Oavid C.,Shaw d,o Ronald J. Taylor D.o".tr.a'l,o, Boroq, Wo F W.' r'o .t,.o, L 86 g.d !4o11lo 98ll5 Polljnation Ecologyof an Alpine Fell-FieldCommunity in the North Cascades Abstract 'ruh-!f '{ rlr loliiirlion.''1!1og\of an alpir tul]ficld lo.areit ir LheNIounr Ilater areaoJ washingtonStar. ras ronducred iru.nsth' Lumtrrr''ol l93l llllhation svndrocsGtraregie!)ofth.dorrinanrptantswerearemophrrv.g,ine.arjze.t.nlomoph ilr' and sl"ializ'd ent'nophilv lrs.cr 'Ihe !isitationsro ptantspecies werc q"-tir;,"t "".l i"""",g prenorog! nut $as denrin,n"u. inldtant pollinrrorsrere t,unblcl,rs, srrplid nr"., -a ,,-*"ri iii"., "i'];,". ,",0",,,,,"" $ere hurrerliesand p'imitivf llic' Plantserhitririne specializ*1 entornophily appearcdro oinin;e comperi,i"' l, .""p"-,r"" of ltowerjng NIanyot rheplants lrhiliring rinrcs. gL:neralizedenrooopt,ili norercrt s1mhron",.r,, p".r,.,p.f* ' "r" .,\ ,,",a*,arion to alra.t h.ge nunbcrs 1. 1, ,..r.,i,.. 1 , r-t'^\ .,.,4Lhi F tt,{pr: Introduction rcducrng competition for pollinators. Foraging behavior of flies and butterflies is variable Pollin.rriuner-ul'rgr i. a rapidh gror.ing -uh- anJ "olJ-fa.lrr,,rrnJ' lesslell known (Proctor and yco l9?3, Faegri dr- inline.l bi,,log\.rccen \ e,ndVand"r Pijl l,r7q,.In gnrreral.ili,.. proier erpanJirrglrnrrr .r nrinrarilrdc", riprir, to an .i- llo\1crj sith n,rn-con.erl,d rerarrl., Jo not perimenlal science.Howerer, although therc are .peeializ".und appcarirr rlpirr,.r"ommunitie. a, number of excellent tcxts, c.g., Faegri and earll in the season.Buttcrflies preler tubular Vander Pijl (1979),Jones and LitJe (1983),proc- llorcrs with toncealed rcwards, have a higher tor and Yeo (1973), and Richards (1978), ancl level of floral constancythan flies, and app"ar nunrerou:arlr"ter , "nc, rningpollination biolugr. much later in the season. rhcrcare lp\ .rLdic.thar de.rl sp,.rificallr uirh F,'r6rr.'rn, trnalpin. plrnt r'umrnunl\\!a\ pollirrati.'nnr,,logr oiLrll,irr,, "ornmuliri... I hi. !'.lp.tc,lb., au5. ,ri irss irn plir.irr . la,k "f d i,ru is espcciallv truc of the North Cascades. r. bance, and, perhaps, more obvious plant-inscct The nost comrnonh cited insect pollinaror coadaptations,i.e., relationship betr,reenfloral groups (orderslfamilies)in alpine areasof North rnorphologr/color and trpe of insect pollinator. Amcric.aare bumtriebecs(Hl menopteralApidae); By delinition (Douglasand Bliss l97T) the alpine srrphid flies (DiprcraiSvrphidae); Muscoid flies ls that area in the mountains abore the limit of (Diptera/Anthomvidae,Muscidae, Calliphoridae, upright tree growlh, characterizcd by soil and Sarcophagidae, Tachinidac); and buttcrllies r,arh"r errrern,..(Bli.: Iq? t. Billing. lo74t.Ou|. (LepidoprcraiPapiiionoidea, Lvcacnrdae, -lutl\ , L,n.i-ttsd,'f ,rnalr.e. ui tlosnring Satyridae,Nvmphalidae)([Ioldenke 1976, l9?9; phenologv and insect visitation. Flowerini ltoldenke and Lincoln 1979; Levcsquc and phenologyis an irnportant componcnt of poilina, Burger 1982: Bauer, l9B3). tion ecologvbecause it determinesthe availabili_ Bumblebeesare social insecls and nlust tr of resourccsto animal pollinatorsano thc com- foragc for colont nceds as ueli as rlclr own. petilir.e rclationships among plants for these Accordinglr lhe) foragc ven intcnsirch,ald visit poliinators (Levin and Andcrson l9?0, Mosquin nurit.r,'u.rl,,\1cr-. \. a t,h,,,..Ine,.ulonr es.urnp- 1971,Pojar 197,1,Heinrich l9?.5,procror lO7B, a gcneralistrole. r isiting a n ide variet.r, of flor er Plcasalts 1980).The pattern of pollinator rroe.. visita_ Hnu,r"r. ,n,lir,drr.rl.r,rrd ru -1,,.,.ialize lron rs rmportanl (nra.itrr) becau-qeit ha-sa direct efTect nrr,'rr, ur tt\u-rr,., ie- x1. n, gt\H,' tlnrc on thc relroductive successand gene flow rate tH.inrich lq-bd. lo,,rt.\lanr r,l.,ri-p""i,.. arn of plants (Nlacior l9?1, Procror and yco l9?3, nrore'or-less .lependcnt on buntblebecs for Richardsl9?8, Facgri and Vanrlerpijl 1979),anj pollination anrl havedeveloped sequential llorer_ makcs it po-ssibieto quartjtati\.ell assessrre rm_ ing tirncs (Pojar l9?4; Ileader l9?5; Heinrich portance o1specific polJinatorsn,ithin an aipine l9?5. 1976b; PleasanrsJ980; Bauer l9B3), (in this case)coinrnunitl. \"rthr'n-' Srien"r. \ o'. r,().\o. l, l'tgr, 2l Methods specics,including each of multiple visitsby single insects,were reL'ordedboth while walking slowly minute ilatch The selected study site was an alpine fell-field along the lransectsand during 20 plots. The number of locatedlear Mt. Baker on Cho$der Ridge, a pro- periods of the 2 m squarc limited bv iime po-qedresearch natural area (Ta,\'orand Douglas \tatch periodsand transectsrvere In addition to the 19?8)(Figure I). The ridge is relativclv inacccs- to a maxirnun! of sjx per daY from the study area, sible irnd remains urrdisturbed. The arca of quantitalire data collccted sd: olong th' lull sampling consisled of a 20 x 20 rn plot on a p,'|lirrrt"rLeh,r i',r nnltsLI 'lurinstl'' moderateSE slopeat ca.2041m elevation.The rnngrh't Chu*d.r Ri,lg.p' riodi,.rllr rock,r ridgctop $a-q sparsela- vegetatcd b1 su rmers of 1980-l9B'1. \!J- lu collP,I repr,5l.rrldli\"s clumpcd, cushion plants, a typical fell-field com' \rj allpnrpl tnadp insectfor iden- munitl (Tallor and Douglas 1978). fhc commu- of eachdiscernable flower-r'isiting Identificationsuere nity stmcture as dctermincd in August 1980, tification to gcrtusor famill. al (19?6) and lt'cre con- using the cxperirncntaldcsign describedbl Bliss madc using Borrer el (Western Washington (1963).In total, sixtr 20 x 50 crn quadrats \{ere firrned by G. Kraft used for nreasurirlgcovcrage (following f)aubert- Unir.ersit,r'). and eight syr- mire 1959, l968) and frcquenc,v lmporlance or An anahsis of four bumblebees to supplement prominencet alues$ere cirlculatedfor eachplant phid fly pollcn loads uas made bast'don observedin_ speciesb)-mulliplying its mean perccnt covcr bY constancvdeterninations corbiculae were thc squarcroot of its frequencl'.Plants were iden- sect behavior. For bumblebee-", insecl as uscd, tified using Hitchcock and Cronquist (1973)and usedifor syrphid flies the entire the gut as well Hitchcock er a1.(1955-1969) thus countsincluded pollen *ithin PerccIIt pollcn The pollination studv was carried out during as grains attached erternallY insect the surnmerof l98I. Plant speciesof the fell-field tvpes was determined for each quantified using fbur community \r'erc assigned a floral color class' Flowering phenologr vas io(raliono[ the following the s1'stemdescribed by Kevin (1972a). 20 m permancnt lransects.The rnarkirg the northern The color classassignment does not relate to the transectsvas establishedbJ areaat I meter insect visual rangc, trhich at least in sonle cascs and southernborders of the slud) choosing a lneler e\tends into the ultra-r'iolctspectrun. Follotring inlervals (l-20) ard randomly rvithin each of Proctor and Yco (1973),floral morphologv uas locus (l-4, 6-9, ll-I4, lfi'19) from flo$ers (flouer classified into the follo*ing t,rpes:(l) open- the four 5+neter intervals. All open e.g, more-or-lessbowlshapecl $ ith exposedrcrards; clustersin the caseof denseinlloresccrces, Pha<:eLirtsericea, (2)partially exposed usuailvsome lorlion of the those of Orltropis catnPestris, Lant:eolatum) periarth iuscd re-qullingin sornevhdtdif1icult ac- SoLiLago nultiradiala, and Sedant thc lranseclwere ccssto rc$arcls;(3) cLoscd llover structured i withirl a one meter swathalong oncc each$cek sucli a r,at so as to exclude visitation L! non- counted.Phenolo€ry was recordcd season. specializedpollinators; ('t) small tubular flowers throughout the l981 f1o*ering lrith short tubtlar corollas,e.g., co Fosilae,lr ith littlc restriction of rcwards; (5) large tubular- "tongur:d" Results and Discussion long tubular floners requirilg long Ridge fell-fielcl in-.ectsto rcach concealednectar. On the basis The planl -rpeciesof the ChoNder l, alolg rvith their of floral rnorphologl, plant specics\rerc assrgned communit-rare listed in Table strateg-l' pollination strategies: lind (anernophilr'), prominencc value (l'V), pollinirtion " '1.,r. ti'ilL'f:' gcneralist (gencralized entomophil-v),specialist flnralnrorphulugr.l1.,ra' cnd i'r'Pcl f)t1'tropis (specializedentomophil,r'). See table 1 fbr pollina- Dominant planls, bas.d on PVs, nerc lgroplro conr tion slrategicsand related charactcristicsof the canrpestris,Cerasliunt arNense, predominantplant spcciesof our studl- nun, Phlox clLlfLLsa,and Potentilla dixerslfulia. (69 Within the 20 \ 20 m studv afea,insect grouP Bare ground erceeclcrl.50 Pcrcent coveragr fell-fieldrr)nrrnunities actir.il.,-was quantifit'd using 20 m transects(ran- pcrcenl),a characteri-cticof wcre scattcred' domll selcctedfronr metcr loci I through 20) and (Douglas anclBliss 197?).Plants exhibited a cushion 2 m squareobserr'ation plots (randonll.r-selcctecl t,-vpicalilclurnped, and most frornthr 100possible). All inscctrisits lo flo*cr grol!th form. 22 ShJ\ und Ta\l,,r Among lhe prirrcipal plant species, the "open" but probably only exploratorily since so few fioral morphology was most common, visitations were recorded. Finally, bumblcbees lbllorved in order of decreasing occurrence by \'!erc "inc'onspicuous" unavailableto take advantageof thc earlv- (graminoids),,,small tubular,' flo".ring:rnd r.rr ahundrnr Phti ,!illuto du'r- (compositae), "partially exposed,,',,largc ing the l98l season(See Table 2). Horvcver,we tubular," "closed." and The lattcr trlo types have frequentlv observedquecn bumLrlebeesfor, '!ere each reprcsented by a single abundant aging on PhLox tliJfusa on Chowder Ridge. species. Itredominant floral colors ryere vello{ Pollcn types collectedfrom four bumblcbees and white. suggest that those bees were majoring on lwo speciesat one time (see Table 3). F ower V sitors Syrphid Jlies-Syrphids, represenrcd lry ser.eralspccies, did not becomeabundalt in lgBl Tablc 2 prcsentsnurnbers of insectvrsrts to until late July. Aftcr this time they uere frequent flowers or inflorescelces of principal plant visitors to rnost gencralist plants and ner(j ob- specres,as determined by watch periods and served to visit species with olher pollinations transects.Unfortunately, based on supplementary strategies, including graminoids (Carer obscrvations, the numbers are biased.