97
north? Subsequently they could have used
the Ancestral Plains Stream to populate the
several Nebraska drainages.
In any case, the map above shows that the
Ringed crayfish does not appear to like the
streams in the glaciated areas. The only
exception to this is their presence in the Big
Blue River basin. It is possible that the Big
Blue is a remnant of the Ancestral Plains
Stream. The map shows that this species is
common in the North Platte and Republican
River basins which suggests that these were
glacial refugia for the Ringed crayfish.
Though, perhaps, "glacial refugia" is a poor
term as they were not directly impacted by
the ice. The map also shows that they are
common in the Loup and Big Blue River
basins which might indicate that these two
basins were once connected. The two
isolated population centers in the Niobrara
River are interesting. The Niobrara began
forming some 20,000 years ago and
captured streams from the Elkhorn and Loup
basins as it migrated west.
215, 225
Is it
possible that the population center in the
middle Niobrara River had its origin in a
stream captured from the Loup? Also, there
is a second population center in the extreme
western Niobrara River. Might the upper
Niobrara have been a part of the North Platte
River in the distant past? Of course, one
cannot rule out that these are recent
introductions but bait bucket introductions
are usually found near a reservoir or fishing
lake. There are none in these areas. Again,
a genetic study might help us resolve these
questions.
.
