2010 NORTHEASTERN NATURALIST 17(4):629–638
Salamander Diversity at C.F. Phelps Wildlife Management
Area, Fauquier and Culpeper Counties, Virginia
Jay D. McGhee1,* and Michael D. Killian2
Abstract - Salamander guilds are important components of ecosystems and may
be declining in Virginia. Consequently, information on salamander diversity and
abundance is needed. Our objective was to assess salamander diversity at one site in
the Rappahannock River watershed: the C.F. Phelps Wildlife Management Area. We
randomly selected stream and upland terrestrial sites to run 50-m transects, for both
quadrat and natural cover searches. We assessed diversity using a Shannon-Weiner
index on all captures (larval and adults) and assessed diversity in on-site catchments.
We found 11 of 13 expected species, with Ĥ ' = 1.33 ± 0.05 SD, Ĵ ' = 0.55 for all
captures, and Ĥ ' = 1.18 ± 0.08 SD, Ĵ ' = 0.49 for non-larval diversity. A single catchment
(Fishing Run) was considered more diverse than other catchments on site. We
conclude that C.F. Phelps Wildlife Management Area supports a relatively diverse
salamander community. Management efforts should focus on maintaining stream
structural diversity and monitoring the effects of agricultural activities such as fertilizer
use, erosion, and habitat fragmentation and loss.
Introduction
Salamander communities often represent an important component
within ecosystems and function as substantial links in food chains, maintain
lower-level prey diversity, slow leaf-litter processing, affect soil
dynamics, and act as pathways for energy transfer between aquatic and
terrestrial habitats (Davic and Welsh 2004). Despite their importance,
however, we have an incomplete understanding of salamander life histories
and community interactions. This is particularly problematic in the face of
global amphibian declines, the solutions for which require a sophisticated
comprehension of salamander diversity, ecology, and monitoring methods
(Heyer and Murphy 2005, Williams and Berkson 2004). Intensive surveys
of potential habitat are therefore beneficial to increase our understanding
of current levels of salamander diversity, which we define as the combination
of species richness (the number of species) and evenness (the relative
abundance of species), in a community (Lloyd and Ghelardi 1964, McIntosh
1967). In the Rappahannock River watershed of northern Virginia,
short-term surveys of amphibian diversity have been conducted at military
bases out of concern for possible declines, but no results of extended surveys
have been published (Mitchell 1998). Our overall goal was to conduct
1Randolph-Macon College, Ashland, VA 23005. 2Department of Biological Sciences,
University of Mary Washington, Fredericksburg, VA 22401. *Corresponding author
- jaymcghee@rmc.edu.
630 Northeastern Naturalist Vol. 17, No. 4
a more intensive two-year survey to assess salamander diversity on a wildlife
management area within this region.
Assessing species diversity can be expensive and time-consuming, so
it is important to establish the sampling intensity required to adequately
estimate this parameter. In addition, it is desirable to assess diversity on
multiple habitat scales. This approach can enable researchers to determine
whether species diversity is primarily a product of richness within sites (alpha
diversity) or species turnover between sites (beta diversity) and allow
managers to pinpoint those sites that require the most protection (Gering et
al. 2003).
Our study had three objectives: 1) to determine salamander species diversity
at C.F. Phelps Wildlife Management Area (WMA) in the Piedmont
portion of the Rappahannock River watershed, 2) to determine differences
in salamander diversity within the study site in order to identify areas of
management interest, and 3) to assess the number of samples required to
detect the total number of salamander species (species richness) and species
diversity (species richness and evenness) detected by the survey.
Field Site Description
Seventeen salamander species (approximately one-third of all species
known from Virginia) have been recorded within the Rappahannock River
drainage, located largely within the Piedmont region of the state (Mitchell
and Reay 1999). The C.F. Phelps WMA is located within this drainage
and borders the river. This WMA of 1837 ha (4539 acres) is located in
southern Fauquier and eastern Culpeper counties. Several small streams
cross the property, and empty into the Rappahannock River, which borders
the WMA western edge. The land consists of pine and hardwood
forest of mixed age, approximately 400 ha of open habitat formerly used
for agriculture, and a 1.2-ha man-made pond situated in the middle of
the WMA. Elevations range from 200–400 m above sea level. Thirteen
species of salamanders are expected to occur on the property, based on
past species occurrences in Fauquier and surrounding counties (Mitchell
and Reay 1999): Ambystoma maculatum Shaw (Spotted Salamander),
A. opacum Gravenhorst (Marbled Salamander), Desmognathus fuscus
Rafinesque (Northern Dusky Salamander), D. monticola Dunn (Seal
Salamander), Eurycea bislineata Green (Northern Two-lined Salamander),
E. guttolineata Holbrook (Three-lined Salamander), Gyrinophilus
porphyriticus Green (Spring Salamander), Hemidactylium scutatum Temminck
and Schlegel (Four-toed Salamander), Notophthalmus viridescens
Rafinesque (Red-Spotted Newt), Plethodon cinereus Green (Red-backed
Salamander), P. cylindraceus Harlen (White-spotted Slimy Salamander),
Pseudotriton montanus Baird 1850 (Mud Salamander), and P. ruber Sonnini
de Manoncourt and Latreille (Red Salamander).
2010 J.D. McGhee and M.D. Killian 631
Methods
Salamanders were sampled from an aggregate of stream and terrestrial
transects. We selected sampling locations by first locating stream sites occurring
nearest to a randomly selected GPS location on the property and
then moving up or downstream by a randomly selected distance of 0–50 m.
From these sites we ran a 50-m transect downstream, and sampled five
1-m2 quadrats, laid randomly within 10-m increments (Jaeger 1994, Jaeger
and Inger 1994, Mitchell 2000). Quadrats were placed such that 1/2 to
1/3 of their area covered the bank bordering the stream and, depending on
stream width, all together they covered the entire stream or covered only
one side of the stream. We searched quadrats by removing large cover objects
such as rocks and decaying wood, searching through leaf pack, and
dragging fine-mesh aquatic dip nets across the stream bottom (Mitchell
2000). In August 2007, we realized that stream banks might provide adequate
habitat for some species and decided to incorporate another 1-m2
quadrat search on the banks bordering each stream quadrat. This addition
essentially increased our quadrat samples to 10 per stream, five in the
stream and/or bordering it and five on the bank of the stream. We searched
these bank quadrats by moving large cover objects such as rocks and decaying
wood and searching through leaf litter.
We selected terrestrial transect sites by randomly selecting an azimuth
and meter distance (0–200 m) from the starting point of the stream site.
We employed two types of terrestrial survey methods: leaf-litter quadrat
searches (LLQ) and natural-cover searches (NC). For LLQ quadrat searches
we laid a 50-m transect and sampled five 1-m2 quadrats, laid randomly within
10-m increments (Jaeger 1994, Jaeger and Inger 1994, Mitchell 2000).
Fifty-meter natural-cover searches were conducted 10 m distant and parallel
to quadrat searches. Observers searched a 3-m-wide strip by overturning all
natural-cover objects, such as large rocks, pieces of bark, and fallen limbs
and logs (Heatwole 1962, Hyde and Simons 2001). In addition, we searched
opportunistically on cool, wet nights. Night-search transect locations were
randomly selected but constrained to occur within 50 m of a road on the
WMA. We visually searched the ground and under natural-cover objects
within a 50-m transect covering a 3-m width (Hyde and Simons 2001). For
all transect types, we identified captured salamanders to species, and measured
snout–vent and total lengths (Petranka 1998).
We analyzed capture data using the Shannon-Weiner estimate (Ĥ '),
which measures both species richness and evenness (Krebs 1999, Lloyd et
al. 1968). The Shannon-Weiner estimate derives from information theory,
which measures the amount of order in a system or, specific to biodiversity,
the variability of species in a system (Krebs 1999, Margalef 1958). The
estimate increases with both the number of species captured—an estimate
of species richness—and with the degree to which individuals captured are
632 Northeastern Naturalist Vol. 17, No. 4
evenly distributed across all detected species (Krebs 1999). The Ĥ ' can reach
large values, but can be standardized to range between 0–1 by dividing by
the maximum possible Ĥ ' for all species captured in a study. This value of
relative diversity (Ĥ '/Ĥ
max) we refer to as Ĵ ' (Zar 1999).
To determine differences in diversity within the study area, we divided
it into five stream catchments, from largest to smallest: Persimmon Run,
Fishing Run, Mine Run, Western Tributaries (a set of small unnamed
streams on the western side of the property), and Eastern Stream. We
counted the number of species found in each area and calculated Shannon-
Weiner indices for these smaller catchments. For the two catchments that
appeared to carry the most species, we used a Monte Carlo rarefaction
analysis to determine the most diverse habitat, presumably the habitat of
greatest management concern (Hurlbert 1971, Tipper 1979). For the watershed
with the largest number of individuals, we used ECOSIM to randomly
sample from the known capture data, and restricted our number of captures
to the lower total sample size of the catchment with which we wished to
make a comparison (catchment with the second-highest number of captures)
(Gotelli and Entsminger 2004). We performed this random sampling
for 1000 iterations, and calculated 1000 Shannon-Weiner estimates. We
then calculated a 95% confidence interval for the estimate and compared it
to the catchment with the second-highest number of captures. If the smaller
community falls within the 95% CI, this implies no statistical difference
between the sites (Gotelli and Entsminger 2004). The advantage of this
method is that it makes no a priori assumptions regarding the probability
distribution of the data (i.e., Gaussian distribution), a difficult assumption
to justify when the number of species (data points) is relatively small. Finally,
we graphically analyzed the number of transects required to capture
all the species found during the study, using the Shannon-Weiner index as
our dependent variable (Krebs 1999, Scott 1994).
Results
We suveyed from 13 April 2007 to 21 April 2009. We sampled 78 stream
transects with 390 stream quadrats and 295 stream-bank quadrats. We
sampled 88 LLQ transects with 440 quadrats, 89 NC transects, and 39 night
transects. We captured a total of 516 salamanders, comprised of 129 adults
and 387 subadults (juveniles and larvae). We found 11 of the 13 species expected
based on Mitchell and Reay (1999). We did not capture any Spring or
Mud Salamanders. Red-backed Salamander dominated our captures (Fig. 1).
We calculated a Ĥ ' = 1.33 ± 0.05 SD. We estimated relative diversity (Ĵ ')
as 0.55, meaning our distribution of captured species was 55% of the maximum
(most uniform) distribution possible. Within our samples, we noticed a
tendency for Two-lined Salamander and Spotted Salamander larvae to occur
in a clumped distribution, possibly after hatching from single egg masses.
This tendency for members of the same species to occur together acts to
2010 J.D. McGhee and M.D. Killian 633
negatively bias Ĥ ' (Krebs 1999). To offset this, we decided to calculate a
Shannon-Weiner estimate after removing larvae of all species (Ĥ ' = 1.18 ±
0.08 SD, Ĵ ' = 0.49 ).
Smaller catchments within the property differed in both number of species
and non-larval individuals captured (species, individuals, Ĥ ' ± SD,
n = number of transects): Fishing Run (8, 53, 1.40 ± 0.13, 85), Eastern
Stream (5, 27, 1.16 ± 0.15, 23), Mine Run (5, 32, 0.88 ± 0.19, 18), Persimmon
Run (6, 121, 0.84 ± 0.10, 93), and the Western Tributaries (4, 22, 0.75
± 0.20, 34). We compared Persimmon Run to Fishing Run by randomly
sampling capture data from Persimmon Run, limited to a total capture of
53 individuals. From 1000 iterations, we calculated Ĥ ' = 0.81 ± 0.11 SD.
This resulted in confidence intervals ranging from 0.56–1.02, implying
significantly less diversity in Persimmon Run than in Fishing Run. We
detected only one species unique to a particular watershed: the Four-toed
Salamander, captured in the Eastern Stream catchment. We captured all
species found on site with 94 transects; however, 10 of these species
were captured within only 30 transects, and nine within 13 transects. Our
Shannon-Weiner estimates ranged from between 0.67–1.78 over the entire
sampling period. This range decreases to 1.33–1.45 after all observed species
were captured, but does not indicate that the estimate has reached its
asymptote (Fig. 2).
Discussion
Discounting larvae, the distribution of individuals among the species
we detected was 49% of the maximum distribution possible, and skewed
Figure 1. The number of individuals, excluding larvae, captured per species on the
C.F. Phelps Wildlife Management Area, Fauquier and Culpeper counties, VA, April
2007–April 2009.
634 Northeastern Naturalist Vol. 17, No. 4
heavily toward the Red-backed Salamander. This pattern of a single numerically
dominant species combined with many rare species is well
documented (MacArthur 1972, Preston 1948) and matches the salamander-
guild patterns described by Davic and Welsh (2004). Based on their
review of five studies with at least 1000 captures in forested landscapes,
they found that a single species—often the Red-backed Salamander—
tended to dominate salamander communities. Those factors that determine
shifts in numerical dominance among salamander species are largely
unknown (Davic and Welsh 2004). Terrestrial salamanders are thought to
prefer areas with many cover objects, high soil moisture, neutral soil pH,
lower temperatures, and ready access to lower soil layers as predation refugia
(Bogert 1952, Heatwole 1962, Mathewson 2009, Spotila 1972). The
Red-backed Salamander is smaller than many of our expected terrestrial
species, is a habitat generalist, and so may better exploit soil systems with
these features than larger species in the area, particularly if prey or some
other habitat feature is limited.
Alternatively, McGill and Collins (2003) suggest that this pattern
can be explained based on a combination of the independent distribution
of species across a landscape and the pattern of species ranges: high
density concentrations of individuals diffusing outward to lower density
concentrations. This explanation would mean individuals of a single species
are common in a few habitats, and rarer in many others. Given these
assumptions, sampling at any particular site will result in collecting many
individuals from the small set of species common for that area and collecting
a few individuals from each of a wider range of rarer species, resulting
in the hollow curve pattern we obtained.
Figure 2. Shannon-Weiner estimates as sampling effort increases on the C.F. Phelps
Wildlife Management Area, Fauquier and Culpeper counties, VA, April 2007–April
2009. The cumulative number of captured species are shown with arrows.
2010 J.D. McGhee and M.D. Killian 635
Our survey failed to detect Spring and Mud Salamanders. C.F. Phelps
WMA occurs on the extreme eastern edge of the range of the Spring Salamander
in Virginia, and this species is likely to occur only rarely in the area
(VDGIF 2010). Similarly, C.F. Phelps WMA lies just outside the western
edge of the range of Pseudotriton m. montanus (Eastern Mud Salamander)
in Virginia, and our study area had few of the bog, swamp, or floodplain forest
habitats associated with this sub-species (Petranka 1998, VDGIF 2010).
Consequently, we anticipated this sub-species would be rare in the area.
We were able to detect 84% of the species we expected to find, however,
which implies that diversity patterns have not changed substantially since
the Mitchell and Reay (1999) atlas was published. We captured fewer adult
Marbled and Spotted Salamanders than we had initially expected. Adults of
both species tend to occur in bottomland forests and floodplains, but are most
active on cool rainy nights, and only seasonally, which may account for their
relatively small numbers in our total catches (Petranka 1998).
Our results agree loosely with the Mitchell (1998) survey of three military
sites near our study area. He reported a diverse amphibian complex with
no evidence of aquatic amphibian declines at Quantico Marine Corps Base,
approximately 40 km distant from our study site, and Fort A.P. Hill and Fort
Belvoir, each approximately 60 km distant. However, relative abundances
differed between sites, with the Mitchell aquatic captures being dominated
by Spotted, Seal, Northern Dusky, Two-lined, and Spring Salamanders,
whereas our aquatic samples were dominated by the Two-lined Salamander.
This variability would be expected to the extent that habitat differs between
sites, but Mitchell performed a set of short-term surveys over a wider
geographic area, and the difference in methodologies makes it difficult to
compare diversity between these sites.
Although the general pattern of species dominance remained the same,
we found that stream catchments on our study area differed in salamander
diversity. The largest streams, Persimmon Run and Fishing Run, were the
most diverse, and Fishing Run was significantly more diverse than Persimmon
Run. Fishing Run sites were often shallower than those in Persimmon
Run and had a greater variation in habitat, including seeps and Castor
canadensis Kuhl (Beaver)-modified and deeper waters. We suggest that
stream structural diversity be maintained at Fishing Run, and action be taken
to minimize agricultural and roadway runoff to this stream. Ephemeral
streams should be maintained for Marbled Salamander, along with clear,
shallow streams with seepages and bog habitats for Red and Three-lined
Salamanders (Petranka 1998). Coarse woody debris and fallen logs will
provide cover objects for terrestrial species such as the Red-backed and
Slimy Salamanders (Petranka 1998).
The majority of species were found in multiple or all catchments, implying
that alpha, or within catchment, diversity explains more of our diversity
estimate, than beta, or between catchment, diversity. We did find one species
636 Northeastern Naturalist Vol. 17, No. 4
unique to a catchment: the Four-toed Salamander on the Eastern Stream site
at the southern edge of the property. Although the status of the Four-toed
Salamander is unknown, its specialized use of moss mats, particularly of
Sphagnum moss near still water, for egg-laying, means populations are potentially
at risk from habitat loss or degradation (Blanchard 1923). Petranka
(1998) suggests managers should retain a mature deciduous tree canopy over
potential habitat to retain moisture, allow the deposition of coarse woody
debris, and promote moss growth by raising earth to form hummocks around
vernal pools and marshes.
Sampling effort is an important component of survey design. We found
with our methods that the majority of species could be captured within 13 or
fewer transects, while rarer species or those most difficult to detect with our
sampling design, required considerably greater effort. A precise estimate of
diversity, to include a precise estimate of evenness, would be almost impossible
to achieve in a short-term survey. While species richness estimates may
be achieved quickly, this will tend to positively bias the Shannon-Weiner
estimate because species numbers will be increased to a greater extent than
the relative abundances of those species. We suggest that, at a minimum,
long-term intensive surveys are important to provide validation data for
future common short-term and less intensive surveys.
Acknowledgments
We thank Joe Ferdinandsen, manager of C.F. Phelps WMA, for his cooperation,
along with R. Hughes. We thank University of Mary Washington students Carly Byers,
Sarah Almahdali, Jennifer Clary, Hillary Adams, and Ramsey Hanna for their
field work assistance. We thank the students of J.D. McGhee’s animal ecology classes
in Fall 2007 and 2008 for their help in field sampling. Three anonymous reviewers
made numerous and useful comments during manuscript review.
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