1991. 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 characteristics. 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). 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ManuscriptreceivedFebruary1990, revisedJuly1990.

Ontogenetic and Seasonal Changes in Webs and Websites of a Desert Widow Spider

Similar Ontogenetic and Seasonal Changes in Webs and Websites of a Desert Widow Spider