Demographic noise can lead to the spontaneous formation of species

¹ Theoretical Physics Division, School of Physics & Astronomy, The University of Manchester Manchester, M13 9PL, UK
² School of Biological Sciences, Queen's University Belfast - Belfast, BT9 7BL, UK

^a alan.mckane@manchester.ac.uk

Received: 7 December 2011
Accepted: 19 January 2012

Abstract

When a collection of phenotypically diverse organisms compete with each other for limited resources, the population can evolve into tightly localised clusters. Past studies have neglected the effects of demographic noise and studied the population on a macroscopic scale, where cluster formation is found to depend on the shape of the curve describing the decline of competition strength with phenotypic distance. Here we show how including the effects of demographic noise leads to a radically different conclusion. Two situations are identified: a weak-noise regime in which the population exhibits patterns of fluctuation around the macroscopic description, and a strong-noise regime where clusters appear spontaneously even in the case that all organisms have equal fitness.