California gnatcatcher: Umbrella species failure?

September 20, 2001

Protecting "umbrella" species is a popular conservation short-cut. The idea is that protecting a species with a large range will automatically preserve biodiversity. But this may not be true, particularly for invertebrates: new research shows that protecting the California gnatcatcher fails to preserve three insects in southern California's coastal sage scrub.

"The strategy of using a single vertebrate species as an umbrella for the whole fauna of California coastal sage scrub is flawed," says Daniel Rubinoff of the University of California at Berkeley in the October issue of Conservation Biology. "Insects are almost never considered in conservation planning, the idea being that...because they are 'bugs', they are somehow less vulnerable than vertebrates." Invertebrates account for more than 80% of the animals in terrestrial ecosystems.

Historically, there were only 3 million acres of coastal sage scrub and more than 85% has been lost to agriculture and urban development, making it among the most endangered habitat types in the U.S. This habitat is a global hotspot of species found nowhere else and nearly 100 species are at- risk. In San Diego County, efforts to protect coastal sage scrub have used the California gnatcatcher -- a threatened songbird -- as an umbrella species because it is virtually restricted to nesting in this habitat.

To test how well the California gnatcatcher serves as an umbrella species, Rubinoff surveyed 50 coastal sage scrub patches in San Diego County for three insects that depend on this habitat. These insects (two butterflies and a moth) lay their eggs only on a buckwheat characteristic of this habitat.

Rubinoff found that the California gnatcatcher occurred in nearly all of the patches. However, this was not true for the three insects studied. One of the butterflies (Apodemia mormo) occurred in four-fifths of the patches, the other (Euphilotes bernardino) in two-thirds and the moth (Hemileuca electra) in only a fifth.

The occurrence of these insects depended on the size of the patch, not the presence of the California gnatcatcher. The smallest patches that had A. mormo, E. bernardino and H. electra were about 3, 5 and 26 acres, respectively. The patches studied ranged from 3 to 825 acres, and the occurrence of the gnatcatcher did not depend on patch size.

All of the patches with the moth also had both of the butterflies, suggesting that these patches were higher- quality habitat. While some coastal sage scrub patches are relatively intact, others have only a few dozen native shrubs surrounded by non-native weeds.

Because the California gnatcatcher occurs on habitat patches that lacks the three coastal sage scrub insects studied, Rubinoff calls the bird a "false" umbrella species. "Assuming that any single species will function as conservation surrogate may be an error worse than making decisions without the use of umbrellas at all," he says.
For faxes of papers, contact Robin Meadows

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