Monitoring the Shenandoah salamander in Shenandoah National Park

The Shenandoah salamander (Plethodon shenandoah) is a federally endangered species found only within the boundaries of Shenandoah National Park, Virginia.  This terrestrial salamander is isolated to approximately 6 km² of dry talus slopes at high elevations in the park.  Results of previous research suggest that P. shenandoah is competitively excluded to suboptimal talus habitats by the red-backed salamander (Plethodon cinereus) and have implicated competition as the dominant driver of extinction risk for this species.  Recent occupancy analysis, however, suggests that climate change appears to be the dominant driver of extinction risk for P. shenandoah and that the risk may be exacerbated further when climate change interacts with competition. 

In response to these concerns, biologists at Shenandoah National Park have initiated a research and monitoring effort with USGS to examine the current distribution patterns of P.shenandoah and identify optimal management actions to ensure persistence of the species. 

“Plethodon shenandoah”

Monitoring the Shenandoah salamander

Efforts in 2007-09 were focused on exploring design tradeoffs, investigating potential interspecific competition between P. shenandoah and P. cinereus, and establishing the extent of the current distribution of P. shenandoah within Shenandoah National Park.  Results from this work suggest that local habitat variables (e.g. vegetation type, soil type, proportion of cover such as soil, cobble, moss) are only weakly related to site occupancy of P. shenandoah.  Because this early work occurred mainly on north-facing talus slopes above 900m, efforts to systematically sample the full range of habitat conditions in high-elevation habitats of the park for occupancy of the species were needed.  Given emerging concerns about the potential effect of park management activities, future climate change, and the persistence of this species, a more robust understanding of the range and occupancy of this species was warranted.

Accordingly, sampling effort in 2011-2012 focused on defining the lower elevational bound of the species and examining occupancy within a larger ‘area of inference’ surrounding known P. shenandoah habitat.  We employed stratified random sampling to describe occupancy of the full range of habitat conditions, and used robust occupancy methods to provide unbiased estimates of P. shenandoah occupancy across a 57 km² area surrounding the species’ known range. Results suggest that a combination of physiographic covariates (elevation, aspect) and local-scale covariates (average leaf litter and soil depth) are the best predictors of P. shenandoah occupancy.  In addition, these sampling efforts confirmed a lower elevational boundary between 875 and 900m.  Future work will focus on incorporating P. cinereus and interaction between the species to examine the role of competition in determining the distribution of P. shenandoah and predicting future occurrence given climate projections for high-elevation habitats within Shenandoah National Park.

“Sampling a monitoring transect in high elevation talus habitat in Shenandoah
National Park”

“Processing Plethodon shenandoah individuals at a high elevation monitoring site in Shenandoah National Park.”

Assessing effects of future climate conditions

This study is focused on the critical uncertainty associated with understanding how the effects of temperature and humidity influence both the potential to limit distributions of one or both species, and change the nature of the interaction between the species; this research design investigates these relationships by using innovative three-dimensional mesocosms to examine growth and behavior differences in response to climate and competition treatments.  We designed this experiment to directly test P. shenandoah’s response to competition under realistic climate conditions, with an overall goal to predict P. shenandoah’s response to climate projections 30 to 70 years from now. 

In order to focus on the effect of competition together with climate, we designed a unique experimental chamber with habitat and climate conditions that mimic reality by (1) developing a 3-dimensional space that looks and feels like the high elevation talus habitats where these salamanders occur together in Shenandoah National Park and (2) creating realistic environmental conditions in the chambers by working with climate scientists at the University of Virginia to develop current and future climate scenarios for these high elevation habitats.  We constructed 60 of these chambers to house 2 adult male salamanders in each, paired for intra- and interspecific competition treatments.  We are looking at two response variables: (1) behavior in terms of surface frequency and (2) fitness in terms of body condition.  Surface frequency has implications for effective monitoring in that it will provide information on how competition under climate change affects surface detection probability.  Body condition allows us to measure the impact of climate and competition stressors on the experimental salamanders. 

In partnership with the Smithsonian Institute’s Department of Conservation Biology, we implemented a pilot study in 2011 using P. cinereus striped and unstriped color morphotypes as surrogates for P. shenandoah to (1) test design to ensure that it’s ready to house an endangered species and (2) test each morphotype’s response to competition under different climate scenarios.  We were interested in this response because there is recent research suggesting ecological differentiation between these two color morphotypes, with some of that research associating surface frequencies with population declines. 

The results showed that the design would successfully house P. shenandoah and also implicated competition with the striped morphotype as a driver of surface frequency for the unstriped morphotype without an explicit effect on fitness.  The P. shenandoah study was initiated in May, 2012 and is currently in progress.  Understanding the nature of the complex interactions between these species under different climate scenarios will provide tools for making biologically based decisions to help preserve P. shenandoah populations under the threat of a changing climate.  

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“Three-dimensional experimental chamber that mimics underground talus rock habitat and a soil and leaf-litter forest floor surface.”

“A salamander using a burrow to enter an underground interstitial space in one of the experimental chambers.”

“Observing salamander behavior in underground habitat.”

“Experimental chambers fitted with an automated misting system and heat cables between the soil surfaces and lids to create realistic climate conditions.”