In Wildlife Ecosystems, Diversity Is Key, Study Finds

Biodiversity is often a celebrated thing, with conservation groups around the world aiming to preserve areas that have lots of different plant and animal species. But it hasn’t always been so. In the 1970s the renowned Australian scientist Robert May proposed that within an ecosystem, greater diversity caused greater instability.

There is evidence to the contrary, though, and ideas have slowly changed over the years. Now, in a paper published in PLOS ONE, researchers have presented a mathematical proof demonstrating that greater ecosystem diversity creates greater stability. The key lies in the way species interact, the researchers say.

Authors on the paper include Professor Hernan Makse (The City College of New York, The Graduate Center), postdoctoral researcher Flaviano Morone, Ph.D. student Francesca Lucini, and a colleague from Rutgers University.

The reason that May got the result he did, Makse and co-authors say, is that he created his mathematical models of ecosystems using linear relationships between species. But real interactions aren’t that simple, the authors argue.

Consider a bee pollinating a flower, Makse said. The bee collects pollen and nectar from the flower for food and pollinates the flower in the process, helping it produce seeds. In a linear relationship, the more bees pollinate the flower, the more the flower will benefit. In a nonlinear relationship, though, the flower doesn’t get any additional benefit past a certain number of bees.

In an ecosystem model that considers all species to interact linearly, an increase in species leads to instability. But a model that incorporates nonlinear relationships will show greater stability when more species are added, the authors show.

Similar nonlinear terms also appear in models for gene regulation, neurons, and information diffusion, the authors say.

“The linear model is always an approximation of the nonlinear model, which is more realistic,” Makse said. “It is a more plausible model and agrees with all observations.”