Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 2: Spartina Distribution and SpreadThe first 40 or 50 years <strong>of</strong> spread in Willapa Bay producedless than 10 ha <strong>of</strong> S. alterniflora. Beginning with a verysmall number <strong>of</strong> hybrids in <strong>the</strong> 1970s or 1980s, <strong>the</strong> overallcoverage <strong>of</strong> <strong>the</strong> hybrid has grown to about 1,500 ha.At a rate <strong>of</strong> increase <strong>of</strong> about 12% per year, similar to S.alterniflora in Willapa Bay, San Francisco Bay would haveonly about 3.4 times <strong>the</strong> area <strong>of</strong> <strong>the</strong> initial introductionssome 30 years later. If <strong>the</strong> two introductions <strong>of</strong> S.alterniflora had amounted to about one ha <strong>of</strong> S. alterniflora,<strong>the</strong>re would be only 3.4 ha now. I speculate that withouthybridization, this conference would not have occurred.Transgressive traits confer greater fitness upon a subset<strong>of</strong> hybrids than ei<strong>the</strong>r parent exhibits. We entertain <strong>the</strong>hypo<strong>the</strong>sis that <strong>the</strong> key trait is increased self-compatibility <strong>of</strong>some hybrids. This would erase <strong>the</strong> weak Allee effect thatwe see in Willapa Bay as increased self-compatibility allowssingle plants to set abundant seed.The presence <strong>of</strong> hybrids means that control <strong>of</strong> nonnativecordgrass in San Francisco Bay will require researchand understanding beyond that required in Willapa Bay.Biochemical systematics are needed to detect hybrids at lowfrequency, in order that hybrids can be removed before <strong>the</strong>marsh is overrun by <strong>the</strong>m. Strategies concerning which andhow much hybrid cordgrass to eliminate for effective controlwill require understanding <strong>of</strong> <strong>the</strong> dynamic mechanisms <strong>of</strong>hybrid spread. Research on <strong>the</strong>se subjects is just beginning.REFERENCESAyres, D.R., D. Garcia-Rossi, H.G. Davis, and D.R. Strong. 1999.Extent and degree <strong>of</strong> hybridization between exotic (Spartinaalterniflora) and native (S. foliosa) cordgrass (Poaceae) inCalifornia, USA determined by Random Amplified PolymorphicDNA (RAPDs). Molecular Ecology 8:1179-1187.Ayres, D.R., D.R. Strong, and P. Baye. 2003. Spartina foliosa – acommon species on <strong>the</strong> road to rarity? Madroño 50: 209-213.Ayres, D.R., D.L. Smith, K. Zaremba, S. Klohr, and D.R. Strong.2004. Spread <strong>of</strong> exotic cordgrasses and hybrids (Spartina sp.) in<strong>the</strong> tidal marshes <strong>of</strong> San Francisco Bay, California, USA.Biological Invasions 6: 221–231.Civille, J.C., K. Sayce, S. Smith, and D.R. Strong. 2005.Reconstructing a century <strong>of</strong> Spartina invasion with historicalrecords and contemporary remote sensing. Ecoscience 12:330-338.Daehler, C.C. and D.R. Strong. 1997. Hybridization betweenintroduced smooth cordgrass (Spartina alterniflora; Poaceae)and native California cordgrass (S. foliosa) in San Francisco Bay,California, USA. American Journal <strong>of</strong> Botany 84:607-611.Davis, H.G., C.M. Taylor, J.C. Civille, and D.R. Strong. 2004a. AnAllee effect at <strong>the</strong> front <strong>of</strong> a plant invasion: Spartina in a Pacificestuary. Journal <strong>of</strong> Ecology 92:321-327.Davis, H.G, C.M. Taylor, J.G. Lambrinos, and D.R. Strong. 2004b.Pollen limitation causes an Allee effect in a wind-pollinatedinvasive grass (Spartina alterniflora). <strong>Proceedings</strong> <strong>of</strong> <strong>the</strong>National Academy <strong>of</strong> Sciences USA 101: 13804-13807.Faber, P. 2000. Grass wars: good intentions gone awry. CaliforniaCoast & Ocean 16, #2. Summer 2000. 1-5.Strong, D. R. and D.R. Ayres. 2009. Spartina introductions andconsequences in salt marshes: arrive, survive, thrive, andsometimes hybridize. In B.R. Silliman, E.D. Grosholz, and M.D.Bertness, eds. Human impacts on salt marshes: a globalperspective. Berkeley, California; London: University <strong>of</strong>California Press.Taylor, C.M., Davis, H.G., Civille, J.C., Grevstad, F.S. and A.Hastings. 2004. Consequences <strong>of</strong> an Allee effect on <strong>the</strong> invasion<strong>of</strong> a Pacific estuary by Spartina alterniflora. Ecology. 85:3254-3266.-63-