Spatial variation in demographic processes and the potential role of hybridization for the future

Context Spatial variation in life history traits plays a crucial role in shaping the current and future dynamics of populations, particularly in systems where expanding hybrid zones could further shape population structure. The demographic responses of local populations to fine-scale habitat heterogeneity have consequences for species at a broader scale and demographic responses often vary across spatial scales. Objectives We evaluated spatial variation in population size and demographic traits (e.g., survival, individual growth, movement, and reproduction) of a montane endemic species of lungless terrestrial salamander across elevation and stream distance gradients representing broad and fine spatial scales, respectively. Methods Using 4 years of mark-recapture and count data from the Plethodon shermani x P. teyahalee hybrid system, whereby phenotypic hybrids occur at mid-elevations between low and high elevation congeners, we modeled demographic rates across environmental gradients and spatial scales using a combination of tools including individual growth models, and a spatially explicit Cormack-Jolly Seber model and Integrated Population Model. Results We found that high elevation animals grow faster and move more, especially far from streams, likely as a result of local microclimate conditions. Survival was highest but recruitment rates were lowest at low elevations and significantly declined with distance to stream. We also found that phenotypic hybrids at low elevations had higher survival probabilities. Conclusions Our study reveals nuanced spatial variation in demographic rates that differ in magnitude depending on the scale at which they are assessed. Our results also suggest that animals exhibit demographic compensation across abiotic gradients, underscoring the need for future conservation and management efforts to implement spatially explicit and dynamic strategies to match the demographic variation exhibited by populations across space.