2011 SOUTHEASTERN NATURALIST 10(4):591–608
Carabidae (Ground Beetle) Species Composition of
Southern Appalachian Spruce-Fir Forests
Carmen Chavez Ortiz1 and Robert A. Browne1,*
Abstract - During 2003 and 2004, carabid beetles were collected from the 9 largest
spruce-fir sites located in the southern Appalachian Mountains. Thirty-seven species were
identified from 1817 individuals of Carabidae caught in these habitats. When adjusted for
sample size, carabid beetle diversity was highest at Grandfather Mt., NC and lowest at
Mt. Rogers, VA. Results from non-metric multi-dimensional scaling (NMS) ordination
analysis indicate that carabid species found in spruce-fir forest cluster independently
from those found in deciduous lower-elevation forests. There were no correlations between
carabid species diversity and habitat area, isolation, and elevation.
In the southeastern US, spruce-fir forests form a distinct ecosystem which occurs
on only a few mountains in the Appalachians Mountains of Virginia, North Carolina,
and Tennessee at elevations greater than 1370 m (White et al. 1993). These
high-elevation areas are characterized by colder temperatures, higher humidity,
and higher rainfall (1250 to 2500 mm per year) than surrounding lower elevations.
During the last glacial maxima, forests dominated by Picea rubens Sargent
(Red Spruce) and Abies fraseri Pursh (Poir) (Fraser Fir), covered a large portion
of the southeastern US, but these species were restricted to the highest elevations
as the climate warmed, and these habitats are now considered to be Pleistocene
relicts (Delcourt and Delcourt 1984). During the 19th and 20th centuries, logging
and associated fires reduced Southern Appalachian spruce-fir forests by as much as
90%. More recently, the widespread infestation of Adeleges picea Ratzeburg (Balsam
Woolly Adelgid) has killed more than 80% of mature Fraser Fir, with additional
damage from heavy metal deposition and acid rain (White et al. 1993).
Since the spruce-fir forests are restricted to mountain tops, they are embedded
in a matrix of lowland, primarily hardwood forests dominated by species
of Quercus (Oak) and Fagus (Beech). While the differences between forest
types may not always act as an absolute barrier, the changes in microhabitat are
substantial and are believed to significantly limit the movement of many organisms,
e.g., Desmognathus wrighti King (Pygmy Salamander; Crespi and Browne
2003), Desmognathus organi Crespi, Browne, and Rissler (Northern Pygmy
Salamander; Crespi et al. 2010), and Galaucomys sabrinus Shaw (Northern Flying
Squirrel; Arobogast et al. 2005, Browne et al. 1999). For these organisms,
spruce-fir forests could potentially function as islands. In the current study, we
assess a number of possible factors that could influence the composition and
diversity of communities inhabiting nine spruce-fir “sky-island” forests in the
southern Appalachians. We test the relationship between species diversity (using
1Department of Biology and Environmental Program, Wake Forest University, Winston-
Salem, NC 27106. *Corresponding author - firstname.lastname@example.org.
592 Southeastern Naturalist Vol. 10, No. 4
several indices) and area, isolation, and elevation, using ground beetles (Coleoptera:
Carabidae) as our model taxa.
Carabid beetles have proven useful in biodiversity studies since they have
high species diversity and their taxonomic identification is relatively uncomplicated
(Erwin 1996, Koivula et al. 2002). Relatively high numbers of individuals
can be collected per unit of effort, potentially providing high statistical power for
hypothesis testing. The carabid beetles in the southern Appalachians are mostly
flightless and have limited dispersal capabilities (Larochelle and Lariviere 2003).
Most of the carabid species found in eastern North America are generalist invertebrate
predators (Larsen et al. 2003).
The variety of climatic zones and complex topography of the southern Appalachians
has been associated with a highly diverse biota with a relatively high
level of endemics. This general observation would also apply to the Carabidae of
the southern Appalachian Mountains, which form a species-rich mountain fauna
(Carlton and Bayliss 2007, Darlington, 1943, Noonan et al. 1992) with numerous
endemic species, especially within the tribes Trechini and Cychrini (Barr 1979,
1985; Kane et al. 1990). In the southern Appalachians, Carabidae speciation was
probably enhanced by ancestral species moving into lower elevations during the
Pleistocene period and then becoming isolates in higher elevations. This same
process may have also contributed to the rapid speciation of other species groups
in the region (Barr 1985).
While there have been numerous studies of carabid species assemblage in
European boreal forests (e.g., Butterfield et al. 1995; Desender et al. 1999; de
Warnaffe and Lebrun 2004; Jukes et al. 2001; Kiovula et al. 2002; Niemelä
1990; Niemelä et al. 1992, 1993, 1996; Paquin 2008), fewer studies have been
conducted in North America, with the majority focusing on the north temperate
forests of the eastern portion of the United States (Jennings and Tallamy 2006,
Larsen et al. 2003, Lenski 1982, Liebherr and Mahar 1979). Although there are
substantial collection records for Carabidae in the southern Appalachians (see
Barr 1979, Carlton and Bayliss 2007, Darlington 1943, Kane et al. 1990, Noonan
et al. 1992) they are primarily qualitative in nature, with wide variation in search
effort and seasonality.
The principal objectives of this investigation were: 1) to identify carabid species
found in southern Appalachian spruce-fir forest sites; 2) to measure carabid
diversity via a variety of approaches for each site and for the cumulative sample;
3) to determine if species composition varied among sites; 4) to determine if
carabid species found in spruce-fir forest cluster independently from those found
in deciduous lower-elevation southern Appalachian forests; 5) to test for correlations
between carabid species diversity and habitat area, isolation, and elevation;
and 6) to determine if individual carabid species were significantly associated
with wood or stone microhabitats.
Materials and Methods
Collection of carabid beetles
We collected beetles from nine spruce-fir sites (Table 1, Fig. 1). The areas
of spruce-fir forest patches included in this study ranged from 138 ha for
2011 C. Chavez Ortiz and R.A. Browne 593
Whitetop Mt. to 18,390 ha for Great Smoky Mountains. Maximum elevations
of the collection sites ranged from 1344 m at Grandfather Mt. to 2008 m on Mt.
Mitchell (for more detailed descriptions of each site see While et al. ).
Adult carabid beetles were collected during two periods: 6/21/2003–10/27/2003
and 3/20/2004–10/30/2004. Carabid beetles were collected during the day by
using the active search method, i.e., manual active searching of the ground, under
rocks, and under the bark of dead trees. Although some carabid species are
Table I. Description of sites and collections of carabid beetles.
Latitude, Elevation No. No. No.
Site Code longitude (m) Area (ha) indiv. genera spp.
Grandfather Mt., VA GF 36º05.958', 1324 285.73 196 8 20
Richland Balsam/ RIPI 35º20.700', 1874 1740.05 186 6 15
Mt. Pisgah, NC 82º57.937'
Roan Mt., NC/TN RM 36º06.461', 1859 713.61 170 6 18
Water Rock Knob, NC WR 35º27.555', 1798 537.42 184 9 18
Mt. Mitchell, NC MI 35º46.149', 2008 4337.92 181 8 13
Mt. Rogers, VA MR 36º38.122', 1616 639.28 130 6 11
Whitetop Mt./ WTEG 36º38.310', 1646 138.29 161 8 18
Elk Garden, VA 81º36.373'
Balsam Mt., NC BA 35º33.335', 1618 931.76 118 7 15
Great Smoky Mts., NC/TN GSM 1606–1920 18,390.10 491 10 22
Total 1817 13 39
Figure 1. Map of
the study area with
spruce-fir zones indicated
594 Southeastern Naturalist Vol. 10, No. 4
nocturnal, this approach allowed us to find beetles that were resting, inactive,
or hiding, and hence could include species that are often classified as nocturnal.
At each site, collections occurred during at least two different calendar months
between May and September. Three locations of approximately 200 m2 each were
sampled within each spruce-fir site, with a total search time of 20 h at each site.
Thus, the basic unit of replication was 20 h of search time for each sample site.
For ordination analysis using non-metric multi-dimensional scaling (described
subsequently), Carabidae were also collected from three hardwood forest sites.
Two sites (KE and BF) were located in the Great Smoky Mountains National
Park, adjacent to the Kephart and Bradley Fork trails (675 m and 885 m elevation,
respectively), with the third site (BRCK) located in Blue Ridge National
Park at Cumberland Knob (890 m elevation). Collections from the hardwood
sites utilized the same techniques and were made during the same time periods
as spruce-fir sites.
Collected individuals were preserved in alcohol and brought to the laboratory
for measurements and taxonomic identification. All collected beetles were
measured for body length (tip of mandibles to apex of elytra) and identified to
the species level using morphological keys (primarily Ciegler 2000). Comparisons
with specimens housed at the Smithsonian National Museum of Natural
History and Louisiana State University were also used in assigning species
identifications. All beetles collected are stored in the Biology Department of
Wake Forest University.
The majority of beetles collected were larger than 3 mm in length. Since we
did not collect soil samples, there is a high probability that smaller-sized beetle
taxa (<3 mm), such as Trechini and Bembidiini, were underrepresented due to
their small size. Therefore, our collections of carabid beetles do not represent
the entire community of the family Carabidae, but instead should be considered
as assessments of the carabid species >3 mm found on the forest floor up to 2 m
above the forest floor. Alternative sampling methods, such as pitfall traps, nocturnal
collection, fogging and vegetation beating, would probably yield different
results than those we obtained (Greenslade 1964, Günther and Assmann 2004,
Gutiérrez and Menéndez 1997, Lenski 1982). The goal of this study was to obtain
survey data that was comparable among sample sites.
We examined the effect of two habitat variables.
1) Area: The areas of all spruce-fir forests included in this study were measured
from GIS maps using ARC View program and based on previous unpublished data.
2) Isolation: The degree of isolation among the spruce-fir forest sky-islands was
estimated using three different indices. First, we measured how far north or south
a spruce-fir sky-island is located in km; this served as a measure of distance from
the large continuous tracks of spruce-fir forest in the northeastern US. Second,
we estimated isolation based on the distance from a specific spruce-fir forest
sky-island to the nearest spruce-fir forest sky-island in km. Finally, we calculated
an isolation index, I, which incorporates all other patches as potential source
2011 C. Chavez Ortiz and R.A. Browne 595
populations, but is weighted by their distances and areas. This index is estimated
by the following formula, where A is area and d is distance: .
I = Σ(1 / dij)Aj
We used several different indices to assess carabid diversity (for detailed
descriptions of indices, see Magurran 2004): species richnesss (raw number of
species per site), Shannon-Wiener diversity, Shannon’s evenness, Fisher’s alpha,
PIE (probability of interspecific encounter), dominance (the fraction of the collection
represented by the most common species), and rarefaction score.
Species accumulation curves
Species accumulation curves plot the number of individuals versus number
of species in a sample and thus adjust species number for total sampling effort.
As more individuals are collected only the rarest species are presumed to be
excluded from a collection; therefore, when all species are collected, the plotted
line reaches a horizontal asymptote. Smoothed species accumulation curves were
constructed using EstimateS 7.52 (Colwell, 2005). For comparative purposes,
and for computation of rarefaction scores, S was estimated at n = 100 individuals
for each site.
The effects of area, isolation, and elevation on species richness and the other
diversity indices were examined using linear regression. We created a matrix
indicating how many individuals of each species were collected per site. Using
this data, we constructed two different dissimilarity matrixes based on Jacard’s
index of dissimilarity (J) and Sorenson’s index of dissimilarity (S) (see Magurran
2004 for detailed description of dissimilarity indices). Using both dissimilarity
matrices, we compared the composition of the carabid species assemblages at the
9 spruce-fir sites and, for comparative purposes, at three hardwood forest sites
using the ordination technique non-metric multi-dimensional scaling (NMS).
NMS allows for differences to be easily observed graphically. We also looked at
the relationship between dissimilarity in composition and geographic distance by
performing Mantel tests, which calculate the correlation between the dissimilarity
in the species composition between pairs of communities and the geographic
distances between those pairs (Mantel 1967). For this test, we calculated the
dissimilarities in the species composition using both the Sorenson’s and Jacard’s
A total of 1817 individuals from the 9 spruce-fir sites were identified, representing
37 species of the Carabidae family (Table 2). The Great Smoky Mts. had the
highest number of individuals: 491. The other 8 sky-island sites averaged 168 ±
31 individuals. Sample sizes for the hardwood sites BF, KE, and BRCK used for
596 Southeastern Naturalist Vol. 10, No. 4
Table 2. Matrix for Carabidae taxa present/absent at nine spruce-fir sites. See Table 1 for site abbreviation codes. Average body length (in mm) with 95%
confidence limit is recorded for the species at that site. A blank entry for body length measurement indicates that the species was not collected at that site.
An entry of “na” for 95% confidence limits indicates that n < 3 for that species at that site. The last column indicates if there was a difference (P < 0.05) of
whether that species was associated with wood, under stones, or both wood and under stones. If the column is blank, the sample size was insufficient (n <
10) to test for habitat preference.
Species BA GF GSM MI MR RIPI RM WR WTEG Habitat
Agonum sp. 8.50 8.13 7.80
6.35 0.31 na
Atranus pubescens Dejean 8.00
Calosoma scrutator Fabricius 22.00
Carabus goryi Dejean 22.00 21.00 21.00
na na na
Dicaelus teter Bonelli 15.00 16.00 16.33 Both
na na 2.87
Harpalus spadiceus Dejean 10.50 8.00 11.00 9.00 9.00 Stone
na 0.12 na 4.30 na
Harpalus pensylvanicus De Geer 17.00 16.00 15.00 16.40 Both
na na na na
Oodes fluvialis LeConte 9.00
Platynus angustatus Dejean 14.22 12.53 12.70 13.70 14.00 13.14 12.60 12.67 13.50 Wood
0.84 0.39 0.25 0.51 0.33 2.48 1.72 3.79 2.48
Platynus decentis Say 13.00 12.00 14.00 Both
na na na
Platynus tenuicollis LeConte 12.00
2011 C. Chavez Ortiz and R.A. Browne 597
Table 2, continued.
Species BA GF GSM MI MR RIPI RM WR WTEG Habitat
Gastrellarius honestus Say 8.06 8.06 8.14 7.98 8.23 8.10 8.02 8.58 8.02 Wood
0.11 0.12 0.03 0.06 1.11 0.50 0.42 0.59 0.30
Pterostichus acutipes Barr 14.00 Stone
Pterostichus adoxus subspecies a Say 13.07 12.50 13.48 12.75 13.06 13.47 13.70 13.26 13.11 Wood
0.44 0.27 0.31 0.16 0.12 1.52 1.21 0.54 0.77
Pterostichus adoxus subspecies b Say 11.00 13.00 14.00 Wood
1.06 0.39 na
Pterostichu coracinus Newman 14.86 14.56 14.41 14.33 14.00 15.50 15.50 14.64 14.50 Both
1.12 0.79 0.18 1.43 na na 2.48 0.88 na
Pterostichus lacrymosus Newman 16.00 14.46 14.36 14.92 15.00 15.00 14.00 Both
na 0.51 0.49 0.63 na na na
Pterostichu moestus Say 18.00 17.00 Stone
Pterostichus mutus Say 12.33 11.00 11.00 Both
2.87 na na
Pterostichus palmi Schaeffer 12.00 11.00 12.00 12.00 11.00 Stone
na 1.88 0.87 na na
Pterostichus relictus Newman 15.75 15.00 Stone
Pterostichus rostratus Newman 13.86 14.33 14.07 14.33 15.00 13.17 14.00 15.00 Both
0.51 0.20 0.50 0.25 na 0.79 na na
Pterostichus diligendus Chaudoir 12.00 11.00 12.50
na na na
Pterostichus stygicus Say 13.00 16.00 12.50 12.00
na 0.12 na na
Pterostichus superciliosus Say 16.22
598 Southeastern Naturalist Vol. 10, No. 4
Table 2, continued.
Species BA GF GSM MI MR RIPI RM WR WTEG Habitat
Pterostichus tristis Dejean 12.39 11.84 12.99 12.85 12.33 12.63 11.9 13.75 12.67 Wood
0.28 0.47 0.22 0.33 0.38 1.42 0.53 1.10 1.30
Pterostichus sculptus LeConte 13.00
Maronetus debilis LeConte 8.50 8.50 8.00 10.00 8.00 Wood
na na 0.13 na na
Scaphinotus andrewsii Valentine 16.00 19.50 16.73
na na na
Scaphinotus elevatus Fabricius 18.00 20.27 Wood
Scaphinotus guyoti LeConte 30.00
Scaphinotus tricarinatus Casey 21.12 20.71 20.33 Wood
0.82 2.24 1.28
Scaphinotus viduus Dejean 30.00 27.00 29.00 Wood
na na 7.45
Scaphinotus violaceus violaceus 19.75 17.00 19.00 19.00 Wood
LeConte 2.38 na 2.00 na
Sphaeroderus bicarinatus LeConte 16.80 17.00 17.13 Wood
0.31 na 2.48
Sphaeroderus canadensis canadensis 11.00 12.00 11.00 10.00 Wood
Chaudoir 0.42 na na na
Sphaeroderus canadensis lengi 11.20 11.83 11.00 11.75 11.25 Wood
0.56 0.38 na 0.80 2.47
Sphaeroderus schaumi Chaudoir 20.00
Sphaeroderus stenostomus lecontei 16.00 14.00 16.33 15.00 15.00 15.00 Wood
Dejean 2.48 na 0.51 na na na
2011 C. Chavez Ortiz and R.A. Browne 599
comparison in NMS ordination analysis were n = 21, 33, and 133, respectively.
Combining spruce-fir and hardwood sites, the total number of Carabidae collected
was n = 2004.
Five species were collected at all spruce-fir sites: Gastrellarius honestus, Platynus
angustatus, Pterostichus adoxus, Pterostichus coracinus, and Pterostichus
tristis (Table 2; see Ciegler 2000 for authorities for the remaining species listed in
Table 2). These 5 species were also the most abundant, accounting for 73% of all
the carabids collected. When an additional species, Pterostichus rostratus, which
occurred at all but one site, is added, the total increases to 83%. The majority of
species (28) accounted for less than 1% of the total carabid beetles collected from
all sites. For 26 species where there was sufficient sample size to test for microhabitat
preference (goodness-of-fit-tests: P < 0.05), 5 species were significantly
associated with stones, 14 species were significantly associated with wood (living
and dead), and 7 species were found in both habitats. Every Cychrine beetle collected
was associated with wood.
Nearly half of all individuals for the combined spruce-fir sites were from the
genus Pterostichus, with nearly 90% of all individuals from just three genera:
Pterostichus, Gastrellarius, and Platynus (Fig. 2). The composition of the five
most commonly found Carabidae genera differed (χ2 test: P <0.001, df = 8) among
sites (Table 3). There was no significant correlation with either site latitude or
longitude and the per cent composition for any of the five most common genera.
Since the French Broad River has often been cited as a significant low-altitude
barrier for organisms occurring in the higher altitudes of the Southern Appalachians
(e.g., Browne and Ferree 2007, Crespi et al. 2003), we tested whether the
Figure 2. Composition of Carabidae genera from all spruce-fir sites combined.
600 Southeastern Naturalist Vol. 10, No. 4
proportions of each of the five most common genera of Carabidae (Table 3) were
significantly different between the sites south of the French Broad River (GSM,
BA, WR, and RI) and the sites north of the French Broad River (MI, RM, GF,
WT, and MR). A significant difference was found for Sphaeroderus (for southern
sites: mean ± s.d = 1.20 ± 0.837; for northern sites: mean ± s.d. = 6.00 ± 3.367;
t = 3.121, P = 0.017), but not for the other four genera. We also tested for correlation
between the proportions of each genus at each site. Only the relationship
between Pterostichus and Gastrellarius was significant (r = -0.831, P = 0.0055),
i.e., the higher the proportion of Pterostichus at a site, the lower the proportion
of Gastrellarius and vice-versa.
Differences in body length (Table 2, Fig. 3) occurred among the five most common
genera (completely randomized design ANOVA: F = 72.82, P < 0.0001).
Tukey’s tests indicate that Gastrellarius and Sphaeroderus differ significantly in
length from the remaining genera, with overlap between Platynus and Pterostichus
and between Scaphinotus and Sphaeroderus. For Cychrines, a distinct size progression
occurs among genera, with Maronetus dominant at 8–9 mm, Scaphinotus
dominant between 9–17 mm, and Sphaeroderus dominant at >17 mm.
As estimated by raw species counts, the Great Smoky Mts. had the highest
number of species from a spruce-fir sky-island (Table 4). However, after adjusting
for sample size, other diversity measures ranked Grandfather Mt. as the
most diverse site. Grandfather Mt. was the most diverse site as measured by
the Shannon-Weiner index and Fishers’ alpha (2.33 and 5.67, respectively) and
had the highest evenness value (0.78). Consistent with high evenness, Grandfather
Mt. also had the lowest dominance value, with the most abundant species
accounting for 27% of the total number of individuals collected. Grandfather
Mt. also presents the highest probability of encountering two different species
in any random pair as determined by the PIE diversity index, with a probability
Table 3. Composition by genera for Carabidae from nine southern Appalachian spruce-fir forest
sites. See Table 1 for site abbreviations. PT = Pterostichus, GA = Gatrellarius, PL = Platynus,
SC = Scaphinotus, SP = Sphaeroderus, HA = Harpalus, Ag = Agonum, MA = Maronetus, CA =
Carabus, RE = remaining genera.
Site PT GA PL SC SP HA AG MA CA RE
GF 42 47 3 4 3 <1 0 <1 <1 <1
RIPI 51 31 2 7 8 <1 0 0 0 0
RM 24 69 1 5 <1 <1 0 0 0 0
WR 81 2 13 2 1 <1 <1 <1 0 <1
MI 78 8 10 <1 <1 1 0 <1 2 0
MR 26 32 5 34 2 0 0 0 <1 <1
WTEG 54 35 4 <1 2 4 0 0 0 <1
BA 67 14 7 0 8 <1 2 1 0 0
GSM 38 24 21 7 7 <1 2 <1 0 <1
2011 C. Chavez Ortiz and R.A. Browne 601
value of 0.87. In contrast, Mt. Rogers was the least diverse site and also had
the lowest evenness value.
For all locations, the species accumulation curves (Fig. 4) do not reach an
obvious inflection point, indicating that increasing sampling size would continue
to add new species to the survey for each site. The site with the largest sample
size (the Great Smoky Mts.) continues to add new species, even for a sample size
of approximately 500 individuals. Rarefaction scores (Table 4), based on 100
individuals collected from each site, show a range of species diversity estimates
among sites, with the highest value at Grandfather Mt. approximately twice as
large as the lowest value at Mt. Rogers.
Figure 3. Profile of
body lengths for the
five most common
genera of Carabidae
all spruce-fir sites.
The width of the figure
to the proportion of
individuals with that
Table 4. Diversity indices for carbid beetle assemblages of spruce-fir sites. See Table 1 for site abbreviations.
See text for definition of terms. Dom. = dominance.
No. No. Shannon- Fisher’s Probability Rare-
Site individ. spp. Weiner Evenness Alpha of encounter Dom. faction
GF 185 20 2.329 0.778 5.69 0.870 0.265 16.220
MR 129 11 1.057 0.441 2.87 0.470 0.713 9.532
BA 118 15 2.066 0.763 4.55 0.814 0.373 14.448
WTEG 160 17 1.850 0.640 5.20 0.755 0.350 15.343
MI 204 12 1.760 0.686 3.09 0.778 0.358 10.304
WR 183 17 2.041 0.706 4.94 0.807 0.301 15.066
RM 169 18 2.247 0.778 5.09 0.849 0.325 15.038
RIPI 194 14 1.733 0.640 3.79 0.721 0.479 12.266
GSM 501 21 2.266 0.713 5.25 0.849 0.271 15.478
602 Southeastern Naturalist Vol. 10, No. 4
Factors influencing diversity
In order to determine patterns in species composition of carabid beetles in the
spruce-fir forest sites, we correlated each of the diversity indices with area and
elevation. For area, there was a positive but non-significant relationship between
absolute number of species and spruce-fir area (r2 = 0.345, P = 0.09). When adjusted
for samples size via rarefaction analysis, the correlation between species
and area was lower (r2 = 0.167, P = 0.73). There were no significant correlation
between any of the diversity measures and elevation of each spruce-fir site (e.g.,
the correlation between species number and elevation was r2 = 0.073, P = 0.48).
Carabid species composition
We investigated carabid beetle species composition via ordination and by
Ordination. In plots of the NMS analysis based on both the Jacard’s and Sorenson’s
dissimilarity matrices (Fig. 5), the spruce-fir forest sites form a distinct
cluster, indicating similarity in composition. The composition of Carabid beetles
in the three hardwood forest sites (BF, KE, and BRCK), are distinct from sprucefi
r forest communities.
Mantel’s test. Even if isolation does not significantly affect species richness,
it may influence species composition. If the beetles disperse among patches, then
nearby patches would be expected to be more similar than patches that are more
distant. Mantel’s tests, based on both the Jacard’s and Sorenson’s dissimilarity
Figure 4. Species accumulation curves used to calculate rarefied species richness. See
Table 1 for site abbreviations.
2011 C. Chavez Ortiz and R.A. Browne 603
indexes, found no significant relationship between geographic distance and community
composition (based on Sorenson’s index: r = -0.00008, P = 0.48; based
on Jacard’s index: r = -0.003, P = 0.46).
We collected beetles using the active search method. The most commonly
used alternative method, pitfall traps, has been demonstrated to have several
limitations. For example, pitfall traps are limited in the area sampled. Pitfall
traps are also criticized for giving non-representative samples, since they are
potentially biased by differences in activity among beetle species and may also
be sensitive to environmental variation such as the structure of the forest floor
(Adis 1979). In contrast, active searching has the advantage of being selective
for the target organisms and also allows collection of beetles inhabiting other microhabitats
that are not on the ground (such as the bark of dead trees, the base of
living trees with loose bark, and cracks in rocks). However, active searching also
has its limitations. For example, the historical records indicate that the complete
carabid beetle community also includes a large number of smaller species, such
as those of the genus Trechus (Noonan et al. 1992), which are primarily found
in soil or soil litter. In future studies investigating carabid beetle communities
of the spruce-fir forests, a more complete record would be obtained by using a
combination of sampling techniques (Larochelle and Lariviere 2003).
The collections analyzed in this study included 37 species of carabid
beetles. Based on the records of Darlington (1943) and Barr (1979, 1985), the
most common species from our collections were also present in their collection.
Since abundance data were not provided in their publications, we were
Figure 5. Non-metric multidimensional scaling (NMS) of Jacard’s dissimilarity index
based on species presence/absence. Sites enclosed within the ellipse are southern Appalachian
spruce-fir forest sites; sites outside the ellipse are southern Appalachian hardwood
604 Southeastern Naturalist Vol. 10, No. 4
unable to investigate if the pronounced environmental changes that have occurred
in the southern Appalachians over the past several decades have led to
corresponding changes in carabid beetle diversity and composition. More recent
information provided by the All Taxa Biological Inventory (ATBI) of the Great
Smoky Mountains National Park reports the presence of all the beetles collected
in our study (Carlton and Bayliss 2007). The number of endemic species
found in this study is substantially reduced in comparison with the ATBI list,
but it is important to note that the ATBI includes smaller-sized species and also
encompasses a vast area of hardwood forest and lower-elevation forest; sprucefir
forest accounted for only a minimal part (<5%) of the whole area sampled in
the GSM. With the ATBI data, there is again insufficient information on abundances
to allow for quantitative comparisons.
Since the spruce-fir habitats are often separated by large distances and surrounded
by distinctive types of habitat, they can be considered functionally
isolated. Accordingly, we hypothesized that carabid beetle diversity might be
affected by the same processes that affect islands, as described in Macarthur
and Wilson’s (1967) Theory of Island Biogeography. Namely, we predicted that
diversity would increase with area and decrease with isolation. The Theory of
Island Biogeography has previously been applied to other non-island systems
including forest fragments, caves, and mountaintops, which could function as
“sky-islands” (Brown 1971, Browne and Ferree 2007). Contrary to expectations,
we did not find any relationships between diversity and either area or isolation.
The Great Smoky Mts. is the largest continues patch of spruce-fir forest and did
have the largest number of species, but this result can be attributed to the greater
collection effort and greater number of individuals collected at this site. When the
number of individuals was controlled for, via the use of other diversity measures
such as Fisher’s Alpha, PIE, and rarefaction score, no significant relationship was
found between diversity and area.
There was also no relationship between any of the diversity indexes and any
of the measures of isolation. Likewise, there was no relationship between dissimilarity
in species composition and distance between patches (as analyzed with
Mantel’s test). The lack of an isolation or distance effect indicates that either
carabid beetles are dispersing equally between all sites regardless of distance or
that carabid beetles are not significantly dispersing and similarity in species composition
is primarily due to similar extinction trajectories after isolation. Given
the degree of isolation between many of the sites, species composition based primarily
on differential extinctions and not due to colonization or dispersal seems
more likely. These results are consistent with other studies examining mountaintop
communities. Brown (1971) tested MacArthur and Wilson’s (1967) theory for
the small-mammal communities (excluding bats) inhabiting the isolated peaks of
the Rocky Mountains in Nevada. Brown found a steeper species-area curve than
typical of insular biotas and did not find any relationship between the numbers of
species and isolation. He concluded that colonization occurred during the Pleistocene
and that the current communities are relicts. He also concluded that the
extinction rate has been low and the immigration rate approaches zero (Brown
2011 C. Chavez Ortiz and R.A. Browne 605
1971). In consequence, the study system is not at equilibrium (i.e., colonization
does not equal extinction) as predicted by MacArthur and Wilson.
The data from this study indicate that body length for the five most common
genera in the spruce-fir habitats ranged from 8 mm for Gatrellarius up to 34 mm
for Sphaeroderus. These 5 dominant carabid genera concur in their strong preference
for forests with shaded understories and moderately moist soil covered with
thick leaf litter. These species are also nocturnal and generally take shelter during
the day under the loose bark of trees (either fallen or standing) or under logs and
stones. They are almost all flightless, are moderate runners, and frequently climb
trees. When disturbed, adults of these species emit chemicals from the pygidial
glands as a defense mechanism. Although individuals of all five genera share
many traits, including that they are all invertebrate predators, there is specialization
within that broad category. Scaphinotus and Sphaeroderus are the dominant
genera of tribe Cychrini, a highly distinct guild due to their particular body shape
and their specialized feeding habitats, preying almost exclusive on snails and
slugs. Their mouth parts are highly adapted to their prey, showing an elongated
mandible and “spoon-like” palpomeres (Arnett and Thomas 2001, Larochelle
and Lariviere 2003). Their body architecture is also structured in such a way that
the pronotum and head are flexible enough to enable the beetle to get inside of the
snail shell and reach the prey easily. The body-length profiles indicate that there
are distinct differences in length between the larger Sphaeroderus and the relatively
smaller Scaphinotus. The remaining genus within the Cychrini, Maronetus, has
a body length that ranges from 7.7 to 10.2 mm. Thus, the three genera of Cychrines
have a nearly step-wise progression in length from Maronetus to Scaphinotus to
Sphaeroderus. For the three most common non-cychrine genera, Gastellarius has
minimal overlap with any of the four genera. Platynus and Pterostichus do have
some size overlap, although the largest number of Platyni are approximately 12
mm versus approximately 14 mm for Pterostichus. Although Platynus and Pterostichus
are described as generalized invertebrate predators (Ciegler 2000), they
may specialize in different prey items, may have different temporal preferences
(seasonal or circadian), or may occur in different habitats.
This study has limitations and should be considered as an initial attempt at examining
the carabid species assemblages of the southern Appalachian spruce-fir
forests. For all locations, the species accumulation curves do not reach an obvious
inflection point, indicating that increasing sampling size would continue to add
new species to the survey for all sites. Although sampling occurred during at least
two different calendar months between May and September, additional sampling
(e.g., monthly over at least one year) would be needed to detect seasonal specialists.
Additional years of collection would be required to increase the probability of
detecting rare species and to estimate annual turnover rates in the species composition
at each site and for the meta-population. Our hand-collection technique almost
certainly had biases (e.g., towards larger size, more active individuals, and individuals
found from 0 to 2 m from the ground). Additional collection techniques are
thus needed for comprehensive sampling (Liu et al 2007).
606 Southeastern Naturalist Vol. 10, No. 4
We thank the Great Smoky Mountains National Park, Blue Ridge National Park, Pisgah
National Forest, Jefferson National Forest, and Mount Mitchell State Park for collection
permits. We also thank Terry Erwin, Chris Carlton, and Victoria Bayless for taxonomic assistance
and Ken Feely for assistance with data analysis. Financial assistance was provided
by the Wake Forest Environmental Program and the Science Research Fund.
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