printable versionBirds, butterflies and bacteria: The same law of biology appears to apply to all
BY SANDRA HINES
Brendan Bohannan
The connection between species richness and area occupied, recognized by biologists for more than 100 years as a fundamental ecological relationship in plant and in animal communities, has been discerned for the first time at the microbial level.
A pair of papers in the Dec. 9 issue of the journal Nature, one focused on bacteria and another on a microbial fungi, shows that the number of species present—the diversity—increases as the area they occupy increases.
"The results suggest that this relationship may be a universal law common to all domains of life," said former Stanford graduate student Claire Horner-Devine, now a research assistant professor at the University of Washington and lead author of the paper concerning bacteria.
Horner-Devine co-authored the bacterial study with her former adviser, Brendan Bohannan, an assistant professor of biological sciences at Stanford; Jennifer Hughes, a former postdoctoral fellow in the Bohannan lab, now an assistant professor at Brown University; and Melissa Lage, a graduate student at Brown.
"The search for generalities has been especially challenging in ecology," Bohannan said. "This work supports the idea that the species-area relationship is a truly general pattern, applying to elephants and bacteria and everything in between."
Jessica Green of the University of California-Merced is lead author of the fungi paper, which is co-authored by Andrew Holmes of the University of Sydney; Ian Oliver of the University of New England in New South Wales, Australia; and Mark Westoby, David Briscoe, Mark Dangerfield, Michael Gillings and Andrew Beattie of Macquarie University in New South Wales.
Crucial roleBacteria and fungi may well comprise the bulk of species on Earth and, despite their small size, play roles in everything from global climate change to water purification to recycling of dead plants, animals and other matter.
"Bacteria, for example, decompose organic material that, among other things, provides the majority of nitrogen needed by the plants we eat," Horner-Devine explained. "So understanding the distribution and basic ecology of one of the most abundant and diverse groups of organisms on Earth is crucial."
The idea that the number of species increases as the area increases, referred to as the "species-area relationship," may seem obvious to anyone who has compared a garden-size patch of wildflowers to an entire meadow and realized how many more kinds of flowers there are in the latter, Horner-Devine noted. Still, some scientists thought microbes might be different.
"There has been a long-standing idea that microbes are so abundant and so small that all the different types of bacteria are mixed up all the time and are, therefore, randomly distributed," Hughes added.
Predictable distributionThe researchers took advantage of mathematical formulas previously developed for plant and animal communities that describe how many more types, or species, can be expected to be shared from two samples taken far apart—for example, at opposite ends of a field or a lake—than from two samples taken close together.
The researchers were the first to couple this ecological thinking with information about microbes found using molecular tools developed in just the last 10 years, Horner-Devine said. She and her colleagues conducted their analyses by comparing DNA from bacteria sampled across a half-acre in a New England salt marsh. (Green and her co-authors sampled the microbial fungi Ascomycota in desert soils in a 62-square-mile national park in Australia.)
If the composition of bacteria is different in different places, then they might be performing various biological tasks differently, Hughes explained. "For example, a salt marsh in Rhode Island may behave differently in terms of how it buffers Narragansett Bay from nitrogen pollution than a similar looking marsh in San Francisco Bay," she said.
"Our data firmly establishes that, like plants and animals, microbes are not randomly distributed but rather exhibit spatially predictable, aggregated patterns at multiple spatial scales," Green noted.
Both studies received funding from the National Science Foundation. The bacteria work also was supported by the American Association of University Women, and the fungi work by the Australian Research Council and the New South Wales Resource and Conservation Assessment Council.
Sandra Hines is the assistant director of news and information at the University of Washington.
