Neutral speciation in realistic populations

Abstract

de Aguiar et al. have shown that basic patterns of species diversity found in nature can be described by a neutral model of speciation in which species emerge simply as a consequence of local mating and mate preference for genetic similarity. Their results have been cited as support for the neutral theory of biodiversity. However, because the mutation rates considered in their work are much larger than those experienced by living organisms, there is still some question as to whether speciation will occur in this type of model under realistic conditions. Here, I develop a variant of the neutral model that includes a realistic mechanism for organism dispersal. I explore speciation in the model for a class of mobile organisms (butterflies), and I find that speciation does occur under conditions consistent with butterfly populations, albeit on narrow landscapes. The model also appears to exhibit scaling behavior—specifically, if the model is “scaled up” by increasing the area of the landscape while holding its length to width ratio and population density constant, the number of species tends to an asymptotic value. The results suggest that it is possible to infer speciation patterns in large populations by simulating much smaller, computationally tractable populations.