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Many areas worldwide are under attack from plants and animals that have moved
in from elsewhere and become pests. As this ScienCentral News video reports,
biologists have now found out why they're often so successful, and might have
a way to slow them down.
Don't Be Crabby
Either by accident or intentionally, humans have moved plants and animals around
the world. These "introduced" or "invasive" species often
create problems for what’s already living there, including people. The
newcomers sometimes find their new digs much more accommodating than the old
place, and biologists give several reasons for this. The most common is that
there are fewer predators and a better supply of food. However, Mark Torchin,
a research biologist at the University of California, Santa
Barbara’s Marine Science Institute may have found another reason,
and a way to slow them down—the parasites that often keep species in
check at home.
Working with his colleague at the Institute, Armand
Kuris, and Valerie McKenzie and Kevin Lafferty of the Western
Ecological Research Center and Andrew
Dobson of Princeton
University, they studied 26 different introduced species and their parasites.
They compared the parasites a species had in its old home to the parasites
that were still with the species in its new home, and reported in the journal
Nature
that moving to new quarters seems to allow species to get away from many of
their parasites.
Torchin’s team found that “at home, an average animal species has
16 parasites.” However, when it moves to a new home, “it generally
brings only three of those parasites with it.” Torchin says the species
does pick up an average of four new parasites in its new location, but he
points out that’s “only half the number of parasites in the introduced
range compared to where it’s native."
The green crabs in Europe are small...
...while the U.S. invaders are much larger. images: UC-Santa Barbara
The solution, Torchin suggests, could be intentionally introducing the crab’s
old enemies as biological control agents to its new home. However, he cautions,
to prevent the introduced parasites from becoming pests themselves, scientists
would need to be sure “that those biological control agents are specific
to the target pest and they don’t impact the native species.”
Crab vs. Crab
Torchin calls species that find new homes “introduced species,”
reserving the term “invasive species” for those that become pests.
A serious example of the latter is the European Green crab, which, as its
name implies, originally was from Europe. It has spread along major portions
of both coasts of the U.S. and to South Africa, Australia, Tasmania and Japan.
A barnacle that can castrate the green crab keeps the population down in Europe,
but those barnacles have never made it to the introduced areas.
Without parasites to keep it in check, the American version is many times larger
than those typically found in its native habitat. Torchin says the green crabs,
which are not commercially valuable, “both prey on and out-compete native
species” and can decimate native shellfish including popular seafood
items such as Dungeness Crabs.
“If you get a replacement of the Dungeness Crab by the Green Crab,”
Torchin notes, “people, particularly the fishermen, are not going to
be very happy.”
Funding: NCEAS (National Center for Ecological Analysis and Synthesis), NSF-NIH,
Smithsonian Institution, National Sea Grant.
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