The ties that bind: Fine scale habitat associations of terrestrial salamanders and implications for population dynamics

Background/Question/Methods

One of the core objectives of ecology is to describe the distribution and abundance of organisms. The underlying mechanisms driving these scale-dependent patterns can often be explained in light of competition, movement, physiology, or any combination of these biotic processes as well as their interaction with the abiotic environment. At the most fundamental level, an organism’s performance is constrained by the abiotic environment that it inhabits. Limiting factors such as temperature, moisture, or nutrients can affect population dynamics by influencing growth, survival, and fecundity. As such, the distribution and abundance of organisms across the landscape often coincides with favorable abiotic environments. In topographically complex landscapes, the distribution of these environments is non-random with warmer, more xeric conditions existing on exposed slopes and ridges, and cooler, hydric or mesic conditions occurring in ravines or sheltered coves. To gain insight into the interplay between topography, abiotic environments, and species’ abundance across the landscape, we studied the western slimy salamander (Plethodon albagula) in east-central Missouri. Using a hierarchical generalized linear mixed model to correct for imperfect detection, we developed a spatially explicit model to describe the abundance and distribution of salamanders across a 1300 ha landscape. We also used multi-state models to determine if reproduction (presence of gravid females) and recruitment (presence of juveniles) was uniform across the landscape. 

 Results/Conclusions

A total of 487 salamanders were observed across 135 plots. The average detection rate over 7 observation periods was 0.164, and was influenced by date, presence of cover objects, time since rain, and temperature. Abundance estimates ranged from 0.084–4.89 salamanders per plot. The best predictors of abundance were canopy cover, topographic wetness, topographic position, solar exposure, and the interaction between wetness and solar exposure. The spatial relationships of these parameters are such that abundance is generally predicted to be highest in forested ravines with lower solar exposure. Maximum temperature was not a meaningful parameter in the abundance model, but estimates of abundance were negatively correlated with maximum temperature across the landscape. We also found a disconnect between reproduction and recruitment; given that a site was occupied, the probability of encountering a gravid female remained high across all temperatures (0.73–0.94), but the probability of encountering a juvenile at the same sites decreased as maximum temperature increased (0.38–0.96). Our spatial model highlights the importance of the abiotic environment in shaping patterns of abundance, and gives preliminary insight into mechanisms limiting population growth.