sympatric speciation

…alternative to allopatric speciation is sympatric speciation, in which reproductive isolation occurs within a single population without geographic isolation. In general, when populations are physically separated, some reproductive isolation arises. How genetic divergence can happen within a population of individuals that are continually interacting with one another is usually difficult…

…chiefly in the tropics that sympatric species (that is, those whose ranges overlap), sometimes closely related, may be found. Although there may be some altitudinal and other ecological separation of sympatric species, virtually nothing is known about possible partition of environmental resources among swifts; as many as three closely similar…

…where it occurs together (sympatry) with the common opossum. The coarse coat of long guard hair overlying the shorter, dense underfur may be either pale gray (gray phase) or mainly black (black phase). Rare in the north, black-phase individuals are more common in the southern United States and farther…