For many years the wolves and moose of Isle Royale National Park in Lake Superior have shown that wolves do not wipe out their prey. When wolves become abundant enough that the disappearance of prey seems probable, the wolves die back.
On the other hand, when wolves have declined to few in number, the moose population expands and begins to decimate its prey — the moose-edible vegetation of the island.
This rough balance has existed ever since wolves colonized the island one hard winter. In 1949 a pair of wolves walked over to the island on the frozen lake. The pair found an island overrun with moose. The moose themselves had migrated to the island 40 years earlier.
The wolf population expanded, of course, and brought the moose number in check (and more). Then the wolves began to starve off and the cycle began.
The moose prefer aspen, and they do well eating it. However, they mostly wiped that out before the wolves came. Ever since, they have relied primarily on the less nutritious balsam fir and lichens.
Both the moose and the wolves are also subject to inbreeding. It is especially a problem for the wolves, all of which descended from the original pair. So, in addition to the cyclic malnutrition when the moose population drops too low, the wolves have been seen to suffer from increasing genetic defects. One of these is poor reproduction even when there is enough food.
Down to just 8 wolves, they seem doomed without outside genes from new wolves. There have been up to 50 wolves at a time on the island, although many scientists think a stable number is about 25. It should be noted that there have always been wide fluctuations around this “mean.” The eight wolves seem to have gained a brief reprieve with the birth of 2 or 3 pups in 2013 after several years with none. Nevertheless, it is hard to see how the unaugmented population can survive much longer. It is less and less likely that the lake will freeze and wolves from Minnesota, Michigan or Wisconsin find their way to the island.
The wolves and their relationship to the moose and the vegetation have been studied since 1958. Dr. Rolf Peterson, in particular, is the person most closely associated with the studies. He would like to see some genetic rescue. Dr. Dave Mech, however, who is another avid student of the island’s wolves is reported to want to first let natural events play out.
With the wolf population so low, we would now expect the moose population to be expanding. It is. However, it is increasingly suffering from tick infestation. This is a problem for moose in general during winters, but Isle Royale has seen warmer winters as the climate changes. This makes the effects of the bloodsucking arachnids more severe.
Rolf Peterson recently sent out the following letter.
The National Park Service is interested
to receive your input on the pending decision regarding the future
management of wolves on Isle Royale. Please send your input to the
following email address:
ISRO_Wildlife@nps.gov (note the “underscore” between ISRO and Wildlife)
The Park Service is considering three
options: (1) do nothing, even if wolves go extinct; (2) allow wolves to
go extinct (if that is what they do), and then introduce a new wolf
population; or (3) conserve Isle Royale wolves with an action known as
genetic rescue by bringing some wolves to the island to mitigate
inbreeding.
While expressing your view, consider
providing as much detail on the reasons for your preference, as the Park
Service believes the reasons for your view are as important as your
view. If you have any questions on the process or anything relating to
providing input, please do not hesitate to ask me.
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