Separation, without geographical isolation, of populations into separate macroevolutionary lineages.
Sympatric speciation can occur as a consequence of habitat isolation, due to evolution of asexual reproduction from sexual reproduction, or because of the development of polyploidy, such as has been documented especially in plants. The latter involves processes known as autopolyploidy and allopolyploidy.
Parapatric speciation also represents a means by which speciation occurs, like sympatric speciation, without imposition of geographical barriers. It differs from sympatric speciationm, however, in that the two populations that are diverging still nonetheless occupy more or less separate ranges. Sympatric speciation in addition is unlikely the primary means by which most speciation events occur but rather is an alternative mechanism that occurs in addition to allopatric and peripatric as well as parapatric modes of speciation.
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