what are the types of speciation and how do they occur?

Sympatric speciation occurs when populations (groups) of a species that share the same habitat become reproductively isolated from each other this can be caused by numerous phenomenon. The most common is alteration in the the number of chromosomes within offspring causing them to be infertile or abort in vitro.Allopatric speciation is speciation caused by either geographic change or human interference (formation of lakes or farming practice). This change separates groups of the same species preventing interbreeding and gene flow.