Potential Niche Expansion of the American Mink Invading a Remote Island Free of Nativepredatory Mammals Page: 3
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.W P LO S ONE Potential niche expansion of an invasive predator
[23,24]. The mink expansion may have been favored by the lack of other mammalian competi-
tors and the lack of potential predators [22]. Additionally, and given a lack of some of the natu-
ral food sources found in its native range, including freshwater fish, crayfish, and amphibians
[16], on this island mainland birds and rodents became important components of mink's diet
[24,25]. The consumption of rodents and birds is more important for mink inhabiting inland
territories (96% of ingested biomass) as compared to the marine coastline, where mink rely
mainly on marine fish (72% of ingested biomass) [25]. Therefore, we hypothesized that the
lack of potential predators and competitors, together with a more diurnal and terrestrial prey
given the low abundance or general lack of freshwater prey, have resulted in the mink expand-
ing its spatial niche (expressed in changes in occupancy) and temporal niche (changes in activ-
ity patterns) on Navarino Island, as compared to native habitats where mink restricts most of
its activity near water (<100 m) and is mostly crepuscular and nocturnal. We predicted a spa-
tial niche expansion from semi-aquatic habitats along rivers and coastlines (its natural niche)
that will be expressed in mink occupying the marine coastline, freshwater systems, but also
more terrestrial habitats away from water sources. In addition, we predicted a temporal niche
expansion expressed as an increase in mink diurnal activity as its main prey, birds and rodents,
present also diurnal activity. We sought to evaluate our predictions by using camera traps to
investigate i) the habitat variables that determine mink patterns of seasonal occupancy dynam-
ics in the marine coastal-terrestrial environment by fitting a Bayesian hierarchical multi-sea-
son occupancy model; ii) the relationship of mink occupancy and activity in terrestrial habitats
at different distances from freshwater sources by fitting single season Bayesian occupancy
model and determining mink detection rate; and iii) the seasonal daily mink activity patterns.
We used occupancy instead of abundance given the difficulties to identify mink individuals
[26].
Methods
Study area
We conducted this study on the northern slope of Navarino Island (55S, 68W, ca. 2500
km2), located south of Tierra del Fuego, within the Cape Horn Biosphere Reserve (CHBR; Fig
1). The CHBR protects the pristine Magellanic Sub-Antarctic ecoregion [27]. The climate has
a strong oceanic influence, with a mean annual temperature of 6 5 C and uniform precipi-
tation with an annual average of 467 mm [28]. The topography presents a mountain landscape,
encompassing four distinct habitat types: shrublands along the marine coasts, deciduous and
evergreen forests on the slopes up to 500 m in altitude, moorlands including meadows and
peatlands, and high-Andean vegetation above the tree line [28] (Fig1). Many of the current
meadows are the result of invasive American beaver (Castor canadensis) activity that has trans-
formed part of the native forest into meadows [28].
The vertebrate fauna on Navarino Island is restricted to birds, mammals, and fish. Amphib-
ians and reptiles are absent [28]. Birds are the most abundant group with approximately 34
species from 20 families, with 18 species being Passeriformes [29]. Terrestrial mammal species
are scarce. There are only two species of native rodents, two species of native bats, and one
native ungulate [30]. In addition to the mink, American beavers, muskrats (Ondatra zibethi-
cus), and house mice (Mus musculus) were introduced on Navarino [30]. Also cows, horses,
pigs, dogs, and cats can be found freely roaming in many sectors of the island [30]. In the
freshwater systems, freshwater crabs are absent and only three species of native fish and two
introduced salmonids can be found in low abundances, with a mean abundance for all species
being <0.04 fish/m2 [31]. In contrast, the marine fish and crustacean fauna in the BeagleChannel is rich and abundant with more than 50 species [32]. On Navarino Island, mink lack
PLOS ONE I https://doi.org/10.1371/journal.pone.0194745 April 4, 2018
3 /18
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Crego, Ramiro D.; Jiménez, Jaime E. & Rozzi, Ricardo, 1960-. Potential Niche Expansion of the American Mink Invading a Remote Island Free of Nativepredatory Mammals, article, April 4, 2018; San Francisco, California. (https://digital.library.unt.edu/ark:/67531/metadc1132743/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Liberal Arts & Social Sciences.