Distribution, Movement, and Activity Patterns of an Intertidal Wolf Spider Pardosa Lapidicina Population (Araneae, Lycosidae)

10 Pages·1997·11.5 MB·English

by  Douglass H Morse

1997. The Journal of Arachnology 25:1-10
DISTRIBUTION, MOVEMENT, AND ACTIVITY PATTERNS
OF AN INTERTIDAL WOLF SPIDER PARDOSA LAPIDICINA
POPULATION (ARANEAE, LYCOSIDAE)
Douglass H. Morse: Department of Ecology and Evolutionary Biology, Box G-W,
Brown University, Providence, Rhode Island 02912 USA
ABSTRACT. The wolf spider Pardosa lapidicina Emerton 1885 occupies cobble beaches above the
tide line about Narragansett Bay, Rhode Island, USA, and migrates back and forth with the tides. To my
knowledge this is the first explicit report of such behavior in a spider. The species is common, attaining
densities ofover 30 individuals/0.5 m ofshoreline. The spiders are confined to the beach from April until
November, and 33% or more of the population moves back and forth with diurnal tides during clear or
warm weather. Individuals may migrate on one day but remain above the tide line on the next. Small
numbers remain on the highest part of the beach through most or all of the winter; others retire into the
adjacent coastal scrub. Spiders occupy both stretches of open beach and beach with fringing salt-marsh
grass (Spartina aiterniflora) beds. Those in the latter habitat do not migrate through Spartina after it has
reached high density in June, remaining confined to the upper reaches of the beach. Numbers of F.
lapidicina on open stretches of the beach exceed those in Spartina areas, and they appear to experience
highermortality inthe latterarea. Spiders inthelow intertidalmovefrequently andhuntactively (cursorial
strategy), those above the tideline move only 0.1 times as often and sun-bask frequently (sit-and-wait
strategy). Individuals hunting in the low intertidal may capture more than one prey per day, including
Diptera, Collembola, and amphipods.
Although spiders are primarily terrestrial, during most ofthe year, using this remarkable
or sometimes occupants ofthe fresh water sur- behavior to exploit periodically available hab-
face (BristO'We 1958; Levi 1967), several spe- itat. Here I document P. lapidicina'^ abun-
cies frequent salt marshes (e.g.. Teal 1962; dance, distribution, movements, periodicity
Dobel et al. 1990) and otherintertidalhabitats, and prey on a cobble beach in Narragansett
where they may even withstand tidal inunda- Bay. I then compare these results with those
tion (e.g., Bristowe 1923; Bames & Bames ofother lycosids and with otherreports ofspi-
1954; Roth & Brown 1976). A few even live ders in the intertidal zone. In particular, this
permanently within the rocky intertidal zone, analysis permits me to evaluate the hunting
experiencing regular submersion, some for strategies of Pardosa C.L. Koch 1848, vari-
most ofa tidal cycle (Hickman 1949; Lamoral ously described as either sit-and-wait or cur-
1968; McQueen & McLay 1983). Others re- sorial (e.g., Bristowe 1958; Ford 1978), and
treat to higher sites in the vegetation as the rate of prey capture, frequently stated not to
&
tide encroaches (Bristowe 1958). The wolf exceed one per day (Edgar 1970; Nyfeller
spider Pardosa lapidicina Emerton 1885 (Ly- Benz 1988).
cosidae), the subject ofthis paper, exploits the Pardosa lapidicina is a dark-colored wolf
mm
intertidal span ofcobble beaches in Narragan- spider of 6~9 length, the females some-
sett Bay, Rhode Island, USA, moving from what larger than the males (Kaston 1948).
above the high-tide line to the low as the tide Mature adults weigh 30-70 mg or more, and
recedes, and retreating in front of its return. large immatures in early September weigh
To the best of my knowledge, this behavior 15-35 mg (Eason 1969; D.H. Morse, unpubl.
has notpreviously beenexplicitly documented data). Like other Pardosa (Vogel 1971; Low-
in a spider. Although not tolerating submer- rie 1973; Fujii 1974), they are small, cursorial,
sion like a few species that frequent intertidal and nomadic. Members of the population de-
areas, it occupies the marine-land interface scribed here, both males and females, are a
(high beach, intertidal) almost exclusively uniform dull black. Voucher specimens of P.
1
2 THE JOURNAL OF ARACHNOLOGY
Terrestrial¥egetatioii the Spartina. The Spartina areas average 7.5
m
in width, and are dense, except forthe land-
ward edges. There, stem densities in the upper
50 cm range between 0.25-0.5X that of the
center, which averages 348.3 ± 48.6 stems/
= m
0.25 {n 10). Spartina ends about 10
m
from the top of the beach and 5 above the
lowest tides (Fig. 1).
A windrow of Spartina straw occurs high
m
on the beach, usually 1-3 from its upper
edge. Above Spartina, this windrow often
reaches 30 cm in height and 125 cm in width.
Buildups are much less extensive on the open
beach, even absent in the longest stretches.
— Bertness (1984) describes the study area in
Figure 1. Diagram of part of study area with further detail. The land above the beach is
both open cobble beach and Spartina areas. Tran- covered by second-growth forest and scrub,
sects denoted as a) high-tide census, Spartina area; with hackberry Celtis occidentalis, red oak
b) high-tide census, cobble beach; and c) low-tide Quercus rubra, and red cedar Juniperus vir-
census, with 0.5 X 0.5 quadrats, on cobble beach. giniana under 20 m dominating the tree level,
and bittersweet Celastrusscandens, greenbrier
lapidicina have been deposited in the National Smilax sp., and poison ivy Rhus radicans of-
Museum of Natural History, Smithsonian In- ten climbing into this canopy. Other than for
stitution. the vines, ground cover is sparse.
THE STUDY AREA METHODS
—
Spiders were studied at the HaffenrefferEs- Transects.- -Transects were laid out in sev-
tate of Brown University, Bristol, Bristol eral places on the main study sites and in
County, Rhode Island, from September 1993- Spartina-occupicd sites between them (Fig.
m
September 1995. The study area is a cobble 1). Spiders were counted in 0.5 wide strips
beach on the west shore of Mt. Hope Bay, a centered on those lines. All rocks in these
partially sheltered eastern arm ofNarragansett transects were moved during a census, per-
Bay. Tides range from 0.6-2.1 m (x = 1.4 m), mitting an accurate count. Two types of cen-
and the distance from the top (landward edge) suses were ran. At a site on an open beach I
ofthe beach only reached by severe storms to counted spiders at low tide in 0.5 m X 0.5 m
the lowest intertidal averages 23 m. Mostcob- quadrats along a gradient from the top to the
bles range from 10-30 cm in diameter, and bottom of the beach. I ran this census weekly
larger stones and bedrock protrude in some or biweekly over the study period, and it per-
places. At the lower intertidal levels, some mitted me to assess both their numbers and
bladder wrack seaweed Fucus vesiculosus, as distribution overthe supratidal —low tidal gra-
well as a variety of encrusting organisms, dient (Fig. Ic). I also counted spiders in a se-
m
grow on the larger stones. ries of0.5 wide transects at high tide every
The four main study sites are cobble beach- other week during the second year of the
m
es, 30-120 long, punctuated by fringing study. Three areas were chosen randomly on
salt-marsh grass Spartina altermflora that has the open beach (Fig. lb) and three above
invaded the beach in several places (Fig. 1). Spartina regions(Fig. la). Six transects were
Observations and experiments were conduct- run at randomly-selected sites in each ofthese
ed on three of the beaches, with all collecting areas, for a total of 18 transects on the open
confined to the fourth, to avoid any possible beach and 18 in the Spartina regions. Census
effects of resulting changes in population methods followed those for the long-term
numbers on censuses or behavior. The inter- transect described above, except that I merely
vening Spartina areas vary between 125-150 counted the total in each strip, making no ef-
m
in length. Additionally, two narrow corri- fort to document the position ofindividuals in
dors of cobble beach (5 m, 2 m) ran through the gradient from the top of the beach to the
MORSE—INTERTIDAL WOLF SPIDERS 3
m
water. These transects averaged 10 or less periods. I remained stationary duringthesepe-
in length, fluctuating with tidal height, and riods, measuring actual distances after the ob-
reached nearly down to the uppermost fringes servations. Movements of individuals splashed
of Spartina where it grew. by surf were measured for shorter periods of
Census at low tide.—Spiders were also pe- 2.0-2.5 min, the time during which they
riodically counted near the low tide line, both moved at high velocities.
directly between Spartina and the low-tide Distribution in wiiiter.^-I used several
line and at the same height on open beaches. methods to establish the presence and distri-
m
This area ranged between 2-5 in width, de- bution ofP. lapidicina in the forest above the
pending on the daily height ofthe tide. During beach. In September 1993, six plastic jars (9
these censuses I kicked the rocks in the entire cm diameter) were sunk into the earth flush
m
area being censused to flush spiders forcount- with the surface in the scrub woodland 3
ing. Efforts to calibrate this and the more above the beach. All were placedequidistantly
time-consuming, hand-turning technique used along the periphery of the first beach, main-
in the transect studies indicated that “kick- tained through the fall, and their contents col-
sampling” yielded counts approximtely half lected weekly. Thejars were partly filled with
those of hand-sampling. leaves and litter to minimize possible preda-
Movements,~To determine whether all in- tion and permit subsequent release. Litter
dividuals migrated down the open beach, I above the beach was also searched for spiders
conducted a mark-and-recapture (re-sight) between September-November 1993. Ten
test. At low tide on Day 1 individuals from a of leaf litter were turned with a coarse rake
stretch of 40 m along the beach were dusted each month between May-November 1994,
m m
with powdered micronite dye, red in the mid- both at 3 and 5-10 above the beach.
dle-low intertidal and yellow above the pre- Activity and prey capture.—Focal obser-
vious high tide. On the following day individ- vations of spiders on the beach permitted
uals were censused at both levels by compilation of activity patterns and time bud-
kick-sampling. The one-day interval between gets. Prey capture was recorded when noted,
marking and censusing assured mixing of the and 10 min observation periods ofindividuals
individuals, since spiders in the intertidal had permitted quantification of the frequency of
to retreat to the supratidal during the follow- attacks and captures.
ing high tide. Two high tides thus intervened
RESULTS
between the marking and the census, but the
interval was short enough to minimize effects Population density and size.—The week-
of molt, mortality, and recruitment. Three ly/biweekly transect census taken at low tide
such markings were conducted, but inclement over the entire study period provided a com-
weather on the day following marking pre- parison among seasons. The maximum count
m
vented quantitative sampling on two of these of spiders in this 0.5 wide transect during
occasions. late Autumn 1993 was 37 (Fig. 2). If repre-
m
To determine the timing of movements up sentative of this 32 long beach, over 2000
and down the beach, white plastic strips 167 individuals entered winter in this one area
X 3 cm (length X width) were placed flush alone. In Spring 1994, I recorded a maximum
with the substrate, and movements of spiders of 20 spiders, suggesting a 45% loss of indi-
across them recorded, along with their direc- viduals over the severe winter of 1993-94.
tion, overentire tidal cycles. Three strips were Autumn counts in 1994 were only roughly
used simultaneously, one per observer, for a half those of 1993, and those of 1995 were
total length of 5 m. intermediate between those of 1993 and 1994
I measured frequency ofmovement both in (Fig. 2). The cohort hatched in Spring-Sum-
the low intertidal and high intertidal -suprati- mer 1994 never attained the densities of the
dal areas ofthe openbeach by observing focal 1993 cohort during Autumn 1993; however,
individuals for periods of up to 30 min, since their maximum numbers in Spring 1995 ex-
some moved only infrequently. To measure ceeded those from the preceding autumn (Fig.
rates ofmovement by individuals going down 2), suggesting low winter mortality and colo-
and up the openbeach, Itimed spidersmoving nization from adjacent areas.
toward and away from the water for 10 min Numbers ofadults decreased rapidlyduring
4 THE JOURNAL OF ARACHNOLOGY
Figure 2.—Total numbers of spiders counted at low tide each 1-2 week period in 0.5 m wide transect
on open beach, and numbers captured in pitfall traps.
the summer, coinciding with the appearanceof Spatial distribution.““Numbers of both
young (Fig. 2), strongly suggesting that few if adults and juveniles on bare cobble sites ex^
any individuals survived more than one year. ceeded those on Spartina sites (Fig. 3, F =
The last adults were seen on this transect on 0.01 in a binomial test). During spring and
17 August 1994 and 1 August 1995, although summer, adults at bare cobble sites exceeded
occasional individuals were subsequently seen those at Spartina sites by 40% in 1994, and
elsewhere in the study area on later dates, the nearly two-fold in 1995. Differences were
last being two adults on 10 October 1994. considerably smaller among early juveniles.
—
m
Figure 3. Censuses at high tide in 0.5 wide transects on open beaches and in Spartina areas.
MORSE—INTERTIDAL WOLF SPIDERS 5
—
Table L Numbers of Pardosa at low tide on turf before new grass sprouted in the spring,
shoreline below Spartina and at same height on continuing while shoots were sparse and only
open beach. a few cm tall (late March-late April). Num-
bers on the beach below Spartina reached
m
35/100 at such times. As the grass grew
Num- Num- Length
taller and denser in May, only occasional spi-
ber ber of shore Spi-
Habitat counts spiders (m) ders/m ders pmenetrated it (< 1 vs. 20-65 individuals/
100 near the low-tide line on the open
Below Spartina 21 0 235 0 beach). No spiders were seen below Spartina
Low open beach 8 175 295 0.6
after early June.
Narrow breaks The movement of spiders into the adjacent
in Spartina 8 38 40 1.0
forest during late fall was sudden and marked
(Fig. 2). In 1993, I searched weekly for indi-
viduals under stones and in the litter within a
m
with numbers on the open beach averaging 5 strip above the beach, as well as moni-
m
only 10% higher than those above Spartina toring six pitfall traps located 3 above the
through September 1994, before strongly di- beach. Neither the searches nor the pitfall
verging in late September. A similar pattern traps yielded any spiders until 14 November
occurred in 1995, although numbers diverged 1993, when 15 individuals were captured in
by early September (Fig. 3). the pitfall traps (Fig. 2), and other individuals
Spartina growth generated an absolute bar- were found under rocks and in the vicinity of
rier to the movement of spiders into the low the traps. Several more individuals were cap-
intertidal area during most of the season. In tured in the traps over the following two
six, 0.5 m wide transects made down the weeks, and then captures declined to only 1-
beach through Spartina in late summer, no 2/week, with the last individuals captured on
spiders were found between the landward 12 December 1993 (Fig. 2). In monthly
edge of Spartina and the low water line. Spi- searches of litter from May-November 1994
m
ders migrating down the adjacent bare cobble (0.1-10 above beach), I found no individ-
m
beach moved no more than 8 laterally onto uals until 6 November, when I located three.
the rocks below the Spartina fringe. At the Numbers of individuals on the beach de-
landward edge of the Spartina, spiders pene- clined markedly on the first week in 1993 that
trated no more than 40 cm into the vegetation. spiders were captured in the pitfall traps, and
During summer and autumn I neverfound spi- in subsequent weeks only a few individuals
ders in the low rocky areas immediatelybelow were recorded on the beach (0-4). However,
Spartina, but found them common near the spiders occupied this site until snow and ice
low-tide line on adjacent open cobble beaches completely covered it on 5-6 January (Fig. 2).
(Table 1). They also readily moved through I also found Pardosa at this site on 12 March
narrow corridors in Spartina into the low in- (Fig. 2), shortly after snow and ice had melted
tertidal in densities comparable to or greater from the upper edge of the beach. Numbers
than those of the wider beaches (Table 1). of individuals on the main transect also de-
Seasonal change.-—I did not find individ- clined during the snowless 1994-95 winter,
uals in the low intertidal area after 16 October although seldom to the level of 1993-94 (Fig.
or before 17 April in the transect census, al- 2). However, they largely disappeared from
though recording them in the low intertidal the replicated transects (Fig. 3), suggesting
during other field work as early as 25 March that activity on the beach was confined to a
and as late as 20 October. Thus, the spiders few sites during t—he middle of the winter.
confined movement into the lower reaches of Daily activity. At low tide spiders ranged
the intertidal to the warmer part of the year. over the entire vertical expanse of the open
Even then (17 April-16 October), significant- cobble during the day in dry, warm weather,
ly more spiders (> 2.5X) occupied the high although large numbers, usually a majority,
beach than the area below the wrack line in occupied the supratidal part. Numbers of in-
the transect (x^ 38.9, = 1, P < 0.001 in dividuals at or above the neap high-tide line
a one-sample test). (the level at which algal wrack accumulated),
In contrast, spiders moved over Spartina about 5 m below the rock-forest interface, ex-
6 THE JOURNAL OF ARACHNOLOGY
—
Table 2. Results of mark-resight test of spiders
captured and marked in supratidal and low-middle
intertidal areas during low tide in May 1995, Re-
sightings made one day after marking.
Resight- Resight- Sight-
ing ing ing
Number same opposite un-
Site marked color color marked
Supratidal 120 24 12 64
Low & mid-
intertidal 113 28 16 71
Distancefromtopofbeach (m)
—
Figure 4. Distribution of spiders at or near low
tide from landward edge of beach to water. Cu- m m
mulative results of 0.5 X 0.5 quadrats pooled into back over a 5 wide stretch 12.5 below
1 m bars. Low-tide line variable, but 15 mormore. the uppermedge of the beach. Extrapolated to
the 120 of this beach, over 600 adults and
1650 young moved from the high tidal to the
ceeded those below it, cumulatively overfour- low tidal area on that day. Spiders moved al-
fold (Fig. 4: G = 103.6, P < 0.001 in a G- most constantly across the counting strips, but
test, df = 1, for adults and subadults; G = the greatest numbers lagged the outgoing tide
29.1, P < 0.001 in a G-test, df = 1, for ju- considerably, preceding the low tide by only
veniles), although the area below the high-tide 30-45 min (Fig. 5). Several even crossed
line was often three ormore times greaterthan downward after low tide, and a trickle of in-
the upper area. dividuals continued moving downward foran-
Spiders sheltered under rocks during peri- other 2.25 h (Fig. 5). Thus, a majority oftheir
ods of rain and heavy overcast. After record- time in the low intertidal was spent as the tide
ing no individuals at the surface on three oc- returned toward its mid-point. Although sev-
casions (September-October 1993), I confined eral spiders returned only shortly before water
fieldwork to favorable weather. On two night inundated the census strip, the largestnumbers
visits during warm weather (> 15 °C), all spi- preceded the resurging tide by 45-60 min
ders were also sheltered under rocks. (Fig. 5). Adults and young did not clearly dif-
Not all individuals selected the same levels fer in times of movement.
ofopen cobble beach on subsequent days (Ta- Movement down the beach at low tide pro-
ble 2), although significantly more were re- ceeded at 17 m/h (2.8 ±1.9 m/10 min, n =
m
sighted at their original marking level than 10), from below the wrack line to within 2
predicted by chance (Z = 1.833, one-tailedbi- of the water line. Return up the beach was
nomial test, P < 0.05 for above the high-tide more rapid: spiders within 5 m of the edge of
line, Z = 1.658, one-tailed binomial test, P < the water on an advancing tide moved 42 m/h
0.05 forthe intertidal). The two groups didnot {n = 11) (7.0 ± 4.2 m/10 min), a rate that
differ in their tendency to shift from one level would take them the entire breadth of the
to the other on the following morning (G = beach in under one hour. Eight individuals
0.08, df = 1, P > 0.7 in G-test), or in rate of splashed by surf moved even faster for short
recapture (G = 2.06, df = 1, P > 0.1 in G- periods after this stimulus (2.0-2.5 min), cov-
test). Individuals carrying egg sacs or young ering 2-3 m (70.9 ± 7.8 m/hr) over this short
did not venture into the lower tidal reaches: I period. This movement consisted of several
m
have yet to record such a spider over 5 consecutive runs of up to 1 m, punctuated by
below the high-tide line. rests ofonly a few seconds. The low variance
Movement and activity.—Considerable of this sample (extremes — extrapolated rates
numbers of individuals moved up and down of60-75 m/hr) suggests that these spiders had
the beach, the juveniles beginning in their approached their maximum possible speeds.
third instars. During a representative mid-day, In contrast, most upward movements of un-
low-tide episode on 19 July 1994, a minimum disturbed spiders ranged between 5-50 cm
of 26 adults and 69 young moved down and (15.2 ± 8.2 cm, n = \1 individuals and 182
MORSE—INTERTIDAL WOLF SPIDERS 7
—
Figure 5. Movements by spiders up and down tide line over a 5 m white plastic barrier placed 12.5
m below the upper edge ofbeach (mid-tide) on a routine day, 19 July 1994. Time in hours ofday, period
denoted as “dry” (< 0700~“>1500) refers to time the barrier region was not covered with water. Adults
andjuveniles combined.
moves), only two moves exceeding this dis- eventually managed to crawl out onto a near-
—
tance (75, 60 cm). by stone and retreat rapidly upshore {P
Spiders were significantly more active in 0.004 in a two-tailed Binomial Test). I never
the low intertidal than above the tide line, saw any suggestion that these spiders re-
even when they were not migrating. Move- mained —submerged during a tidal cycle.
ments in the low intertidal area {n = 11) oc- Prey. I observed 34 attacks or captures in
curred over 10 times as frequently as those in the low intertidal, an average of 1.6/h (Table
=
the high intertidal and supratidal {n 10) at 3). Spiders attacked small flies feeding in the
the same time (every 29.2 ± 37.1 sec vs. ev- low intertidal (seaweed flies (Coelopafrigida,
ery 412.8 ± 624.9 sec; P < 0.001 in a two- Coelopidae)), Collembola (Anurida maritima,
tailed Mann Whitney C/-test), a reflection of Hypogastruridae), and unknowns, many of
the individuals in the low intertidal being con- which probably were flies. Additionally, sev-
stantly on the move, often hunting, while eral apparent strikes were noted, for whichthe
those in the high intertidal were largely sun- target was not seen. Probably most of these
basking. strikes were directed at Collembola (see Table
A
Spiders usually avoided direct contact with 3). majority of observed attacks directed at
the water, but regularly reached the water’s both the flies and Collembola was successful.
edge, although most frequently stopping a Other untimed observations on hunting and
minimum of 0.5 m from it. Nine individuals prey capture resembled these. Additionally,
washed into the water by unusually high four captures of newly-molted amphipods
waves curled their legs under them, and all (Orchestia sp.) warrant note. Amphipods are
abundant under the rocks of the intertidal
— (scud, Jassa sp.; Gammarus sp.) and near the
Table 3. Prey attackedandcapturedbyPardosa
on low beach, June-August (21.17 h observations). wrack line (beach fleas, Orchestia sp.).
*Spider snapped in same way as it attacked prey, DISCUSSION
but object not seen.
Intertidal area.—The tide-punctuated mi-
Prey Attacked Captured Captures//h gratory movement of P. lapidicina is highly
unusual (or unreported), I have not found a
Diptera 6 4 0.19 similar pattern in the literature for any spider,
Collembola 10 7 0.33 although Lamoral (1968) reported that the
Others 8 2 0.09
permanently intertidal Desis formidabilis
Not seen* 10
(O.P.-Cambridge 1890) (Desidae) from South
Total 0.52+
Africa exhibited a strong sense of tidal
8 THE JOURNAL OF ARACHNOLOGY
rhythm, remaining in their nests when tides (e.g., Comstock 1940; Bristowe 1958), and
were high at night, their normal period of ac- the previously-noted authors go to consider-
tivity. However, P. lapidicina's behavior does able ends to “correct” the record. Ford (1978)
somewhat resemble that of P. pullata (Clerck noted that his P. amentata (Clerck 1757) spent
1757), a European species Bristowe (1923, no more than 278 sec/day moving (0.0032%/
1958). Bristowe (1958) reported them “lying day). The P. lapidicina in the supratidal and
idly on the pebbles piled up by the sea”, but high intertidal areas exhibited a sit-and-wait
did not indicate whether they routinely moved pattern closely resembling the one described
down into the intertidal as P. lapidicina does. by the more recent workers, which simulta-
However, he noted that these P. pullata re- neously allowed them to sun-bask on clear
treated up the tide line into vegetation when days. Those on the low beach, however,
exceptionally high tides occurred, but were moved much more frequently, often stalking
occasionally trapped by these tides. If so and leaping at flies, active behavior similar to
trapped, they curled their legs under them, as that described by Bristowe and other earlier
does P. lapidicina, and floated passively on workers. In light of these striking differences
the wave until it receded, depositing them on and the disagreement in the literature, detailed
the pebble substrate. Then they ran toward the time budgets of a representative range of spe-
land before the next wave arrived, and simi- cies are needed.
larly to P. lapidicina, always succeeded in es- The high rates of movement observed in
caping.
wave-splashed spiders resembled the maxi-
Pardosa lapidicina is common enough to mum movement rates of both P. lugubris
play an important energetic role in the inter- (Walckenaer 1802) and Xerolycosa nemoralis
tidal zone. Such a role would not be unusual,
(Westring 1861) continually chased by Bris-
since spiders, especially lycosids, are the towe (1939), who found that they could run a
dominant invertebrate predators in some maximum of 1.8 and 1.5 m, respectively, be-
streamside (Vlijm et al. 1963), salt-marsh fore experiencing temporary exhaustion.
(Schaefer 1974), grassland (Van Hook 1971)
and forest habitats (Moulder & Reichle These figures amppear comparable to the rapimd
moves of 2-3 seen in bursts of up to 1
1972). — by P. lapidicina not subjected to these artifi-
Effect of Spartina barriers. Spiders of
the open beach appeared to be more success- cial stimuli.—
Hunting. Studies of lycosids in the field
ful than those in the Spartina areas. Densities
reveal very low percentages of individuals
were almost always higher on the open beach,
found feeding on prey (2% -Nakamura 1982;
ailmtmhaotuugrhedicfofheorretncedsurwienrgeminiidti-aslulymmsemral.lHinotwh-e 6% -Nyffeler & Benz 1981a), consistent with
ever, the rapid decrease in numbers of spiders a low intake rate. Some lycosids are estimated
to capture no more than one prey per day in
ilnowtehresSupravritvianlathaerreeasthdaunrionngthteheopfaelnl bseuagcgheesst.s the field (Edgar 1970; Nyffeler & Benz 1988),
Spiders in the Spartina areas may have been although they routinely accept several per day
in poorer energetic condition than those from in the laboratory (Miyashita 1968; Samu
the open be—ach. 1993). Observations in this study suggested
Activity. The behavior of individuals in that individuals in the low intertidal area rou-
supratidal and intertidal areas differed mark- tinely captured more than one prey per day;
edly. In the supratidal area, spiders movedrel- however, many of those prey were tiny col-
atively infrequently and often sunbasked. lembolans, which provide only a minute store
Their behavior resembled that ofseveral other of resources. Although amphipods are abun-
Pardosa species, which employ sit-and-wait dant on the beach, they typically have hard
behavior almost exclusively, waiting until carapaces and hence may be difficult to pro-
&
prey come very close to them (Edgar 1969; cure (Moulder Reichle 1972), unless they
Kronk & Riechert 1979; Nakamura 1982) or have recently molted. All amphipod prey in
even touch them (Fuji! 1974; Ford 1978), only this study had recently molted. Other small
then rapidly attacking. Traditionally, lycosids, lycosids also take small prey (Fitch 1963;
including Pardosa, have been considered cur- Dondale et al. 1972; Nyffeler & Benz 1981a,
sorial predators that tracked down their prey 1981b) and experience considerable difficulty
MORSE—INTERTIDAL WOLF SPIDERS 9
&
taking any with a hard carapace (Moulder Connecticut StateGeol. Nat. Hist. Surv. Bull. 70.
Reichle 1972). 874 pp.
&
Kronk, A.E. S.E. Riechert. 1979. Parameters af-
ACKNOWLEDGMENTS
fecting the habitat choice ofa desert wolfspider
I thank J. Blumenstiel, A. Choi, C. Harley, Lnoylc.o,7s:a15s5a-nt1r6i6t.a Chamberlin and Ivie. J. Arach-
and M. Weiss for assistance in the field, R.L. Lamoral, B.H. 1968. On the ecology and habitat
Edwards for identifying Pardosa lapidicina adaptations of two intertidal spiders, Desisfor=
and other spiders, and C. Harley forcomments midabilis (O.P. Cambridge) and Amaurobioides
on the manuscript. africanus Hewitt, at “The Island” (Kommetjie,
Cape Peninsula), with notes on the occurrenceof
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