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Morphologically
if they appear identical physically
Biologically
interbreeding and producing fertile offspring
Evolutionary
Interbreeding groups are reproductively isolated and evolve separately from each other
Speciation
When new biological species are created
Alopatric Speciation
Popukations of species become isolated due to geographic separation
Sympatric Speciation
Two separate species evolve even thought they share the same geographic rea
Adaptive Radiation
Single species evolve into multiple diffrent but closely related species