Sympatric speciation

Sympatric speciation occurs when new species arise from a single ancestral species while inhabiting the same geographic region. No physical barrier separates the populations; instead, reproductive isolation happens due to other factors (genetic changes, behavioral shifts, etc.) in the shared habitat.

• "Sym" means same -- in sympatric speciation, organisms live in the same place, but something divides the gene pool (for example, a sudden genome change like polyploidy in plants, or a switch to a different food source or mating preference).
• Polyploidy (having extra sets of chromosomes) is a common cause of rapid sympatric speciation in plants; a polyploid offspring can't reproduce with the original population, effectively creating a new species.
• Sympatric speciation can also occur through ecological niche differentiation: subgroups of a population exploit different resources or habitats in the same area and become specialized (e.g., fish in the same lake adapting to different diets or depths, eventually becoming separate species).

• If a question describes speciation without a geographic barrier (e.g., a plant doubling its chromosome number to form a new species on the spot), that's sympatric speciation.
• Be ready for examples like apple maggot flies adapting to a new host plant in the same area (initial step towards sympatric speciation), or cichlid fish diversifying in the same lake by specializing in different diets.
• A test might contrast allopatric vs sympatric: remember that sympatric is speciation in the same area (no physical isolation), often via genetic quirks or niche partitioning.