THESPATIAL DYNAMICS OFLlNYPHHD SPIDERS INWINTER WHEAT K.D. SUNDERLANDandCJ.TOPPING1 Sunderland, K.D. andTopping, CJ. 1993 1111: Thespatial dynamicsof linyphiid spiders in winter wheal. Memoirs ofthe Queensland Museum 33 (2): 639-644. Brisbane. ISSN 0079-3835 Thedensiu of linyphiid spiders was monitored accurately throughoutthe growing season in a fieldofwinterwheat in southeast England in 1990and 991, Numbers increased untii 1 harvestin 19*^1,butdeclinedbeforeharvestin 1990,possiblyduetodroughtconditions.The patternofnatality in 1991 closely mirrored the patternofchangein density, suggestingthat reproduction, rather than immigration,was the predominant factor underlying (he increase indensity.Aerial activity,as measuredbydepositiontrapsandarotary trapinthefield,and a suction trap at the edge ofthe field, increased progressively during the growing season. Results from a short-term field caging technique, used to measure net migration rates, indicated that there was little immigration before July {thereafterhigh sampling variance, caused by aggregation in weedy patches, precluded meaningful analysis).QA/t7/iea<?, Unyphiidae, spatialdynamics, winterwheal, density, natality, migration. Keith SunderlandandChm Topping, HorticultureResearch International, Utttehamplon, West Sussex BNJ7 6LP, England; 7current address; Scottish Agricultural College, Craihstone, Bucksbum, AberdeenAB2 9TR. Scot/and, UK; SSeptember, I99L There are few studies of ihc population Density Sampling dynamics oi predators. For example, Stiling Twenty-five 144m2 squares were marked out (1988), in an examination of the incidence of inside a 60 x 60m area (adjacent to one edge of density-dependence in invertebrate populations, the field in 1990 and 30m from the nearest edge quotes 62 population dynamics studies; ofthese in 1991). Fifteen density samples were taken at 60 relate to phytophages, 2 to parasitoids and each sampling interval (approximately weekly) none-to predators. There are also few population followingaLatinSquaredesign. ThesampleWill consisted of a randomly-selected 0.5m2 area of dynamics studies of migratory species, because ground delimited by a metal ring and sampled of lhe methodological problems involved in using a vacuum insect net (D-vac). Vegetation quantifying migration. The present study, ofthe and the top lem of ground, within the 0.5m- population dynamics of linyphiid spiders (the sampled by D-vac. werethen immediately hand species concerned are all migratory predators), searched for spiders. The suction catch was kept was undertaken tocollect somebasic data inthis at 10°C and returned to the laboratory for live- neglectedarea, andalsobecausethesespeciesare sorting. Therefore spiders were collected from known to be valuable predators of crop pests 7.5m2ofhabitat(crop,groundsurfaceandimme- (thSeunmdaeirnlatnrednedlsnfio,rt1o9t8a6l)l.iTnhypihsiipdasp;ercosnusmidmearraitsieosn dSiuantdeesrulba-nsdu,rfa1c9e9)2)o.neTahcehoDc-cvaascionco(lTloepctpeidngoannldy about 50% ofthe total numberofspiderspresent will be given to individual linyphiid species in in a sample unit, the other50% were uncovered laterpublications. by hand-searching (sec also Sunderland et aL, METHODS AND MATERIALS 1987). Natality Total spider density was measured throughout omloswtionfttehregwrhoewaitng(cs.eva.soPnasotfi1c9h9e)0iinnas1o7uhtahfeiaesltd itnhtAeedfruivelaltlds,faaednmjdaalceeinntlciatnroyctpehhreiait6de0sdxwi6endr0iemvicadoruleaall,elcyatteiwdneef9rkcolnmy England. In 1991,density,natalityandmigration diameter plastic Petri dishes lined with moist weremeasuredina3hafieldofwinterwheat lev. filter paper. The dishes were returned immedi- Riband), 24km from the 1990 study field. The ately to a ventilated box m the study field and fields were treated with agrochemica! applica- examined at weekly intervals. Mean daily tions, following normal farm practice: insec- temperatures in the Petri dishes did not diverge ticides were no! required in eitheryear. fromfieldtemperatures (measuredontheground ) ) 64fJ MfcMOIRSOPTHEQUEENSLAND MUSEUM surface. undeT weed cover) by mote than I°C whichtherefore receivedonly aerialimmigrants. warmerinspring,coolerinsummer).Thedishes As the crop grew, the deposition traps were I were inspected at weekly intervals and the fol- progressivelyraisedonwoodensupportstomain- lowing statistics recorded fj) proportion of tain the levelofthefluidsurfaceconstantlyatca. spiders producing eggsacs in the first week of 5cmabove the topofthe cropcanopy, The traps incarceration, (ii) lime (days) to emergence of wereemptiedatapproximately weekly intervals. $pjderbngs,(iii)numberofspiderlingsemerging, Nomenclature follows Roberts (1987). and(iv)numberofundevelopedeggs(bydissec- tion of the eggsac). These results were used, in RESULTS conjunction with information on the density of adult females, tocalculate dailynatalityrates for The study was based on data from more than each species and then combined to give a com- 39,000 individuals belonging to 53 specie posite spider natality curve, species were dominant (Table 1). All species belongtothefamilyLinyphiidae,withtheexcep- Net MigrationRate tion of the tiriiagiiathid Pachygnatha degeeri. Lepthyphantes tenuis was the most abundant Migration to and from small areas ofthe crop was suppressed by the use of ten itainJess steel species in 1991 and the second most abundant in spider-proof cages. The cages were circular, 1990.Speciescompositionwassimilarin thetwo p0e.r5fmor2abtyiolnsmmtmal'lt2a(j*tdoomsamdaelloftomaelslhowwiptahss3agxe2o.5f Myeeairosn,etthaeruornelsytrinsotwaabslereldaitfifveerleynmceosrebeaibnugndUainatt firs? insist linyphiid spiders). The bases of the in 1990, the reverse being true for Oedothorax cageswere sealedwithsufficientcompacted soil spp. Here, allspiders are treated as agroup. In 1990, density of total spiders increased in to prevent entry or exit of any spiders. Total spider density inside the ca^es was assessed as spring to reach a peak of 7Snv: on 18 June and above. Becuus.: d were moved toa new thereafter declined, apart from a short-lasting peak (made upentirely ofimmature spiders)just location withinthe LatinSquareeachweek,there was assumed to be insufficient lime for the beforeharvest (Fig. 1) Thepattern wasdifferent processes of natality and mortality to be sig- in 1991 (Pig. 2); spider density built up in two nificantly affected by the changed microclimate sups(thefirstinMay/June,thesecondinAugust) to reach a peak of 123m-2 just before harvest. bcinhesatinwdgeeeentihnecadcgeaengdseista;yndtfhreuornmecfaoogrneeeddwipaferfeteksreontfcoestthheeincnretoxhpte Msleiaghntlayirhitgehmeperraitnur1e9s90in(J1u5n.eiaCa)ndtJhualny 1w9e9r1e wereconsideredtobea measureofnetNfigftU (il6l8^mCm),inb1u9t90raicnffa1ll9lwmams icnon1s9i9d1e)r.abTlhye lseomwie-r drought conditions in the summer of 1990 may AerialDensiiv OF SWDEBS have had a deleterious effect on spider survival. A46cmPropellerSuctionTrap(Taylor, 195? ), with an airthroughput ofTOm"" uiin J and a sam- pling heightof 142cm above the ground surface. Species 1-' M1 1991 locatedattheedgeofthestudyfield, wasemptied Mettmeuirurestris(C.L.Koch) -:_ > 5.4 daily. In addition, arotary insect net was used to l^pthypbatUestenuis(Blackwall 27.H :•.1 J collect spiders within the field, 25cm above the Eriganeatra(Blackwall) 9.S 1 *.. lop of the crop canopy. The 10m long rotorarm MilUrianainerrans(O.P.-CambridgeI 5 - 0.4 travelled at 6.3m sec~J and the 56 x 25cm net at Eri^anepromiscua(OTVCambndpej 5.0 the end ofthe rotor arm (which was designed to ErigmtKdentipalpiB(Wider) : 2 5.0 sample air isokineticaUy, (Taylor, 1962)) PmchysnailuidegeeriSundcvall :.o n : processed 53.8m3 min'1 and was also emptied Bathyptwmesxa:ctiix(BlnekwaM) 2,7 H ') daily. To measure rates of input ofspiders into Oc-dotheratfttscus1RUckwalt : i '.. • the field, a set of seven deposition traps were Oettuthorairetuxus(Weslring) 2.1 3.9 deployedat 15m intervals betweenthe rotor and Fitnamtitnopssuit:i'from(Wider) 1.0 0.1 the 60x 60marea. Each trapconsistedofa 10cm Otilothrtraxapicatus(B\uc\w^\\} 0.3 6.9 edetehpy,lenIemg2l1yfcioblre(g2l0a:s1s)tprlauys, f1il%leddewteirtghenwta,tefritatinndg Olhers* 5,0 6.6 inside a 1.6m2 metal tray containing the same TABLE I. Species composition of adult spiders in fluid. The outertray acted as a barrier to prevent density samples in 1990 (n=1562) and 1991 (n= spiderswalkingfrom thecropintothe innertray. 1457). SPATIALDYNAMICSOFLINYPHIIDS 641 Dale M 95%CL SPIDER DENSITY IN A FIELD 9April 2.1 (-1.2-5.4) OFWINTER WHEAT IN 1990 23April 2.2 (-2.3-6.7) 1Harvest 1 May -2.0 (-8.7-4.7) 14May 2.7 (-11.8-17.2) 2! Maj -12.8 (-29.5-3.9) 11June -16.5 (-33.9-0.9) 18June -8.0 (-23.1-7.1) M*W 3July 0.7 (-13.2-14.6) 9July 2.9 (-10.4-16.2) j I I 17July -5.1 (-26.7-16.5) Jan Feb Mar Apr May Jul Aug Sep 23July 1.8 (-20.5-24.1) SPIDER DENSITY IN A FIELD 29July -9.5 (-43.8-24.8) OFWINTERWHEAT 5August 24.2 (-19.9-6S.3) IN 1991 (solid line) 19August 12 7 (-41.4-66.8) 9September -10.0 (-52.7-32.7) 95%CLOFMIGRANTS I 60 (verticaldashedline) 24September 7.1 (-19.6-33.8) TABLE2.Indicesofnetaerialmigration,M(95%CL), in 1991. circumstantialevidencethatreproduction (asop- Feb Mar Apr May Jun Jut Aug Sep posedtoimmigration)isthepredominantprocess driving increasein density ofspidersinthefield. SPIDER DENSITY IN CAGED Dataonmigrationcanbeexaminedinthelightof AREAS OFWINTERWHEAT this hypothesis. Aerial activity of spiders, as IN 1991 measured by catches in the 1.4m suction trap at the edge ofthe field, tended to increase steadily E 60 from March to August, and this was followed by a much larger increase in September (Fig. 5). A similar pattern of aerial activity was evident in- sidethefield, asindicatedby thecatchin deposi- tiontrapsandintherotarytrap(Fig. 6).Toassess whether there had been a a net gain or loss of Jan Feb Mar Apr May Jun Jul Aug Sep spidersfromthefieldoveraparticularperiod,the density of spiders inside caged areas was com- FIGS. 1-3. Total spider density in a field of winter paredwiththedensity outside,togiveanindexof wheat: 1990 (Fig. 1); 1991 (solid line) and 95% CL net migration (M); of number of migrants m~2 (vertical dashed lines) M = (F2-F1)-(C2-F1) = F2-C2 (Fig. 2); incaged areas, 1991 (Fig. 3). where Fl and F2 are densities in the uncaged Density in the caged areas of the crop in 1991 partofthefieldinweeks 1 and2respectively,and followedasimilarpatterntothatinuncagedareas C2 is the density in the caged part ofthe field in (Fig. 3). 95% confidence limits increased during week2. (F2-F1 representschangeinnumbersdue July and August (Figs 2, 3)duetoaggregation of tonatality, mortality and migration, whereasC2- spidersin weedypatchesofthecrop(significant- Fl represents change in numbers due to natality ly more spiders in weedy than bare areas; paired and mortality alone, because migration was sup- t-test, n = 5 dates, p= 0.05). pressed by caging). The standard error of M is The pattern ofchange in density with respect calculated as the square root of [SE F22 + SE M totimeisexamined, below, in relationtonatality C22]; the 95% CL's on are therefore large and migration for 1991. because they are compounded of two standard M Natality rates were c. 4m 2 day1 in the spring, errors.Valuesof areshowninTable2.Positive briefly 10-15m"2day 1 inlateJuly,then8m"2day"' values indicate immigration and negative values in August. The pattern of daily natality was indicateemigration.However,all95%CL'sspan similartothepatternsforimmaturespiderdensity the range from negative topositive and therefore (Fig. 4) and total spider density (Fig. 2); this is nosignificantnetmigrationcanbedemonstrated. 642 MEMOIRS OFTHEQUEENSLANDMUSEUM DAILYCATCHOFSPIDERS INA 1.4MSUCTIONTRAP ATTHEEDGEOFAFIELD OFWINTERWHEATIN 1991 Jan Feb Mar Apr May Jun Jul Aug Sep FIG. 4. Total immature spider density ( •) and total Feb Mar Apr May Jun spider natality (continuous line) in a field ofwinter wheatin 1991. DAILYCATCHOFSPIDERS • INAROTARYTRAP These95% CL's areplottedon thecurveoftotal andIN7SQMOF q spider density (Fig. 2); the extent of the dotted IDNEPAOSFIIETLIDONOFTRWAIPNSTER"""WHEAT lineaboveandbelowthedensitycurveshowsthe IN 1991 amount of immigration and emigration, respec- tively, thatcouldhaveoccurredbetweenanytwo dates. The following conclusions can be drawn; (i)anymigrationthatmayhaveoccurredin April was small (i.e. on a similar scale to density sam- pMlaiyngavnadriJaunncee)i,t m(iui)stifailsmomihgarvaetiboenenococnurarsemdaliln 0--0-. J*&A#/ tsicoanl,e,anbdut(itihi)erienJcuoluyl,dAuhgauvsetbaenednSaelpatregmebeemri9gr5a%- Feb *Mat' I A'pr'I Ma"y I' " *JuMlti IAugt 11 tStept CL's were very large (due to spideraggregation, see above), with no obvious bias in favour of eitherimmigration oremigration. FIGS.5,6. Dailycatchoftotalspidersin winterwheat fieldin 1991. 5. In 1.4msuctiontrapatedgeoffield; 6. In rotary trap(•)andin 7m ofdepositiontraps . DISCUSSION densities of lycosid and linyphiid spiders vary There appear to be no previous quantitative greatlyaccordingtolocation (Table3). Densities arachnological studies in whichtheseasonal pat- areoften lowerin graminaceous crops (Table 3). ternsofnatalityandmigrationarecomparedwith The peak spiderdensity of 123m2 in the present the seasonal pattern of density using consistent study is comparable with, if somewhat greater units. Examples of other arachnological studies than, densities recorded in cereals by other involvingdensityornatalityestimationaregiven authors (Table 3). In common with the present below.Themajorityofinvestigationswhereden- investigation, nearly all the studies in Table 3 sity has been measured are for grassland; peak reported large confidence limits due to aggrega- Species Family Habitat Density Authors) Geolycosagodeffroyi(L.Koch) Lycosidae pasture 1 Humphreys, 1976 TrochosaterricolaThorell Lycosidae grassheath 70 Workman, 1978 Pardosapalustris(Linnaeus) Lycosidae alpinemeadow 9 Steigen, 1975 TABLE 3. Oedothoraxfuscus(Blackwall) Linyphiidae pasture 155 DeKeerandMaelfait, 1987 Maximum density Erigoneatra(Blackwall) Linyphiidae pasture 318 DeKeerandMaelfait, 1988 estimates (number m Erigonearctica(White) Linyphiidae dunegrass 330 vanWingerden, 1977 ) in a range of arachnological Totalspiders Festucagrass 840 Duffey,1962 studies. Totalspiders ryegrass 43 Alderwiereldl,1987 Totalspiders maize 49 Alderwiereldt,1987 OedothoraxandErigone Linyphiidae winterwheat 53 NyffelerandBenz, 1988 Totallinyphiids winterwheat 60 Fraser,1982 Totalspiders winterwheat 75 Sunderland1987 SPATIALDYNAMICSOFLiNYPHULn M.-v lion of spiders There seem to be no previous phenology ofballooning spiders at two locations publications describing the seasonal pattern of ineasternTexas.JournalofArachnology 13:HI* spider natality, but a few authors <eg Steigen. 120. 1975; Workman, 1978i haverecorded natalityat DEKEER,R.& MAELFA1T,J.P. J987.Lifehistory of specifictimesofyear. Schaefer11978)estimated Oedothoraxftiscus (BlackwalL 1834) (Araneae, Linyphiidac) in a heavily grazed pasture. Revue U\r egg density of the linyphiid Fioronia buc- d'Ecologieetde Biologic duSol 24: 171-185 c1u5t1enmta2 idnepgernasdsilnagndondurlioncgattihoen sTprhiengmtaoxbiem9u8m- 198(8A.rOanbesaeer,vaEtriiognosnionnaet.h)eliinfeachyecalveiolfyEgrriagzoendetpfa/sp- springnatalityofthe LinyphiidErigotxearaica in ture. Pedobiologi332: 201-212. coastalgrasslandwasclaimedtobe2584m"2(van DUFFEY, E. 1956. Aerial dispersal in a knownspider Wingerden, 1977), which is considerably greater population. Journal of Animal Ecology 25: 85- than the total natality (8 dominant linyphiids.i of 111 A 789nr2betweenMarchandOctoberinthepresent 1962. population study of spiders in limesione study: this difference may underly the re]- grassland. Journal of Anirnai Ecology 31: 571- spafsene&s of spiders in crops compared with 599. natural grassland (Table 3). Although the inten- FRASER, AM. 1°82. Theroleofspidersindetermin- sity of aeronautic activity has been measured ing cereal aphid numbers'.Thesis(Univcrsilv od EastAnglia) 121p. Ltting stickytraps(Duffey, 1956,vanWingerden, GREENSTONE. M.H.. MORGAN, C.E. & L97T, Greenstone et ai. 1985), window traps HULTSCH, A.L. 1985 Spider ballooning- (Mcijer, 1976;DeKeerandMaclfait, 19S7, 1988) development and evaluation of field trapping and suction traps (Dean and Sterling, 1985; methods (Araneae). Journal ot Arachnology 13- Sunderland, 1987, 1991), there appear to be no 337-343. previous attempts todirectly quantifythe impact HUMPHREYS, W.F. 1976. The population dynamics* ol migration on population density. The use of of an Australian wolf spiderT Oeofycesa godef- short-term field cages in the present study f>o\i([, Koch 1865)(Araneae: Lycosidae).Jour- pmiigorvaitdieodnus(eefxuclepetstwihmaetnessaomfptlhienugppvaerrilainmcietsbe1-0 MEIJnEaRl.ofJA.ni1m9a7l6.EcTolhoegyi4m5mi:g5r9a-8t0i.on of spiders (Araneida) info a new polder. Ecological En came very large) and it is expected that this tomolugy 2: 8}-90, technique will yield better results when data are NYFFELER,M.&BENZ,G. 1988. Preyandpredaior. analysed Tot individual species. Inaddition,when importance of micryphanlid spiders in winter the rotary trap has been calibrated, it should be wheatfieldsandhavmeadows JournalofApplird possible to estimate rates of aerial immigration Entomology 105; 190-197. and emigration froma comparison ofdeposition ROBERTS, MJ. I9S7. The spiders ofGreat Britain and rotorcatches. and Ireland, Vol. 2.*(Hartcy Books: Colchester England) ACKNOWLEDGEMENTS SCHAEFER, M. 1978. Some experiments on the regulation of population density in the spider WethankMt BewseyandMrReeves(HRI)for SFiyomrpoonsiiaaobfucthceutZeonollaogi(cAarlanScoicdiae:tyoLifnLyopnhidiodnac4)2.. 'ructing therotary trap MrFenlon (HRI) fur 203-210. statistical advice, and DrJe?pson and MrThomas STE1GEN. A.L. 1975, Energetics in a population of Southampton University)loruseful discussions. Pardoia palustris (L.)(Araneae, Lvcosidaej "i »T' he work was funded hy tbo Natural Environ- Hardangervidda. Pp 129-144 tn F Wielgo ment Research Council (Jomi Agriculture and (ed). 'Fennoscandian tundra ecosystems Part 2V Environment Programme) and the Ministry of (Springer: Berlin). Agriculture, Fisheries and Food. The first author STILrNG. P. 1988. Density-dependent processes And is grateful to the British Council for the oppor- Afenei)maflactEocrosloignyi5n7s:ec5t81p-o5p9u3l.ations. Journal of tunityto deliverthis paperin Australia. SUNDERLAND,K.D. 1987.Spidcisandcciealaptuds in Europe. Bulletin SROPAVPRS 1987/X/l; 82- LITERATURECITED 102. 1991.Theecology ol spideisinccrcalaProceedings ALDERWEIRELDT.M. 1987. Density fluctuationsol ofthe6th International Symposium on Pestsand spiders on maize and Italian ryegrass fields Diseases ot Small Grain Cereals and Maize. Mededclingen van de Fakultcit LamtbaiHv- BoardofPlantProtection. Halle/Saale,Germany wcLctischappen Kiiksuiuvcrsitcit Gfittl 52. 273- 1:269-280. 282. SUNDERLAND, K D. FRASER, A.M. & DIXON DEAN DA & STERLING. W.L 1085 Size and AFG 1986. Field and laboratory studies on f 644 MEMOIRS OFTHEQUEENSLAND MUSEUM money spiders (Linyphiidae) as predators of TOPPING, C.J. & SUNDERLAND, K.D. 1992. cereal aphids. Journal of Applied Ecology 23: Limitationstotheuseofpitfalltrapsinecological 433-447. studiesexemplifiedbyastudyofspidersinafield SUNDERLAND, K.D., HAWKES, C,STEVENSON ofwinterwheat. Journal ofApplied Ecology 29: TP.O,WMECLBLR,IDWE.,,CL.HEA.,MSBMEARRST,,RL..JE..,&SCOAPRP,TEP.RI.,, WING4E85R-D49E1N., W.K.R.E. VAN 1977. 'Population O.C.R. 1987. Accurateestimationofinvertebrate density in cereals. Bulletin SROP/WPRS dynamics of Erigone arctica (White) (Araneae, Linyphiidae)'. (Thesis, Free University: Amster- 1987/X/l: 71-81. TAYLiOnRin,seLc.tRs.uc1t9i5o5n.trTahpse.sAtnannadlasrdoifzaAtpipolnieodfaBiiro-lfolgoyw WORKdaMmA).N1,47pCp.. 1978. Life cycle and population 43: 390-408. dynamicsofTrochosaterricolaThorell(Araneae: 1962.Theabsoluteefficiencyofinsectsuctiontraps. Lycosidae) in a Norfolk grass heath. Ecological Annals ofApplied Biology 50: 405-421. Entomology 3: 329-340.