Predicting and mapping Plethodontid salamander abundance using LiDAR-derived terrain and vegetation characteristics

Aim of the study: Use LiDAR-derived vegetation and terrain characteristics to develop abundance and occupancy predictions for two terrestrial salamander species, Plethodon glutinosus and P. kentucki, and map abundance to identify vegetation and terrain characteristics affecting their distribution.Area of study: The 1,550-ha Clemons Fork watershed, part of the University of Kentucky’s Robinson Forest in southeastern Kentucky, USA.Materials and methods: We quantified the abundance of salamanders using 45 field transects, which were visited three times, placed across varying soil moisture and canopy cover conditions. We created several LiDAR-derived vegetation and terrain layers and used these layers as covariates in zero-inflated Poisson models to predict salamander abundance. Model output was used to map abundance for each species across the study area.Main results: From the184 salamanders observed, 63 and 99 were identifdied as P. glutinosus and P. kentucki, respectively. LiDAR-derived vegetation height variation and flow accumulation were best predictors of P. glutinosus abundance while canopy cover predicted better the abundance of P. kentucki. Plethodon glutinosus was predicted to be more abundant in sites under dense, closed-canopy cover near streams (2.9 individuals per m2) while P. kentucki was predicted to be found across the study sites except in areas with no vegetation (0.58 individuals per m2).Research highlight: Although models estimates are within the range of values reported by other studies, we envision their application to map abundance across the landscape to help understand vegetation and terrain characteristics influencing salamander distribution and aid future sampling and management efforts.Keywords: Zero-inflated Poisson model; Kentucky; Cumberland plateau; Plethodon glutinosus; Plethodon kentucki.

Genetic divergence correlates with the contemporary landscape in populations of Slimy Salamander (Plethodon glutinosus) species complex across the lower Piedmont and Coastal Plain of the southeastern United States

A primary goal of landscape genetics is to elucidate factors associated with genetic structure among populations. Among the important patterns identified have been isolation by distance (IBD), isolation by barrier (IBB), and isolation by environment (IBE). We tested hypotheses relating each of these possible patterns to genetic divergence in the Slimy Salamander (Plethodon glutinosus (Green, 1818)) species complex across the lower Piedmont and Coastal Plain of Georgia, USA, and adjacent areas of South Carolina, USA. We sequenced 2148 total bp, including three regions of the mitochondrial genome and a nuclear intron, and related genetic distance to GIS-derived surrogate variables representing possible IBD (geographic distance), IBE (principal components of 19 climate variables, watershed, and normalized difference vegetation index (NDVI)), and IBB (streams of fourth order and higher). Multiple matrix regression with randomization analysis indicated significant relationships between genetic distance and two principal components of climate, as well as NDVI. These results support roles for environment (IBE) in helping to drive genetic divergence in this group of salamanders. The absence of a significant influence of IBD and IBB was surprising. It is possible that the signal effects of geographic distance and barriers on genetic divergence may have been erased by more recent responses to the environment.

POPULATION ECOLOGY OF THE NORTHERN SLIMY SALAMANDER (PLETHODON GLUTINOSUS) IN EAST-CENTRAL ILLINOIS

The importance of plethodontid salamanders in forested habitats has been recognized for decades and more recently plethodontids have been touted as a model taxon for monitoring ecosystem integrity and recovery. However, basic demographic data that are crucial to conservation and management plans are currently lacking for many species and regions. The objectives of our study were to characterize the population density, biomass, and capture success of a peripheral population of Plethodon glutinosus to provide a comparison for eastern populations and set a baseline for future monitoring of Midwestern populations. We estimated the population density of P. glutinosus at our site to be 0.41 salamanders/m2, with an estimated biomass of 0.70 g/m2. We did not find any evidence for temperature or precipitation affecting capture success. Our results showed that our density estimate falls within the range of other population ecology studies of Plethodon and sets a baseline for other peripheral Midwestern populations.

Role of temperature in determining relative abundance in cave twilight zones by two species of lungless salamander (family Plethodontidae)

Lungless salamanders of the family Plethodontidae have historically been considered to be passive conformers to their surrounding thermal environment because there is no evidence that they thermoregulate behaviourally in the field. In contrast, plethodontids readily choose optimal temperatures when placed on experimental thermal gradients. It has been hypothesized that restriction to moist habitats prevents these salamanders from exploiting thermally diverse microhabitats in nature. We tested this hypothesis, as well as the hypothesis that response to temperature differs among plethodontid species, by investigating the thermal ecology of two species (Cave Salamander, Eurycea lucifuga Rafinesque, 1822, and Northern Slimy Salamander, Plethodon glutinosus (Green, 1818)) occupying twilight zones of six caves in northwestern Georgia. We recorded inside and outside temperatures, as well as the number of each species, for each of three seasons (summer, fall, spring) over 13 years. We also tested for differences in thermal preference along experimental gradients in the laboratory. We further generated environmental niche models (ENMs) to investigate the potential role of abiotic variables, including environmental temperature, in determining the geographic range of each species. We found that both species responded to cave temperature in such a way as to suggest that these salamanders thermoregulate behaviourally when given a diversity of thermal options within a relatively constant moisture regime. We also determined that E. lucifuga prefers lower temperatures than P. glutinosus. ENM analysis indicated that, while abiotic variables both strongly influence the ecological niche of both species, the range of E. lucifuga is strongly predicted by them. The geographic distribution of P. glutinosus is apparently heavily influenced by the presence of closely related, contiguous neighbors with similar niche requirements.

Re-evaluating niche conservatism versus divergence in the Woodland Salamander genus Plethodon: a case study of the parapatric members of the Plethodon glutinosus species complex

The Woodland Salamander genus Plethodon Tschudi, 1838, consists of terrestrial lungless salamanders, has been cited as an exemplar of a lineage characterized by niche conservatism. This conclusion has contributed to broader hypotheses dealing with the role of niche conservatism in speciation and the maintenance of species diversity. We re-evaluated these salamanders using newly published techniques designed to detect niche conservatism versus niche divergence using computer-based niche modeling and spatial analysis within a phylogenetic framework. We specifically studied parapatric neighbors in the species complex of Plethodon glutinosus (Green, 1818) to determine if there is evidence of a role for niche divergence at speciation or if niche conservatism characterizes the complex as has been reported for the larger genus. We found that new statistical approaches yield different results from earlier work, suggesting that niche divergence has been a much more important player in the speciation process than has heretofore been understood. Although different parts of the overall Plethodon phylogeny may be characterized by different rates of niche evolution, the rapidly burgeoning area of research centered on niche conservatism appears to be in a state of flux with regards to methods that give consistently repeatable results.