Sympatric speciation occurs more commonly in plants than animals and occurs less than allopatric speciation. The different species occupy the same habitat but have evolved to fill different niches or have become reproductively isolated in some way.Hybridisation occurs when two species interbreed to form fertile offspring. The offspring cannot interbreed with either parent species and there is no gene flow between the parents and offspring.Resident and transient orcas avoid each other and do not interbreed. Although they inhabit the same waters, they hunt different prey species, vocalise differently and have different social structures.