How can i define Speciation Without Physical Isolation?

You are most likely defining SYMPATRIC SPECIATION.





Sympatric speciation is the genetic divergence of various populations (from a single parent species) inhabiting the same geographic region, such that those populations become different species.





The most popular explanation for sympatric speciation is the disruptive selection model, whereby homozygous individuals, in particular environmental conditions, have a greater fitness than those with alleles heterozygous for a certain trait. Through natural selection, homozygosity would be favored, eventually leading to speciation, wherein populations which have diverse homozygosities, adapted to different biomes, would become physically or reproductively disrupted.





Sympatric divergence could also result from sexual conflict.





Disruption may also occur in polygenic traits (i.e., traits that result from the combined effects of multiple genes). For example, the Medium Ground Finch (Geospiza fortis) is showing gene pool divergence in a population on Santa Cruz Island. Beak morphology conforms to two different size ideals, while intermediate individuals are selected against. Some characteristics (termed Magic Traits) such as beak morphology may drive speciation because they also affect mating signals. In this case, different beak phenotypes may result in different bird calls, providing a barrier to exchange between the gene pools.





Allochrony is another example of allopatric speciation, in which populations utilizing the same resources become isolated because they consume the resources at different times, either because of seasonal or circadian differences. For example, one population may predominate in the summer, while another predominates in winter; or one population may be diurnal, while the the other is nocturnal.





Sympatric speciation events are vastly more common in plants, as they are prone to developing multiple homologous sets of chromosomes, resulting in a condition called polyploidy. The polyploidal offspring occupy the same environment as the parent plants (hence sympatry), but are reproductively isolated.