Combining thermal and hydric constraints for spatially predicting the activity suitability of Neotropical Leptodactylid frogs

Abstract

Amphibians balance their thermal and water budgets depending on their physiological state and the physical environment, with both factors capable of constraining activity. Most mechanistic assessments emphasize thermal over water constraints, potentially missing important aspects of amphibian ecophysiological patterns. Here, we evaluate the potential role of thermal and hydric constraints on the activity time of three Neotropical frogs ( Leptodactylus fuscus , L. mystacinus , and L. macrosternum ) across their geographic distribution. We inferred environmental suitability based on heat and mass transfer principles through a mechanistic modeling procedure anchored to empirically obtained laboratory and field data. We integrated species‐specific thermal, hydric, and performance attributes with their immediate physical environment (ground‐level microclimate) under nocturnal conditions, while allowing for the interactive response of retreating into shelter when facing physiological heat or water stress. Our results demonstrate the desiccation‐prone role of smaller body sizes in increasing hydric restrictions and inhibiting activity, even under thermally adequate conditions, as well as the role of shelters as thermal and hydric refugia. More strikingly, thermal‐induced restrictions in activity were linked to low temperatures rather than warmer conditions, indicating that their engagement in activity is mostly driven by the lower thermal bounds of their functional organismal performance. These findings provide a broader picture of climatic constraints on anuran activity and distribution, as well as insights into how species may respond to changing climatic conditions.