread and larger species, Desmognathus conanti, competitively excludes the smaller more narrowly distributed, D. abditus, from stream centers and cooler temperatures, but ex situ mesocosm experiments indicated an interaction between temperature and intra‐ versus inter‐specific competition on D. abditus body condition. At current temperatures, D. abditus body condition increased in the presence of the larger D. conanti, but at elevated temperatures, D. abditus body condition tended to decline in the presence of the larger species relative to intraspecific competitors. We also noted that individuals at future temperatures prioritized growth differently than individuals at current temperatures by shifting allocations away from growth in length to growth in mass consistent with responses of other organisms to stressful conditions that could result in declining reproductive rates. This study demonstrates that processes in size‐structured communities may interact with temperature to affect species’ future success.