KESKUSTELU

Oppikirjassa ja perinteisesti on muistaakseni korostettu allopatrista lajiutumista: maantieteellisesti eristyksissä kehittyy uudet lajit esim. eri saarilla tai vuoriston erottamana.
Sympatrista lajiutumista (ei maantieteellistä eristystä, vaan samalla alueella, syynä vaikka eri vuodenaikaan pariutuminen tms) on pidetty vähäisenä ja kiistanalaisempana:

http://users.utu.fi/veijor/ebp/ebpnetti5/sld014.htm

Kuitenkin olen viime aikoina ollut näkevinäni ja kuullut että sympatrinen olisikin tärkeämpi lajiutumisen muoto, esimerkkinä otettu Amazonin sademetsä, jossa hirmuisesti lajeja samalla alueella, jopa hehtaarilla.

EVOLUTIONARY BIOLOGY:
Speciation Standing in Place
Elizabeth Pennisi

Surprising some evolutionary biologists, studies of birds, fish, trees, and insects show that it doesn't take a mountain chain, island, or other geographic quirks to create a species.

...

Charles Darwin recognized allopatry as a driving force of speciation. But he also thought populations could diverge into separate species in the absence of physical barriers, an idea now called sympatric speciation, or simply sympatry. However, his successors were at a loss to explain how this could happen, and they could find few examples. By 1907, textbooks dismissed sympatric speciation, and 35 years later, Mayr virtually tossed the idea out of modern evolutionary thinking with his strong antisympatry rhetoric. Since then, few researchers have taken sympatry seriously.

...

At least, says Giacomo Bernardi, an evolutionary biologist at UC Santa Cruz, "evolutionary biologists are at last essentially agreeing that sympatric speciation is possible."