The origin and patterns of species diversity are fundamental themes in ecology and evolutionary biology. Insular systems play an important role in biogeography, and the species richness within an insular system is classically determined by the balance between the rate of speciation plus net migration and the rate of species extinction. A recent wave of studies integrating comprehensive phenotypic, phylogenetic, and environmental data is accumulating additional macroevolutionary insights at unprecedented scales. In this talk, to study the recurrent speciation rate under natural selection and historical contingency, I adopted a simple multi-species two-island model and considered interspecific competition on each island. As the number of species increases on an island, the competition intensifies, and the size of the resident population decreases. By contrast, the number of migrants is likely to exhibit a weaker than a proportional relationship with the size of the source population due to rare oceanic dispersal. If this is the case, as the number of species on the recipient island increases, the impact of migration strengthens and decelerates the occurrence of further speciation events. According to our analyses, the number of species can be stabilized at a finite level, even without extinction.