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Spartina species of the mid-low intertidal areas are powerful ecological engineers that are highly valued where they are native. Elsewhere, they overgrow native salt marsh and open intertidal mudflats, diminish biota, increase costs of managing wildlife, and interfere with human uses of estuaries. Huge efforts have been mounted to kill some populations of invading Spartina. All large Spartina invasions are by S. densiflora (2n = 7x = 70) or S. alterniflora (2n = 6x = 62) or hybrids between the hexaploid species (2n = 6x). Hybridization is a recurrent theme in Spartina; the allododecaploid S. anglica (2n = 12x = 120) and the hybrid swarm in San Francisco Bay arose through the introductions of S. alterniflora into the range of native Spartina species. The ancient hybrid S. densiflora also hybridized with native Spartina species. Hybridization promotes the evolution of highly invasive populations and hampers control efforts. Whether Spartina, native and not, would protect the shore as sea levels rise depends upon unimpeded areas for upward marsh growth and sufficient sediment, conditions that are often not satisfied.
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Supplemental Figure 1: Changing genetic composition of Spartinaalterniflora and S. alterniflora × foliosa hybrids in San Francisco Bay. Percentages of S. alterniflora, F1 hybrids, cryptic hybrids, and other large or plants suspected of hybridity, by RAPD genetic analysis. Numbers above the columns are the number of plants analyzed each year (data on F1 hybrids in 1998, and cryptic hybrids in 1998 and 2002 were not available). Samples were collected throughout the SF Bay. See Hogle 2011a, her figure 1.5, for locations of plants suspected of hybridity, and her figure 1.7 for locations of cryptic hybrids. Control work against large-statured plants began in 2004. The San Francisco Estuary Invasive Spartina Project (http://www.spartina.org) generously shared their data on cryptic hybrids. Supplemental Figure 2: STRUCTURE diagram of genetic composition determined through 17 microsatellite loci of Spartina foliosa (1, blue), S. alterniflora from the US East/Gulf Coast (2, red) and a second source population (3, yellow), established hybrid plants (4 and 5 at Alameda, 8 at Hayward, 11 and 12 at Robert’s Landing), and 2003 and 2004 seedling cohorts (6 and 7 at Alameda, 9 and 10 at Hayward, 13 and 14 at Robert’s Landing). Alameda is 16 km north of Robert’s Landing and Hayward is 2 km further south from Robert’s Landing. Each bar represents the proportional membership in each group of an individual plant. Plants and seedlings reflect the genetic signature of each S. alterniflora source population. The arrow indicates an isolated, highly self-fertile plant at Robert’s Landing (solid green) that was the seed and pollen parent of large numbers of seedlings at Robert’s Landing in 2003 and 2004 (Sloop, Ayres & Strong 2009). Redrawn from Sloop, Ayres & Strong 2011. Supplemental Figure 3: Clapper rail counts as compared to hybrid Spartina remaining. From http://www.spartina.org/project_documents/clapper_rails/project-clra2010.htm Supplemental Figure 4: Spartina alterniflora remaining in Willapa Bay, WA through the herbicide spraying project. http://agr.wa.gov/PlantsInsects/Weeds/Spartina/docs/SpartinaReport2010.pdf Download Supplemental Figures 1-4 as a single PDF.