When it comes to ecology and zoology, policy actions tend to ignore the system and focus on turning one knob. Then, when the ripple effect is felt throughout the ecosystem, a new knob is turned.

Sometimes the problem with that approach becomes obviously early on, especially in California, where various federal and state bodies are always in court with each other trying to fulfill their legal mandates while species suffer. And what happens when the eradication of an invasive species threatens an endangered species? 

In a new study published inl Science, researchers from the University of California, Davis examine the case of the California Clapper Rail -- a bird found only in the Bay -- that has come to depend on an invasive salt marsh cordgrass, hybrid Spartina, for nesting habitat. Its native habitat has slowly vanished over the decades, largely due to urban development and invasion by Spartina. Since the California Clapper Rail only exists in one place, it is automatically listed as endangered.

What would getting rid of the invasive species do at this point? Probably nothing good. Is it possible to restore the old habitat? What happens to the birds?

"Just thinking from a single-species standpoint doesn't work," said co-author and UC Davis environmental science and policy professor Alan Hastings. "The whole management system needs to take longer, and you need to have much more flexibility in the timing of budgetary expenditures over a longer time frame."

The scientists combined biological and economic data for Spartina and the Clapper Rail to develop a modeling framework to balance conflicting management goals, including endangered species recovery and invasive species removal, given budgetary constraints.

While more threatened and endangered species are becoming dependent on invasive species for habitat and food, examples of the study's specific conflict are rare. The only other known case where the eradication of an invasive species threatened to compromise the recovery of an endangered one is in the southwestern United States, where a program to eradicate Tamarisk was cancelled in areas where the invasive tree provides nesting habitat for the endangered Southwestern Willow Fly-catcher.

"As eradication programs increase in number, we expect this will be a more common conflict in the future," said co-author and UC Davis professor Ted Grosholz.

The scientists used data from Grosholz's lab as well as from the Invasive Spartina Project of the California Coastal Conservancy in their analysis.

Spartina alterniflora was introduced to the San Francisco Bay in the mid-1970s by the Army Corps of Engineers as a method to reclaim marshland. It hybridized with native Spartina and invaded roughly 800 acres. Eradication of hybrid Spartina began in 2005, and about 92 percent of it has been removed from the Bay. The cordgrass has also invaded areas of Willapa Bay in Washington State, where efforts to eradicate it are nearly complete, and invasive Spartina has been spotted and removed from Tomales Bay, Point Reyes and Bolinas Lagoon in California.

The study, led by UC Davis postdoctoral fellow Adam Lampert, was funded by the National Science Foundation Dynamics of Coupled Natural and Human Systems Program.

Co-authors include UC Davis environmental science and policy professor James Sanchirico and Sunny Jardine, a PhD student at UC Davis during the study and currently assistant professor at University of Delaware.

"This work is significant in advancing a general, analytical framework for cost-effective management solutions to the common conflict between removing invasive species and conserving biodiversity," said Alan Tessier, program director in the National Science Foundation Division of Environmental Biology.