SPECIES FORMATION IN SIMPLE ECOSYSTEMS

In this paper we consider a microscopic model of a simple ecosystem. T he basic ingredients of this model are individuals, and both the pheno typic and genotypic levels are taken in account. The model is based on a long range cellular automaton (CA); introducing simple interactions between the individuals, we get some of the complex collective behavi ors observed in a real ecosystem. Since our fitness function is smooth , the model does not exhibit the error threshold transition; on the ot her hand the size of total population is not kept constant, and the mu tational meltdown transition is present. We study the effects of compe tition between genetically similar individuals and how it can lead to species formation. This speciation transition does not depend on the m utation rate. We present also an analytical approximation of the model .