Spiders Associated with Early Successional Stages on a Virginia Barrier Island

6 Pages·1996·5.4 MB·English

by  Stephen R Johnson

1996. The Journal ofArachnology 24:135-140
SPIDERS ASSOCIATED WITH EARLY SUCCESSIONAL
STAGES ON A VIRGINIA BARRIER ISLAND
Stephen R. Johnson1: Department of Biology, Virginia Commonwealth University,
Richmond, Virginia 23284 USA
ABSTRACT. Communities consisting of small shrubs and larger pre-thicket plants ofMyrica cerifera
(Myricacae) and Baccharis halmifolia (Asteraceae) were sampled by sweepnet in early June, July and
August of 1995 to estimate the density and diversity of spider communities associated with these shrubs
during early successional stages of thicket development. This was initiated as part of a larger study
intended to determine establishment patterns of these two shrubs in graminoid dominated swales (low-
lying wetlands between dune ridges). The species Hentzia palmarum (Hentz 1832), Erisflava (Peckham
& Peckham 1888) (Araneae, Salticidae) and Misumenops celer (Hentz 1847) (Araneae, Thomisidae) were
common to both Myrica and Baccharis; however, densities differed between shrubs. Habronattus agilis
(Banks 1893) (Salticidae) was uncommon and only found on Myrica while the infrequent species Poul-
tonella alboimmaculata (Peckham & Peckham 1883) (Salticidae) was only found on Baccharis. The
greatest differences in spider densities were between the early transitional swale site and the developing
thicket (later transitional swale) site. Insect communities sampled had greater observed differences in
structure between the two shrubs than were found with spiders.
Much ofthe work dealing with spiders and of larger clumps containing both Myrica and
spider assemblages has focussed on the role Baccharis. As the island ages, Myrica and
of spiders as predator control agents in both Baccharis in the older swales gradually de-
natural and man-altered ecosystems (Reichert velop into a thicket. Immature thickets contain
& m
Lockley 1984; Nyffeler et al. 1987; Reich- large Myrica (1-2 canopy spread) and scat-
ert & Bishop 1990). Less-studied aspects of tered smaller (0.25-1 m canopy spread) indi-
spider ecology are the habitat requirements of viduals of both Myrica and Baccharis. While
species and the dynamics ofguild structure in many Myrica plants are large, there is no con-
natural habitats. tinuous canopy coverage as is found in the
While many spiders may be generalistpred- mid-island or bay-side thickets (Young et al.
ators, many species may have fairly strict hab- 1995).
itat requirements. Species may segregate by In the most recently established swale,
habitat or be cryptically adapted to hunt on many individuals of both Myrica and Bac-
selected plant substrates (Dobel et al. 1990; charis show visible signs of herbivory (pers.
&
Coetzee et al. 1990; Cutler 1992; Cutler obs.). Such herbivory may alter the ultimate
Jennings 1992). Spiders in selected habitats composition of the thicket community by re-
may also utilize woody plants as habitat is- stricting growth of certain plants or by elim-
lands (Ehmann 1994). inating individuals (Kraft & Denno 1982;
On mid-Atlantic barrier islands, vegetation Krischik & Denno 1990). Spiders associated
behind the foredune grades from xeric grass with Myrica and Baccharis may in turn alter
dominated communities into graminoid dom- insect distribution and density such that im-
inated swales. Established swales are soon pact of herbivory may be lessened and plants
colonized by waxmyrtle (.Myrica cerifera) and are better able to compete (Crawley 1983;
groundsel tree (.Baccharis halmifolia). These Reichert & Lockley 1984).
plants in the colonizing swale are found as The purpose of this study was to 1) inves-
widely scattered small individuals or as part tigate spider species and composition of as-
semblages associated with small and pre-can-
'Present Address: Southern ScienceCenter, 700Ca- opy-closure plants of Myrica cerifera and
jundome Blvd., Lafayette, Louisiana 70506 USA. Baccharis halmifolia and 2) estimate seasonal
,
135
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136 THE JOURNAL OF ARACHNOLOGY
—
Figure 1. The Virginiaportionofthe DelMarVa
peninsula and the associated barrier islands which
make up the Virginia Coast Reserve. The two field
sites, developing thicket (DT) and colonizing swale
(CS), are shown on the insert depicting the north
half of Hog Island.
patterns ofdistribution and density ofthe most
common spiders and potential prey insects on —
these shrubs. This study represents a portion Figure 2. Depiction of the developing thicket
of a larger study designed to determine the (on the left) and the colonizing swale (right) show-
ing the relative density of plants and pattern of
dynamics of colonization of M. cerifera and sweep sampling. Baccharisplants are shown in sol-
B. halmifolia on newly established barrier is- id black. Large and medium Myrica plants are
land swales. shown with crosshatching; small plants are left
METHODS clear.
Study sites.- Field work was conducted on
Hog Island (37°40'N, 75°40'W). This island is estimate spider and insect densities and dis-
part of the Virginia Coast Reserve and is the tributions on developing shrub thickets on
primary LTER site within the VCR (Dueseret barrier islands, four distinct sites were select-
al. 1976; Hayden et al. 1990). The north end ed which included developing shrub thicket
of Hog Island is actively accreting while the and early transitional swale. These commu-
south end of the island is eroding. Shrub nities are separated by a well developed xeric
thickets are well developed along the middle dune ridge (Figs. 1, 2).
of the island and along the bay side. Due to Spiders and insects were collected with a
the creation of new swales at the north end, sweepnet. Unidentified species were pre-
new thickets are forming east of the mid-is- served in alcohol and sent to Bruce Cutler at
land thicket (Young et al. 1995). Therefore, to the University of Kansas for identification.
P
JOHNSON-—SPIDERS OF BARRIER ISLAND SHRUBS 137
—
Figure 3. Estimated densities of the four primary species composing the spider guild on Myrica
cerifera in June, July and August of 1995. Vertical bars indicate one standard error of the mean. Letters
indicate significant differences ( < 0.05) in density between site.
Most insects were identified using field guides method gives an estimate of spider and prey
&
(Horror White 1970; Heifer 1987). Ants insect density/m2
.
were identified by Deborah Waller at Old Do- Two samples (50 sweeps/sample) were also
minion University. Voucher specimens of the taken in the graminoid dominated areas ofthe
spiders are located at the University of Kan- colonizing swale around individual Myrica
sas. and Baccharis plants in June, July and Au-
Four sweepnet samples were taken at each gust. These additional samples were taken to
of the four study sites along linear transects survey spider and insect species diversity in
running parallel to the dune ridge. These 16 swales and to qualify any overlap of species
samples were equally divided between the de- between swale graminoids and shrubs.
veloping thicket and the early transitional Data for spider and insect density changes
ANOVA
swale and included sweeps of 100 Myrica or with season were analyzed by 2-way
Baccharis plants in either habitat (Fig. 2). (site X season) in SAS using ana = 0.5 (Zar
This 16 sample collection procedure was re- 1984; SAS Institute 1988).
peated in early June, July and August, 1995. RESULTS AND DISCUSSION
Density of Myrica and Baccharis shrubs at
both study sites were counted using 15 quad- Density ofspiders on both shrubs was high-
m
rats, each five 2 delineated with cornerposts est in August. This increase from the previous
,
and a tape measure. The estimated density of two measurement periods was primarily due
spiders and prey was then determined by mul- because of the increase in density of Hentzia
tiplying the number of individuals per plant palmarum (Araneae, Salticidae) (Figs. 3, 4).
(total «/100) by the density of plants/m2 This There were no differences in density in Hen-
.
P
,
138 THE JOURNAL OF ARACHNOLOGY
—
Figure 4. Estimated densities of the four primary species of the spider guild on Baccharis halmifolia
in June, July, and August. Vertical bars indicate one standard errorofthe mean. Letters indicate significant
(P < 0.05) differences in density between sites.
tzia palmarum on Myrica between habitats. found on both Myrica and Baccharis but was
On Baccharis H. palmarum was more com- primarily found in the early transitional swale
,
mon in the developing thicket but was more site. While it was found on Myrica in the de-
evenly divided between habitats in August. veloping thicket, it was never found there on
Similarly to H. palmarum Habronattus agilis Baccharis. The changes in density of E.flava
,
(Araneae, Salticidae), also showed signifi- from June to significantly ( < 0.05) lower
cantly (P < 0.05) higher densities in August. densities in July and August show a trend op-
It was only found on Myrica and was most posite to that found forHentziapalmarum and
frequently captured in the developing thicket perhaps also Habronattus agilis.
(Fig. 3). Erisflava may have been more common on
Misumenops celer (Araneae, Thomisidae) Myrica and Baccharis plants in the early tran-
had the highest density of individuals on both sitional swale because it was a prominent
Myrica and Baccharis in July. On Myrica member of the surrounding graminoid com-
Misumenops celer had significantly (P < munity. In these areas, E. flava was found in
0.05) higher density in the early transitional a density of 21 individuals/100 sweeps in
swale. This pattern was also evident for Bac- June, 30/100 sweeps in July and 45/100
charis’, however, there was no significant dif- sweeps in August. These numbers are not ex-
ference in density between the sites. Also on pressed as a density/m2 because an intensive
Baccharis, M. celer had significantly (P < study of the swales was beyond the scope of
0.05) higher density in plants of the devel- this study. Nevertheless, the apparent increase
oping thicket (Fig. 4). in estimated density suggests a trend opposite
Eris flava (Araneae, Salticidae) was also to that found on Myrica and Baccharis over
2 7
JOHNSON—SPIDERS OF BARRIER ISLAND SHRUBS 139
—
the measurement period. Erisflava may have Table 1. Estimated densities of Oecanthusful-
been responding to a rapid increase injuvenile toni Walker on Myrica cerifera at the colonizing
planthoppers (unidentified) which were found swale and developing thicket sites. Numbers rep-
in density of 62 individuals/100 sweeps resent the mean ± one standard error. Letters (a, b)
among graminoids in August. Other spiders of indicate significant (P < 0.05) differences in den-
the graminoid dominated swale community sity.
were, in order of highest to lowest density,
Developing Colonizing
Mangora gibherosa (Hentz 1847) (Araneae,
thicket swale
Araneidae), Tetragnatha versicolor Walcken-
aer 1981 (Araneae, Araneidae), Marpissapik- June 5.1 ± 2.3a 3.4 ± 1.6a
ei (G.& E. Peckham 1888) (Araneae, Saltici- AJuulgyust 08..36 ±± 03..13ab 03..74 ±± 02..10ab
dae) and Tibellus oblongus (Walckenaer 1802)
(Araneae, Philodromidae).
Another prominent component ofthe spider
community on Baccharis was Poultonella al- sociated with Myrica and Baccharis are very
boimmaculata (Araneae, Salticidae). Like M. similar in species diversity but chiefly differ
celer, P. alboimmaculata had the highest es- in density with Baccharis supporting fewerin-
timated density on Baccharis in July; how- dividuals. Both shrubs growing in the early
ever, it was not found in June and was found transitional swale share one species, Erisfla-
in very low numbers in August (Fig. 4). This va, with the surrounding swale community.
species has been found in the upper midwest Generally spider diversity and density differed
and on the east coast in New York State but most between sites rather than between shrub
has not been previously observed on the Vir- species. Though species were generally iden-
ginia barrier islands (Cokendolpher & Horner tical for both shrubs, the rare jumping spider
& Poultonella alboimmaculata was only found
1978; Steitenroth Horner 1987). Therefore,
this may represent a new southeastern record on Baccharis.
for the species (J. C. Cokendolpher & B. Cut- ACKNOWLEDGMENTS
wleer,reperasl.socofmomu.n)d.mTohsetsecoPm.maolnbloyimamsascouclitaattead I thank Donald R. Young and Kathy Tolliv-
er for support and inspiration for this project.
with the ants, Forelius pruinosus (Roger) in
the early transitional swale and with Cremat- LITERATURE CITED
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clara P. alboimmaculata was never found as- der genus Poultonella (Araneae: Salticidae). J.
,
sociated with that species. Arachnol., 6:133-139.
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athnedafnitvse,sDpoelciiecshoodfearpuhsidm-atreinadeinFgoraenlt,s.CArmemoantg- DobEenlt,omHo.lG..,NRe.wF.s,De1n0n3o:,14&5-J1.4A.7.Coddington. 1990.
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