When isolated, genetic differences arise and accumulate in populations. If the isolation lasts long enough, then such changes become more and more, and the process of speciation can begin.
Depending on the form of isolation of populations, two types of speciation are distinguished: allopatric and sympatric.
Speciation that occurs due to geographical isolation is called allopatric, or geographic.
With allopatric speciation, new species arise as a result of the division of the range of populations of the original species by rivers, seas, mountains, deserts and other physical barriers.
As a result of isolation between them, gene exchange is interrupted. The emergence of genetic differences gradually leads to the inability of individuals from isolated populations to cross, which later becomes the reason for the formation of new species.
- the emergence of species of lily of the valley in Europe and the Far East, associated with the division of the original area into parts during the onset of a glacier;
- the presence of two subspecies of the American squirrel and three subspecies of the blue magpie living in different regions of North America;
- appearance of the gray tit in the Asian part of the great tit range.
Speciation that occurs due to biological isolation is called sympatric.
In the presence of biological isolation, populations of one species are located within the original range, but cannot interbreed due to biological differences between their individuals. A new species is formed in the same area.
Ecological and sudden sympatric speciation are distinguished.
Ecological speciation is caused by ecological isolation, which is associated with a shift in the timing of flowering, mating, spawning, or with different breeding sites.
- in the African lake Victoria there are more than 500 species of cichlid fish, which differ from each other in appearance, lifestyle, behavior;
- the formation of seasonal races of some plants (large rattle, white mari), differing in flowering time;
- the coexistence of seasonal races with different spawning periods in a number of fish species (herring, perch, carp, etc.);
- the presence in the central strip of several species of tits, differing in food specialization.
Sudden speciation occurs as a result of mutation, polyploidy, or hybridization of species with subsequent chromosome doubling. In these cases, reproductive isolation occurs within one generation and the formation of a new species occurs quickly within the same population.
- coexistence of potato forms with 12, 24, 48 and 72 chromosomes;
- the presence of large-leaved rose forms with 14 and 28 chromosomes;
- presence of diploid, triploid and tetraploid races of wild strawberry in one area.