Temperature and Moisture Interact to Shape Body Size of Appalachian Salamanders Across Elevation

Abstract

Aim: To investigate the mechanisms underlying body size variation in Plethodontid salamanders along elevational gradients and to determine the effects of climate variables (elevation, temperature, precipitation, and humidity) on body size. Location: Southern Appalachian Mountains, USA. Taxon: Fourteen species of Plethodontid salamanders. Methods: We used a historical dataset to analyse body size variation across elevation. We assessed the independent effects of elevation, temperature, precipitation, and humidity on body size. To test causal hypotheses regarding these climate variables and their interactions, we built a structural equation model (SEM). Results: For 13 of 14 species, we found that body size generally had negative correlations with temperature and precipitation and positive correlations with elevation and humidity, though the strength of the relationships varied. The one remaining species showed different body size patterns in relation to elevation and the three climate variables compared to all other species. Our SEM revealed that precipitation and humidity are the strongest predictors of salamander body size. Body size was not directly impacted by temperature but indirectly through the effects of temperature on humidity levels. Main Conclusions: Our study emphasises the importance of considering both temperature and moisture when examining body size patterns of ectotherms. We found that precipitation, often overlooked, plays a significant role in shaping body size in salamanders, challenging traditional views that focus solely on temperature. These findings highlight the need to integrate multiple, interacting climate variables to better understand organismal traits and to predict responses of organisms to climate change.