Intraspecific resource competition as a cause of sympatric speciation

[In most models of speciation], the fitness value of an animal is determined by the genotype it has, and the habitat in which it lives. In a more realistic model it should also depend on how much necessary resource is available for the animal and the competition from other genotypes for this resource. Models can be constructed which take into account such competition between genotypes. In a special case one can find the exact conditions for the stable coexistence of two incipient species, which have some degree of gene flow between them but also slightly different resource utilization distributions. An interesting property of this class of models is that they show how sympatric speciation can occur in a species where all animals live in the same habitat and under the same fitness regime, but differ, due to their genetic constitution, in their resource utilization.