It's not the number of species per se. The study, published in the Oct. 15 issue of Science, shows that competition between animals, plants and other forms of life is a sideshow. Instead, the true measure of a community's biological health and stability is the wherewithal of just some species to withstand environmental changes, such as a warmer climate, a chemical change in the atmosphere or changes in land use. That is not to say, Ives stressed, that biodiversity has no practical importance. It does, especially in the face of unpredicted, large-scale environmental shifts, he said.
Biodiversity is an insurance policy against unknown environmental fluctuations and disturbances.
With little diversity, an ecosystem like this one experiencing drought is more likely to be harmed in the face of an environmental change. Ives and his students suggest that ecologists should shift attention from the interactions among species, and instead focus on how different species react to different environmental assaults. The report is based on a mathematical analysis of the ebb and flow the variability of populations of organisms encountering environmental stress. Like an analysis of the stock market, the model looks at variability through time, and identifies stability in an ecological community as a measure of how much populations of species fluctuate in the face of environmental change. Ives hopes his study will contribute to a better understanding of ecosystem dynamics and how ecosystems change along with the larger environment.