Dr. Stefano Allesina, University of Chicago – Ecological Stability

Jan 24, 2013

In today’s Academic Minute, Dr. Stefano Allesina of University of Chicago explores the link between an ecosystem’s diversity and its stability.

Stefano Allesina is an assistant professor in the Department of Ecology and Evolution at the University of Chicago.  His research is focused on the application of network theory to biology, with a specific focus on food webs, the networks describing who eats whom in an ecosystem. He holds a Ph.D. from the University of Parma, Italy.

About Dr. Allesina

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Dr. Stefano Allesina – Ecological Stability

Ecologists are interested in the relationship between the diversity of an ecosystem and its stability. Are species-rich environments, such as rainforests, which can contain tens of thousands of species, somehow less vulnerable to disruption?
In 1972, physicist and former head of the Royal Society Robert May shook the world of ecology by proposing a simple mathematical model of ecosystems that made a provocative prediction: the greater the number of species, the less stable the ecosystem. This means that we should not be able to observe ecosystems with a large number of species in nature. But all around us we see a vast diversity of species, so May speculated that nature must employ (quote) "devious strategies" to maintain species diversity.

Ecologists have spent the last forty years trying to find these devious strategies, building increasingly elaborate versions of May's model in attempts to square it with reality. In the journal Nature, my student Si Tang and I chose instead to return to May's original model and make a subtle change.

In May's model, the type of interaction between species is drawn at random. However, in nature species can either interact as predator and prey, or they can compete for the same resources, or they can cooperate -- such as plants and pollinators.
When these interactions are built separately into May's model, they produce very different results. With a predator-prey relationship ecosystems can support an infinite number of species. Conversely, ecosystems built upon exclusively competitive or cooperative relationships are highly unstable.
The revised model suggests that Earth's rich ecosystems are stabilized by a backbone of "eat or be eaten" predator-prey pairs. Our work demonstrates the undiminished power of May's elegant model to prompt important questions about nature's laws 40 years after its publication.