<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> SpartinaChapter 2: Spartina Distributi<strong>on</strong> and SpreadPOLLEN LIMITATION IN A WIND-POLLINATED INVASIVE GRASS, SPARTINAALTERNIFLORAH.G. DAVIS 1 ,C.M.TAYLOR 2 ,J.G.LAMBRINOS 3 ,J.C.CIVILLE 4,5 AND D.R. STRONG 1,41 Center for Populati<strong>on</strong> Biology, University <str<strong>on</strong>g>of</str<strong>on</strong>g> California, Davis, 2320 Storer Hall, One Shields Ave., Davis, CA 95616;hgdavis@s<strong>on</strong>ic.net2 Department <str<strong>on</strong>g>of</str<strong>on</strong>g> Ecology and Evoluti<strong>on</strong>ary Biology, Tulane University, 6823 St. Charles Ave., New Orleans, LA 701183 Department <str<strong>on</strong>g>of</str<strong>on</strong>g> Envir<strong>on</strong>mental Science & Policy, University <str<strong>on</strong>g>of</str<strong>on</strong>g> California, Davis, One Shields Ave., Davis, CA 956164 Secti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Evoluti<strong>on</strong> & Ecology, University <str<strong>on</strong>g>of</str<strong>on</strong>g> California, Davis, One Shields Ave., Davis, CA 956165 Current address: 2731 Be<str<strong>on</strong>g>the</str<strong>on</strong>g>l St. NE, Olympia, WA 98506; jciville@comcast.netLimits to, and <str<strong>on</strong>g>the</str<strong>on</strong>g> c<strong>on</strong>sequences <str<strong>on</strong>g>of</str<strong>on</strong>g>, pollen availability in wind-pollinated plants have been littlestudied. Reproductive failure or depressi<strong>on</strong> because <str<strong>on</strong>g>of</str<strong>on</strong>g> a lack <str<strong>on</strong>g>of</str<strong>on</strong>g> available mates could lead topopulati<strong>on</strong> demographic c<strong>on</strong>sequences for many species. Of particular interest is how pollenlimitati<strong>on</strong> affects <str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> spatial spread <str<strong>on</strong>g>of</str<strong>on</strong>g> invasive plants. We performed a manipulative pollenadditi<strong>on</strong> and exclusi<strong>on</strong> study to investigate <str<strong>on</strong>g>the</str<strong>on</strong>g> role <str<strong>on</strong>g>of</str<strong>on</strong>g> pollen limitati<strong>on</strong> in an invasive perennialestuarine grass, Spartina alterniflora. We found pollen impoverishment at <str<strong>on</strong>g>the</str<strong>on</strong>g> low density leadingedge <str<strong>on</strong>g>of</str<strong>on</strong>g> a large invasi<strong>on</strong>, causing an eight fold reducti<strong>on</strong> in seed set am<strong>on</strong>g low density plants,though not am<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g> high density plants. We found pollen loads <strong>on</strong> stigmas to be determined bypollen availability in <str<strong>on</strong>g>the</str<strong>on</strong>g> air. Fur<str<strong>on</strong>g>the</str<strong>on</strong>g>rmore, <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> airborne pollen is dictated by <str<strong>on</strong>g>the</str<strong>on</strong>g> spatialpattern <str<strong>on</strong>g>of</str<strong>on</strong>g> plants, with much more pollen available over c<strong>on</strong>tinuous meadows than in areas <str<strong>on</strong>g>of</str<strong>on</strong>g> lowplant density. The delay <str<strong>on</strong>g>of</str<strong>on</strong>g> appreciable numbers <str<strong>on</strong>g>of</str<strong>on</strong>g> seed persists for decades until vegetative growthcoalesces plants into c<strong>on</strong>tinuous meadows, and this has slowed <str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> spread <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> invasi<strong>on</strong>.Keywords: Allee effect, invasive species, pollen limitati<strong>on</strong>, Spartina alternifloraWhen Willapa Bay, Washingt<strong>on</strong> was first col<strong>on</strong>ized bySpartina alterniflora in <str<strong>on</strong>g>the</str<strong>on</strong>g> 1890s, <str<strong>on</strong>g>the</str<strong>on</strong>g> very slow rate <str<strong>on</strong>g>of</str<strong>on</strong>g>spread gave little reas<strong>on</strong> for c<strong>on</strong>cern. However, by <str<strong>on</strong>g>the</str<strong>on</strong>g>1980s, <str<strong>on</strong>g>the</str<strong>on</strong>g>re were vast areas <str<strong>on</strong>g>of</str<strong>on</strong>g> seedling recruitment andlarge meadow formati<strong>on</strong> <strong>on</strong> mudflats previously unoccupiedby any o<str<strong>on</strong>g>the</str<strong>on</strong>g>r species <str<strong>on</strong>g>of</str<strong>on</strong>g> emergent plant. In 1995, <str<strong>on</strong>g>the</str<strong>on</strong>g> problemhad grown so daunting that <str<strong>on</strong>g>the</str<strong>on</strong>g> Washingt<strong>on</strong> State Legislaturedeclared <str<strong>on</strong>g>the</str<strong>on</strong>g> Spartina invasi<strong>on</strong> an “envir<strong>on</strong>mentalemergency.” As with many invasive organisms, S.alterniflora maintained an initially low pr<str<strong>on</strong>g>of</str<strong>on</strong>g>ile due to a “lagtime” between col<strong>on</strong>izati<strong>on</strong> and rapid spread (e.g., Kowarik1995). In this paper, we examine <str<strong>on</strong>g>the</str<strong>on</strong>g> ultimate mechanisticcause resp<strong>on</strong>sible for <str<strong>on</strong>g>the</str<strong>on</strong>g> Spartina lag phase and <str<strong>on</strong>g>the</str<strong>on</strong>g>c<strong>on</strong>sequences <str<strong>on</strong>g>of</str<strong>on</strong>g> its cessati<strong>on</strong>.<strong>Invasive</strong> S. alterniflora recruits <strong>on</strong>to open Pacificmudflats as seeds drift in <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> tides yearly, leaving noseedbank (Woodhouse 1979). Seedlings <str<strong>on</strong>g>the</str<strong>on</strong>g>n growrhizomatously into widely spaced circular cl<strong>on</strong>es.Eventually, <str<strong>on</strong>g>the</str<strong>on</strong>g>se isolated cl<strong>on</strong>es grow toge<str<strong>on</strong>g>the</str<strong>on</strong>g>r to formc<strong>on</strong>tinuous meadows. Individuals within a low-densitypopulati<strong>on</strong>, such as isolated cl<strong>on</strong>es <str<strong>on</strong>g>of</str<strong>on</strong>g> S. alterniflora, maysuffer from depressed reproducti<strong>on</strong> due to a lack <str<strong>on</strong>g>of</str<strong>on</strong>g> sexualpartners. This syndrome, known as an Allee effect (Allee1931), will cause populati<strong>on</strong>s to go extinct if <str<strong>on</strong>g>the</str<strong>on</strong>g> populati<strong>on</strong>density drops below a threshold. A less well-knownmanifestati<strong>on</strong> is <str<strong>on</strong>g>the</str<strong>on</strong>g> weak, as opposed to str<strong>on</strong>g, Allee effect.Under <str<strong>on</strong>g>the</str<strong>on</strong>g> weak Allee effect, <str<strong>on</strong>g>the</str<strong>on</strong>g> per capita rate <str<strong>on</strong>g>of</str<strong>on</strong>g> growth(<str<strong>on</strong>g>the</str<strong>on</strong>g> growth rate for individuals within <str<strong>on</strong>g>the</str<strong>on</strong>g> populati<strong>on</strong>) isdepressed when populati<strong>on</strong> density is low, but neverbecomes negative as occurs with a str<strong>on</strong>g effect. We surmisethat <str<strong>on</strong>g>the</str<strong>on</strong>g> Allee effect in Willapa Bay Spartina is weakbecause existing individuals are perennial; while <str<strong>on</strong>g>the</str<strong>on</strong>g>y maymake very few seeds when <str<strong>on</strong>g>the</str<strong>on</strong>g>y are isolated, <str<strong>on</strong>g>the</str<strong>on</strong>g>y surviveuntil populati<strong>on</strong> density becomes high with meadowformati<strong>on</strong> and <str<strong>on</strong>g>the</str<strong>on</strong>g> Allee effect ends.To find whe<str<strong>on</strong>g>the</str<strong>on</strong>g>r density has an effect up<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> number<str<strong>on</strong>g>of</str<strong>on</strong>g> seeds a plant can produce and <str<strong>on</strong>g>the</str<strong>on</strong>g> viability <str<strong>on</strong>g>of</str<strong>on</strong>g> those seeds,we collected five inflorescences from 20 individual S.alterniflora plants at five different sites within Willapa Bayin <str<strong>on</strong>g>the</str<strong>on</strong>g> year 2000 (L<strong>on</strong>g Island, Peninsula, Palix River,Shoalwaters, Porter Point). At each site we collected half <str<strong>on</strong>g>the</str<strong>on</strong>g>inflorescences from low density cl<strong>on</strong>es (all individualsisolated within bare mud) and half from high densitymeadows. We assessed both seed set (# seeds / # florets /inflorescence) and germinati<strong>on</strong> percentage (# germinati<strong>on</strong>s /# florets / inflorescence). We found that c<strong>on</strong>siderably fewerisolated cl<strong>on</strong>es (37%) than meadow plants (92%) could setany seed at all. Fur<str<strong>on</strong>g>the</str<strong>on</strong>g>rmore, for <str<strong>on</strong>g>the</str<strong>on</strong>g> plants that could set atleast some seed, <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow plants had a much higherproporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> seeds (0.30) than <str<strong>on</strong>g>the</str<strong>on</strong>g> isolated cl<strong>on</strong>es (0.08)(Davis et al. 2004a). Finally, <str<strong>on</strong>g>the</str<strong>on</strong>g> seeds <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> isolated cl<strong>on</strong>eswere much less viable with a proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.13 germinating-91-
Chapter 2: Spartina Distributi<strong>on</strong> and Spread<str<strong>on</strong>g>Proceedings</str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Third</str<strong>on</strong>g> <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>C<strong>on</strong>ference</str<strong>on</strong>g> <strong>on</strong> <strong>Invasive</strong> Spartinaas opposed to a proporti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.34 <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow plants’seeds germinating. There was no obvious effect <str<strong>on</strong>g>of</str<strong>on</strong>g> proximity<str<strong>on</strong>g>of</str<strong>on</strong>g> neighboring cl<strong>on</strong>es <strong>on</strong> isolated individuals. While somelow density areas were more crowded than o<str<strong>on</strong>g>the</str<strong>on</strong>g>rs, <str<strong>on</strong>g>the</str<strong>on</strong>g>re wasno obvious trend towards relatively higher or lower seed setas l<strong>on</strong>g as <str<strong>on</strong>g>the</str<strong>on</strong>g> cl<strong>on</strong>es were not touching <strong>on</strong>e ano<str<strong>on</strong>g>the</str<strong>on</strong>g>r. Thissuggests that <str<strong>on</strong>g>the</str<strong>on</strong>g> cl<strong>on</strong>es need to merge toge<str<strong>on</strong>g>the</str<strong>on</strong>g>r before <str<strong>on</strong>g>the</str<strong>on</strong>g>step-wise increase in seed set is achieved by meadowindividuals. This work is reported in full in Davis et al.(2004a).We <str<strong>on</strong>g>the</str<strong>on</strong>g>n investigated whe<str<strong>on</strong>g>the</str<strong>on</strong>g>r pollen limitati<strong>on</strong> could be<str<strong>on</strong>g>the</str<strong>on</strong>g> mechanism behind <str<strong>on</strong>g>the</str<strong>on</strong>g> Allee effect in Willapa BaySpartina. While this may appear to be an intuitivehypo<str<strong>on</strong>g>the</str<strong>on</strong>g>sis, pollen limitati<strong>on</strong> is generally assumed not tooccur in wind-pollinated plants, such as grasses, c<strong>on</strong>ifers andoak trees. There are many studies <str<strong>on</strong>g>of</str<strong>on</strong>g> pollen limitati<strong>on</strong> inanimal-pollinated plants (Burd 1994; Lars<strong>on</strong> & Barrett2000), very few <str<strong>on</strong>g>of</str<strong>on</strong>g> wind-pollinated plants, and n<strong>on</strong>e beforethis <strong>on</strong>e <str<strong>on</strong>g>of</str<strong>on</strong>g> wind-pollinated invasive plants. Pollen limitati<strong>on</strong>in animal vectored plants can diminish reproducti<strong>on</strong> andc<strong>on</strong>strain invasi<strong>on</strong> success (Bar<str<strong>on</strong>g>the</str<strong>on</strong>g>ll et al. 2001; Parker1997). Using simulati<strong>on</strong> and analytic models, we askedwhe<str<strong>on</strong>g>the</str<strong>on</strong>g>r <str<strong>on</strong>g>the</str<strong>on</strong>g> Allee effect in Willapa Bay Spartina could haveslowed <str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> invasi<strong>on</strong> and found it did produce a lagtime (Taylor et al. <str<strong>on</strong>g>the</str<strong>on</strong>g>se proceedings; Taylor et al. 2004).We c<strong>on</strong>ducted an observati<strong>on</strong>al and manipulative studyto assess <str<strong>on</strong>g>the</str<strong>on</strong>g> role <str<strong>on</strong>g>of</str<strong>on</strong>g> pollen limitati<strong>on</strong> in <str<strong>on</strong>g>the</str<strong>on</strong>g> ability <str<strong>on</strong>g>of</str<strong>on</strong>g>Willapa Bay S. alterniflora to set seed. To see if <str<strong>on</strong>g>the</str<strong>on</strong>g>re is adifference in pollen depositi<strong>on</strong> rates <strong>on</strong> stigmas, we collectedstigmas from isolated cl<strong>on</strong>es and high density meadows overthree different sites (Cedar River n = 20; B<strong>on</strong>e River n = 40;Palix River n = 94) and screened <strong>on</strong>e lobe (half) <str<strong>on</strong>g>of</str<strong>on</strong>g> stigmasfor pollen load. We found that meadow plants’ stigmascaptured nine times <str<strong>on</strong>g>the</str<strong>on</strong>g> pollen that <str<strong>on</strong>g>the</str<strong>on</strong>g> isolated cl<strong>on</strong>es’ did.Isolated plants <strong>on</strong> average had less than <strong>on</strong>e pollen grain perstigma lobe while meadow plants had more than six.Although plants at individual sites differed in <str<strong>on</strong>g>the</str<strong>on</strong>g>ir pollenloads, in every case, <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow plants always had more(Davis et al. 2004b). Interestingly, <str<strong>on</strong>g>the</str<strong>on</strong>g> Cedar Rivercollecti<strong>on</strong>s had very little pollen with even meadow plantshaving <strong>on</strong> average less than <strong>on</strong>e pollen grain per stigma lobe,probably because it rained <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> day <str<strong>on</strong>g>of</str<strong>on</strong>g> collecti<strong>on</strong> and <str<strong>on</strong>g>the</str<strong>on</strong>g>previous two days suggesting pollen flow is inhibited <strong>on</strong> wetdays and possibly rainy years.To find how pollen depositi<strong>on</strong> changes over awindward-to-leeward gradient and to see if <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g>pollen in <str<strong>on</strong>g>the</str<strong>on</strong>g> air is correlated with <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> pollendeposited <strong>on</strong> stigmas, we set out pollen traps and collectedadjacent stigmas. We set 10 traps al<strong>on</strong>g each <str<strong>on</strong>g>of</str<strong>on</strong>g> six transects.Oriented al<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g> directi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> prevailing wind: two inwindward isolated cl<strong>on</strong>es (I & II), <strong>on</strong>e al<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g> windwardmeadow edge (III), <strong>on</strong>e in <str<strong>on</strong>g>the</str<strong>on</strong>g> windward meadow (IV), <strong>on</strong>ein <str<strong>on</strong>g>the</str<strong>on</strong>g> leeward meadow (V) and <strong>on</strong>e 100 m from <str<strong>on</strong>g>the</str<strong>on</strong>g> leewardside <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow across an unvegetated channel (VI)(Davis et al. 2004). We found extremely high correlati<strong>on</strong>between <str<strong>on</strong>g>the</str<strong>on</strong>g> pollen loads <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> traps and stigmas (r = 0.99)supporting <str<strong>on</strong>g>the</str<strong>on</strong>g> hypo<str<strong>on</strong>g>the</str<strong>on</strong>g>sis that <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> pollen <strong>on</strong>stigmas is c<strong>on</strong>trolled by pollen abundance <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> wind. On<str<strong>on</strong>g>the</str<strong>on</strong>g> pollen traps, we found very little pollen anywhere in <str<strong>on</strong>g>the</str<strong>on</strong>g>isolated cl<strong>on</strong>es or al<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow edge. Pollen loadsincreased inside <str<strong>on</strong>g>the</str<strong>on</strong>g> windward end <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow andincreased yet more dramatically at <str<strong>on</strong>g>the</str<strong>on</strong>g> leeward end <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>meadow. However, <str<strong>on</strong>g>the</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> pollen droppedprecipitously across <str<strong>on</strong>g>the</str<strong>on</strong>g> unvegetated channel suggesting that<str<strong>on</strong>g>the</str<strong>on</strong>g> gap was too far for nearly all <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> airborne pollen tocross (Davis et al. 2004).To c<strong>on</strong>clusively determine whe<str<strong>on</strong>g>the</str<strong>on</strong>g>r isolated cl<strong>on</strong>es aremaking fewer seeds than <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow plants because <str<strong>on</strong>g>of</str<strong>on</strong>g>pollen scarcity, we performed a manipulative experiment bysupplementing and excluding pollen received byinflorescences and leaving c<strong>on</strong>trol inflorescences open toambient pollen availability. Twenty-four plants received alltreatments and a fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r 20 plants received pollen additi<strong>on</strong>and c<strong>on</strong>trol treatments <strong>on</strong>ly. We found <str<strong>on</strong>g>the</str<strong>on</strong>g> pollen exclusi<strong>on</strong>treatment reduced seed set in <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow plants by morethan sixfold, but caused no reducti<strong>on</strong> in <str<strong>on</strong>g>the</str<strong>on</strong>g> isolated cl<strong>on</strong>es.The pollen additi<strong>on</strong> treatment had no effect <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> seed set<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> meadow plants, but did raise that <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> isolatedcl<strong>on</strong>es by more than threefold. We were not able to saturate<str<strong>on</strong>g>the</str<strong>on</strong>g> plants’ inflorescences with pollen, as an inflorescencehas receptive stigmas for about 10 days (~3 days per stigma)and we were able to supplement <strong>on</strong> <strong>on</strong>ly three c<strong>on</strong>secutivedays. This is likely <str<strong>on</strong>g>the</str<strong>on</strong>g> reas<strong>on</strong> why <str<strong>on</strong>g>the</str<strong>on</strong>g> isolated cl<strong>on</strong>es’pollen additi<strong>on</strong> seed set was not as high as <str<strong>on</strong>g>the</str<strong>on</strong>g> meadowplants’ ambient c<strong>on</strong>trol (Davis et al. 2004). These resultsindicate that isolated cl<strong>on</strong>es, col<strong>on</strong>ists at low density, areextremely pollen-limited whereas seed set in <str<strong>on</strong>g>the</str<strong>on</strong>g> highdensity meadow is not limited by pollen. This work isreported in full in Davis et al. (2004b). We found that anAllee effect c<strong>on</strong>tributed to <str<strong>on</strong>g>the</str<strong>on</strong>g> lag time in spatial spread <str<strong>on</strong>g>of</str<strong>on</strong>g> S.alterniflora in Willapa Bay. Fur<str<strong>on</strong>g>the</str<strong>on</strong>g>rmore, this Allee effectappears to be <str<strong>on</strong>g>the</str<strong>on</strong>g> result <str<strong>on</strong>g>of</str<strong>on</strong>g> pollen limitati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> col<strong>on</strong>izingcl<strong>on</strong>es at <str<strong>on</strong>g>the</str<strong>on</strong>g> leading edge <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> invasi<strong>on</strong>. In <str<strong>on</strong>g>the</str<strong>on</strong>g> studiesoutlined here, and also in two years <str<strong>on</strong>g>of</str<strong>on</strong>g> unpublished data, wec<strong>on</strong>sistently found that isolated individuals set very fewseeds. However, <str<strong>on</strong>g>the</str<strong>on</strong>g>se studies were d<strong>on</strong>e in <str<strong>on</strong>g>the</str<strong>on</strong>g> singlelocati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Willapa Bay, so similar results may or may notbe duplicated in o<str<strong>on</strong>g>the</str<strong>on</strong>g>r locati<strong>on</strong>s. We found a wide range inself-compatibility <str<strong>on</strong>g>of</str<strong>on</strong>g> Spartina alterniflora from <str<strong>on</strong>g>the</str<strong>on</strong>g> nativerange (Davis 2005), so <str<strong>on</strong>g>the</str<strong>on</strong>g> ability <str<strong>on</strong>g>of</str<strong>on</strong>g> isolated plants to use<str<strong>on</strong>g>the</str<strong>on</strong>g>ir own seeds in different locati<strong>on</strong>s may be largelyinfluenced by <str<strong>on</strong>g>the</str<strong>on</strong>g> source <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> col<strong>on</strong>izing individuals. Itwould be advisable for managers <str<strong>on</strong>g>of</str<strong>on</strong>g> o<str<strong>on</strong>g>the</str<strong>on</strong>g>r invaded areas toc<strong>on</strong>firm <str<strong>on</strong>g>the</str<strong>on</strong>g> lack <str<strong>on</strong>g>of</str<strong>on</strong>g> seeds in isolated Spartina alterniflorabefore discounting <str<strong>on</strong>g>the</str<strong>on</strong>g>ir potential as significant seed sources.-92-
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