Oct. 26, 2000 MINNEAPOLIS / ST. PAUL--A study of DNA from the threatened California gnatcatcher and the abundant Baja (Mexico) gnatcatcher has shown no differences that would place the two birds in different subspecies. Therefore, destroying the California bird's habitat through development will not threaten the species, or any subspecies, as a whole, said University of Minnesota evolutionary biologist Robert Zink, who headed the study. But, said Zink, the finding points up the risk of trying to preserve habitat based on the status of only one species. The study is published in the October issue of Conservation Biology.
The California gnatcatcher lives in what is termed "coastal sage scrub (CSS)," most of which exists in fragments isolated by freeways, building tracts and other barriers insurmountable to the small, weak-flying bird. The CSS extends into the Baja peninsula of Mexico, where the Baja gnatcatcher, which strongly resembles the California gnatcatcher, lives. Whereas only about 2,000 pairs of gnatcatchers live in southern California, hundreds of thousands are thought to live in Baja, where they are not currently threatened. Hundreds of thousands of acres of high-priced real estate have been protected from development in California because the California gnatcatcher is on the U.S. Fish and Wildlife Service's Threatened Species list and would be wiped out if extensive building were permitted.
But it wouldn't be wiped out because it's the same as the abundant Baja bird, said Zink.
"The bird population extends from Los Angeles to the tip of the Baja, with random geographical differences in genetic makeup," he said. Further, he said, the bird is probably already doomed in California because its habitat is so fragmented there. That is, whenever a species or population exists in small isolated patches, it's only a matter of time before a series of catastrophes wipes out those patches, one at a time. However, Zink said he doesn't see his study as a green light for unrestricted development.
"This shows the danger of pinning the hopes of an ecosystem on a single species," he said. "It shows us that we should form our conservation efforts on sets of species unique to a particular kind of environment. Other species are restricted to CSS and are relatively unstudied, and many do not share the gnatcatcher's extensive distribution to the southern tip of the Baja peninsula. Hence, further loss and fragmentation of CSS in the United States might entail a large genetic cost, if indeed not extinction, for other species. That is, California gnatcatcher preservation should be coupled to preservation of CSS, rather than the reverse. This study shows how many dimensions are part of the process of conservation."
Zink's colleagues in the study were George Barrowclough of the American Museum of Natural History; Jonathan Atwood of the Manomet Center for Conservation Sciences, Manomet, Mass. (now at the Antioch New England Graduate School, Antioch, N.H.); and Rachelle Blackwell-Rago of the Bell Museum of Natural History, University of Minnesota. Zink is a professor at the Bell Museum and the University of Minnesota department of ecology, evolution, and behavior. The study was funded by several sources, including the U.S. Navy, the National Fish and Wildlife Foundation, Southern California Edison, trustees of Manomet Center for Conservation Sciences, the Building Industry Association of Southern California, Transportation Corridor Agency, Chevron Land and Development, the University of Minnesota and the National Science Foundation.
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