1. Comparison of Two Artificial Cover Object Grid Densities for Sampling Terrestrial Salamanders JohnRyan A. Polascik and Brian P. Mangan King’s College, Environmental Program, Wilkes-Barre, PA
Abstract
Artificial cover objects (ACOs) have been widely used for studying terrestrial salamanders. While ACOs offer a degree of sampling standardization beyond natural substrates, their successful use can be a function of many variables, including those related to their deployment density. We conducted this study to determine the influence of ACO density on salamander diversity and abundance beneath cover boards in a riparian forest. Each of our five study plots contained a 10X10 grid with boards spaced 5 m apart and another grid with boards spaced 1 m apart. The ACOs were placed in the sampling plots during late April or early May and were checked every three weeks from June through November. Red-backed Salamander was most often observed (77%), followed by Eastern Newt (eft form, 18.3%), Spotted Salamander (4.6%), and Four-toed Salamander (0.1%). In general, we found both salamander diversity and abundance to be highly variable among the plots. Plots with few salamanders were in areas subject to periodic flooding. However, in undisturbed plots we observed greater species diversity and relative abundances in 5 m grids. In addition, plots with ACOs spaced 5 m apart also had more instances of multiple salamanders beneath individual boards. Our results suggest that researchers should consider ACO deployment density when designing studies to assess terrestrial salamanders.
Introduction
Artificial Cover Objects (ACOs) are commonly used for sampling terrestrial salamanders (Houze and Chandler 2002). Compared to other methods such as pitfall traps, they reduce the likelihood of injury and mortality because they approximate the natural refuge that these animals seek.
This method is not without limitations, however. For example, some researchers have questioned the sampling bias that might be associated with the creation of artificial habitat in sampling plots (Marsh and Goicochea 2003). In addition, the influence of factors such as monitoring intervals, moisture retention and the materials used to make the ACOs have been questioned. Another possible factor that could influence the outcome of sampling with ACOs is the density in which they are deployed in sampling plots. Therefore, the purpose of our study was to quantify the influence of ACO density on the resulting estimates of salamander species richness and relative abundance in sampling plots in a riparian forest.
Methods
This study was conducted in a riparian forest along the Susquehanna River near Berwick, PA. This area is nature preserve owned and maintained by a local electric utility. In addition to providing habitat for wildlife, this area is also used for public outdoor recreation and agriculture. We located our forest sample plots throughout this preserve on the basis of forest area available for ACO deployment.
Methods (cont’d)
ACOs were made from cross-sections of trees harvested within 1.5 km of the study area. All ACOs had a radius ≥ 30 cm and were at least 2.5 cm thick. In each of the five sampling plots, 200 boards were arranged in 10X10 grids spaced at 5 m or 1 m-intervals. Cover boards were placed in the plots in late April through early May. The ACOs were checked for salamanders every three weeks from June through November. Salamanders were identified to species, weighed to the nearest 0.1 g and measured for both total and snout-vent length (nearest mm).
Results and Conclusions
In 8000 individual board inspections we observed 895 salamanders (many were likely repeat observations) from among four species. Red-backed Salamander (Plethodon cinereus) was beneath 77% of occupied ACOs, followed by Eastern Newt 18.3% (Notophthalmus viridescens, eft form), Spotted Salamander 4.6% (Ambystoma maculatum), and Four-toed Salamander 0.1% (Hemidactylium scutatum).
In general, we found salamander diversity and abundance to be highly variable among our sampling plots (Figures 1 and 2). In Plots 1, 2, and 5, very few salamanders were observed. These plots, however, are flooded periodically which could prevent the establishment of terrestrial salamander populations in these areas of the forest. While Plot 3 contained sizable numbers of salamanders, large numbers of ACOs were moved or overturned by raccoons during numerous sampling periods.
The undisturbed Plot 4 contained the greatest diversity and abundance of salamanders observed in our study. Within this plot species richness and relative abundance were greatest in the 5-m grid. However, the 1-m grid came close to matching the richness measured by the 5-m grid.
The proportion of ACOs with multiple salamanders was much greater in the 5-m grid in Plot 4 (Figure 3). It is not clear if these multiples are a function of ACO density, salamander density, or some other factor.
More research is required to understand the influence of ACO grid density on estimates of the diversity and relative abundance of terrestrial salamanders. Furthermore, this work needs to be done in forest systems free of disturbances such as flooding.
Figure 1. Total number of salamanders encountered per plot.
Figure 2. Total number of species found at each plot. Note: both P. cinereus morphs were counted as separate species.
Literature Cited
Houze, C.M., and R.C. Chandler Evaluation of coverboards for sampling terrestrial salamanders in South Georgia. Journal of Herpetology 36(1):75-81.
Marsh, D.M., and M.A. Goicochea Monitoring terrestrial salamanders: Biases caused by intense sampling and choice of cover objects. Journal of Herpetology 37(3):
Acknowledgements
PPL Susquehanna Riverlands for allowing us to conduct this study on their land and for providing the trees that were used to make ACOs. Jeff Hartman, Patrick Murray and everyone who contributed to cutting, marking and distributing ACOs in the field.
Figure 3. Proportion of ACOs with multiple salamanders by plot.