|By Maryann Whitman
the Buffalo and Native Grasses Home
to the Range
Common wisdom has assumed that exotic plants
thrive on our continent because they lack
natural enemies in their new range.
Not so, says a recent paper in the journal Science.
Findings suggest that native herbivores (the deer and
the antelope of song) suppress the abundance of exotic
plants. Further, exotic herbivores (cattle, pigs, Old
World goats, and rabbits) facilitate abundance and
species richness of exotic plants. The researcher suggests
that our native herbivore population has been driven
close to extinction by settlers who also introduced
their Old World herbivores. This replacement of native
with exotic herbivores “eliminates an ecosystem
service, helps alien plant invasions, and triggers
an invasional ‘meltdown.’” I wonder
if we can teach our native deer to suppress our alien
The search is on to find some way to
identify either species or habitat characteristics
that predict invasiveness of exotic species in given
areas. A researcher out of University of California
at Davis, considered all the grasses known to be
growing in California, and confirmed what
had been assumed as common sense – the
more genetically related the exotic invader is to
the species growing on a site, the less
likely that invader will be able to move in.
the ’90s, some research on invasives was
done using small, controlled plots. The results showed
that the greater the diversity of natives in a planted
plot, the less likely that the plot was invaded by
exotic plants, and the exotic plants that did invade,
did less well.
It’s All One Piece. Millions
of acres of rangeland in the western states
have been taken over by spotted knapweed
(Centauria maculosa). The cattle won’t
eat it – the elk have modified migration
routes to avoid heavily infested areas, and land
stewards are training dogs to help them find new
patches of knapweed so they can eradicate them.
the 1970s, a natural enemy of knapweed, a gall
fly, was imported, tested, and released. Thirty
years later a biologist reports in Ecology Letters
fly has not halted the spread of knapweed … but
it has changed the ecosystem dynamics.” The
fly causes the knapweed to form a gall which
protects the flies’ eggs. Deer mice have
learned to climb the stalks, during the winter
months, to feed on the larvae of the fly in the
gall. During a season that would normally kill
most of the deer mice, they are instead thriving.
Populations of deer mice have tripled with this
new food supply. These mice can carry hantavirus,
which in a human being can cause a fatal form
of pneumonia. With their increased numbers they
are more likely to come in contact with humans.
And we wonder where our rare diseases come from.
possible that over time the pendulum will swing
back and the populations will even out. However,
they will even out at higher numbers than the
system originally entertained because the new
food source came from outside the system. What
effect this will have and on whom can only
Biologists researching bio-controls
agree that exotic insects “are too liberally
released…three times as
many exotics have been released as there
are target species.” “Rather
than reduce grazing,” (which helps spread
the invasive plants), contends one researcher
from the University of Nebraska, “the
agriculture officials release beetles, and
the ranchers go on grazing.”
I would argue
that along with reducing grazing by exotic
herbivores, the agriculture officials also
need to consider densely, overseeding with
a broad diversity of appropriate native plants.
Appropriate in that they are not closely
related to the exotic aliens that are already
occupying the soil.
Maryann is Editor of the Wild Ones Journal, and comes to the position with an extensive background in environmental matters of all kinds.
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