The results have important implications for understanding the biodiversity crisis, said researcher Erika S. Zavaleta, assistant professor of environmental studies at the University of California, Santa Cruz. Previous experiments relied on random species removal rather than realistic patterns of loss, which turn out to be quite dissimilar.

"We replicated natural patterns and processes and found that both patterns of abundance and the order of species loss matter a great deal," said Zavaleta, who conducted the five-year study with Kristin B. Hulvey, a doctoral student in environmental studies at UCSC. "This defines a new direction for research."

In the realistic loss scenario, entire groups of plants with unique functions disappeared faster than expected by chance, and invader resistance declined dramatically. The results suggest that biodiversity losses in natural systems can have far greater impacts than indicated by randomized-loss experiments.

The five-year study is among the first to combine conservation biology's focus on the order of species loss with experimental scrutiny of the consequences of those losses. It was conducted at the Jasper Ridge Biological Preserve at Stanford University.

After four years of observation to understand natural patterns of species loss, 70 research plots were planted with common annual grasses, rare summer-flowering forbs, and rare native bunch grasses. Plots reflected six levels of species diversity. Half of the plots were then invaded with Centaurea soltitialis L. (yellow starthistle), one of the most ecologically and economically damaging weeds in California.

"Then we watched how
'"/>

Contact: Jennifer McNulty
jmcnulty@ucsc.edu
831-459-2495
University of California - Santa Cruz
11-Nov-2004