Biodiversity as insurance in the face of change

It has been a truism, long held by scientists, environmentalists and others, that biological diversity and the intricate, interdependent web of biological relationships it fosters is a must for maintaining the health and stability of any ecosystem.

But the argument has never been carefully honed, and there is no consensus among scientists regarding this central question of biology: Just why are diversity and competition so important to balancing the overall health of ecosystems?

Now, a group of scientists from UW–Madison, writing in the Friday, Oct. 15, edition of the journal Science, suggests that simple diversity may be less important than how individual animals, plants or microbes respond to environmental change.

“It’s not the number of species per se. It’s how they respond to the environment that’s important,” says Anthony Ives, a UW–Madison associate professor of zoology and the lead author of the study published in the nation’s leading scientific journal.

The primary result of the study is 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 says.

“The more species you have, the greater the likelihood you’ll have some (organisms) that are tolerant of environmental change. Biodiversity is an insurance policy against unknown environmental fluctuations and disturbances.”

The idea, posited by Ives and co-authors Kevin Gross and Jennifer Klug, UW–Madison graduate students, suggests that ecologists should shift attention from the interations among species, and instead focus on how different species react to different environmental assaults.

The basis of the report published this week in Science is a mathematical analysis of the ebb and flow — the variability — of populations of organisms encountering environmental stress. “It is explicitly modeling the variability, which hasn’t been done before,” says Ives.

According to Gross, the model, like an analysis of the stock market, 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.

The hope, according to the Wisconsin scientists, is that the model will contribute to a better understanding of ecosystem dynamics, how ecosystems change along with the larger environment.

The work, says Ives, should not be considered an argument against the importance of biodiversity.

“What biodiversity gives you is a greater chance that there will be tolerant species present to help retain the function of the ecosystem,” he says.