Jeffrey P. Copeland

Wolverine gene flow across a narrow climatic niche

Wolverines (Gulo gulo) are one of the rarest carnivores in the contiguous United States. Effective population sizes in Montana, Idaho, and Wyoming, where most of the wolverines in the contiguous United States exist, were calculated to be 35 (credible limits, 28 52) suggesting low abundance. Landscape features that influence wolverine population substructure and gene flow are largely unknown. Recent work has identified strong associations between areas with persistent spring snow and wolverine presence and range. We tested whether a dispersal model in which wolverines prefer to disperse through areas characterized by persistent spring snow cover produced least-cost paths among all individuals that correlated with genetic distance among individuals. Models simulating large preferences for dispersing within areas characterized by persistent spring snow explained the data better than a model based on Euclidean distance. Partial Mantel tests separating Euclidean distance from spring snow-cover-based effects indicated that Euclidean distance was not significant in describing patterns of genetic distance. Because these models indicated that successful dispersal paths followed areas characterized by spring snow cover, we used these understandings to derive empirically based least-cost corridor maps in the U.S. Rocky Mountains. These corridor maps largely explain previously published population subdivision patterns based on mitochondrial DNA and indicate that natural colonization of the southern Rocky Mountains by wolverines will be difficult but not impossible.

Characteristics of Wolverine Reproductive Den Sites

Successful wolverine (Gulo gulo) reproduction may be linked to the availability and quality of reproductive dens sites, but little is known about wolverine reproductive dens, especially in North America. We present descriptions of wolverine dens in Idaho and Alaska, compare them to dens in other regions, and propose factors that may influence den-site selection. Our study includes 8 den sites used by 3 females over 4 years in northwestern Alaska and 7 sites used by 2 females over 4 years in central Idaho. We categorized reproductive dens of wolverines as either natal (used during parturition) or maternal (used subsequent to the natal den and before weaning). Dens in Alaska were usually long, complex snow tunnels with no associated trees or boulders. In contrast, dens in Idaho were always associated with fallen trees or boulders. All dens were covered with at least 1 m of snow. With few exceptions, wolverine dens described to date have been located in alpine, subalpine, taiga, or tundra habitat. Reports of dens in low elevation, densely forested habitats are rare. Factors which may have influenced selection of den sites included thermoregulatory advantages, protection from predators, suitability of the site during the spring thaw, and location of rearing habitat. We recommend managers consider limiting wolverine harvests and reducing human disturbance in wolverine denning g habitat.

The bioclimatic envelope of the wolverine (Gulo gulo): do climatic constraints limit its geographic distribution?

We propose a fundamental geographic distribution for the wolverine (Gulo gulo (L., 1758)) based on the hypothesis that the occurrence of wolverines is constrained by their obligate association with persistent spring snow cover for successful reproductive denning and by an upper limit of thermoneutrality. To investigate this hypothesis, we developed a composite of MODIS classified satellite images representing persistent snow cover from 24 April to 15 May, which encompasses the end of the wolverine’s reproductive denning period. To investigate the wolverine’s spatial relationship with average maximum August temperatures, we used interpolated temperature maps. We then compared and correlated these climatic factors with spatially referenced data on wolverine den sites and telemetry locations from North America and Fennoscandia, and our contemporary understanding of the wolverine’s circumboreal range. All 562 reproductive dens from Fennoscandia and North America occurred at sites with persistent spring snow c...

Distribution and Broadscale Habitat Relations of the Wolverine in the Contiguous United States

Abstract Conservation of the wolverine (Gulo gulo) at the southern extent of its North American range requires reliable understandings of past and present distribution patterns and broad-scale habitat relations. We compiled 820 verifiable and documented records of wolverine occurrence (specimens, DNA detections, photos, and accounts of wolverines being killed or captured) in the contiguous United States from museums, the literature, and institutional archives. We spatially referenced 729 records with areal precision ≤1 township (93.2 km2) and temporal precision ≤10 years. Historical records (1827–1960) were located primarily in the western mountains and Great Lakes region. However, our data suggest that the historical distribution of wolverines in the Cascade Range and Sierra Nevada was disjunct, contradicting previous interpretations. Our results indicate that wolverine range in the contiguous United States had contracted substantially by the mid-1900s. Current records (1995–2005) are limited to north-central Washington, northern and central Idaho, western Montana, and northwestern Wyoming. We investigated potential relations between wolverines and alpine vegetation, cold temperatures, and spring snow cover by comparing the distribution of historical wolverine records with Kuchlers potential natural vegetation types, Holdridges climatic life zones, and EASE snow-cover maps during the latter portion of the wolverine denning period (15 Apr–14 May). In the western mountains, historical wolverine records generally occurred in or near alpine vegetation and climatic conditions, especially at the limits of their distribution in the Cascade Range, Sierra Nevada, and southern Rocky Mountains. However, the only habitat layer that fully accounted for historical distribution patterns was spring snow cover. Causal factors for the extirpation of wolverines from the southern portions of their range in the contiguous United States are unknown, but are likely related to high levels of human-caused mortality and low to nonexistent immigration rates.

SYNTHESIS OF SURVIVAL RATES AND CAUSES OF MORTALITY IN NORTH AMERICAN WOLVERINES

Abstract Understanding population vital rates is fundamental to the evaluation of conservation options for wolverines (Gulo gulo). We estimated survival rates and causes of wolverine mortality in trapped and untrapped populations within montane, boreal, and tundra environments using data from 12 North American radiotelemetry studies conducted between 1972 and 2001. Rates were based on data for 62 mortalities of 239 radiomarked wolverines. Mortalities included 22 wolverines that were trapped or hunted, 3 road or rail killed, 11 that were predated, 18 that starved, and 8 deaths of unknown cause. Annual survivorship rates were estimated for sex and age class using Kaplan-Meier staggered-entry techniques. Survival was substantially lower in trapped (<0.75 for all age–sex classes) than in untrapped (>0.84 for all age–sex classes) populations. Human-caused mortality was mostly additive to natural mortality for wolverines in a management context. Logistic growth rate estimates indicated that trapped populations would decline (λ ≅ 0.88) in the absence of immigration from untrapped populations (λ ≅ 1.06). We recommend a system of spatial harvest controls in northern, continuous populations of wolverines and reduction of harvest along with more spatially explicit conservation measures in southern metapopulations.

Climate change predicted to shift wolverine distributions, connectivity, and dispersal corridors

Boreal species sensitive to the timing and duration of snow cover are particularly vulnerable to global climate change. Recent work has shown a link between wolverine (Gulo gulo) habitat and persistent spring snow cover through 15 May, the approximate end of the wolverines reproductive denning period. We modeled the distribution of snow cover within the Columbia, Upper Missouri, and Upper Colorado River Basins using a downscaled ensemble climate model. The ensemble model was based on the arithmetic mean of 10 global climate models (GCMs) that best fit historical climate trends and patterns within these three basins. Snow cover was estimated from resulting downscaled temperature and precipitation patterns using a hydrologic model. We bracketed our ensemble model predictions by analyzing warm (miroc 3.2) and cool (pcm1) downscaled GCMs. Because Moderate-Resolution Imaging Spectroradiometer (MODIS)-based snow cover relationships were analyzed at much finer grain than downscaled GCM output, we conducted a second analysis based on MODIS-based snow cover that persisted through 29 May, simulating the onset of spring two weeks earlier in the year. Based on the downscaled ensemble model, 67% of predicted spring snow cover will persist within the study area through 2030-2059, and 37% through 2070-2099. Estimated snow cover for the ensemble model during the period 2070- 2099 was similar to persistent MODIS snow cover through 29 May. Losses in snow cover were greatest at the southern periphery of the study area (Oregon, Utah, and New Mexico, USA) and least in British Columbia, Canada. Contiguous areas of spring snow cover become smaller and more isolated over time, but large (.1000 km 2 ) contiguous areas of wolverine habitat are predicted to persist within the study area throughout the 21st century for all projections. Areas that retain snow cover throughout the 21st century are British Columbia, north-central Washington, northwestern Montana, and the Greater Yellowstone Area. By the late 21st century, dispersal modeling indicates that habitat isolation at or above levels associated with genetic isolation of wolverine populations becomes widespread. Overall, we expect wolverine habitat to persist throughout the species range at least for the first half of the 21st century, but populations will likely become smaller and more isolated.

Sources and Patterns of Wolverine Mortality in Western Montana

Abstract We instrumented 36 wolverines (Gulo gulo) on 2 study areas in western Montana and one study area on the Idaho–Montana (USA) border: 14 (9 M, 5 F) on the Pioneer study area, 19 (11 M, 8 F) on the Glacier study area, and 3 (2 M, 1 F) on the Clearwater study area. During 2002–2005, harvest from licensed trapping accounted for 9 (6 M, 3 F) of 14 mortalities, including individuals from all 3 study areas. Based on Akaikes Information Criterion adjusted for small sample sizes (AICc) rankings of 8 a priori models, a trapping model and a trapping-by-sex interaction model were equally supported (ΔAICc < 2) in explaining wolverine survival. Estimated annual survival was 0.80 when we did not consider harvest, whereas additive mortality from harvest reduced annual survival to 0.57. Glacier National Park in the Glacier study area provided some refuge as evidenced by an annual survival rate of 0.77 compared to 0.51 for the Pioneer Mountain study area. We incorporated these survival rates into a simple Lefkovitch stage-based model to examine rates of population change. The finite rate of population change (λ) for the Glacier study area was 1.1, indicating a stable to slightly increasing population, whereas λ for the Pioneer study area was 0.7, indicating a 30% annual population decrease during our study. Changes in λ for both study areas were most sensitive to adult survival. In 2004, we used a Lincoln Index to estimate that 12.8 ± 2.9 (95% CI) wolverines resided in the 4 mountain ranges comprising the Pioneer study area, suggesting that small, island ranges in western Montana supported few individuals. Our results suggest that if wolverines are harvested, they should be managed within individual mountain ranges or small groupings of mountain ranges to limit mortality to within biologically defined limits in recognition of the increased vulnerabilities owing to low fecundity and low population numbers in small mountain ranges. We found that refugia, such as Glacier National Park, were important by reducing trap mortality and providing immigrants to the surrounding population, but even large parks were inadequate to provide complete protection to wolverines from trapping as they ranged outside park borders.

Wolverine Confirmation in California after Nearly a Century: Native or Long-Distance Immigrant?

Abstract We photo-verified the presence of a wolverine (Gulo gulo) in California for the first time in 86 years during February 2008. Herein we document the process of determining the origin of this wolverine using genetic, stable carbon (&dgr;13C) and stable nitrogen (&dgr;15N) isotope information. The wolverines origin was significant because it is a state-threatened species and California represents a historically unique genotype of wolverines in North America. We obtained both photographs and noninvasively-collected genetic evidence (scat and hair). DNA analysis revealed the animal was a male and not a remnant of a historical California population. Comparison with available data revealed the individual was most closely related to populations from the western edge of the Rocky Mountains. This represents the first evidence of connectivity between wolverine populations of the Rocky and Sierra Nevada Mountain Ranges.

Wolverine Conservation and Management

Abstract This Special Section includes 8 peer-reviewed papers on the wolverine (Gulo gulo) in southern North America. These papers provide new information on current and historical distribution, habitat relations at multiple spatial scales, and interactions with humans. In aggregate, these papers substantially increase our knowledge of wolverine ecology and population dynamics in North America, in many cases replacing previous speculations and informed judgments with empirical information. North American wolverines occur primarily in tundra, taiga, and subalpine environments. These environments become increasingly fragmented at southern latitudes, where wolverine populations occur at low densities and are potentially vulnerable to human-caused mortality. The combination of highly fragmented habitat, demographic sensitivity to adult mortality, and low population densities make local wolverine populations difficult to monitor and easy to overharvest. Where populations are fragmented, persistence is critically dependent on dispersal between habitat islands. Although dispersal dynamics are poorly understood, high levels of genetic structure observed in both current and historical populations indicate that dispersal between mountain ranges is limited. Wolverine biology remains poorly understood, and many fundamental issues need additional research.

Comments on Brodie and Post: Climate-driven declines in wolverine populations: causal connection or spurious correlation?

The recent paper by Brodie and Post (“Nonlinear responses of wolverine populations to declining winter snowpack”, Popul Ecol 52:279–287, 2010) reports conclusions that are unsupportable, in our opinion, due to both mis-interpretations of current knowledge regarding the wolverine’s (Gulo gulo) association with snow, and the uncritical use of harvest data to index wolverine populations. The authors argue that, because the wolverine is a snow-dependent species, average annual provincial snowfall, based on weather station data, can be expected to correlate strongly and positively with wolverine population numbers, which in turn can be accurately indexed by trapper harvests. Thus, correlations between declines in wolverine harvests and declining average snowpack are interpreted to reflect a climate-driven decrease in wolverine populations. This conclusion overstates the nature of the wolverine’s association with snow, and makes unsupportable assumptions about the reliability of harvest data as a proxy for population size.