Table Of Content1991. TheJournal ofArachnology 19:40-48
ONTOGENETIC AND SEASONAL CHANGES IN WEBS AND
WEBSITES OF A DESERT WIDOW SPIDER
Yael Lubin and Mandy Kotzman: Mitrani Centerfor Desert Ecology, Blaustein Institute
for Desert Research, Ben Gurion University ofthe Negev, Sede Boqer Campus 84990
Israel
Stephen Ellner: Biomathematics Graduate Program, Department of Statistics, North
Carolina State University, Raleigh, North Carolina USA
Abstract. Morphometricand nestposition variableswereusedtoexaminetheeffectsof
spidergrowthandseasonalityonwebsandwebsitesofthedesertwidowspider,Latrodectus
revivensisShulov(Theridiidae)intheNegevdesertofIsrael.Theformofthewebwassimilar
over the full range ofspider body sizes. All morphometric variables had strong positive
correlationswith spidersize: largerspidersoccupied largernestsin largershrubs. However,
nest characteristics were more highly correlated with spider size than were website char-
acteristics. When theeffectofspidersizewas removedbyregression, morethan 75%ofthe
remainingvarianceconsistedofcorrelated variation in threegroupsofvariablesrelatingto
(1)websitecharacteristics(48%),(2)nestcharacteristics(18%)and(3)capturewebplacement
(12%). Mostnestandwebsitevariablesshowedeffectsofseasonalitythatwereindependent
ofspider size, and may be related to the thermal regime in the nest. The results indicate
that the relative quality ofpotential websites changes seasonally and with spider growth.
We suggest that the costs ofrelocating a web outweigh the advantages ofreaching a new
website, with the result that spiders remain for some time in websites which have become
less suitable.
The habitat requirements ofmany organisms cally, and itis not knownto whatextentchanges
change as they age, resulting in a shifts oftheir in web and website characteristics are due to
“ontogenetic niche” (Werner & Gilliam 1984). growth, seasonal factors or other effects.
Ontogenetic changes in habitat may involve In this study, we use morphometric and nest
changes in living sites, in food requirements or positionvariablestocharacterizeontogeneticand
in otherfactorswhich scale with body size. Such seasonalchangesin thewebsandwebsitesofthe
size-relatedchangesinhabitatrequirementsmay desert widow spider Latrodectus revivensis Shu-
haveparticularlyimportantfitnessconsequences lov. Statisticalanalysisofthesedataallowsusto
for sedentary animals for which the possibilities separate the variation in web and website char-
ofmovingto newsites maybelimited(e.g., Sha- acters due to spider sex, size, season, and other
chak & Brand 1983). factors. In addition, we examine the patterns of
Web-building spiders are relatively sedentary covariation among the morphometric variables
predators(Janetos 1986).Inmostspeciestheweb and their relationships with spider size.
isprimarilyaprey-capturedevicewhoselocation NATURAL HISTORY AND METHODS
andstructurereflectthelocaldistributionofprey
(Riechert&Luczak 1982;Janetos 1986;Riechert Natural history.—Latrodectus revivensis
& Gillespie 1986). Thus, studies ofwebsite re- (Theridiidae)isknownonlyfromtheNegevdes-
quirements have focused mainly on the effects ert ofIsrael (Levi & Amitai 1983). Females ma-
ofpreyabundance(e.g.,Tumbull 1964;Gillespie ture in springorsummer(March to August) and
1981; Olive 1980, 1982; Vollrath 1985). The produceeggsacsthroughoutthesummerandau-
changingrequirements ofdevelopingspidersare tumn(MaytoSeptember;LevyandAmitai 1983).
also likely to affect web structure and website Incubationtimeisaboutonemonth. Someyoung
selection (Enders 1975; Vollrath 1987). How- emerge in mid- to late summer and overwinter
ever, these have not been examined systemati- as juveniles. In other instances, eggs remain in
LUBIN ET AL.-VARIATION IN WEBS AND WEBSITESOF WIDOW SPIDER 41
Figure 1.—SchematicdrawingofthewebofL. revivensis, showing(a)websiteand(b)nestvariablesmeasured
in this study. NH = nest height, SH = shrub height, CD = distance from the nest to the capture web, CH =
heightofthecaptureweb, NT = total nest length, DN = lengthofdense silklayer, DB = lengthofdebrislayer,
DM = nest diameteratedge ofdebris layer, MD = maximum nest diameter.
theeggsacoverthewinterand theyoungemerge on new nests, but may completely obscure the
the following spring. upper halfofan old nest.
Webs of L. revivensis are durable and long- Thespidersareactiveatnightandremaincon-
lasting structures which may persist for up to cealed in the nests during the day. Nocturnal
several months (Zilberberg 1988). Thewebcon- activities include web repairs, renewal of the
sists of separate nest and prey-capture compo- sticky, capture threads and prey capture. Web
nents(Shulov 1948;Szlep 1965;Fig. 1).Thenest, relocation also takes place at night.
built in a shrub, is connected by strong bridging Studyarea.—Thestudysitewaslocatedonthe
threads ofvariable length (a few centimeters to rocky slopes of the Halukim Ridge, near Sede
overa meter) to a horizontal silk platform. The Boqer (30°50'N:34°46'E) in the central Negev
platform is usually placed over an area ofbare region ofIsrael. The ridge runs north-south and
ground beyond the edge of the shrub, and an is dissected laterally by dry watercourses pro-
arrayofstickycapturethreadsissuspendedfrom ducing a reliefofabout 50 m. The area is arid
mm
the platform to the ground. withhighlyvariablewinterrains(about 100
The nest ofL. revivensis consists ofa curved, annually) and is sparsely vegetated with a per-
silk cone (Fig. 1). The top ofthe cone is covered manentshrubland(Evenarietal. 1982). Nestsof
with a dense silk layer, while the lower section L. revivensis occurred in several shrub species,
is a more open mesh. In addition, the nest top including Zygophyllum dumosum, Artemesia
is covered with scattered debris which may in- herba-alba, Reaumuria negevensis, Noaea mu-
clude sand, pebbles, snail shells and feces, plant cronata, and Hammada scoparia, and some-
material,exuviaeandremainsofprey.Thedense times in clumps ofannuals (e.g., Reboudiapin-
silkanddebrislayersareusuallysparseorabsent nata) and grasses.
42 THEJOURNALOFARACHNOLOGY
Thestudyareawasapproximately20 hectares deletion ofmissing values; although the results
ofanorth-facingslopeofasmallwadi. Toreduce ofthetwomethodswerenearlyidentical,listwise
the effects of habitat heterogeneity, we limited deletiongreatlyreducedthesamplesizesforeach
oursearch forspidersto thelowerportion ofthe covariance. PCA identifies a sequence ofuncor-
slope, from the edge ofthe wadi bed to a rocky related “components” (axes) which are linear
m
outcrop about 50 up the slope (Shivta and combinations ofthe original variables. The first
colluvial formations; Olsvig-Whittaker et al. axis is chosen to “explain” as much as possible
1983). ofthe variance in the data, the second axis ex-
Web and website measurements.—We located plainsasmuchaspossibleoftheremainingvari-
andindividuallyflaggedandmappedwebs.Webs ance, and so on.
andwebsiteswerecharacterizedwith the follow- Weapplied PCAtoacorrelation matrixofthe
ing measurements (Fig. 1): height of the nest, raw data and ofthe Box-Cox transformed data
height ofthe shrub, height ofthe capture plat- (Joliffe 1986). To determine the extent to which
form and its distance from the nest, total nest spider size alone was the basis ofthese correla-
length, length ofthe dense silk layer, the maxi- tions, we removed the effect ofspider length by
mum
lengthofthedebriscovering,nestdiameter regression: each value was replaced by its resid-
at the lower edge ofthe debris layer and maxi- ualdeviation from a regression on spiderlength.
mum nest diameter. We also determined the Quadratic, ratherthan linear, regressionwasused
compass orientation of the nest opening (nest in order to stabilize variances. We then applied
aspect) and the quadrant ofthe shrub in which PCA to the covariance matrix ofthe residuals.
the nest was located (NE, NW, SE, SW). A total PCAofthecovariancematrixofresidualsisuse-
of 350 nests and 226 spiders were sampled in ful in thiscase, becausethe variablesthemselves
this manner between January and August 1987 hadalready been standardizedtoequal variance
and March and August 1988. by thedata transformations. Consequently, high
Spidersinoccupiedwebsweresexed,classified variance ofthe residuals indicates a weak cor-
asjuvenile, subadult oradult, and measured for relation with spider length.
totalbodylengthandlengthofthetibia + patella
RESULTS
of leg IV. For all statistical analyses, we used
body length as a measure ofspider size because Males and females.—Our measurements of
ofconvenienceofmeasurementinthefield. Body male’swebswererestrictedtothoseofjuveniles.
lengthincludestheexpandableabdomenandmay Adultmalesoftenremainedintheirownjuvenile
=
be influenced by spider condition (Anderson webs {n 17), built small nests lacking capture
=
1974), unlike the more rigid cuticle of the leg websattached to nestsoffemales{n 5), shared
=
segments which does not change size during an nestsofadult orjuvenile females (n 26 and 4,
instar (Miyashita 1968). However, body length respectively)oroccupied abandoned nestsoffe-
wascloselycorrelatedwiththelengthofthetibia males (n = 4).
+ patella in L. revivensis {r^ = 0.92, n = 211), Webs ofjuvenile males and females differed
suggestingthatforL. revivensis, spidercondition significantly in all morphometric variables ex-
did not significantly affect the length ofthe ab- cept distance from the nest to the capture web.
domen. However, when we eliminated the difference in
Statistical analyses.—Comparisons between size between males and females by comparing
each pairofmorphometric variables were made onlyfemalesofsizesequivalenttojuvenilemales
mm
using standard regression (linear or polynomial) (<6.5 body length. Fig. 2), thesedifferences
and correlation analyses. To remove heterosce- disappeared. Therefore, web and website char-
dasticity,thedependentvariableofeachanalysis acteristics ofjuvenile males and females were
was transformed using the Box-Cox family of treated as a single data set.
power transformations with maximum-likeli- Effectsofspiderlength.—Thetotalbodylength
hoodchoiceofparameters(Ruppert 1989;Krebs ofspiders in our sample ranged from 1.8-16.8
1989). mm (x = 7.9, SD = 3.8, n = 246 spider mea-
Patterns ofcovariation among morphometric surements; Fig. 2). In the following regression
variables were examined by principal compo- analyses, spiderlength is treated asan error-free
nentsanalysis(PCA;Joliffe 1986).Wecalculated independentvariable(Snedecor&Cochran 1967),
the variances and pairwise covariances of all because the errors in measuring spider length
variables. We used pairwise rather than listwise weresmallandindependentofspiderlengthover
LUBIN ET AL.-VARIATION IN WEBS AND WEBSITESOFWIDOWSPIDER 43
Table 2.—Allometric regression equations for nest
morphometric variables: In y- fio + a,\n X, where
X= nest total length. All regressionsare significant at
P < 0.001 {Ho. a, = 0).
Variable n f- ao a,
Dense silk 290 0.67 0.21 0.70
Debris 291 0.79 -0.31 0.91
Nestdiameter 287 0.84 -0.65 0.93
Maximum diameter 135 0.83 -0.78 1.01
nest length, lengths ofdense silk and debris lay-
JM AM JF AF
STAGE, SEX ers, and nest diameters) than for variables as-
Figure 2.—Total body lengths (in mm) ofL. revi- sociatedwithnest placement in theshrub(shrub
vensisusedinthestudy:boxesshowthemeans(center height and nest height) or with the capture web
lines) and one standard deviation and vertical lines (height and distance from the nest).
showrangesforjuvenileandadultmales(JMandAM, Nestplacementand allometry.—Theheightof
respectively) and forjuvenile and adult females (JF the nest in a shrub was closely correlated with
and AF, respectively). Juvenile males were all sub- shrub height. Over the entire range of shrub
adults;juvenilefemalesincludedallimmatureandsub- heights of 15 to 122 cm, nest height was ap-
adult stages. proximately % ofshrub height (r^ = 72.7%, n =
318). The allometric equation, nest height =
the range ofsizes encountered (r’ = 0.04, P > 0.69(shrubheight)"’®, onlyslightlyimprovedthe
0.1; based on 5 replicate measurements ofeach amount of variance explained by shrub height
=
of 29 spiders). Pooling all measurements, the {P- 73.0%).
standarddeviationofthemeasurementerrorwas Variationin thelengthofthedebrislayer, nest
0.23mm(95%Cl:0.19-0.29mm),whichismuch diameter and maximum nest diameter can be
smaller than the standard deviation of spider described by allometric regressions on total nest
length in our full data set (SD = 3.84 mm, n = length (Table 2). The length of dense silk in-
252 spiders). creased linearly up to nest lengths of approxi-
Spider length explained a significant amount mately 75 mm, butdidnot increase with further
ofthe variation in all weband website variables increase in nest length. Variation in this char-
(Table \, P < 0.001 in all cases). Theamount of acterwasbestdescribedoverallbytheallometric
variation explained by spider length was higher equation, dense silk length = 0.2(total nest
=
for variables that describe the nest itself (total length)"'' {P 0.67).
Table 1.—Regression equations for the effect ofspider length on nest and website morphometric variables.
The slopes ofall ofthe regressions are significantly different from zero {P < 0.001). The equations are ofthe
form: = ao± a,x + a2X\ wherex= spiderlength.
Variables n r~ \ a„ a, a2
WEBSITE
Nest height 111 0.27 0.18 1.62 0.02 0.001
Shrub height 111 0.34 0.12 1.44 0.01 0.0001
Capture web distance 142 0.21 0.11 1.32 -0.004 0.0009
Capture web height 46 0.52 -0.06 0.89 -0.006 0.0001
NEST
Nest length 175 0.85 0.47 1.74 0.88 -0.025
Dense silk length 172 0.66 0.19 1.2 0.13 -0.005
Debris length 173 0.76 0.27 1.27 0.23 -0.008
Nest diameter 171 0.90 0.14 1.14 0.07 -0.002
Maximum diameter 109 0.92 0.18 1.12 0.13 -0.004
44 THEJOURNALOFARACHNOLOGY
Table3.—Correlationsamongwebsiteandnestvariables.Correlationsbasedontherawdataareshownabove
thediagonal; belowthediagonal are thecorrelationsamongresiduals, afterremovingtheeffectofspiderlength
byregression(seeMethods: Statisticalanalyses). NH = nestheight,SH = shrubheight,CD= distancefromnest
tocaptureweb, CH = captureweb height, NT = total nest length, DN = lengthofdensesilklayer, DB = length
ofdebris layer, DM = nest diameter. * = nonsignificant correlations (P> 0.05).
NH SH CD CH NT DN DB DM
NH
0.85 0.64 0.43 0.55 0.32 0.47 0.48
SH 0.81 0.54 0.46 0.63 0.37 0.54 0.56
CD 0.63 0.49 0.31 0.41 0.19 0.42 0.41
CH * * 0.77 0.39 0.66 0.65
NT 0.25 0.23 * 0.42 0.71 0.87 0.91
DN -0.14 * -0.22 * 0.37 0.77 0.69
DB * * 0.27 0.46 0.57 0.87
DM * * * 0.45 0.42 0.48
—
Covariationofweband websitevariables. All Websitevariables(nest height, shrubheight,and
variables were significantly and positively cor- distance to the capture web) accounted for 48%
relatedwitheachother(Table3; < 0.01,except ofthe residual variance (PCA axis 1, Table 4).
for the height ofthe capture web against its dis- The second axis, which loaded mainly on nest-
tance from the nest, 0.02 < P < 0.05). The re- concealment variables (dense silk and debris),
siduals had fewer significant correlations and accounted for 18% ofthe residual variance, and
somenegativecorrelations,indicatingthatmany thethirdaxisloadedmainlyoncapturewebheight
correlationsin the original variableswere due to (12% ofthe residual variance). Thus over 78%
the effect ofspider length on all variables. As a ofthe variance in web and website morphomet-
result, PCA ofweb and website variables using ricdatamaybesummarizedbyfourindependent
the rawdatawasnot veryinformative (Table 4). axes ofvariation: spider size and the three clus-
The first axis, which accounted for 63% ofthe ters ofmorphometric variables identified by the
variance, loadedevenlyonallvariablesandsim- first three PCA axes.
ply reflects the positive correlation among the Seasonal differences in nest and website char-
variables; the remaining axes could not be in- acteristics.—Climatic conditions in the central
terpreted intuitively. Negevdifferconsiderablyinwinterandsummer.
Clearer patterns were found in PCA ofthe re- There is a “cold season” (November to April;
sidualsafterremovingtheeffectsofspiderlength. mean monthly temperature 13.4° C, range of
Table 4.—Principal components analysis (PCA) ofwebsite and nest variables. The first two PCA axes are
shown forthe PCA based on the raw data (left side oftable) and the first three PCAaxes based on analysis of
theresiduals,afterremovingtheeffectofspiderlength(rightsideoftable).Thepercentofthevarianceexplained
by each axis is shown. Variables are abbreviated as in Table 3.
PCA axes based on
Data Residuals
Variable 1 2 1 2 3
%
Variance
explained 63 16 48 18 12
NH 0.12 0.20 0.32 0.03 -0.07
SH 0.12 0.15 0.27 0.03 -0.10
CD 0.09 0.19 0.28 -0.06 0.10
CH 0.12 -0.05 0.03 0.17 0.41
NT 0.15 -0.07 0.04 0.14 0.03
DN 0.11 -0.15 -0.05 0.25 -0.20
DB 0.14 -0.10 0.01 0.22 -0.05
DM 0.14 -0.08 0 0.10 -0.05
LUBIN ET AL.-VARIATION IN WEBS AND WEBSITESOF WIDOW SPIDER 45
Table 5.—A comparisonofspiderwebsiteandnestvariables in “hot”and “cool” seasons. Shownare means
and standard deviations ofall measurementsand probabilities for/-testsperformedon the rawdata (Pdata) and
on the residuals, after removing the effeet ofspider length (P,es,d)- SL= spider length, MD = maximum nest
diameter; all otherabbreviationsas in Table 3. * = P < 0.05, ** =/>< 0.01, *** = P < 0.001.
Cool Hot
Variable Mean SD N Mean SD N P P
dala rcsid
—
SL(mm) 7.2 2.8 126 8.6 4.5 126
NH(cm) 20.2 9.7 139 29.1 13.0 180 ***
SH (cm) 31.7 11.6 140 43.4 18.2 180 ***
CD(cm) 13.4 7.9 95 28.3 19.9 71
CH (cm) 12.3 2.7 32 11.1 6.3 16 ns ns
NT(mm) 55.2 22.4 118 65.8 37.3 178 ns
DN(mm) 25.4 10.0 114 19.8 9.2 177 ***
DB(mm) 31.6 11.8 114 31.9 19.8 178 ns ***
DM (mm) 22.4 9.3 112 26.1 16.3 176 *
MD(mm) 29.7 10.9 34 41.1 22.2 101 ***
means 9.8-18.0° C) and a “hot season” (May to differ from those of similar-sized juvenile fe-
October,meanmonthlytemperature23.4°C,range males. Eggsac nests made by some females ap-
21.1-25.5° C). peared to bewiderand more barrel-shaped than
Therewerestatisticallysignificantseasonaldif- nests made by subadult and juvenile females,
ferences in most ofthe morphometric variables, possiblytoaccommodatethelarge,sphericalsacs.
bothintherawdataandafterremovingtheeffect Nest diameter and the lengths ofthe layers of
of spider length (Table 5). In the hot season, densesilkanddebrisallscaledallometricallywith
spiders were found in taller shrubs, built nests total nest length. For linear dimensions of the
higher above the ground and built capture webs nest, isometry is the appropriate null model.
furtherfromtheirnests.Nestdiameterandmax- However,nestdimensionsalsoscaletobodysize,
imumdiameterwere both greaterin the hot sea- andtheallometricequation (v=ax'’) isgenerally
son, but the dense silk layer was shorter in the a good descriptorofbody size relationships(Pe-
hot season. Nests were longer in the hot season, ters 1983). Allometric scaling may indicate that
but this appears to be the result ofthe seasonal a functional relationship exists among the vari-
difference in spider length (Table 5). The height ables which depends on their geometry (La-
ofthecapturewebdidnotvarybetweenseasons. Barbara 1989).
In the hot season, nests occurred more fre- Both the dense silk layer and the debris pro-
quently on the east side of shrubs than on the vide protection for the spider from predators,
west side (x- = 8.85, P < 0.005, n = 76 nests), whethermechanicallyorbycrypsis(Konigswald
buttheirdistributionwithrespecttotheN-Saxis etal. 1990). In theinitial stagesofnestconstruc-
was random (x- = 0.47, P > 0.1). In the cold tion, L. revivensisbuilds a thin silk cap, consist-
season the distribution ofnests with respect to ingofa fewthreads only(which will become the
shrub quadrant was random (x^ = 0.728, P > topofthenest),andthendescendstotheground
0A,n= 125).Theorientationofthenestopening and carries up bits ofdebris which it attaches to
was not significantly different from random in the top ofthe cap. Thus, protection from visu-
both seasons (Rayleigh test; cold season: 106 ally-orienting predators is obtained quickly and
nests; hot season: 68 nests), nor were there sig- with a minimal outlay ofsilk and activity, both
nificantdifferencesamongwebs ofjuvenilesand ofwhichareenergeticallyexpensive(Lubin 1973;
adults in either season. Prestwich 1977). If the spider remains at that
DISCUSSION website, both debris and dense silk are added to
the nest on successive nights.
Scalingofnestand websitecomponents.—The Nests in the hot season had proportionately
form oftheweb isremarkablyconstantoverthe shorterlengthsofdensesilkrelativetothedebris
full range of spider sizes, from newly emerged layer. This may be related to the thermal regime
youngto adults. Webs ofjuvenile males did not within the nest. Temperatures during the day
46 THEJOURNALOFARACHNOLOGY
inside the dense-silk portion of the nest were by spider length or by seasonal effects consists
consistentlyhigherthan in the lower, open mesh of correlated variation in website and capture
portionofthenest,duetothegreaterflowofcool webcharacteristics(residual PCAaxis 1). Anad-
airthrough the open mesh portion than through ditional 18% was attributed to correlated vari-
the dense silk (Lubin et al. unpubl.). By increas- ation in nest characteristics (axis 2). Distance to
ing the size of the debris layer without a con- thecapturewebwasacomponentofaxis 1; thus,
comitant increase in the dense silk, shade and alargershrubisassociatedwithagreaterdistance
protectionareprovidedwithoutreducingairflow to the capture web. However, the variation in
through the nest. the height ofthe capture web was also identified
Nests were generally placed % ofthe way up asaseparatecomponentofthe PCA(axis 3). We
the shrub, but were located significantly higher conclude that the capture web and nest are rel-
in the hot season than in the cold season. The atively independent structures, and factors af-
portion ofthe shrub above the nest can provide fectingcapturewebandnestplacement maydif-
substantial shade and concealment from visual fer.
predators (Konigswald et al. 1990). In summer, Theresidual varianceinwebsitesnotaccount-
spiders place theirnests higherin shrubs (and in ed for by either spider size or seasonal effects
taller shrubs), perhaps in order to take better may be due to imprecise site selection (see Ja-
advantage ofconvectivecooling. The placement netos & Cole 1981), or to other factors that we
of large nests in large shrubs is intuitively ob- didnotmeasure. Such factorsmayinclude: vari-
vious, as small shrubs may provide insufficient ation in body condition, hunger and reproduc-
support and cover for large nests. It is less clear tive status of the spider, spatial and temporal
why small nests are not found in large shrubs. variation in food supply. Riechert (1974) docu-
Given the tendency fornests to be built%ofthe mented the importance ofrelatively short-lived
way up in shrubs, the upper branches of large phenomena(e.g.,thepresenceofffowersandoth-
shrubsmaybeunsuitable(e.g.,toowidelyspaced) er insect attractants) in explaining the distribu-
for suspending small nests. tion ofa desert web-buildingspider,Agelenopsis
Somewhat surprisingly, nest openings were aperta (Agelenidae), and showed that such cues
randomwithrespecttocompassorientationboth may influence the choice ofa website (Riechert
in summer and winter. In open habitats, a di- 1985). In orb-weaving spiders, which may re-
urnal orb-weaver, Micrathena gracilis (Walcke- locate their webs frequently, site selection and
naer), was shown to orient its web to reduce ex- movement have been correlated with the avail-
posure to direct insolation (Biere & Uetz 1981). ability of web supports (Enders 1975; Hodge
Similarly, the funnel openings of a desert age- 1987a),thedegreeofdisturbancetowebs(Hodge
lenid, Agelenopsis aperta (Gertsch) tend to face 1987b) and food availability (Olive 1982; Voll-
north in summer(Riechert & Tracy 1975). Both rath 1985).
species, however, were exposed regularly to di- The residual variance in nest characteristics
rect solar radiation, the former while sitting on may reflect differences in site quality, for ex-
itswebandthelatterwhile baskingandhunting. ample, in the thermal regimes prevailing in dif-
Latrodectus revivensis is mainly nocturnal and ferent shrubs or the presence ofsuitable debris
does not bask. fornestconcealment. Theamountsofdense silk
Sources ofvariation in web and website char- anddebris might varywith immediateneeds for
acteristics.—Thesourcesofvariationinweband crypsis against a heterogeneous background, or
website characteristics separate into three main in responsetotheperceivedriskofpredation. In
components: (1) spider size, (2) seasonal effects some orb-web spiders, variable development of
and (3) residual variation. All morphometric stabilimenta (linesorzigzags ofdense silk in the
variables had strong positive correlations with orb; Robinson & Robinson 1970) and ofother
spider size: larger spiders occupied larger nests web “decorations” (e.g., bits ofdebris) has been
in larger shrubs. Nest-size variables were more correlatedwiththeirdegreeofexposuretovisual
tightly correlated with spider length than were predators (Eberhard 1973; Lubin 1975, 1986).
website or capture web variables. Seasonal dif- These results suggest that the relative quality
ferences accounted for some variation in most ofdifferentwebsiteschangesseasonallyandwith
web and website characters after removing the the spider’s ontogeny. Changes in nest require-
effect ofspider length. mentscan be accommodatedby modificationof
Nearly halfofthe variance not accounted for theexistingnestortheconstructionofanewnest
LUBIN ET AL.-VARIATION IN WEBS AND WEBSITESOFWIDOW SPIDER 47
at the same site, but changes in website require- residencetimeoftheorbweavingspider,Micrathe-
ments may necessitate moving to a new site. nagracilis. Psyche, 94:363-371.
Whilenestsaremodifiedregularlyandarethere- Janetos, A. C. 1986. Web-siteselection: Areweask-
ingtherightquestions?Pp. 9-22,InSpiders:Webs,
fore tightly correlated with spider size, the large
variation observed in shrub and capture web Behavior, and Evolution (W. A. Shear, ed.). Stan-
ford University Press, Stanford, California.
characteristics suggests that the spiders remain Janetos,A.C.&B.J.Cole. 1981. Imperfectlyoptimal
forsometimein websites that havebecome less animals. Behav. Ecol. Sociobiol., 9:203-209.
suitable. Nonetheless, website relocation occurs Joliffe, I. T. 1986. Principal Component Analysis.
several times in the spider’s lifetime (Zilberberg Springer-Verlag, New York.
1988) and the choice of new websites is influ- Konigswald,A., Y. D. Lubin& D. Ward. 1990. The
encedbythespider’ssizeandbythetimeofyear. effectivenessofthenestofadesertwidowspiderin
The decision to move to a new website may re- predatordeterrence. Psyche, 97:75-80.
flectatrade-olfbetweentheadvantagesofreach- Krebs, C. J. 1989. Ecological Methodology. Harper
and Row, New York.
ing a more suitable website and the costs ofre-
LaBarbara, M. 1989. The evolution and ecology of
locating, such as an increased risk ofpredation
body size. Pp. 69-98, In Patterns and Processes in
and the energetic costs of movement and web the History ofLife (D. M. Raup & D. Jablonski,
construction. eds.). Dahlem Konferenzen 1986. Springer-Verlag,
Berlin.
ACKNOWLEDGMENTS Levy,G. & P.Amitai. 1983. Revisionofthewidow-
B. RothandA. Kotzman helpedwiththe field spidergenus Latrodectus(Araneae: Theridiidae) in
work and D. Ward and Y. Ayal commented on Israel. Zool. J. Linnean Society, 77:39-63.
a draft of the manuscript. We are grateful for Lubin,Y. D. 1973. Webstructureandfunction: The
nonadhesive orb-web of Cyrtophora nwluccensis
theirhelp.ThestudywassupportedbytheU.S.- (Doleschall)(Araneae: Araneidae). Forma et Func-
Israel Binational Science Foundation (Grant tio, 6:337-358.
#8600092 to YL and SE, and a Bergmann Me- Lubin,Y. D. 1975. Stabilimentaandbarrierwebsin
morial Research Award to SE). This is Publi- the orb webs ofArgiope argentata (Araneae: Ara-
cation No. 106 ofthe Mitrani Center for Desert neidae) on Daphne and Santa Cruz Islands, Gala-
Ecology, BlausteinInstituteforDesert Research. pagos. J. Arachnol., 2:119-126.
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