Space, sympatry and speciation

Abstract

Sympatric speciation remains controversial. 'Sympatry' originally meant "in the same geographical area". Recently, evolutionists have redefined 'sympatric speciation' non-spatially to require panmixia (m = 0.5) between a pair of demes before onset of reproductive isolation. Although panmixia is a suitable starting point in models of speciation, it is not a useful definition of sympatry in natural populations, because it becomes virtually impossible to find or demonstrate sympatry in nature. The newer, non-spatial definition fails to address the classical debate about whether natural selection within a geographic overlap regularly causes speciation in nature, or whether complete geographic isolation is usually required. We therefore propose a more precise spatial definition by incorporating the population genetics of dispersal (or 'cruising range'). Sympatric speciation is considerably more likely under this spatial definition than under the demic definition, because distance itself has a powerful structuring effect, even over small spatial scales comparable to dispersal. Ecological adaptation in two-dimensional space often acts as a 'magic trait' that causes pleiotropic reductions of gene flow. We provide examples from our own research. © 2009 European Society for Evolutionary Biology.