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2008 SOUTHEASTERN NATURALIST 7(2):323–330
Diet of Western Slimy Salamander, Plethodon albagula
(Caudata: Plethodontidae), from Two Mountain Ranges in
Joseph R. Milanovich1,2,*, Stanley E. Trauth1, and Tanja McKay1
Abstract - We identified stomach contents of 80 Plethodon albagula (Western
Slimy Salamander) from two mountain ranges in Arkansas (Ozark and Ouachita)
to examine if regional differences in diet occur. Museum specimens from 1985 to
2005 were used from locations throughout each mountain range. Although a wide
variety of prey were found in stomachs, Hymenoptera: Formicidae and Coleoptera:
Carabidae were found to be the most important food items in the diet of P. albagula.
Ants and beetles constituted 85% abundance of their total diet (79.6% Ozark
and 90.1% Ouachita) and 52.2% of their total biomass (42.6% Ozark and 64.1%
Ouachita). Seventy-eight and 87% of individuals examined from the Ozark and
Ouachita Mountains, respectively, consumed ants (65% total, 83% for animals with
food items in their stomachs), whereas 55% in the Ozarks and 58% in the Ouachitas
consumed at least one family of beetle. Occurrence and biomass of prey items that
did not include ants and beetles showed P. albagula to be a euryphagic predator,
with 9.7% of diet being comprised of other prey types (27.3% biomass). Furthermore,
importance values indicate ants were the most important prey item for P.
albagula in both the Ozark and Ouachita samples, with carabid beetles (Ozark) and
all beetles (Ouachita) being second most important. Jaccard Index indicated Ozark
and Ouachita specimens shared 80% similarity in diet. Our data suggest P. albagula
in Arkansas have high dependence upon ants and beetles, yet appears to be an opportunistic
and euryphagic predator.
The Ozark and Ouachita Mountains of Arkansas are two distinct and
dissimilar regions. The Ozark Mountains in northern Arkansas underwent
a series of uplifting and eroding events, creating plateaus of horizontal layers
consisting of sandstone, shale, and limestone. The Ouachita Mountains
in southern Arkansas were formed by folding and faulting events, creating
long parallel ridges consisting primarily of sandstone, shale, and chert
(Smith et al. 1984). The Arkansas Valley is an intermediary zone between
the two mountain ranges and acts as a natural separation of the two regions,
which collectively are considered the Interior Highlands. One difference
between these regions can be seen in fl ora and fauna. The Ozark Mountains
are primarily oak-hickory forests and contain cave-dwelling vertebrate
and invertebrate species (Robison and Allen 1995, Smith et al. 1984). In
1Department of Biological Sciences, Arkansas State University, PO Box 599, State
University, AR 72467. 2Current address - Daniel B. Warnell School of Forestry and
Natural Resources, University of Georgia, Athens, GA 30602. *Corresponding author
324 Southeastern Naturalist Vol.7, No. 2
contrast, the Ouachita Mountains are dominated by oak-pine forest habitat
and are much drier when compared to the Ozark Mountains. Both regions
contain vertebrates and invertebrates endemic to Arkansas (Robison and
Allen 1995), and the Ouachita region is home to three endemic salamander
species not found in the Ozarks (Smith et al. 1984, Trauth et al. 2004). The
disparity in habitat between these two regions led us to question if there are
differences between diets of Plethodon that occur in both mountain ranges.
We examined Plethodon albagula Grobman (Western Slimy Salamander),
a large woodland salamander common in parts of Texas and throughout the
Interior Highlands of Arkansas, Oklahoma, and Missouri (Baird et al. 2006,
Conant and Collins 1998, Trauth et al. 2004). Diet studies throughout North
America have been performed on or included P. glutinosus Green (Slimy Salamander)
(Britton 1981, Davidson 1956, Hamilton 1932, Jensen and Whiles
2000, Powders and Tietjen 1974), the sister species of P. albagula (Highton
et al. 1989); however, few studies have examined the diet of P. albagula. Oliver
(1967), Britton (1981), and Crowell (1981) conducted diet analysis on P.
glutinosus (currently P. albagula) from central Texas and northwest Arkansas,
but these studies were limited to specific localities and covered few counties
of P. albagula’s range. Our study investigated the diet of P. albagula across
two ecoregions and covered the majority of its range. Our goal was to quantify
gut contents of P. albagula, an abundant salamander within both the Ozark and
Ouachita Mountains of Arkansas (Trauth et al. 2004), and assess differences
between populations in the two ecoregions.
Materials and Methods
Using museum specimens from the Arkansas State University herpetological
collection (ASUHC), we examined the stomach contents of 40 P.
albagula from the Ozark Mountains and 40 individuals from the Ouachita
Mountains. Collection dates ranged from 30 October 1985 to 17 September
2005 and were primarily during spring and fall months (n = 58 in March,
April, and May; n = 20 in September, October, and November; and n = 2 in
December, January, and February). Samples represented the entire range of
P. albagula in Arkansas and included 18 counties.
Salamanders were sacrificed using a 20% chloretone solution, fixed in 10%
formalin, and stored in 70% ethanol within 48 h of capture (only specimens
preserved by S.E. Trauth were used to minimize variability of preservation
techniques). For each specimen, we measured snout–vent length (SVL) using
a ruler, determined sex (when SVL > 50 mm) by locating testes or ovaries,
and recorded season of capture. Stomachs were dissected and placed in 70%
ethanol until contents were identified. Gut contents were identified, if an
entire organism or a head alone were present, to the lowest possible taxon
(Triplehorn and Johnson 2005). Prey items were totaled for both the Ozark
and Ouachita specimens to determine abundance (total number of prey) and
frequency (number of animals which consumed each prey item) of prey. Biomass
(volume of prey item) was estimated by measuring maximum width
2008 J.R. Milanovich, S.E. Trauth, and T. McKay 325
(widest lateral points) and length (widest anterior to posterior points) for some
prey items using a dissection microscope. Volume (mm3) was estimated as a
cylinder using length as the axis and width as the diameter (Maerz et al. 2005).
Whenever possible, volume was estimated for up to five individuals from each
family, and a mean volume was used to calculate biomass. Due to the limited
number of whole-body specimens for some prey families, biomass could not
be estimated for eight families. Biomass estimates were used to assess the extent
to which each prey item could be used for caloric intake.
To compare the importance of prey items between the two regions,
importance values (Anderson and Mathis 1999, Powell et al. 1990) were calculated
for each prey taxon where volume could be determined. Importance
values (Ix) were calculated using the equation:
Ix = [(nx/N) + (vx/V) + (fx/F)]/3,
where nx, vx, and fx, are the number, volume, and frequency of prey item x, and
N, V, and F are the summations of the number, volume, and frequency of all
prey items, respectively. Importance values range between 1 and 0 and represent
the relative importance of a single prey taxon in the entire diet. Jaccard’s
index of similarity (Jaccard 1912) was calculated between the Ozark and
Ouachita diet samples. The Jaccard index (JI) produces a value in the form of
a percentage, which represents the degree to which two samples are similar. JI
values were calculated using the equation:
JI = j/r * 100,
where j is the number of taxa found in both samples, and r is the number of
taxa found in one sample or the other.
For specimens examined, SVL ranged from 30 to 75 mm (mean ± SD = 58.9
± 9.4). Ozark specimens ranged from 39 to 72 mm SVL (mean ± SD = 59.3 ± 7.2
mm), whereas Ouachita specimens ranged from 30 to 75 mm SVL (mean ± SD =
58.4 ± 11.3). The Ozark sample included 21 females, 14 males, and 5 juveniles;
the Ouachita sample included 18 males, 14 females, and 8 juveniles. Seventeen
specimens (21%) had empty stomachs (8 Ozark, 9 Ouachita) and were omitted
from further analysis.
In total, 538 prey items were identified (186 in Ozark and 352 in Ouachita
samples) from 18 different prey taxa. Gut contents consisted primarily
of hymenopteran and coleopteran prey, particularly ants of the subfamilies
Myrmicinae and Formicinae (Fig. 1). Overall, ants comprised the majority
of prey items in terms of abundance, frequency, and biomass (Fig. 1).
Ants were found in 83% of stomachs that contained food items (78% in
Ozark and 88% in Ouachita). They accounted for 82% of abundance (70%
in Ozark and 88% in Ouachita) of prey items and 34% of total biomass. In both
ecoregions, beetles were found to be the second-most frequently consumed
prey (Fig. 1), with carabid beetles being the most frequent coleopteran prey
326 Southeastern Naturalist Vol.7, No. 2
Ranked importance values indicated that ants were the dominant prey
category for both the Ozark and Ouachita samples (Table 1). For the Ozark
samples, the importance value for ants was about three times greater than the
next-most important prey categories, carabid beetles and all beetles combined
(Table 1). All other prey items were less important than both ants and beetles
Figure 1 (above and opposite page). (a) Abundance, (b) percentage of total food
items, and (c) percent of biomass of food items found in P. albagula stomachs (n
= 32 in Ozarks, n = 31 in Ouachitas). Individuals with empty stomachs were not
included in analysis.
2008 J.R. Milanovich, S.E. Trauth, and T. McKay 327
Table 1. Importance values (IV) for P. albagula in Arkansas. In parentheses, total number of
prey, total volume of prey (ml), and frequency of each prey type, respectively.
Prey taxon Ozark Ouachita
Formicidae 0.44 (131 / 0.57 / 25) 0.64 (311 / 1.36 / 27)
Total Coleoptera 0.16 (26 / 0.29 / 14) 0.14 (16 / 0.33 / 13)
Carabidae 0.18 (17 / 0.79 / 11) 0.07 (6 / 0.28 / 5)
Curculionidae 0.008 (1 / 0.01 / 1) 0.05 (8 / 0.05 / 6)
Elateridae 0.03 (3 / 0.14 / 2) -
Staphylinidae 0.02 (2 / 0.09 / 2) 0.01 (1 / 0.04 / 1)
Scarabidae 0.06 (2 / 0.45 / 2) 0.04 (1 / 0.22 / 1)
Scutelleridae 0.03 (1 / 0.18 / 1) -
Gastropoda - 0.06 (5 / 0.25 / 3)
Diplopoda 0.06 (5 / 0.28 / 4) 0.07 (6 / 0.33 / 4)
Chilopoda 0.07 (5 / 0.46 / 3) 0.08 (5 / 0.46 / 3)
Araneae 0.04 (6 / 0.02 / 4) 0.03 (5 / 0.01 / 4)
Isopoda 0.05 (6 / 0.21 / 2) 0.01 (2 / 0.08 / 2)
(IV range from 0.008 to 0.07; Table 1). The importance value for ants in the
Ouachita specimens was nearly five times greater than that for all beetles combined
(0.14). The Jaccard Index indicated an 80% similarity between diets of
Ozark and Ouachita salamanders.
328 Southeastern Naturalist Vol.7, No. 2
The euryphagic diet of P. albagula is consistent with other Plethodon,
including P. glutinosus (in some regions currently P. albagula: Altig and
Brodie 1971, Britton 1981, Crowell 1981, Davidson 1956, Hamilton 1932,
Jensen and Whiles 2000, Oliver 1967, Powders and Tietjen 1974, Whitaker
and Rubin 1971, Wilson and Larsen 1988). Although the importance of ants
and beetles has been shown in Plethodon cinereus Green (Redback Salamander)
(Hamilton 1932), Plethodon jordani metcalfiBrimley (Southern Greycheeked
Salamander), Plethodon jordani shermani Stejneger (Red-legged
Salamander) (Whitaker and Rubin 1971), and P. glutinosus (Britton 1981, Davidson
1956, Jensen and Whiles 2000, Pope 1950, Powders and Tietjen 1974),
no prior study has found such a significant consumption of ants by Plethodon.
For example, the next-highest frequency and abundance of ants found in any
large Plethodon diet samples were found by Powders and Tietjen (1974) and
Davidson (1956), respectively, for P. glutinosus. Remaining studies on large
Plethodon show ants range from 2 to 80% by frequency and 1 to 37% by abundance
(Altig and Brodie 1971, Crowell 1981, Jensen and Whiles 2000, Pope
1950, Powders and Tietjen 1974, Reagan 1972, Whitaker and Rubin 1971,
Wilson and Larsen 1988). Britton (1981) found ants in nearly 80% of P. albagula
(formerly P. glutinosus) stomachs from northwest Arkansas, but ants
combined for only 38% of total prey items found in hillside specimens. Crowell
(1981) found ants were 23% (abundance) of all prey items and were found
in 41% of the samples. Davidson (1956) found ants in 73% of P. glutinosus
specimens, but they combined for only 42% of abundance.
With respect to beetles and other large Plethodon, frequency ranged from
13 to 80% and abundance from 5 to 26% (Altig and Brodie 1971, Crowell
1981, Jensen and Whiles 2000, Pope 1950, Powders and Tietjen 1974, Reagan
1972, Whitaker and Rubin 1971, Wilson and Larsen 1988). The highest
abundance and frequency of beetles was found by Davidson (1956) for P.
glutinosus and Oliver (1967) for P. g. albagula, respectively. Crowell (1981)
found beetles in 80% of P. albagula stomachs, but they only amounted to 9%
of total abundance, while Oliver (1967) found 64% frequency and 39% abundance
of ants and 8% frequency and abundance for beetles in P. g. albagula.
For P. albagula (formerly P. glutinosus) in Arkansas, Diptera were found to be
more important than ants and beetles in other studies (38% abundance, 57%
frequency; Crowell 1981).
Our data show ants and beetles to be the most consumed prey of P. albagula
across Arkansas. One possibility for our findings is a difference between
time since capture and sacrifice between our study and others, as chitinous
prey (such as ants and beetles) are likely to take longer to digest and thus can
appear to be a more common prey in diet samples. In comparable studies this
time period ranged from immediately to 12 h after capture, while in our study
the majority of animals were sacrificed within 24 hrs, although they were kept
cool up until death, which limits digestion considerably.
2008 J.R. Milanovich, S.E. Trauth, and T. McKay 329
The comparison of diet between the Ozark and Ouachita regions revealed
differences in the importance of some individual taxa, but overall similarity of
taxa preyed upon. Britton (1981) showed a relationship between availability
of prey and prey selection in P. glutinosus (currently P. albagula) in Arkansas
and found a disparity in diet composition between two different microhabitats.
Plethodon glutinosus inhabiting hillside and seepage microhabitats fed on
prey items that were found in higher abundance in those areas, suggesting this
species is an opportunistic predator and highlighting differences in prey consumption
among microhabitats. In this study, importance values confirmed
the dominance of ants and beetles in the diet of P. albagula inhabiting both
the Ozark and Ouachita Mountains. Ants were a more important prey item for
salamanders inhabiting the Ouachita Mountains when compared to the Ozark
Mountains. Overall, the importance of ants and beetles, and the similarity
among importance values and regions (JI = 80%) for the remaining prey items,
was comparable for P. albagula across Arkansas. This indicates that regional
differences in diet exist on a fine scale, but become less important as the range
of investigation increases.
Our study revealed slight variations in diet between P. albagula from the
Ozark and Ouachita mountain ranges in Arkansas; however, throughout much
of its range, abundance, frequency, biomass, and importance of prey appear to
be similar. Therefore, although variation in diet composition may exist for P.
albagula among microhabitats, differences appear to be smaller as the scales
increases. Specific microhabitat differences in prey selection by P. albagula,
and possibly many large Plethodon, appear to combine on a larger scale to
lessen specific differences.
We thank the many individuals who collected and deposited voucher specimens
into ASUHC. Specimens were collected under the authority of the Arkansas Game
and Fish Commission through scientific collection permits issued to S.E. Trauth
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