Out of sight, out of mind: Fine-scale measurements reveal microclimate heterogeneity for plethodontid salamanders

Small-bodied species comprise the bulk of global biodiversity, yet the environmental conditions to which they are exposed are poorly understood. The resulting knowledge gap is notable for ectothermic plethodontid (Family Plethodontidae) salamanders that are highly sensitive to fine-scale microclimate (i.e., thermal and hydric) variation. Consequently, quantifying and mapping microclimate patterns is critically important to understanding the future persistence of plethodontids. The objectives of this research were to (1) characterize thermal heterogeneity at plethodontid-relevant scales, (2) assess factors influencing microclimate structure along stream-forest ecotones, and (3) compare salamander body surface temperatures with those in their surroundings. Accordingly, we incorporated the collection of thermal (i.e., ~500 infrared thermographic images), hydric (i.e., percent soil moisture), and habitat (e.g., canopy cover) data with salamander surveys at ground surface and subsurface retreat (i.e., rock, wood) microhabitats in 2023 and 2024. Our use of infrared thermography (IRT) offered a novel perspective on the full range of thermal mosaics occurring in plethodontid microhabitats that would likely be missed by traditional approaches (i.e., deployment of one datalogger per microhabitat). Specifically, we observed that the thermal landscape was highly heterogeneous (range: 8.19–45.36°C) across all sampled microhabitats and spatiotemporally dynamic. Retreats were 5°C cooler on average (by up to ~10°C on average) than the ground surface, yet even within a given wood or rock retreat, temperature measurements varied by up to 9.64 and 8.69°C, respectively. Within the thermally heterogeneous landscape, individual salamander body surface temperatures closely matched average retreat temperatures (R² = 0.93) and were relatively consistent within and between sampling rounds/years. While average retreat temperatures were comparatively similar along the stream-forest gradient, average soil moisture was greatest (>9%) at 1 m and least (<4.5%) at 100 m. Ultimately, we found that stream-forest ecotone landscapes exhibited remarkably complex microclimate structure characterized by retreats that were decoupled from conditions occurring just a few centimeters above at the ground surface. By challenging previous assertions that temperatures under a given rock or log are relatively homogeneous, these findings are instructive for assessing the accuracy of models aimed at predicting future plethodontid persistence.