In sympatric speciation, a species splits into two without any separation of the ancestral species' geographic range. With the exception of hybrid speciations, it has been a source of recurrent controversy whether sympatric speciation ever happens.
Sympatric speciation can be compared with the allopatric and parapatric theories of speciation.
Speciation in Phytophagous insects is a possible example of sympatric speciation.
How could sympatric speciation occur?