Tidal and seasonal effects on survival rates of the endangered California clapper rail: Does invasive Spartina facilitate greater survival in a dynamic environment?

Biological Invasions
By: , and 

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Abstract

Invasive species frequently degrade habitats, disturb ecosystem processes, and can increase the likelihood of extinction of imperiled populations. However, novel or enhanced functions provided by invading species may reduce the impact of processes that limit populations. It is important to recognize how invasive species benefit endangered species to determine overall effects on sensitive ecosystems. For example, since the 1990s, hybrid Spartina (Spartina foliosa × alterniflora) has expanded throughout South San Francisco Bay, USA, supplanting native vegetation and invading mudflats. The endangered California clapper rail (Rallus longirostris obsoletus) uses the tall, dense hybrid Spartina for cover and nesting, but the effects of hybrid Spartina on clapper rail survival was unknown. We estimated survival rates of 108 radio-marked California clapper rails in South San Francisco Bay from January 2007 to March 2010, a period of extensive hybrid Spartina eradication, with Kaplan–Meier product limit estimators. Clapper rail survival patterns were consistent with hybrid Spartina providing increased refuge cover from predators during tidal extremes which flood native vegetation, particularly during the winter when the vegetation senesces. Model averaged annual survival rates within hybrid Spartina dominated marshes before eradication (Ŝ = 0.466) were greater than the same marshes posttreatment (Ŝ = 0.275) and a marsh dominated by native vegetation (Ŝ = 0.272). However, models with and without marsh treatment as explanatory factor for survival rates had nearly equivalent support in the observed data, lending ambiguity as to whether hybrid Spartina facilitated greater survival rates than native marshland. Conservation actions to aid in recovery of this endangered species should recognize the importance of available of high tide refugia, particularly in light of invasive species eradication programs and projections of future sea-level rise.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Tidal and seasonal effects on survival rates of the endangered California clapper rail: Does invasive Spartina facilitate greater survival in a dynamic environment?
Series title Biological Invasions
DOI 10.1007/s10530-013-0634-5
Volume 16
Issue 9
Year Published 2014
Language English
Publisher Springer
Contributing office(s) San Francisco Bay-Delta, Western Ecological Research Center
Description 18 p.
First page 1897
Last page 1914
Country United States
State California
Other Geospatial Arrowhead Marsh, Cogswell Marsh, Colma Creek, Laumeister Marsh, San Francisco Bay