Count Data of a Critically Imperiled Salamander in South Carolina

By Theresa McManus

Abstract

In South Carolina, the green salamander (Aneides aeneus) is listed as “Critically Imperiled” by the Department of Natural Resources, making population dynamics such as abundance and survivability of particular interest. Green salamanders inhabit a specialized niche of moist crevices in rock outcrops and are the only arboreal salamander in South Carolina. While their range extends from Northern Alabama to Southern Pennsylvania, the population in the Blue Ridge Escarpment is disjunct from the larger Appalachian population. The count data obtained during this internship will contribute to a two-year mark-recapture study using Pollock’s robust design across 20 sites to produce estimates of population sizes and survivability in upstate South Carolina. Results to date indicate a weak positive correlation between the average number of salamanders observed per day and site elevation (p = 0.064, SE = 0.005); however, it is important to note organism count data is not equivalent to population abundance. This study will continue through Summer 2021; these and future count data and photo identification will be used to estimate population abundances and individual survivability.

tree salamander

Introduction

Salamanders are one of the most abundant vertebrates inhabiting vertical rock habitats throughout the Appalachian Mountains (Smith et al. 2017). Compared to other species of salamanders in the Southeastern United States, green salamanders (Aneides aeneus) inhabit a highly specialized niche of moist crevices and trees (Waldron and Humphries 2005).  Green salamanders also have highly permeable skin that is critical for cutaneous respiration and osmoregulation, making them susceptible to bioaccumulation of pollutants in the environment. (Hopkins, 2007) The relative abundance and occupation of diverse niches also makes salamanders an important component of ecosystems that have the potential to impact higher trophic levels (Hopkins, 2007). Green salamanders, like many amphibians, follow metapopulation dynamics. A metapopulation is a group of habitat patches that are suitable for a species that may be temporarily connected when individuals disperse to new patches (Smith & Green, 2005). In this project, we surveyed 20 suitable habitats for green salamanders in hopes that a better understanding of the species will offer insight into the best management practices for the future. 

crevice salamander

Ongoing Objectives

(1) Investigate the extent of individual mobility and site fidelity at the rock crevice level (their immediate habitat) across five sites; 

(2) Determine if crevice shape and size affect the temperature and humidity microclimate the salamanders exist in; 

(3) Participate in a mark-recapture study to estimate population size across twenty sites;

(4) Collect tissue samples to genetically estimate population connectivity across twenty sites.

Materials and Methods

We are continuously surveying 20 sites located in Greenville, Pickens, and Oconee counties following the two-tiered survey necessary for Pollock’s robust design. This survey style requires a nested visitation design (Figure 1). Primary periods were defined as each day the site was surveyed, with each survey being separated by two weeks. Secondary periods were nested within primary periods and only separated by a number of minutes. This design allowed us to assume an open population between primary periods, where birth, death, immigration, and emigration could occur and be accounted for. Conversely, secondary periods assumed a closed population, where these four population dynamics were assumed not to occur. When individuals were found, we took dorsal photos for photo identification to follow the mark-recapture project design. Count data was analyzed in a linear model as a response to site size, elevation, basal area, slope, and aspect. DNA samples were also taken via tail clippings for future analyses of genetic population connectivity. This project will continue through Summer 2021 and all count data will then be used to estimate population abundances.

Methods pic

Figure 1: Primary and secondary periods in relation to open and closed populations, respectively.

Results

An ANOVA function was used with the average number of observations per visit in response to the size, elevation, basal area, slope and aspect of each of the 20 sites surveyed (Table 1). As shown in Table 1, elevation was the only weakly significant variable analyzed (p = 0.064).

Table 1: Statistical significance of size, elevation, basal area, slope and aspect of sites on the Aneides aeneus count data across all 20 sites.

Real data table

Figure 2 compares the average number of salamander observations to the elevation of each of the 20 sites surveyed.

new y axis ciur graph

Figure 2: Bar plots of the average number of salamander observations (A) vs the site elevation (B) across 20 sites.

Conclusions

ANOVA results from our linear model predicting salamander abundance as a response to site features showed elevation was the only weakly significant variable (p = 0.064, SE = 0.005). When we compared bar plots of the average number of salamander observations per visit to plots of elevation, a pattern was not evident. The elevation and the average number of observations per visit of site 1250 was the highest for both variables. Because this pattern was not seen throughout the rest of the sites, Site 1250 could be a potential outlier, skewing our results. However, adding sites with an even higher elevation than 1250 to our survey could determine if there is truly a positive correlation between the average number of observations and elevation.

References

Smith, A. M., & Green, M. D. (2005). Dispersal and the metapopulation paradigm in amphibian ecology and conservation: are all amphibian populations metapopulations? Ecography, 28(1), 110–128. 

Smith W. H., Slemp S. L., Stanley C. D., Blackburn MN, and Wayland J. 2017a. Rock crevice morphology and forest contexts drive microhabitat preferences in the Green Salamander (Aneides aeneus). Canadian Journal of Zoology 95:353-358.

Hopkins, W. A. (2007). Amphibians as Models for Studying Environmental Change. ILAR Journal, 48(3), 270–277. 

Waldron, J. L., & Humphries, W. J. (2005). Arboreal Habitat Use by the Green Salamander, Aneides aeneus, in South Carolina. Journal of Herpetology, 39(3), 486–492.