[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re:invasive species

I tend to take the longer view, although the longer time isn't necessarily
millions of years.  Elodea canadensis invaded Great Britian around 1920 and
for a while, became extremely abundant.  Now, however, it seems to have
become much less abundant and much more "neighborly".  It can still be
found, but it does not dominate in most places.  I don't know if anybody
has figgured out the cause of its retreat from dominance.  Starlings
invaded the United States early in the 20th century, and for some time,
they made bluebirds and red-headed woodpeckers quite scarce, by competing
for nest holes.  Now, both bluebirds and red-headed woodpeckers have made a
nice come-back.  Even the zebra mussel is not all bad.  Vallisneria
americana was an endangered species in the turbid, algae-choked bays and
tributaries of Lake Erie, but then the zebra mussel came along and cleared
up the water, and now the Val has grown to the point where it impedes
boats.  This excessive growth is due to excess nutrient enrichment of the
waters, as was the previous pea soup green water.  The arrival of a new
species causes evolutionary pressures on it as well as its new neighbors.
Eventually, they all get settled down in their niches.

Paul Krombholz, in steamy central Mississippi, where the remainants of
Berry could bring rain to the NE part of the state