"I was wondering what would constitute the geographical boundaries of North
America. I was under the impression that the southernmost edge would've been the
southern border of Mexico and would include the Yucatan peninsula."
That's a good question.Basically, the answer comes down to differences between
ZOOGEOGRAPHIC and POLITICAL boundaries.
Most people think North America encompasses Canada, Mexico, the United States
(including Hawai'i), and the islands of the Greater Antilles (Bahamas, Cuba,
Hispaniola, Jamaica, Puerto Rico, etc.). These, however, are political
boundaries. Zoogeographers -- scientists who study the distributions of animals
-- define North America in terms of faunal regions, or realms. They call North
America the Nearctic Region.
As defined by zoogeographers, the Nearctic Region includes the entire
continental landmass south to the Mexican plateau. Specifically, this includes
areas north of 18degN on the Atlantic slope, and 16degN on the Pacific slope of
Mexico, corresponding roughly to the southern range limit of minnows, suckers
and gars, and the northen limit of many Central American species. Areas below
this line, as well as the Greater Antilles, are in the Neotropical Region. The
five native freshwater fishes of Hawai'i are in the Oriental Region.
So, from a political perspective, the blind swampeel is a resident of North
America. But from a zoogeographic perspective, it's not. That's why you won't
see it listed on "official" lists of North Ameican species, like the one
published by Mayden, Page and Miller a few years back.
Another important point:
Don't let the names of the Nearctic and Neotropical Regions lead you to think
that tropical fishes are restricted to the latter. Although the Nearctic Region
is better known for its coldwater fishes, many tropical aquarium favorites, like
the swordtail and Jack Dempsey, call North America home, too.
I hope this clears things up a bit.
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