Spatial ecology of wolverines at the southern periphery of distribution

Abstract

Wolverines (Gulo gulo) in the conterminous United States have experienced range contraction, are uncommon, and have been designated as warranted for protection under the United States Endangered Species Act. Data from the southern edge of the wolverine's circumpolar distribution is sparse, and development of effective conservation strategies would benefit from a more complete understanding of the species' ecology. We captured and radio‐monitored 30 wolverines in the Greater Yellowstone Ecosystem (GYE), tested for seasonal habitat selection by elevation band, and examined a suite of spatial characteristics to clarify our understanding of the wolverine's niche. Wolverines in GYE selected for areas >2,600 m latitude‐adjusted elevation (LAE; n = 2,257 wolverine locations [12 F, 6 M]). Wolverines avoided areas <2,150 m LAE, including during winter when the vast majority of ungulates are pushed to these elevations by deep snow. Wolverine home ranges were large relative to body size, averaging 303 km2 for adult females and 797 km2 for adult males (n = 13 [8 F, 5 M] and 33 wolverine‐years). Resident adults fit with Global Positioning System (GPS) collars used an area >75% the size of their multi‐year home range in an average of 32 days (n = 7 [5 F, 2 M]). Average movement rates of 1.3 km/2‐hr indicated that both sexes move distances equivalent to the diameter of their home range every 2 days or the circumference of their home range in <1 week (n = 1,329 2‐hr movements, n = 12 individuals [7 F, 5 M]). This capability for movement, the short time‐frame over which home ranges were developed, and a lack of home range overlap by same sex adults (${\bar {x}} = 2.1\%\;{\rm overlap}$, 90% CI = 0.0–4.8%, n = 22 pairs) suggested territoriality. We estimated wolverine density to be 3.5/1,000 km2 of area >2,150 m LAE (95% CI = 2.8–9.6). Dispersal movements extended to at least 170 km for both sexes (n = 5 F, 2 M). At the southern edge of distribution, where suitable and unsuitable conditions exist in close proximity, wolverines selected high‐elevation areas near alpine tree‐line where a mix of forest, meadow, and boulder fields were present, deep snow‐cover existed during winter, and low temperatures near freezing can occur throughout the year. Persistence in these areas where the growing season is brief requires large home ranges that are regularly patrolled, a social system that provides exclusive access to resources, and low densities. These characteristics, along with low reproductive rates, are prevalent throughout the species range, indicating that wolverines are specialists at exploiting a cold, unproductive niche where interspecific competition is limited. The vulnerability inherent in occupying this unproductive niche was likely influential in previous declines within the conterminous United States and will remain a factor as wolverines encounter modern human influences. Conserving wolverines in the conterminous United States will require collaborative management over a large geographic scale. © 2011 The Wildlife Society.

Developing priorities for metapopulation conservation at the landscape scale: Wolverines in the Western United States

“…This facultative scavenger occupies a cold, low-productivity niche (Copeland et al, 2010;Inman et al, 2012a,b) that results in sparse population densities ($5/1000 km 2 ) and low reproductive rates (0.7 young/female > 3 yrs/yr) across its range (Golden et al, 2007;Inman et al, 2012a;Persson et al, 2006). As a result, wolverine populations are relatively vulnerable due to their small size and limited capacity for growth (Brøseth et al, 2010;Persson et al, 2009).…”

“…While there has been much recent progress in understanding wolverine distribution and ecology in the contiguous US (Cegelski et al, 2006;Copeland et al, 2010;Inman et al, 2012a;Ruggiero et al, 2007;Schwartz et al, 2009), habitat-related tools remain coarse and estimates of potential or current population size do not exist. It is also unclear which patches of wolverine habitat in the contiguous US are capable of female interchange, male interchange, or both.…”

“…Wolverines were extirpated, or nearly so, from their historical distribution within the contiguous US by about 1930 and unregulated human-caused mortality was likely responsible . Wolverines have recovered to a considerable degree (Anderson and Aune, 2008;Aubry et al, 2007;Aubry et al, 2010;Copeland, 1996;Inman et al, 2012a), however the species will face a new set of habitat-related challenges in the 21st Century such as rural sprawl, roads, recreation, and climate change (Gude et al, 2007;Krebs et al, 2007;McKelvey et al, 2011;Packila et al, 2007). Wolverines were recently designated a candidate for listing in the contiguous US under the US Endangered Species Act (US Fish and Wildlife Service, 2010;US Fish and Wildlife Service, 2013).…”

“…Wolverines were recently designated a candidate for listing in the contiguous US under the US Endangered Species Act (US Fish and Wildlife Service, 2010;US Fish and Wildlife Service, 2013). Wolverine habitat in the contiguous US appears to consist of disjunct patches of mountainous, high alpine areas inhabited at low densities and requiring dispersal across intervening areas (Copeland et al, 2010;Inman et al, 2012a), likely a prime example of a metapopulation (Hanski and Gaggiotti, 2004). The metapopulation concept has evolved from island biogeographic theory (MacArthur and Wilson, 1967) into complex estimates of population viability that are based on the spatial arrangement of habitat patches, habitat quality within and between patches, demographic rates, and dispersal (Akçakaya and Atwood, 1997;Haines et al, 2006).…”

Female breeding dispersal in wolverines, a solitary carnivore with high territorial fidelity

“…In this study, we use location data from 47 adult wolverines (Gulo gulo) monitored during 20 years in northern Sweden. The wolverine is a solitary carnivore with a polygamous mating system (Hedmark et al 2007), intrasexual territoriality Inman et al 2012a) and male-biased natal dispersal (Vangen et al 2001;Flagstad et al 2004). Wolverines occupy arctic tundra and boreal forest zones of Eurasia and North America (Copeland et al 2010) and are adapted to harsh environmental conditions with low productivity by being an opportunistic generalist predator and scavenger that caches food for later use (Inman et al 2012b;Mattisson et al 2016).…”