Re: NANFA-- Rainbow darters in MD

Dave Neely (
Tue, 28 Nov 2000 08:28:49 -0600


>OK, I'm getting a better handle on the rainbow darters in MD question. Has
>their appearance down the Potomac basin been interpreted >purely as the
>result of human activities such as stream >alterations/community
>disturbances, or is it possible that this is a >natural range expansion?
>That's a big question that's not easy to answer; any literature refs

A similar thing happened with Etheostoma zonale in the Susquehanna (also not
native to MD). They appear to have been transferred from Ohio drainage via
bait-bucket to Pine Creek, PA- within 10 years they have spread throughout
the entire system, from NY south to the head of the Chesapeake. (Raesly had
a 1988 paper in Copeia that detailed some of the expansion).

It's possible that Atlantic Slope drainages are just darter-depauparate;
that these systems -could- support 12 or 15spp of darters like some interior
basins, but have simply been constrained by historical drainage patterns.
Perhaps they did... the closest relatives of the MD darter are found in the
interior basins...

The conventional explanation for the lower diversity is that since Atlantic
Slope drainages drain West-East (rather than N-S like the Mississippi and
Gulf drainages), during Pleistocene glaciation, it was difficult for fish in
one drainage to move south to avoid adverse conditions.

Perhaps this is just a BS story, but it makes more sense from a geological
standpoint than other alternatives.


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