PS 67-125
Phase transitions in the coexistence of competitive species

Thursday, August 8, 2013
Exhibit Hall B, Minneapolis Convention Center
Charles K. Fisher, Physics, Boston Univeristy, Boston, MA
Pankaj Mehta, Physics, Boston Univeristy, Boston, MA

One of the most important questions in ecology concerns the role that species-specific characteristics play in determining the structure of ecosystems. It has long been recognized that specialization of organisms into niches can provide a mechanism for species coexistence and the maintenance of biodiversity. In recent years, however, neutral models that ignore species-specific characteristics within trophic levels have been remarkably successful at explaining some macroscopic features of ecosystems. The assumptions underlying neutral models are not believed to be true - species' do have differences, and these differences are often important - and neutral models do not describe all ecosystem characteristics. Nevertheless, the success of neutral models raises the question: when is a neutral approximation accurate enough for describing the large-scale features of an ecosystem?


Here, we present numerical and theoretical evidence that niche and neutral regimes correspond to distinct ecological phases, separated by a phase transition analogous to those observed in magnetic spin systems. The niche-neutral phase transition occurs at a critical environmental carrying capacity. We argue that there is a possibility of an abrupt loss of biodiversity in a stressed ecosystem if the carrying capacity decreases to the critical value.