New Theoretical Foundation for Analyzing Development of Ecological Communities

Research by Jayanth Banavar, professor of physics, and graduate student Igor Volkov, with tephen Hubbell at the University of Georgia and Amos Maritan of the International School for Advanced Studies in Italy, challenges half-century-old ideas about how natural plant and animal communities are put together, according to a paper in the journal Nature.

Conventional ecological theory says that species coexist with one another by being the best competitors in their own ecological niches—or functional roles—in the community. In 2001 Hubbell challenged this theory in his book titled, “The Unified Neutral Theory of Biodiversity and Biogeography.” He argued that many of the ecological patterns we see can often be more simply explained if competing species are treated as if they were essentially identical.

Banavar, Volkov, and Maritan were intrigued by the theory and set out to collaborate on further research, the first fruit of which is the paper in Nature. The paper provides Hubbell’s theory with a mathematically stronger and more general theoretical framework.

“Sixty years ago, the great geneticist and statistician, Ronald Fisher, discovered a mathematical distribution describing patterns of relative species abundance—the pattern of commonness and rarity in species—within ecological communities,” said Hubbell. Beginning with a simple derivation of the Fisher distribution, the team shows how the distribution changes when you restrict the immigration of species into an ecological community. This is a famous unsolved problem in the Theory of Island Biogeography published by renowned biologists Edward O. Wilson and Robert H. MacArthur in 1967.
The neutral theory has been controversial and questions have been raised on its ability to describe ecological data any better than commonly used empirical forms. In a companion “News and Views” piece in the same issue of Nature, John Harte from the University of California in Berkeley says, “To the rescue now come Volkov and theoretical physicists Banavar and Maritan, who have teamed up with Hubbell to perform a mathematical tour de force and a reanalysis of the data.” While previous work required computer simulations whose accuracy could not be estimated easily, “Volkov et al. derive an analytic solution of the neutral theory."

“One of my personal lessons from this interdisciplinary collaboration is that physics may provide fresh approaches to some old problems in ecology,” said Hubbell. “Ecologists often start with an already complex hypothesis and then add even more complexity. Physicists tend to start with the simplest hypothesis they can think of and then add complexity only when they’re forced to by the data."

Jayanth Banavar, Leta Krumrine (Penn State), and Phil Williams (University of Georgia)