Can high biodiversity evolve in a uniform environment?

16 November 2007

Noam Shoresh
Kishony Lab, Department of Systems Biology
Harvard Medical School


Can biodiversity evolve and persist in a uniform environment? This question is at the heart of the Paradox of the Plankton, the contradiction between empirical observations of many species coexisting on few resources and theoretical expectations based on the principle of competitive exclusion. To bridge the gap between theory and observation, previous studies analyzed multi-species states in mathematical models of species interactions and focused on their ecological stability. Evolutionary dynamics, however, have not been considered in this context: it is unknown how mutations impact the stability of previously characterized multi-species states, as well as whether large species consortia can spontaneously evolve.

Using numerical simulations and analytic properties of the standard ecological model of competition for essential resources, we find that species communities that are ecologically stable are destabilized by long-term evolutionary dynamics—the essentiality of resources introduces a strong dependence between the species that leads invariably to catastrophic extinction. Moreover, even when resources number in the hundreds, the number of species in consortia that can spontaneously form during evolution is typically fewer than a dozen.

In the talk I will describe the paradox of the plankton, introduce the model used to describe competition for essential resources, and discuss what happens when evolutionary dynamics is added.

current theory lunch schedule