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Stanford Report, May 13, 1998

Celebrities of Jasper Ridge: 5/98

The celebrities of Jasper Ridge: research projects at the preserve

Since 1960, Stanford's Paul Ehrlich and his students have been studying the population dynamics and genetics of the Bay checkerspot butterfly (Euphydryas editha bayensis) at Jasper Ridge.

Indeed, so many scientific papers and books have been written based on this research that the Bay checkerspot is something of a celebrity in the world of ecology. The National Science Foundation, which supported much of Ehrlich's work, considers this research a model for long-term investigations in population biology.

Bay checkerspot butterfly

Photo by Leo Holub

Ehrlich's research at Jasper Ridge has provided insight into the causes of local extinctions and other fluctuations in plant and animal populations as well as a model for how to run a study project at a nature preserve. Most important, it led to the theory of co-evolution, a now recognized belief that species are dependent on conditions and affected by changes both inside and outside their habitat, that all of nature is related.

In recent years, as populations of the Bay checkerspot have declined at Jasper Ridge, some ecologists have chided Ehrlich and Stanford for not doing more to protect the butterfly. But Stanford has adopted a do-nothing policy on the ridge, essentially deciding to study consequences rather than manipulate natural processes.

Another major long-term project at Jasper Ridge began in 1978: a study by Stanford's Harold Mooney and colleagues of how individual species and groups of plants use the resources of the serpentine grassland and chaparral, and of the relationship between nitrogen content in leaves and photosynthetic capacity. The researchers were able to model the trade-offs that plants of the chaparral are forced to make in response to environmental realities. This work is widely used today by researchers and agronomists alike.

Since 1991, Mooney ­ along with Christopher Field of the Carnegie Institution of Washington, F.S. Chapin III of the University of California-Berkeley and Elisabeth Holland of the National Center for Atmospheric Research ­ has been studying the impact of the elevated atmospheric carbon dioxide on plant communities at Jasper Ridge.

The project is funded by the National Science Foundation and the U.S. Department of Energy and is one of only a few experiments worldwide in which carbon dioxide increases can be studied using an entire ecosystem.

So far, the most significant lesson of these studies lies not in the discovery that elevated carbon dioxide significantly increases photosynthesis but rather that the elevation extends the growing season, favoring late-flowering annuals. That, in turn, will help scientists, farmers and economists respond to changing environmental conditions for plants grown for food, fuel, fiber and other uses.

Another study with practical applications concerns the invasion of Jasper Ridge by Argentine ants ­ those tiny crawlers that invade kitchens and seem resistant to traps and chemicals alike. The ants are an invasive species worldwide and a serious pest of citrus crops in California. They operate differently than most ants, and scientists think that an understanding of the differences may provide a way to develop biological controls.

The study, headed by Deborah Gordon, already has found that Argentine ants usually win when they fight with native ants, that they forage for longer periods throughout the day, and that they are replacing most native ants at an average rate of one hectare per month.

­Yvonne Daley