Invasion of the redlegged
By NED ROZELL
March 05, 2009
In the early 1980s, a schoolteacher in a Southeast Alaska logging
camp ordered a few clusters of frog eggs from a biological supply
company. The teacher and his students succeeded in rearing those
eggs into tadpoles, and then frogs. They enjoyed the frogs until
school ended, when they released the frogs into a nearby pond.
A redlegged frog.
Photo by Lance Lerum
From that act of seeming compassion came an invasion of Chichagof
Island by redlegged frogs, a species Alaska hadn't hosted
before. The frogs have spread over the southeast portion of the
island, and seem to be doing quite well.
Though they appear harmless as they hop through the island's
lowlands, the frogs could push out (by gobbling up) a native
toad that makes its home on Chichagof Island. And that is the
danger of exotics, said biologist Lance Lerum of the U.S. Forest
Service in Klamath Falls, Oregon. Lerum spent more than a decade
in Southeast Alaska before transferring to Oregon.
"My fear was that this
introduced population will be another stressor to western toad
viability," Lerum said over the phone from Klamath Falls.
"In two years of field work, we found thousands of redlegged
frogs, but we didn't find a single western toad in our study
This column is provided
as a public service by the Geophysical Institute,
During a more recent trip, though, Lerum and his coworkers found
150 adult male western toads at one breeding site on the island.
They still exist, but the newfound success of the redlegged frog
is perhaps a threat to young western toads. Frogs will eat almost
anything smaller than themselves.
Even though its Latin name, Rana aurora, seems to fit
its new niche in the state, the redlegged frog is a visitor biologists
wish had never come riding up in a cardboard box. And the redlegged
frog's spread over Chichagof Island may foreshadow a leap to
other places in Southeast, facilitated not by their legs, but
by people, especially little ones, who sometimes make temporary
pets of frogs, take them home, then release them. Biologists
can envision some frogs reaching different locales in Southeast
via rides on the ferry.
Once a species is established and thriving, as is the redlegged
frog, there is usually little we humans can do to reverse the
process. In addition to out-competing or eating other animals,
exotics can spread diseases new to an area. Introductions of
non-native fish and game species are now illegal in Alaska, but
prevention is the key, Lerum said.
"When (the release of the redlegged frogs) happened, it's
what people did," he said. "But now there's a lot more
awareness of the implications of 'bucket biology.'"
The redlegged frog, now enjoying life in Southeast Alaska, has
suffered a bit due to habitat loss on different parts of its
natural range, which extends throughout the Pacific Northwest
to central British Columbia. This led Lerum and his colleagues
Greg Pauly and Santiago Ron to conclude in a recent paper in the Journal of Herpetology that the redlegged frog's introduction
to Alaska may be a good thing for the species in the long run.
"As long as there is no evidence of significant ecological
impacts or high likelihood of subsequent introductions, we suggest
allowing this population to persist," the authors wrote.
"This strategy may benefit future conservation of R.
aurora. Given the global decline of amphibians and declines
of all western North American (frog) species, it may be useful
to allow these disjunct populations to persist as an insurance
against future extinctions."
University of Alaska Fairbanks, in cooperation with the UAF research
Ned Rozell is a science writer at the institute.
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