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Research Ties Human Acts to Harmful Rates of Species Evolution
The New
York Times January 13, 2009
http://www.nytimes.com/2009/01/13/science/13fish.html
Research
Ties Human Acts to Harmful Rates of Species Evolution
By CORNELIA
DEAN
Human actions are increasing the rate of evolutionary change in
plants and animals in ways that may hurt their long-term prospects
for
survival, scientists are reporting.
Hunting, commercial fishing and some
conservation regulations, like
minimum size limits on fish, may all work
against species health.
The idea that target species evolve in response
to predation is not
new. For example, researchers reported several years ago
that after
decades of heavy fishing, Atlantic cod had evolved to reproduce
at
younger ages and smaller sizes.
The new findings are more
sweeping. Based on an analysis of earlier
studies of 29 species - mostly
fish, but also a few animals and
plants like bighorn sheep and ginseng -
researchers from several
Canadian and American universities found that rates
of evolutionary
change were three times higher in species subject to
"harvest
selection" than in other species. Writing in The Proceedings of the
National Academy of Sciences, the researchers say the data they
analyzed
suggested that size at reproductive maturity in the species
under pressure
had shrunk in 30 years or so by 20 percent, and that
organisms were reaching
reproductive age about 25 percent sooner.
In Alberta, Canada, for
example, where regulations limit hunters of
bighorn sheep to large animals,
average horn length and body mass
have dropped, said Paul Paquet, a
biologist at the University of
Calgary who participated in the research. And
as people collect
ginseng in the wild, "the robustness and size of the plant
is
declining," he said.
The researchers said that reproducing at a
younger age and smaller
size allowed organisms to leave offspring before
they were caught or
killed. But some evidence suggests that they may not
reproduce as
well, said Chris Darimont, a postdoctoral fellow in
environmental
studies at the University of California, Santa Cruz, who led
the
work. The fish they studied that are reproducing earlier "on average
have far, far, far fewer eggs than those who wait an additional year
and
grow a few more centimeters," he said in an interview.
Dr. Darimont said
it was unknown whether traits would change back if
harvesting were reduced,
or how long that might take.
The researchers also noted that the pattern
of loss to human
predation like hunting or harvesting is opposite to what
occurs in
nature or even in agriculture.
Predators typically take
"the newly born or the nearly dead," Dr.
Darimont said. For predators,
targeting healthy adults can be
dangerous, and some predator fish cannot
even open their mouths wide
enough to eat adult prey. Animals raised as
livestock are typically
slaughtered relatively young, he said, and farmers
and breeders
retain the most robust and fertile adults to grow their herds
or
flocks.
But commercial fishing nets and other gear that comply
with
conservation regulations typically trap large fish while letting
smaller ones escape. Trophy hunters typically seek out the largest
animals. And for some fish in some areas, as much as 50, 60 or even
80
percent of the stock may be caught every year.
"Targeting large,
reproducing adults and taking so many of them in a
population in a given
year - that creates this ideal recipe for rapid
trait change," Dr. Darimont
said.
Some fisheries scientists have said their studies of fish stock had
not shown a correlation between fishing intensity and growth rates.
And
some wildlife conservationists question the idea that hunting can
have
harmful effects on species.
Dr. Paquet said that although he had
confidence in the new findings,
he knew there would be questions about the
analytical methods he and
his fellow researchers used. "That's expected," he
said. "That's how
science proceeds."
He said he had anticipated that
the work would be "contentious" among
trophy hunters. "Essentially, we are
saying, 'You should not do this
because it is having effects even you might
not like,' " he said.
Daniel Pauly, who directs the Fisheries Center at
the University of
British Columbia, said the new findings "make
sense."
Though Dr. Pauly said he had not seen the new work, he recalled
similar changes in black chin tilapia, fish that live in brackish
water.
He said in an interview that he had studied the fish more than
30 years ago,
when he was a young graduate student doing field work
in Ghana.
After
decades of heavy fishing, the size of the typical adult fish
had shrunk to
about 10 centimeters from about 15 centimeters. But at
the time, he said, "I
did not realize what was happening."
Some fisheries managers are already
suggesting that conservation
regulations should be changed to safeguard
larger fish in protected
species. "Lots of people argue for that because the
big ones are so
fecund," Dr. Pauly said. But he said customers in fish
markets
typically prefer larger fish. And if fishers are not permitted to
keep the big ones, they "must catch enormous quantities of fish to
have
a good tonnage."
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