The American mink The water vole

1
ALIEN INVASION THE AMERICAN MINKS PREDATION ON
THE WATER VOLE
Adam R. Monteith
ABSTRACT
RESULTS
The transplanting of animal species into a
foreign environment interrupts the balance of
that environment and sometimes results in the
endangerment or extinction of a native species.
One example is the introduction of the American
mink into northern England in the mid-twentieth
century.. The mink has preyed on the native
water vole and is driving it to extinction. The
decline in water vole populations in the vicinity
of the mink and the water voles reaction to the
minks presence have been studied. Voles
reaction to the mink has been demonstrated.
Measures to save the water vole are being
investigated.
It was found that some sites had all of the
habitat characteristics of the sites with
breeding colonies, but had no colonies
themselves. At some of the sites, the relative
isolation from the others seemed to account for
the absence of water voles, or for their failure
to breed at those sites. At others, however,
Lawton and Woodroffe witnessed the rapid decline
in the vole population after mink colonized the
area. They also obtained historical evidence
that areas currently described as peripheral
(visited by water voles but not used for
breeding) had previously supported colonies.
Lawton and Woodroffe concluded that isolation and
mink predation accounted for the lack of water
vole breeding at these sites. In addition, the
disappearance of voles in areas of mink predation
increased the mean distance between colonies,
resulting in an increased degree of isolation.
They blame the combination of isolation and mink
predation for lack of vole breeding in about 30
of the sites they studied. Two other scientists,
however, have demonstrated that the water vole
does appear to have some innate ability to sense
the danger posed by the mink. In an experiment
testing the reaction of the water vole to the
odors of two of its common predators, the
American mink and the brown rat, even voles that
had never been exposed to a mink feared its
scent, and avoided it even more strongly than
that of the brown rat (Barreto and Macdonald,
1999). And one of those scientists points out
that the eradication of the predator mink would
be an unrealistic goal, and that water voles
coexist with both American and European mink, as
well as other predators, in other areas of Europe
(Lawson, 1996). In a separate study, it was
found that while vole decline correlates with an
increase in the mink population, it also
correlates with changes in land use, including
intensive grazing by sheep and cattle.
INTRODUCTION
Man's efforts to get all he can out of nature
often conflict with nature's more simple goal of
surviving for as long as possible. In his quest
for greater production, man interrupts balanced
ecosystems, often with serious consequences. One
way such systems are interrupted is by
transplanting a species into a foreign
environment that may or may not be prepared to
deal with the introduction of the alien species.
In the case examined here, the American mink was
transplanted to England in the 1930s to be farmed
for its fur. In the following decades, mink
farming increased and some of the animals escaped
into the wild, where they began breeding. Since
that time, they have preyed on England's water
voles until the voles are nearly extinct. Can
anything be done to prevent their extinction?
Should the American mink be eradicated from the
area, even if it is possible? Can the two
animals coexist? Are there other factors
endangering the water vole that could be altered
to compensate for the threat posed by the mink?
Scientists have been investigating these ideas
for years and have come up with a few answers,
but more research remains to be done.
The American mink The
water vole
CONCLUSIONS
DISCUSSION
The eradication of the American mink, even if it
were desirable, would take decades and be
extremely costly. Though it is the mink that
preys on the water vole, it is man who is
ultimately responsible for the problem of the
voles disappearance, and it is man who must find
a solution to the problem. In addition to mink
predation, agriculture has forced water voles
into a much smaller area of vegetation than they
would otherwise enjoy. Dr. Macdonald is hopeful
that by controlling land use, landowners in
England can allow the water vole to thrive again.
In 1991, New Scientist reported on the findings
of two ecologists who studied the water vole
population at various sites in Yorkshire, England
(Timson, 1991). The ecologists, John Lawton and
Gordon Woodroffe, indexed 39 sites by use by
water voles, suitability of each habitat (plant
species and structural diversity, grass coverage
and bank angle), and disturbance by humans and by
the grazing of domestic animals (Lawton and
Woodroffe, 1991). Water vole and mink footprints
and other tracks were recorded, and at sites
where voles had established breeding colonies,
the change in vole population was measured and
compared to the change in mink population at the
same time. In addition, historical evidence of
previous water vole populations in areas where
mink were currently present were taken into
account. The sites were visited monthly over a
period of two years. Lawton and Woodroffe
discovered three main reasons for low water vole
populations unsuitability of habitats,
isolation, and predation by the American mink.
REFERENCES
Lawton, John H., and Gordon L. Woodroffe. 1991.
Habitat and the distribution of water vole why
are there gaps in a species range? Journal of
Animal Ecology 6079-91. Barreto, Guillermo R.,
and David W. Macdonald. 1999. The response of
water voles, Arvicola terrestris, to the odours
of predators. Animal Behaviour 571107-1112.
Lawson, Trevor. 1996. Man or mink? Geographical
68 Issue 39. Timson, John. 1991. Murderous mink
wipe out water voles. New Scientist 129 Issue
176216.
Presented in BYU BIO100 course, section 042,
Tuesday, 03 November 2003 at 9am.