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22001166 SOUTHEASTERN NATURALIST 1V5o(4l.) :1559,5 N–6o1. 24
Harvestmen (Opiliones) of the Savannah River Site, South
Carolina
Michael L. Draney1,* and Jeffrey W. Shultz2
Abstract - A year-long continuous pitfall trapping program in 8 habitats at the Savannah
River Site on South Carolina’s coastal plain yielded over 4200 individual Opiliones, and the
resulting data set provides a fine-grained description of Opiliones faunistics, habitat distribution,
and phenology in southeastern North America, where Opiliones biology has been
neglected. The 9 species reported from the site include a new state record (Vonones sayi), a
rarely reported species (Bishopella laciniosa), and a common species that was undescribed
at the time of the study (Hadrobunus fusiformis). All species abundant enough to examine
seem to be univoltine and to reproduce in the warm season (adults mostly present in autumn),
but species varied greatly in seasonality and duration of the peak adult sample period
and in their habitat distribution. Leiobunum bimaculatum preferred xeric sites, H. fusiformis
was widely distributed across habitats, and the other species were generally more abundant
in more mesic habitats. Richness estimation showed that the ground-accessible Opiliones
fauna was adequately sampled by this pitfall regime.
Introduction
The harvestmen (Order Opiliones) are the third-most diverse group of arachnids
after spiders and mites. More than 6000 species have been described, and it
is estimated that there are 10,000 species worldwide (Pinto-da-Rocha et al. 2007).
Over 200 species are known from North America (Cokendolpher and Lee 1993),
and they are diverse and ecologically important predator/scavengers in the southeastern
United States. Prior to this investigation, 19 harvestman species were
known from South Carolina, including 3 undescribed Hadrobunus species (Table
1). Although this number is fairly typical for a southern state (Cokendolpher and
Lee [1993] list 20 species from Georgia, 22 species from North Carolina, and 19
species from Tennessee), it is undoubtedly an underestimate because many of
South Carolina's diverse ecosystems remain unsampled (Fig. 1) and the collecting
that has occurred has been largely incidental. It is very likely that elements of
the harvestman fauna of the southern Appalachians—such as Leiobunum calcar
(Wood), L. aldrichi (Weed), Odiellus pictus (Wood), and Caddo agilis Banks—
extend into the far northern portions of the state. Even Phalangium opilio L., a
seemingly ubiquitous introduced species, has yet to be formally recorded. Unfortunately,
the neglected status of harvestmen in South Carolina is also typical of
most other states. Our study is one of the first to take a comprehensive approach
to harvestmen diversity in the region.
1Department of Natural and Applied Sciences, University of Wisconsin-Green Bay, Green
Bay, WI 54311. 2Department of Entomology, University of Maryland, College Park, MD
20742. *Corresponding author - draneym@uwgb.edu.
Manuscript Editor: Robert Jetton
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An intensive study of sheetweb-weaving spiders (Linyphiidae) on the Department
of Energy’s Savannah River Site (SRS) in South Carolina (Draney 1997)
yielded many samples of Opiliones, giving us an opportunity to examine the fauna
of a western region of this neglected state. Knowledge of the Opiliones fauna of
this site is particularly important because the ecosystems of the SRS are among the
most-intensively studied in southeastern North America. The site was established
in 1951 for the production of weapons-grade nuclear materials, and although there
has been considerable research into the effects of radiation on ecological processes,
the site has also been managed as a de facto nature preserve since that time, and
includes large tracts of some of the least-disturbed ecosystems on the southeastern
coastal plain. The Savannah River Ecology Lab has published over 3300 articles
since 1955 (http://srel.uga.edu/Reprint/REPRINTS.pdf). Consequently, this initial
study of the harvestmen of SRS may be important in understanding Opiliones
Table 1. County-level list of Opiliones of South Carolina. See Table 2 for further information about
taxa recorded in the present study.
Species County (source)
Bishopella laciniosa (Crosby and Bishop) Locality unspecified (Holsinger and Peck 1971);
Aiken (present study)
Crosbycus dasycnemus (Crosby) Oconee (Shear 1986)
Eumesosoma nigrum (Say) Colleton, Florence, Jasper
(Cokendolpher 1980)
Hadrobunus fusiformis Shultz Aiken, Beaufort, Colleton (Shultz 2010);
Aiken, Allendale, Barnwell (present study)
Hadrobunus grandis (Say) Colleton (Shultz 2012)
Hadrobunus n. sp. 1 Berkeley, Charleston (J.W. Shultz, unpubl. data)
Hadrobunus n. sp. 2 Darlington (J.W. Shultz, unpubl. data)
Hadrobunus n. sp. 3 Horry (J.W. Shultz, unpubl. data)
Leiobunum bimaculatum Banks Jasper (Davis 1934); Aiken, Barnwell (present
study)
Leiobunum euserratipalpe Ingianni, McGhee, & Greenwood (Bishop 1949)
Shultz
Leiobunum nigropalpi (Wood) Oconee (Ingianni et al. 2011)
Leiobunum politum Weed Beaufort, Berkeley, Colleton, Florence,
Greenwood, Kershaw (Davis 1934)
Leiobunum uxorium Crosby and Bishop Beaufort, Berkeley (Davis 1934); Horry
(McGhee 1970 as L. speciosum; Aiken
(present study)
Leiobunum ventricosum (Wood) Anderson (Gorsuch et al. 1989);
Allendale (present study)
Leiobunum verrucosum (Wood) Berkeley, Darlington (Davis 1934); Aiken,
Allendale, Barnwell (present study)
Leiobunum vittatum (Say) Beaufort, Greenwood (Davis 1934); Aiken,
Allendale (present study)
Metasiro sassafrasensis Clouse and Wheeler Pickens (Clouse and Wheeler 2014)
Metasiro savannahensis Clouse and Wheeler Jasper (Clouse and Wheeler 2014)
Sabacon cavicolens (Packard) Greenville (Hoffman 1955)
Vonones sayi (Simon) Aiken, Allendale, Barnwell (present study)
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ecology since the ecological context of these sites is very well known. The objectives
of this work were to present the first survey of harvestmen occurring on
the SRS, to describe and compare the ground-active Opiliones fauna from major
habitat types at the SRS, and to summarize the basic habitat associations and phenological
patterns of these species.
Methods
Sampling for harvestmen was done by the first author in the context of 2 studies
of spiders (Araneae). Eight habitats were sampled using 2 standard methods:
Pitfall trapping – Ten 8.5-cm-diameter pitfall traps, containing 4% formalin
(with a trace of detergent), each covered by a 39 cm x 19 cm x 9 cm cinder block
rain roof suspended by propping a 7-cm brick at 1 end, were randomly placed (at
10 of 100 possible locations on a grid, each point 5 m apart) within a 0.25-ha (50
m x 50 m) plot, and operated continuously for 1 year (366 days; 1–4 May 1995
through 1–4 May 1996) in each of the 8 habitats. Contents were emptied in 2-week
intervals. Total trapping effort was almost 80 trap-years (8 habitats x 10 traps x 1
year; a few traps were lost due to flooding or animal disturbance), which yielded
14,934 spiders (Draney 1997) and 4288 harvestmen.
Litter sampling – Litter samples were collected 6 times (24–28 April, 26–30
June, 1–5 September, and 13–20 November 1995; 27–28 January and 10–14 April
Figure 1. Map of South Carolina showing location of the Savannah River Site and 1995–
1996 sampling sites 1–8. Numbers in circles are harvestmen species known per county;
most counties are unsampled. For harvestman records by county, see Table 1.
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1996). At each 0.25-ha site, two 0.04-m2 litter samples were collected from each of
5 (of 100) randomly selected 5 m x 5 m subplots by driving a metal cylinder into
the soil and collecting all leaf litter and debris down to mineral soil and hand sorting
and sieving in the laboratory. Total sample effort was 19.2 m2 (0.04 m2 samples
x 10 replicates x 6 dates x 8 habitats), which yielded 1178 spiders (Draney 1997)
but only 11 harvestmen. See Draney (1997) and Draney and Crossley (1999) for
additional site and sampling details.
Weather and climate
The average daily high and low temperatures during the study’s trap year (May
1995–April 1996) were similar to the averages of the 30-year (1961–1990) climatic
normal defined by the World Meteorological Organization (2016), at 24.78 °C and
9.94 °C versus 24.61 ± 0.77 °C (among-year standard deviation) and 11.0 ± 0.64
°C. Average low temperatures during the trap year were slightly lower than average,
being more than 2.78 °C cooler than average in November and December 1995 and
March 1996. Trap-year precipitation was significantly higher than the 30-year climatic
normal mean (143.51 cm versus 119.38 ± 20.83 cm). The trap year saw higher
precipitation than 28 of the 30 years in the 3-decade comparison period (National
Weather Service data for Blackville, Barnwell County, SC, ~20 km east of SRS).
In particular, June 1995 received 14.66 cm more than average, and August 1995
received 18.47 cm more than average.
Sites
These sites are listed here in order from the “youngest” habitats (most recently
disturbed) to the “oldest” habitats (those with longest time since catastrophic
disturbance such as fire or clearcutting). Sites 1–4 form an old field to pine forest
successional sequence; sites 5, 6, and 7 represent typical xeric, mesic, and wet mesic
subclimax forest types, respectively; and site 8 represents a mesic climax forest
type. The majority of the study sites were on “set-aside areas”, part of the DOE’s
research set-aside program. More information on those sites is available at http://
srel.uga.edu/set-asides/set-asides.html.
1. Old field site: Savannah River Ecology Laboratory (SREL) Set-Aside No. 1
(Field 3-412), in Aiken County (33°13'30''N, 81°45'15''W), includes several hectares
of forb–grassland. Maintenance as a pipeline right-of-way by annual mowing
and herbicide applications keeps this habitat in an early successional stage, with no
trees or shrubs. Site vegetation is dominated by perennial grasses interspersed with
extensive mats of lichen (Cladonia spp.). Opuntia humifusa Rafinesque (Prickly
Pear Cactus) is also abundant. Although this site receives the same amount of rain
as the other sites, the excessively drained sandy soils, lack of tree cover, and very
thin litter layer result in very xeric conditions for much of the year.
2. Young pines site: A 5-year-old (in 1996) plantation stand of Pinus palustris
Miller (Longleaf Pine), located on 10 ha near the junction of SRS Road 2 and the
M-Line Railroad in Aiken County (33°18'30''N, 81°43'30''W) represents young
pine stands, which are biotically and abiotically intermediate between typical field
and forest habitats in this region. The leaf-litter layer is thin in this transitional
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habitat, barely covering the well-drained sandy soil, and resulting in a fairly xeric
ground-layer environment for much of the year.
3. Medium pines site: SREL Set-Aside No. 2 in Aiken County (33°21'30''N,
81°41'W) includes about 27 ha of a 27-year-old (in 1996) plantation stand of
Longleaf Pine. This site represents a “medium aged” pine habitat, successionally
intermediate between the young and the mature pine stands. The ~15-m-tall pines
supported a very thick litter layer (November litter depth mean ± std. dev. = 7.60 ±
3.28 cm) on sandy, well-drained soil.
4. Large pines site: SREL Set-Aside No. 4 is an 8.9-ha volunteer Pinus taeda L.
(Loblolly Pine) stand in Aiken County (33°24'N, 81°36'W). It was ~40 years old
in 1996 and is the result of natural succession of an agricultural field abandoned in
1951. The overstory is composed entirely of ~25-m-high Loblolly Pines, and there
is only a sparse, low understory of Quercus spp. (oaks) and pine saplings. Groundcover
is sparse and consists mainly of perennial grasses, Toxicodendron radicans
(L.) Kuntze (Poison Ivy), and Cladonia sp. (reindeer moss lichen). The pine litter is
thick, and woody debris accumulation is heavy. The soil is well drained and sandy.
5. Sandhill scrub oak/pine site: SREL Set-Aside No. 29 is a mature stand of oak
and pine on a sandhill in Barnwell County (33°22'N, 81°31'W), which consists of a
widely spaced canopy of ~10–20-m-tall Loblolly and Longleaf Pines and a thicker
understory of ~3–10-m-tall oaks, mainly Quercus laevis Walter (Turkey Oak) and
Q. stellata Wanghen (Post Oak). The herb layer is very sparse, consisting mostly
of grasses. The site was in forest when the SRS was established in 1951; the oldest
trees were about 81 years old in 1996. The excessively well-drained sandy soils on
the 5–10% slope of the south-facing hillside result in xeric ground-layer conditions.
6. Upland hardwood site: This site, located in SRS Timber Compartment
30 off SRS Road 8-4 in Barnwell County (33°20'N, 81°31'30''W), is a mature
oak–hickory stand consisting of moderate-sized oaks, especially Quercus falcata
Michaux (Southern Red Oak) and Q. marilandica Muenchh. (Blackjack Oak),
and Carya tomentosa Sarge (Mockernut Hickory). This forest was intact when
the SRS was established in 1951, and is probably a relict or regrowth forest which
regenerated after selective logging some time before 1951. The ground layer was
dominated by grasses, Poison Ivy, and Smilax spp. (catbriers), and the soil is a
loamy sand.
7. Riparian hardwood site: SREL Set-Aside No. 6 is a mature bottomland
hardwood stand on the floodplain of Upper Three Runs Creek in Aiken County
(33°14'N, 81°44'30''W). Most of the sampled area occurs on the low floodplain immediately
adjacent to the river. This site was selectively logged in the 1920s and
1930s, but has not been cut or burned since. Portions of the floodplain are shallowly
submerged during the winter. The canopy included Quercus nigra L. (Water Oak),
Loblolly Pine, Liquidambar styraciflua L. (Sweetgum), and Fagus grandifolia
Ehrh. (American Beech), with a diverse and often lush understory and ground layer.
Soils consist of a silty clay flood deposit overlaying a thick s andy layer.
8. Riparian old-growth site: SREL Set-Aside No. 18 is an old-growth riparian
forest on a terrace just above the floodplain of Lower Three Runs Creek in
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Allendale County (33°08'N, 81°26'30''W). This 3.4-ha site includes the oldest
canopy elements found at SRS: Loblolly Pines aged at 196–216 years in 1996. The
canopy also comprised Sweetgum and Liriodendron tulipifera L. (Yellow Poplar).
A dense under-canopy was dominated by Mockernut Hickory and oaks. The shrub
layer and cover is sparse. Soils are well-drained and loamy; the litter layer includes
a well-developed, root-bound humus layer.
Baseline survey
A baseline biodiversity survey was undertaken during the summer of 1992, prior
to the previously described sampling. In each of the following 6 habitats, 20 twoday
(~48-hour) uncovered ethanol pitfalls were run 7 times (27–29 November 1991;
27–28 April;,11–13 May, 16–18 June, 30 June–2 July;,15–17 July, and 2–4 October
1992). These traps were run in 4 lines of 5 traps with 3 m between traps. Harvestmen
were collected by hand and using a sweep net during some of these dates as
well. The sampling intensity was much less than for the 1995 project, yielding only
73 Opiliones specimens (66 from the pitfall trapping and 7 from sweep netting or
hand collection). Therefore, these specimens serve to document additional records,
but analysis of data is restricted to the 1995–1996 pitfall data. For more information
about these sites, see Workman and McLeod (1990) and Davis and Janacek (1997).
1. Rainbow Bay (Set-Aside 16 in Barnwell County; 33°15.6'N, 81°37.9'W) is
one of about 194 Carolina Bays on the SRS (Workman and McLeod 1990). These
are shallow elliptical or ovoid ephemeral (winter-filled) wetlands. Rainbow Bay is
about 1 ha in size.
2. A plantation of Pinus elliotti Engelm (Slash Pine) dominated woods surrounding
Rainbow Bay (Set-Aside 16). Sampling took place outside of the wetland and
within 100 m of it.
3. Powerline cut just northwest of Set-Aside 16 at the junction of Road C-5 and
Road C-5e.3 (Barnwell County; 33°15'43''N, 81°38'4''W), dominated by a thick
bramble cover of Rubus spp. (Blackberry) with some Prunus serotina Ehrh. (Black
Cherry) growing as an overstory.
4. Sandhills xeric pine–oak forest set-aside (Set-Aside 3 in Aiken County;
33°16'57''N, 81°41'9''W) is a relatively undisturbed xeric forest dominated by Turkey
Oak and Longleaf Pine on infertile, very well-drained sandy soil, which is a
remnant ancient beach dune.
5. Beach hardwood riparian woods set-aside (same as site number 7, above).
6. Mixed riparian swamp set-aside (Set-Aside 7 in Barnwell County; 33°9'42''N,
81°43'35''W). This is a seasonally flooded bottomland hardwood forest on the
floodplain of the Savannah River.
Data analysis
All harvestmen were identified by the second author, and vouchers are retained
in the collections of both authors.
We restricted analyses to the 1 year of continuous pitfall trapping in 8 habitats
during 1995–1996. This robust data set features virtually equal sampling effort
among 8 major SRS habitat types and among 26 sampling dates of a continuously
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sampled year (May 1995–May 1996). Therefore, it is possible to compare species
richness, phenology, and habitat distribution among these 8 habitats.
Species richness. We used Estimate S (Colwell 2013) tto estimate the richness
of the ground-dwelling Opiliones fauna at all 8 SRS study sites, both combined
and separately, given the results of the pitfall sampling. The indices use the ratio
of singletons (species represented by only one individual) to doubletons (species
represented by exactly two individuals) in a sample and, with the assumption that
there will be no singletons in a totally sampled assemblage, serve to reflect the
number of unsampled taxa remaining. Thus, estimates could not be obtained from
habitats lacking singletons and doubletons, but we pooled all adult individuals
trapped during a year and analyzed the data as a single sample. We calculated an
abundance-based species richness estimator called Chao 1 (Chao 1987).
We also used Estimate S to determine the similarity of the Opiliones assemblages
in the pitfall samples among all pairs of the eight 1995–1996 habitats. We
used Estimate S (Colwell 2013) to calculate the abundance-based Jaccard sample
similarity index (Chao et al. 2005). The index ranges from 0 (no species shared
between 2 habitats) to 1 (identical species composition and abundance).
Phenology. For the 5 species represented in the 1995–1996 pitfall data by more
individuals than sample dates (n > 26), we calculated an index of seasonality (Is;
Curtis 1978), which uses the proportion of individuals of a species captured in each
month to determine how evenly the species is distributed throughout the year. Since
our sampling periods were biweekly instead of monthly, the index was converted
to a fraction (proportion of the year) and then multiplied by 12 to express the index
as “months”, with smaller numbers denoting more stenochronous species (found as
adults during only a short time each year), and larger numbers denoting relatively
eurychronous species that are more widely distributed seasonally. The index varies
from a minimum of 12/s to a maximum of 12 and is calculated as
Is = 12[(1/Σpj
2)/s], summed over all sampling periods,
where pj = proportion sampled during sampling period j, and s = total number of
sampling periods
Results
Species richness
Altogether, we sampled and examined 4372 Opiliones specimens: 4288 (98.1%)
from the 1995–1996 pitfalls; 66 (1.51%) from the 1992 pitfalls; 11 (0.25%) from the
1995–1996 litter samples, and 7 (0.16%) from 1992 sweep-net and hand-collected
samples. We found 9 species of harvestmen (Table 2). Table 1 and Figure 1 show the
county-level records of Opiliones in South Carolina. One of the counties sampled
here, Aiken, now has the most species reported from any county in the state, with
6. Vonones sayi is reported from South Carolina for the first time here, although
it seems to occur at almost every South Carolina site we have collected, from the
mountains to the coast, and it may well be present in every county in the state (M.L.
Draney, pers. observ.). Bishopella laciniosa (Crosby and Bishop) (Phalangodidae),
a species rarely collected in South Carolina and known from only 2 previous reports
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Table 2. List of Opiliones from the Savannah River site, SC. See text for further information about sites and sampling methods. 1992 Sites: 1 = Rainbow
Bay (Barnwell County); 2 = slash pine surrounding Rainbow Bay (Barnwell County); 3 = powerline cut brambles (Barnwell County); 4 = sandhills (Aiken
County); 5 = beech hardwood (Aiken County); 6 = mixed swamp (Barnwell County). 1995 Sites (1992 site 5 = 1995 site 7): 1 = old field (Aiken County);
2 = young pine plantation (Aiken County); 3 = medium pines (Aiken County); 4 = large loblolly pines (Aiken County); 5 = sandhill scrub oak–pine (Barnwell
County); 6 = upland hardwood (Barnwell County); 7 = beech hardwood (Aiken County); 8 = riparian old growth (Allendale County). See Figure 1.
Counties: AK = Aiken, AD = Allendale, BW = Barnwell. Methods: P = Pitfall trap, L = Litter sorting, H = Hand collected.
Major Clade: Family Species 1992 Sites 1995 Sites Counties Methods
Laniatores: Cosmetidae Vonones sayi (Simon) 1, 2, 5, 6 4, 6, 7, 8 AK, AD, BW P, L
Laniatores: Phalangodidae Bishopella laciniosa (Crosby and Bishop) 7 AK L
Palpatores: Sclerosomatidae Hadrobunus fusiformis Shultz 1, 3, 4, 6 1, 2, 3, 4, 5, 6, 7, 8 AK, AD, BW P,L
Palpatores: Sclerosomatidae Leobunum bimaculatum Banks 1, 2 1, 2, 3, 4, 5 AK, BW P, H
Palpatores: Sclerosomatidae Leiobunum politum Weed 1 7, 8 AK, AD, BW P
Palpatores: Sclerosomatidae Leiobunum uxorium Crosby and Bishop 4, 7 AK P
Palpatores: Sclerosomatidae Leiobunum ventricosum (Wood) 8 AD P
Palpatores: Sclerosomatidae Leiobunum verrucosum (Wood) 5, 6 6, 7, 8 AK, AD, BW P
Palpatores: Sclerosomatidae Leiobunum vittatum (Say) 7, 8 AK, AD P
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(Fig. 1, Table 1), was the only species of the 9 not represented in the 1995–1996
pitfall samples; a single individual was collected from a litter sample at the Beech
Hardwood Set-Aside #6, 1–5 September 1995. The Chao1 richness estimator could
not be calculated on most of the assemblages from individual habitats, because of
lack of singletons and doubletons in the data set. However, when all 1995–1996
pitfall data were pooled, the Chao1 richness estimate was the observed richness of
8 species.
Species composition
The 1995–1996 pitfall samples yielded 1 to 6 species per habitat (median = 3;
Mean = 3.25; Table 3). In general, older and more-mesic habitats yielded more
species than younger and more-xeric habitats (Table 3). The riparian hardwoods
and riparian old-growth habitats each yielded 6 species, and the old field, young
pines, and medium pines habitats each yielded only 2: Leiobunum bimaculatum
Banks and Hadrobunus fusiformis Shultz. Only L. bimaculatum was collected in
the xeric sandhill scrub oak–pine site. Hadrobunus fusiformis was numerically
dominant overall in all habitats except the most xeric site, the old field (dominated
by L. bimaculatum), and the most mesic site, the riparian hardwoods
(dominated by Leiobunum verrucosum (Wood)). Diversity indices were not calculated
to compare habitats because of very different sample sizes among them (n =
5 in sandhill oak–pine to n = 300 in riparian old growth) and because data were
pooled over the course of a year. However, it is apparent that the more-mesic habitats
have more-diverse assemblages of ground-active Opiliones, and that the
species found at the riparian hardwoods site (Table 3) are remarkably evenly distributed
and thus a highly diverse assemblage relative to the other sites.
Similarity among habitats
We used the classic Jaccard index to measure quantitative similarity of species
composition (taking abundance into account) among all pairs of the 8 habitats
Table 3. Habitat distribution of pitfall-trapped Opiliones at the Savannah River Site, SC. Data given
as percent of total adults trapped in 26 biweekly samples from May 1995 to May 1996 (pooled). See
Methods for details about habitats. Habitats: 1 = old field, 2 = young pines, 3 = medium pines, 4 =
large pines, 5 = sandhill oak–pine, 6 = upland hardwoods, 7 = riparian hardwoods, 8 = riparian old
growth.
Total No. of
Habitats adults habitats
Species 1 2 3 4 5 6 7 8 trapped occupied
Hadrobunus fusiformis 3.5 10.8 13.0 6.8 0.0 15.1 6.8 44.2 548 7
Leiobunum bimaculatum 51.2 31.7 3.7 7.3 6.1 0.0 0.0 0.0 82 5
L. politum 0.0 0.0 0.0 0.0 0.0 0.0 66.7 33.3 15 2
L. uxorium 0.0 0.0 0.0 75.0 0.0 0.0 25.0 0.0 4 2
L. ventricosum 0.0 0.0 0.0 0.0 0.0 0.0 0.0 100.0 4 1
L. verrucosum 0.0 0.0 0.0 0.0 0.0 4.8 70.5 24.8 105 3
L. vittatum 0.0 0.0 0.0 0.0 0.0 0.0 56.7 43.3 30 2
Vonones sayi 0.0 0.0 0.0 7.5 0.0 2.5 65.0 25.0 40 4
Habitat Richness 2 2 2 4 1 3 6 6
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sampled by pitfall in 1995–1996 (Table 4). Habitats shared 0–5 species (mean
= 1.54, median and mode = 1). The similarity values ranged from 0 to 1, the
theoretical minimum and maximum. The sandhill scrub oak–pine site (#5; see
Table 3 for site abbreviations) shared no species with upland hardwoods (#6), riparian
hardwoods (#7), and riparian old growth (#8). The old field (#1), young pines
(#2) and medium pines (#3) habitats all shared the same 2 species: Hadrobunus
fusiformis and Leiobunum bimaculatum. Average similarity across all habitat pairs
was 0.38, and the median was 0.325. In general, the Jaccard similarity reflected the
habitat’s time since disturbance. The younger, more-xeric habitats had similar assemblages:
pairs of habitats “1” through “5” always had values of 0.5 or 1.0, with
the exception of 1 pair, the large pines and sandhills oak–pine. Likewise, habitats
“6” through “8” always had values of 0.5 or higher (Table 4).
Habitat distribution of species
The 8 pitfall-sampled species were each recorded from 1 to 7 habitats (median =
2.5, mean = 3.25; Table 3). Hadrobunus fusiformis seems to be a habitat generalist,
Table 4. Species richness (Estimate S) of each habitat, and Jaccard Similarity between pairs of habitats
for adult Opiliones at the Savannah River Site. Catch from the entire year’s pitfalls was pooled.
Habitats: 1 = old field, 2 = young pines, 3 = medium pines, 4 = large pines, 5 = sandhill oak–pine,
6 = upland hardwoods, 7 = riparian hardwoods, 8 = riparian old growth.
First habitat Second habitat S first habitat S second habitat Shared species Jaccard similarity
1 2 2 2 2 1.000
1 3 2 2 2 1.000
1 4 2 4 2 0.500
1 5 2 1 1 0.500
1 6 2 3 1 0.250
1 7 2 6 1 0.143
1 8 2 6 1 0.143
2 3 2 2 2 1.000
2 4 2 4 2 0.500
2 5 2 1 1 0.500
2 6 2 3 1 0.250
2 7 2 6 1 0.143
2 8 2 6 1 0.143
3 4 2 4 2 0.500
3 5 2 1 1 0.500
3 6 2 3 1 0.250
3 7 2 6 1 0.143
3 8 2 6 1 0.143
4 5 4 1 1 0.250
4 6 4 3 2 0.400
4 7 4 6 3 0.429
4 8 4 6 2 0.250
5 6 1 3 0 0.000
5 7 1 6 0 0.000
5 8 1 6 0 0.000
6 7 3 6 3 0.500
6 8 3 6 3 0.500
7 8 6 6 5 0.714
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being present in all habitats except the sandhill scrub oak–pine site (although an
individual was collected from a similar xeric forested site, the sandhill set-aside
# 3 in October 1992; Table 2). The species was common in both the wettest (riparian
hardwoods) and driest (old field) sites, and across the range of disturbance
frequency, from the frequently disturbed old field to the 200-year-old riparian oldgrowth
site. It seems to be the most generalist in its habitat distribution, although
44.2% of the individuals were trapped in the riparian old-growth habitat.
Leiobunum bimaculatum seems to be distributed in more-xeric and morefrequently
disturbed sites (Table 3). It was most abundant (51.1% of specimens) at
the old field site and was absent from the older sites except for the xeric sandhill
oak–pine site. It was the only species found in this xeric site.
The remaining 6 species all seem to be distributed mainly in the more-mesic and
less-frequently disturbed sites. All 6 were absent from the 3 most-xeric and youngest
sites (old field, young pines, and medium pines sites), and from the sandhill
oak–pine site.
Phenology
Overall, adult Opiliones made up 23.5% of total individuals trapped in the
1995–1996 pitfalls. However, this ratio varied widely throughout the year (Table 5);
the pitfall traps sampled between 0 and 5 species of adult harvestmen at any time period;
4 to 5 species were present continuously between late June and early December
(Table 5). There were no immatures trapped during 26 June through 6 September,
and there were only 3 adults trapped during 29 December through 3 May. Immatures
(of all species; these were not further identified) made their appearance in pitfalls
in September and peaked during late February/early March (Table 5). Five species
are abundant enough (Table 5) to describe their seasonal distribution in the samples.
Vonones sayi peaked earliest, in late May/early June, but adults were found during
a long time period, from late February through early October. The other 4 species
had adult peaks in the autumn, with Leiobunum verrucosum peaking in September,
Hadrobunus fusiformis in October, Leiobunum bimaculatum in November, and
Leiobunum vittatum in December. All 5 species seem to be univoltine with a single
reproductive event (indicated by the peak catch of adults), with the possible exception
of Hadrobunus fusiformis. This species was present as adults during a long
time period, from May to December, and there may be a small peak in May/June
in addition to the larger autumn peak. This finding may indicate 2 generations per
year. However, cursory examination of the phenology of putative immature H. fusiformis
(data not shown) favors the univoltine hypothesis. The probable juveniles of
H. fusiformis occur only in the cold-season samples. They appear in the late fall as
the previous generation is still being captured, and start to disappear in late spring
as the next generation of adults begin to appear. Those juveniles did not persist into
the summer or autumn, and this finding seems to indicate a single cohort maturing
primarily in the autumn. It is possible that there are 2 periods of intense activity in
adults, perhaps one reflecting mating and one reflecting foraging activity. Analysis
of immature size distribution would be necessary to definitively demonstrate the univoltine
pattern, and we are currently working out the methodology for this.
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Table 5. Phenology of harvestmen of the Savannah River Site captured by 1 year of continuous pitfall trapping, May 1995–May 1996. Total catch from 8
habitats pooled. Exact dates vary 1–2 days because only half of the habitats were sampled on a given day. Totals for each species include only adult specimens;
all immature specimens pooled as “mixed immatures”. The index of seasonality (IS) was calculated for the 5 species with n > number of sampling
periods, 26. The index is expressed as proportion of year, with smaller proportions denoting more stenochronous species found as adults during only a
short period and larger proportions represent increasingly eurychronous species. H. f. = H. fusiformis, L. b. = L. bimaculatum, L. p. = L. politum, L. u. =
L. uxorium, L. ven. = L. ventricosum, L. ver. = L. verrucosum, L. vit. = L. vittatum, and V. s. = L. vittatum.
Species
Dates Mixed Total Total present as
Sample (1995–1996) H. f. L. b. L. p. L. u. L. ven. L. ver. L. vit. V. s. immatures specimens adults % adults adults
1 3–5 May 55 0 0 0 0 0 0 6 96 157 61 38.9 2
2 15–29 May 25 0 0 0 0 4 0 6 25 60 35 58.3 3
3 31 May–14 Jun 46 0 0 0 0 5 0 18 7 76 69 90.8 3
4 12–26 Jun 10 0 0 0 0 3 0 0 1 14 13 92.9 2
5 26 Jun–10 Jul 16 0 3 0 1 3 0 1 0 24 24 100.0 5
6 10–24 Jul 26 1 3 0 2 14 0 0 0 46 46 100.0 5
7 24 Jul–7 Aug 27 0 6 0 0 14 0 3 0 50 50 100.0 4
8 7–21 Aug 28 1 0 1 0 12 0 2 0 44 44 100.0 5
9 21 Aug–6 Sep 25 3 1 0 0 16 0 0 0 45 45 100.0 4
10 6–20 Sep 55 7 0 0 1 20 0 1 1 85 84 98.8 5
11 20 Sep–4 Oct 53 10 2 0 0 7 0 1 5 78 73 93.6 5
12 4–18 Oct 91 5 0 0 0 4 3 0 9 112 103 92.0 4
13 18 Oct–1 Nov 56 4 0 0 0 1 1 0 94 156 62 39.7 4
14 1–15 Nov 28 28 0 1 0 2 4 0 89 152 63 41.4 5
15 15–29 Nov 2 9 0 1 0 0 4 0 64 83 19 22.9 4
16 29 Nov–13 Dec 2 10 0 1 0 0 13 0 67 84 17 20.2 4
17 13–29 Dec 0 4 0 0 0 0 1 0 96 113 17 15.0 2
18 29 Dec–10 Jan 0 0 0 0 0 0 0 0 110 111 1 0.9 1
19 10–24 Jan 0 0 0 0 0 0 0 0 129 129 0 0.0 0
20 24 Jan–7 Feb 0 0 0 0 0 0 0 0 156 156 0 0.0 0
21 7–21 Feb 0 0 0 0 0 0 0 0 302 302 0 0.0 0
22 21 Feb–8 Mar 0 0 0 0 0 0 0 1 389 390 1 0.3 1
23 8–20 Mar 0 0 0 0 0 0 0 0 334 334 0 0.0 0
24 20 Mar–3 Apr 0 0 0 0 0 0 0 0 215 215 0 0.0 0
25 3–17 Apr 0 0 0 0 0 0 0 0 203 203 0 0.0 0
26 17 Apr–3 May 0 0 0 0 0 0 0 1 303 304 1 0.2 1
Totals 548 82 15 4 4 105 30 40 2695 3523 828
IS (months) 5.13 2.63 n/a n/a n/a 3.85 1.82 1.78
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The index of seasonality (Table 5) varied from highly stenochronous species
with values of less than 2 months (the early maturing Vonones sayi and the late
maturing Leiobunum vittatum) to over 5 months in the case of the eurychronous and
possibly bivoltine Hadrobunus fusiformis. Leiobunum verrucosum, which is clearly
univoltine, is also eurychronous with an Is of almost 4 months.
Discussion
Autecology
This paper gives some of the first quantitative information about phenology and
habitat distribution of the sampled species, and in general this information agrees
with what we gleaned from the literature or have observed from previous collecting
(M.L. Draney, pers. observ.).
Vonones sayi has been most frequently reported in soils with high sand content
(well-drained), including rocky outcrops in otherwise mesic regions, sand along
rivers, and semi-arid regions (Cokendolpher and Jones 1991, Goodnight 1957), and
our results are consistent with this pattern. Vonones sayi was found at SRS in the
mesic sites, which all happen to be underlain by sandy soils, although a heavier, organic-
matter–rich A-horizon characterized the riparian hardwood site (1995–1996
site #7). Cokendolpher and Jones (1991) report highest adult numbers in April and
May in central Texas, which is a little earlier than the late May–early June peak at
SRS. In summer, both adult and immature forms have been found together in Indiana
(Goodnight 1957), consistent with reports of the species living up to 3 years in
the laboratory (Cokendolpher and Jones 1991).
Hadrobunus fusiformis was the most abundant species in our samples, which
is extraordinary considering that the species was not described until more than a
decade after our specimens were collected (Shultz 2010). The description includes
2 specimens from Aiken County, SC, but the rest of the individuals were from the
mountains or near the Atlantic coast. Shultz (2010) speculated that this apparent
disjunct distribution is really an artifact of sampling effort, and the present study
lends support to this idea. This species was the most abundantly sampled species in
our study; we trapped 548 individuals in the 1995–1996 pitfalls, which constitute
66% of total adult Opiliones. Furthermore, it is the most ecologically general of the
species we sampled; it was found in all habitats sampled except for the Sandhills
scrub oak–pine and the pine forest surrounding Rainbow Bay (Site #2 of 1992 survey),
including both recently disturbed and old habitats, both xeric and mesic–wet
habitats, and in deciduous and coniferous forests as well as field and shrub habitats.
These findings indicate that it probably occurs abundantly throughout most of
South Carolina. In previous collections, H. fusiformis tended to be most abundant
in more-open and less-mature environments such as grassland and young or open
woods, a habitat preference that seems to characterize other members of this genus
as well (Shultz 2010). Why this species was particularly abundant at the SRS oldgrowth
site is not known and is not clear from consideration of our data on habitat
age and soil moisture; some other factors must be important.
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Leiobunum bimaculatum occurs mainly on the Gulf and Atlantic coastal plains
(Crosby and Bishop 1924) and is nearly at its northern limit here, except for a
disjunct population in Virginia Beach, VA (Davis 1934; J.W. Shultz, pers. observ.),
which might contribute to its occurrence being limited to xeric and presumably
warmer locations on the SRS landscape. Most collection records of adults from
other localities are in September through November, similar to the present results.
Interestingly, the coloration of the population reported here is rather different from
the classic coloration of the species, which is a generally dark dorsum with large bilateral
white to yellow-white splotches on the carapace and first abdominal tergite.
The pattern exists in the SRS populations, but the contrast of the dark and white
cuticle is very reduced. Although these specimens are nearly 2 decades old, the lack
of coloration is very unlikely to be an artifact of age, as the other sampled taxa do
not show similar coloration changes. In any case, these specimens were killed in
formalin, which preserves coloration much better than with initial immersion in
ethanol (M.L. Draney, pers. observ.).
Leiobunum verrucosum is a widespread species that ranges across the eastern
United States. In Maryland, it overwinters as an immature and matures in late
April–early May. Adults are very abundant in June and then gradually decline
throughout the summer, becoming hard to find by the end of August. However,
the juveniles can be found under objects through the fall and winter (J.W. Shultz,
pers. obervs.). At SRS, the species peaked much later, in mid-September. Although
the seasonality of the species is very different in Maryland and South
Carolina, the differences can probably be explained by the earlier autumn farther
north, and suggests that the species phenology is responding to some aspect of
environmental temperature. As at SRS, other known records of the species are
mainly from wooded habitats. Interestingly, individuals tend to occur on plants
in Maryland, but they seem to be largely ground-dwelling farther north (e.g.,
Ohio; J.W. Shultz, pers. obervs.).
Leiobunum vittatum is another very widespread species, ranging up the Atlantic
coast from Florida to Canada and west to the Great Plains, and even further west
in the south (Cokendolpher and Lee 1993). It is a common “late season” form (it
peaked latest of all SRS species) that is often very abundant. It inhabits a wide
range of habitats but prefers taller woody vegetation (bushes and trees). The sudden
appearance of this species late in the season at SRS likely reflects (1) the climbing
habits of immatures (J.W. Shultz, pers. obervs.) and (2) the elimination of groundliving
competitors late in the season. Subadults of the species are easy to diagnose,
and we recorded none, even from the habitats where the 30 pitfall individuals were
found. The behavior of the immatures might account for this.
Leiobunum vittatum serves as a reminder that the habitat distribution of each
species needs to be taken into a regional context. In the present study, L. vittatum
seems to be restricted to the oldest and most mesic of the habitats at SRS (Table 3),
yet the species seems to be more broadly distributed, including within more-xeric
old field and young forest habitats, farther north in its range (e.g., Wisconsin; M.L.
Draney pers. observ.).
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In Eupnoi Opiliones in general, sexual maturation is usually delayed for some
time (up to several weeks) after the final molt (J.W. Shultz, pers. obervs.). Therefore,
sudden, delayed appearance in pitfalls may reflect males searching for females and
females looking for oviposition sites. The fact that L. vittatum seems to show up suddenly
(Table 5) may be an illustration of this delayed maturation phenomenon.
Leiobunum politum Weed is generally a woodland or edge species in mesic environments.
Like L. vittatum, it is very widespread in eastern North America. The
species can be found on both the ground and low vegetation, but individuals are not
found on tree trunks (J.W. Shultz, pers. obervs.).
Finally, Leiobunum ventricosum (Wood) and Leiobunum uxorium Crosby and
Bishop are both climbing species, which accounts for their rarity in SRS pitfall
samples. It is likely that the biology of many “long-legged” harvestman species
will lead to biases in species representation using pitfall sampling. These species
probably spend a good deal of time foraging and resting on elevated surfaces and
may spend limited time on the ground where they are vulnerable to trapping.
Faunistics
Our additions bring the total Opiliones species recorded from South Carolina
to 20 (including 3 undescribed species; Table 1). The 9 species we found on the
site represent over 40% of the state’s known fauna. Figure 1 highlights the fact
that the state’s Opiliones fauna remains very poorly known. Harvestmen records
are reported from only about one third (17 of 46) of South Carolina counties, and
Vonones sayi, a distinctive species that may be common in a variety of South
Carolina habitats (M.L. Draney, pers. observ.), is here reported from the state for
the first time.
This list should not be considered in any sense a complete checklist for the Opiliones
of the SRS, because the great majority of the sampling was done using one
method, pitfall traps. While pitfall traps are highly effective at determining “activity
density” (i.e., number of active individuals encountered in an area during the
sampling period) of species that wander across the ground surface, they certainly
undersample and may fail to sample both smaller soil- and litter-dwelling species as
well as species that predominately inhabit vegetation. While we did collect some of
these species (for example, the soil-dwelling Vonones sayi and the largely climbing
Leiobunum uxorium, L. ventricosum, and L. vittatum), there are very likely other
species in these categories on the site. Also, sampling was focused on a relatively
small number of sites (over 98% of the specimens from the eight 1995–1996 habitats,
plus limited sampling from 5 other sites), and while these sites were selected
to both represent the most common habitat types on the site and to cover the range
of habitat types from xeric to wet–mesic, not all habitats were thoroughly sampled.
In particular, there was relatively little sampling in wetland areas (other than our
Rainbow Bay and mixed swamp forest sites). Future work in this region should
focus on vegetation sampling, especially of forest canopies, and expand to include
other habitats and microhabitats, especially wetlands and more emphasis on small
litter-dwelling species.
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Our attempts to estimate species richness, however, showed that our 1995–1996
pitfall samples did an adequate job of sampling the ground-active opilionid fauna.
With our overall pitfall data, there were no singletons or doubletons; the rarest
species (L. uxorium and L. ventricosum) were each represented by 4 individuals.
This pattern largely held in estimates of individual habitats as well; there were no
doubletons in individual habitat data, and only the riparian hardwood and riparian
old-growth sites had any singletons (1 species each). Since adequately sampled communities
are composed of species which have all been sampled multiple times, we
can be fairly confident that we sampled most of the ground-active species in most of
the habitats (with the possible exception of the 2 very diverse riparian sites). Overall,
our results lend support to the idea that pitfall trapping is a good method for sampling
ground-level Opiliones. The 1995–1996 pitfall samples yielded 8 of the 9 species
recorded from SRS, including all species except Bishopella laciniosa, a rarely collected
species known from only 2 other instances in South Carolina (Fig. 1).
Our 1995–1996 pitfall data is one of the most intensive sample sets in the literature
for ground-dwelling Opiliones. Only a few other large systematic sampling
efforts have been conducted (Bachmann and Schaefer 1983, Curtis 1978, Jennings
et al. 1984), and the present results show that these systematic efforts can improve
our understanding of the distribution and phenology of harvestman species. In addition,
our data set can be used to assess the value of the less-intensive sampling
we also conducted at SRS. It is apparent that less-intensive surveys do not yield
as many species, but are generally adequate for documenting the most abundant
species on a site. The 1992 survey (n = 73 individuals) yielded 5 of the 9 recorded
species, including all species making up 4% or more of the 1995–1996 intensive
pitfall series (40 or more of n = 828 pitfall individuals). More-intensive sampling
of a few sites and extensive sampling across the landscape will be needed to come
to a detailed understanding of the ecology of North American harvestmen.
Acknowledgments
This research was supported by Financial Assistance Award Number DE-FC09-
96SR1854 From US DOE to the University of Georgia Foundation. B.E. Taylor (SREL) and
D.A. Crossley Jr. (U. Georgia) provided facilities and support to the senior author. Thanks
also to V. Medland, D. Leeper, and C. Stockwell for support during the fieldwork phase
of this research. We thank M. Spaid for help in sorting and packing samples for shipment,
and S. Meyer for access to National Weather Service data and advice on climate-summary
methods. J. Shultz was supported by the Maryland Agricultural Experiment Station.
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