With pristine lands nationwide eyed for development, planners need to carefully select which patches of land are most "worthy" of protection. But one popular shortcut, protecting a so-called umbrella species, may not be all it's cracked up to be. In a study on patches of California coastal sage scrub, conservation of an endangered bird called the California gnatcatcher did not ensure the survival of three endangered insects.
An umbrella species is a plant or animal that shares habitat with other organisms; the hope is that protecting the species by preserving its habitat will benefit a range of other species that share the same habitat. Tests of the umbrella theory have had mixed results, though it's often put into practice anyway. Along the Southern California coast, for example, biologists are working to protect a threatened blue songbird called the California gnatcatcher in order to save neighboring species as well.
Dan Rubinoff, an entomologist at the University of California, Berkeley, wondered whether this approach is working. To find out, he selected 50 patches of land, from 1.3 to 335 hectares, 48 of which harbored gnatcatchers. Then he checked for the presence of three vulnerable insects--the electra buckmoth, the bernardino blue butterfly, and the mormon metalmark butterfly--that subsist on a species of California buckwheat endemic to the sage scrub near the coast.
According to the umbrella species concept, all three insects should show up in almost every patch. Instead, as Rubinoff reports in the October issue of Conservation Biology, the mormon metalmark inhabited 80% of patches; the bernardino blue butterfly turned up in 66%; and the moth was found in just 20%. What's more, the biggest patches were the likeliest to harbor the insects. That means larger patches, rather than those with gnatcatchers, might offer the best protection for the insects, Rubinoff says.
The work shows that gnatcatchers have "no special biological utility" as umbrella species, says conservation biologist Sandy Andelman of the University of California, Santa Barbara. She argues that gauging conservation efforts based on a few species, rather than just one, makes more sense. Taking a close look at this approach is especially important, she says, because conservation plans to save the coastal sage scrub habitat, under heavy development pressures, "are being assembled as we speak."
Pick a Species, Any Species (ScienceNOW, 24 June 1999)
U.S. Geological Survey background on California gnatcatcher
FAQ about critical habitat and the coastal California gnatcatcher
The coastal sage scrub ecosystem