Changes in the population genetics of an invasive Spartina after 10 years of management
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Spartina foliosa is native to the San Francisco, California, Bay and Estuary. Spartina alterniflora was introduced to the Bay in the 1970s and subsequently hybridized with S. foliosa. Backcrossing created an invasive hybrid swarm able to outcompete S. foliosa within its tidal range and spread into higher and lower intertidal zones, drastically altering ecological communities. The San Francisco Estuary Invasive Spartina Project (ISP) has implemented a treatment program that has reduced the net area of invasive Spartina by 96 % from its peak of 323 hectares. An endangered bird, the California Ridgway’s Rail, takes advantage of habitat characteristics supplied by hybrid Spartina, prompting treatment restrictions in some marshes to preserve hybrid Spartina for the benefit of rails. We investigated changes in the population genetics of the invasion after 10 years of eradication efforts and after three subsequent years without eradication in some locations. Our investigation covered three areas: sites surrounding and including the restricted treatment marshes; sites in the southern Bay similar to proposed salt pond restoration projects; and samples collected Baywide. Our results support previous descriptions of a system of self-fertile hybrid plants that supply seed for mostly localized recruitment into available habitat. Compared to published work from 2003 to 2004, before large-scale eradication efforts began, genetic diversity has generally declined and inbreeding within hybrid populations has increased during and after the period of treatment by the ISP. These observations are perhaps due to pollen limitation as a result of the elimination of most hybrid plants by the ISP. We did not detect strong population genetic boundaries Baywide, but a genetically distinguishable localized introduction was detected in 10 of 11 Bay regions, suggesting leptokurtic dispersal. The restricted treatment areas may allow for continued introgression with S. foliosa, recolonization, and longer persistence of these invasive plants in the San Francisco Bay. Proximity to hybrid Spartina threatens the success of major restoration projects.
KeywordsSpartina foliosa Spartina alterniflora San Francisco Estuary Population genetics Hybridization
We are very grateful to the California State Coastal Conservancy for their commitment to manage and fund the San Francisco Estuary Invasive Spartina Project. Data in this paper was collected under the auspices of the ISP. The ISP has received funding from: California State Coastal Conservancy, State Wildlife Conservation Board, CALFED Bay Delta Program, US Fish and Wildlife Service, American Reinvestment and Recovery Act through National Oceanic and Atmospheric Administration, U.S. Environmental Protection Agency, Gordon and Betty Moore Foundation, David and Lucile Packard Foundation, S. D. Bechtel Jr. Foundation, North American Wetlands Conservation Act and National Coastal Wetlands Conservation Grant Program. We thank Ingrid Hogle for GIS expertise and Simon Gunner for help with the experiments on new recruits, and the rest of our co-workers, partners, grantees and contractors, too numerous to name, past and present, for their invaluable contributions to the ISP’s regional coordination, mapping, treatment and revegetation efforts. The comments of two anonymous reviewers and the editors of this special issue greatly improved the manuscript, and we thank them for their efforts. We thank the organizers of the 4th International Conference on Invasive Spartina in Rennes, France (July 2014), and the editors for inviting manuscripts inspired by the conference.
Compliance with ethical standards
The San Francisco Estuary Invasive Spartina Project is funded by the California State Coastal Conservancy. The authors are employees of Olofson Environmental, Inc., which receives funding from the Conservancy.
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