Re: NANFA-- How fish get from A to B

Dave Neely (
Tue, 14 Dec 1999 08:41:26 CST

OK guys and gals, enough is enough. Talk of birds carrying fish/fish eggs
around is always enough to get me going.

ALL available evidence supports the hypothesis that the ichthyofauna of
North America is a product of many different types of events.
We can examine the distribution of fishes, the phylogenetic pattern in
clades of fishes, and patterns of variation that occur in those fishes, and
attribute them to known geological events (eg stream captures, periods of
orogeny, glacial effects, isolation in various drainages, etc), for which we
have a mechanism. Alternatively, we can make up speculative stories for
which we have no valid mechanism(giant Pleistocene fish-carrying pelicans
spreading fish far and wide, Paleoindian aquarists, biblical floods, etc.)

IF shorebirds were capable of spreading fish all over the place, then WHY do
so many species of NANFs have very discrete ranges, tied strongly to river
drainages? How come I can sit on the eastern Continental divide in MD and
PA, and catch Etheostoma olmstedi from streams draining East and Etheostoma
nigrum from streams draining West? How come Waccamaw killifish aren't spread
all up and down the doggone Eastern Flyway? Why does the range of Lucania
goodei stop in the Choctawhatchee when herons fly all they way up the
goldang Mississippi?

There's been a very productive research program concerned with the
zoogeography and evolution of the North American ichthyofauna, starting with
a late 1800s paper by Cope, and continuing to the current day. Check out
Mayden, RL 1992, 'Systematics, historical ecology, and North American
freshwater fishes' for a really good review of the topic. Hocutt and Wiley's
1986 'Zoogeography of NA Freshwater fishes' is another good read.

To be perfectly fair, some aquatic organisms (Daphnia, Physa) that have been
examined MIGHT to be candidates for bird transfer. A recent study looked at
mtDNA haplotypes in Daphnia laevis across North America, and found that
within areas in the Eastern, Central, and Pacific regions, there was little
resolvable variation, but that between the three were deep divergences. They
attributed this to bird transfer within each of the major flyways. An
equally valid explanation is the fact that each of the Flyways corresponds
to major drainage divides... and since there's a fairly large level of
straying between flyways, one would NOT expect the large divergences

In short, bird transfer seems very, very unlikely except in very restricted
situations, and then only over very short distances.


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