Wolf Reintroduction Research Articles

Effects of bison on willow and cottonwood in northern Yellowstone National Park

On the northern ungulate winter range of Yellowstone Park, willow ( Salix spp.) and cottonwood ( Populus angustifolia and Populus balsamifera) have increased in height and cover in some places since the reintroduction of wolves ( Canis lupus) and the subsequent changes in elk ( Cervus elaphus) behavior and population densities. However, in the Lamar Valley, an important part of this winter range, many plants are still intensively browsed and recruitment has been limited. As elk numbers have declined and their distribution has changed in recent years, bison ( Bison bison) have increased on the northern range. To distinguish bison effects from those of elk, we measured browsing that occurred in summer. We found average summer browse rates of 84% for willow and 54% for cottonwood seedlings in the summer of 2010, demonstrating that bison have become significant browsers in the Lamar Valley. Plants were increasing in size except where intensively browsed by bison, suggesting that a release from elk browsing has occurred, and that a trophic cascade is occurring from wolves to plants, mediated by both elk and bison. Release of bison from competition with elk, low levels of predation on bison, and lack of opportunity for migration and range expansion may be factors contributing to a high concentration of bison, with resulting effects on plant communities and biodiversity.

Cougar survival and source‐sink structure on Greater Yellowstone's Northern Range

AbstractWe studied survival and causes of mortality of radiocollared cougars (Puma concolor) on the Greater Yellowstone Northern Range (GYNR) prior to (1987–1994) and after wolf (Canis lupus) reintroduction (1998–2005) and evaluated temporal, spatial, and environmental factors that explain variation in adult, subadult, and kitten survival. Using Program MARK and multimodel inference, we modeled cougar survival based on demographic status, season, and landscape attributes. Our best models for adult and independent subadults indicated that females survived better than males and survival increased with age until cougars reached older ages. Lower elevations and increasing density of roads, particularly in areas open to cougar hunting north of Yellowstone National Park (YNP), increased mortality risks for cougars on the GYNR. Indices of ungulate biomass, cougar and wolf population size, winter severity, rainfall, and individual characteristics such as the presence of dependent young, age class, and use of Park or Wilderness were not important predictors of survival. Kitten survival increased with age, was lower during winter, increased with increasing minimum estimates of elk calf biomass, and increased with increasing density of adult male cougars. Using our best model, we mapped adult cougar survival on the GYNR landscape. Results of receiver operating characteristic (ROC) analysis indicated a good model fit for both female (area under the curve [AUC] = 0.81, 95%CI = 0.70–0.92, n = 35 locations) and male cougars (AUC = 0.84, 95%CI = 0.74–0.94, n = 49 locations) relative to hunter harvest locations in our study area. Using minimum estimates of survival necessary to sustain the study population, we developed a source‐sink surface and we identify several measures that resource management agencies can take to enhance cougar population management based on a source‐sink strategy. © 2011 The Wildlife Society.

Learning from El Lobo: Using 'Wolf Politics' to Cross Physical, Pedagogical, Professional, and Policy Borders

This paper examines, and suggests ways to positively address, challenges in the policy world and the classroom. It includes a fully developed simulation* titled “Wolf Politics” that moves the wolf reintroduction experience of Yellowstone to the Southwest. The paper begins with a brief exploration of the concept of borders; and then it notes that wolves really do cross borders: from country to country, state to state, and out of designated zones into areas where they generate lots of human howling. Responsibility for this issue also crosses all sorts of political borders (federal, state, local; legislative, executive, judicial; and, academic and agency territorialities). Interests involved extend across agencies and agents including media, science, interest groups, and the public at large. Suggestions are made within the paper about how to better prepare future policy participants for dealing with the sort of complex political (wicked) problems they will encounter in ways that might increase democracy, break through “silos” of exclusivity, and – ideally – produce better policy. It is argued that case studies and simulations may play an important pedagogical role and that the topic of “Wolf Politics” is an ideal foci.

A reappraisal of the evidence for regulation of wolf populations

AbstractThe dogma that gray wolf (Canis lupus) population densities in naturally occurring systems are limited almost solely by available ungulate biomass is based upon studies that fit straight line linear regressions (Type 1 numerical response) to data collected at 32 sites across North America. We fit Type 1, 2, and 3 response functions to the data using linear and nonlinear regression as appropriate and found that the evidence supported wolf population regulation by density‐dependence as much as limitation by prey availability. When we excluded 4 of 32 points from the original data set because those points represented exploited or expanding wolf populations the data suggested that wolf populations are self regulated rather than limited by prey biomass by at least a 3:1 margin. In establishing goals for sustainable wolf population levels, managers of wolf reintroductions and species recovery efforts should account for the possibility that some regulatory mechanism plays an important role in wolf population dynamics. © 2011 The Wildlife Society.

Ghosts of Yellowstone: Multi-Decadal Histories of Wildlife Populations Captured by Bones on a Modern Landscape

Natural accumulations of skeletal material (death assemblages) have the potential to provide historical data on species diversity and population structure for regions lacking decades of wildlife monitoring, thereby contributing valuable baseline data for conservation and management strategies. Previous studies of the ecological and temporal resolutions of death assemblages from terrestrial large-mammal communities, however, have largely focused on broad patterns of community composition in tropical settings. Here, I expand the environmental sampling of large-mammal death assemblages into a temperate biome and explore more demanding assessments of ecological fidelity by testing their capacity to record past population fluctuations of individual species in the well-studied ungulate community of Yellowstone National Park (Yellowstone). Despite dramatic ecological changes following the 1988 wildfires and 1995 wolf re-introduction, the Yellowstone death assemblage is highly faithful to the living community in species richness and community structure. These results agree with studies of tropical death assemblages and establish the broad capability of vertebrate remains to provide high-quality ecological data from disparate ecosystems and biomes. Importantly, the Yellowstone death assemblage also correctly identifies species that changed significantly in abundance over the last 20 to ∼80 years and the directions of those shifts (including local invasions and extinctions). The relative frequency of fresh versus weathered bones for individual species is also consistent with documented trends in living population sizes. Radiocarbon dating verifies the historical source of bones from Equus caballus (horse): a functionally extinct species. Bone surveys are a broadly valuable tool for obtaining population trends and baseline shifts over decadal-to-centennial timescales.

Aspen Recovery Since Wolf Reintroduction on the Northern Yellowstone Winter Range

Abstract Quaking aspen (Populus tremuloides Michx.) recruitment and overstory stem densities were sampled in 315 clones in 1991 and 2006 on 560 km2 of the Northern Yellowstone Winter Range (NYWR). A primary objective was to observe if aspen status had improved from 1991 to 2006: evidence of a wolf (Canis lupus) caused trophic cascade. Recruitment stems (height > 2 m and diameter at breast height 2 m) represent the cohort of stems, which will insure the sustainability of the clone. Overstory stem densities declined by 12% (P = 0.04) on the landscape scale when compared with paired t-tests. Overstory stems declined in 58% of individual clones and in 63% of the 24 drainages of the study area. The second objective was to determine which factors influenced changes in aspen density. Winter ungulate browsing (P = 0.0001), conifer establishment (P = 0.0001), and cattle (Bos spp.) grazi...

Forty Freedoms

With the publication of Forty Freedoms, Salmon closes the circle on his “Southwest Trilogy,” begun in 1989 with Home Is the River and followed in 1995 by Signal to Depart. Together the three narratives, all set in the heartland of the Gila River watershed, feature neo-mountain man and conservationist Harley Simmons as he champions a free-flowing river, the reintroduction of grey wolves into the Gila ecosystem, and sport hunting, especially coursing or sight-hounding. There is arguably no writer living who has written more about the Gila River country of southwest New Mexico than Salmon, or one who is better equipped to be its advocate in the face of proposed water impoundment and development schemes. Think Ross Calvin and Aldo Leopold with a measure of Ed Abbey tossed in for seasoning and you get the picture. Forty Freedoms, as its title suggests, is about the necessity of wilderness as it relates to spiritual and physical freedom. In fact, Salmon's title comes straight from Leopold's rhetorical question in A Sand County Almanac: “of what avail are forty freedoms without a blank spot on the map?” The novel, narrated by Simmons's fourteen-year-old son Alvin, is a compelling polemic for wilderness. The plot revolves around Simmons's attempts to stop the privatization of public lands because he knows exactly what local developers plan to do with the land once it is in their hands. In the process, Simmons runs afoul of the law—he kills a goon sent to intimidate him—and hightails it to the mountains, where he is capable of living indefinitely. He is eventually joined by his son and a young runaway girl, and together the three make the high country their sanctuary for long periods of time, earning their living by hunting, trapping, and fishing.

Conflicting stories about public scientific controversies: Effects of news convergence and divergence on scientists’ credibility

Surveys suggest that approximately one third of news consumers have encountered conflicting reports of the same information. News coverage of science is especially prone to conflict, but how news consumers perceive this situation is currently unknown. College students (N = 242) participated in a lab experiment where they were exposed to news coverage about one of two scientific controversies in the United States: dioxin in sewage sludge or the reintroduction of gray wolves to populated areas. Participants received (a) one news article (control), (b) two news articles that were consistent (convergent), or (c) two news articles that conflicted (divergent). The effects of divergence induced uncertainty differed by news story. Greater uncertainty was associated with increased scientists' credibility ratings for those reading dioxin regulation articles and decreased scientists' credibility ratings for those reading wolf reintroduction articles. Unlike other manifestations of uncertainty in scientific discourse, conflicting stories seem to generate effects that vary significantly by topic. Consistent with uncertainty management theory, uncertainty is embraced or rejected by situation.

Bottom-Up Factors Influencing Riparian Willow Recovery in Yellowstone National Park

After the elimination of wolves (Canis lupis L.) in the 1920s, woody riparian plant communities on the northern range of Yellowstone National Park (YNP) declined an estimated 50%. After the reintroduction of wolves in 1995-1996, riparian willows (Salix spp.) on YNP's northern range showed significant growth for the first time since the 1920s. However, the pace of willow recovery has not been uniform. Some communities have exceeded 400 cm, while others are still at pre-1995 levels of 250 cm max. height) willow sites where willows had escaped elk (Cervus elaphus L.) browsing with willow sites that could still be browsed. Unlike studies that manipulated willow height with fences and artificial dams, we examined sites that had natural growth differences in height since the reintroduction of wolves. Tall willow sites had greater water availability, more-rapid net soil nitrogen mineralization, greater snow depth, lower soil respiration rates, and cooler summer soil temperatures than nearby short willow sites. Most of these differences were measured both in herbaceous areas adjacent to the willow patches and in the willow patches themselves, suggesting that they were not effects of varying willow height recovery but were instead preexisting site differences that may have contributed to increased plant productivity. Our results agree with earlier studies in experimental plots which suggest that the varying pace of willow recovery has been influenced by abiotic limiting fac- tors that interact with top-down reductions in willow browsing by elk.

Are wolves saving Yellowstone's aspen? A landscape‐level test of a behaviorally mediated trophic cascade

Behaviorally mediated trophic cascades (BMTCs) occur when the fear of predation among herbivores enhances plant productivity. Based primarily on systems involving small-bodied predators, BMTCs have been proposed as both strong and ubiquitous in natural ecosystems. Recently, however, synthetic work has suggested that the existence of BMTCs may be mediated by predator hunting mode, whereby passive (sit-and-wait) predators have much stronger effects than active (coursing) predators. One BMTC that has been proposed for a wide-ranging active predator system involves the reintroduction of wolves (Canis lupus) to Yellowstone National Park, USA, which is thought to be leading to a recovery of trembling aspen (Populus tremuloides) by causing elk (Cervus elaphus) to avoid foraging in risky areas. Although this BMTC has been generally accepted and highly popularized, it has never been adequately tested. We assessed whether wolves influence aspen by obtaining detailed demographic data on aspen Stands using tree rings and by monitoring browsing levels in experimental elk exclosures arrayed across a gradient of predation risk for three years. Our study demonstrates that the historical failure of aspen to regenerate varied widely among stands (last recruitment year ranged from 1892 to 1956), and our data do not indicate an abrupt cessation of recruitment. This pattern of recruitment failure appears more consistent with a gradual increase in elk numbers rather than a rapid behavioral shift in elk foraging following wolf extirpation. In addition, our estimates of relative survivorship of young browsable aspen indicate that aspen are not currently recovering in Yellowstone, even in the presence of a large wolf population. Finally, in an experimental test of the BMTC hypothesis we found that the impacts of elk browsing on aspen demography are not diminished in sites where elk are at higher risk of predation by wolves. These findings suggest the need to further evaluate how trophic cascades are mediated by predator-prey life history and ecological context.

A novel assessment of population structure and gene flow in grey wolf populations of the Northern Rocky Mountains of the United States

The successful re-introduction of grey wolves to the western United States is an impressive accomplishment for conservation science. However, the degree to which subpopulations are genetically structured and connected, along with the preservation of genetic variation, is an important concern for the continued viability of the metapopulation. We analysed DNA samples from 555 Northern Rocky Mountain wolves from the three recovery areas (Greater Yellowstone Area, Montana, and Idaho), including all 66 re-introduced founders, for variation in 26 microsatellite loci over the initial 10-year recovery period (1995-2004). The population maintained high levels of variation (H(O) = 0.64-0.72; allelic diversity k=7.0-10.3) with low levels of inbreeding (F(IS) < 0.03) and throughout this period, the population expanded rapidly (n(1995) =101; n(2004) =846). Individual-based Bayesian analyses revealed significant population genetic structure and identified three subpopulations coinciding with designated recovery areas. Population assignment and migrant detection were difficult because of the presence of related founders among different recovery areas and required a novel approach to determine genetically effective migration and admixture. However, by combining assignment tests, private alleles, sibship reconstruction, and field observations, we detected genetically effective dispersal among the three recovery areas. Successful conservation of Northern Rocky Mountain wolves will rely on management decisions that promote natural dispersal dynamics and minimize anthropogenic factors that reduce genetic connectivity.

Heterozygosity of the Yellowstone wolves

Heterozygosity of the Yellowstone wolves

Repairing paradise: the restoration of nature in America's national parks

By the turn of the millennium, it had become painfully apparent that the United States had made some serious misjudgments in its interactions with the natural world. The country's treasured national parks, while remaining immensely popular tourist destinations, were not immune to the damage. Preservation alone would no longer be enough; by this time, repair and restoration were necessary. Can the United States reverse the mistaken policies that severely damaged the crown jewels of its national park system? This thoughtful and hopeful book, in turns analytical and personal, investigates that critical question by focusing on four of America's most-loved public paces. In Repairing Paradise , William Lowry, an eminent expert on U.S. natural resource policy, details and assesses four ambitious efforts to reverse environmental damage in the national parks: The reintroduction of wolves in Yellowstone Reducing the impact of vehicle traffic in Yosemite Restoring fresh water to the Everglades Removing structural impairments to river flows in the Grand Canyon Repairing Paradise combines authoritative research with extensive personal experience. Lowry has spent time in all four of the parks --observing conditions, talking to the most informed decisionmakers, and taking photos. He deftly combines his field research with solid public policy analysis to paint an instructive portrait of the mission to restore the natural health and glory of some of the world's most wondrous places.

The Ethics of the Ecology of Fear against the Nonspeciesist Paradigm: A Shift in the Aims of Intervention in Nature

Humans often intervene in the wild for anthropocentric or environmental reasons. An example of such interventions is the reintroduction of wolves in places where they no longer live in order to create what has been called an “ecology of fear”, which is being currently discussed in places such as Scotland. In the first part of this paper I discuss the reasons for this measure and argue that they are not compatible with a nonspeciesist approach. Then, I claim that if we abandon a speciesist viewpoint we should change completely the way in which we should intervene in nature. Rather than intervening for environmental or anthropocentric reasons, we should do it in order to reduce the harms that nonhuman animals suffer. This conflicts significantly with some fundamental environmental ideals whose defence is not compatible with the consideration of the interests of nonhuman animals.

Restoring landscapes of fear with wolves in the Scottish Highlands

The absence of an organism from a landscape for a long time can be a major barrier to the restoration of that species due to factors such as environmental conditions changing since extinction. This can make it difficult to assess the feasibility of reintroduction when an extirpated species cannot, by definition, be observed in the landscape of interest. In such situations, two important options for conservation scientists include: (1) to draw on insights from analogous ecosystems where the organism is extant, or where it has been successfully reintroduced and (2) to undertake research into the reintroduction in the location of interest under controlled experimental conditions. The idea of reintroducing wolves ( Canis lupus) to the Scottish Highlands provides an excellent case study of such a situation. A key argument for reintroduction has been that native red deer ( Cervus elaphus) numbers, considered by many to be ecologically unsustainable, would be reduced through wolf predation. To date, research into the ecological value of reintroduction has focused on this important issue. However, new research, emerging from wolf reintroduction projects in North America, suggests that nonlethal ‘behaviourally-mediated’ effects of wolves also have a profound effect on deer behaviour and consequently on the ecosystems in which they live. In short, deer avoid places or browse less where there is a high risk of wolf predation, which allows previously inhibited tree regeneration. The implications for wolf reintroduction in Scotland are that changes in deer behaviour could be as important as lethal effects, and that fewer wolves may be needed than indicated by predator–prey modelling to have significant positive impacts on ecosystems in the Scottish Highlands. Understanding the relative likely contributions of both lethal and nonlethal effects in the Scottish context will be challenging because nonlethal impacts result from an interaction between deer behaviour in response to wolf predation and particular landscapes and ecosystem features. While a full reintroduction may be far off, research must begin in the near term. There would be considerable scientific merit in establishing a large, controlled experiment (for example on an island or in a fenced area) in the Scottish Highlands to examine the relative lethal and nonlethal effects of wolves on deer and ecosystem restoration. In this paper, a long-term pathway for scientific research to provide sound ecological evidence to inform future decision-makers is proposed.

Interference competition between gray wolves and coyotes in Yellowstone National Park

Factors influencing the outcome of interspecific interactions between sympatric carnivores, along with population-level consequences, are not clearly understood. The reintroduction of gray wolves ( Canis lupus L., 1758) to Yellowstone National Park provides a rare opportunity to study interactions with coyotes ( Canis latrans Say, 1823), which had lived in the absence of wolves for &gt;60 years. We evaluated direct interactions between wolves and coyotes to identify factors influencing the outcomes of interspecific interactions and describe the context and degree of competition and coexistence. Using radio-collared wolves, we documented 337 wolf–coyote interactions from 1995 to 2007. The majority (75%) of interactions occurred at ungulate-carcass sites. Wolves initiated the majority of encounters (85%), generally outnumbered coyotes (39%), and dominated (91%) most interactions. Wolves typically (79%) chased coyotes without physical contact; however, 25 interactions (7%) resulted in a coyote death. Interactions decreased over time, suggesting coyote adaptation or a decline in coyote density. In the majority (80%) of fatal interactions, wolves outnumbered coyotes. However, wolves did not outnumber coyotes in interactions (n = 18) where coyotes chased or attacked/harassed wolves. Our results suggest that wolves are the dominant canid, group size may influence the outcome of interactions, and coyotes must benefit from the access to carrion at wolf-killed carcasses.

Evidence for top predator control of a grazing ecosystem

The importance of top predators in controlling ecological processes in large, intact ecosystems is unclear. In grasslands that support abundant ungulates, top–down control by predators may be particularly important, because of the tight biogeochemical linkages of ungulate prey with plants and soil microbes. Here, I examined the effects of the recent reintroduction of the gray wolf Canis lupus on ecosystem processes in Yellowstone National Park, where herds of grazing ungulates previously have been shown to stimulate several processes, including soil net nitrogen (N) mineralization. Rates of ungulate grazing intensity and soil net N mineralization were compared before and after wolf reintroduction in grasslands ranging five‐fold in aboveground production. Grazing intensity and grassland net N mineralization declined after wolf reintroduction, a likely partial function of fewer ungulates; wolf predation has been one of several factors implicated in causing the decline in Yellowstone ungulates. In addition, the spatial pattern of grazing and net N mineralization changed after reintroduction. A shift in the spatial patterns of grazer‐associated processes is consistent with a growing body of work indicating that wolves have changed habitat use patterns of ungulates in Yellowstone National Park. These findings suggest widespread wolf effects on ungulate prey, plants, and microbial activity that have spatially reorganized grassland energy and nutrient dynamics in Yellowstone Park.

Recovering Riparian Plant Communities with Wolves in Northern Yellowstone, U.S.A.

Gray wolves (Canis lupus) were extirpated from Yellowstone National Park in the 1920s. The ensuing seven decades marked a period when wild ungulates, principally Elk (Cervus elaphus), extensively used woody browse species in the upper Gallatin and northern winter ranges, thus limiting the capability of establishing plants to grow more than 100 cm in height. Following the reintroduction of wolves in the mid-1990s, we evaluated patterns of woody browse species recovery within riparian areas of these winter ranges. Measurements indicated that cottonwood (Populus spp.) recruitment (growth of seedlings/sprouts into tall saplings and trees) was occurring for the first time in several decades. A spatially patchy increase in the heights of young willow (Salix sp.) and cottonwood in the upper Gallatin and northern winter ranges, respectively, was also found within riparian transects comprising nearly 20 km in total length. Within some transects, heights of woody species have begun to exceed 200 cm (the approximate upper browse level of Elk). Results are consistent with the reestablishment of a tri-level trophic cascade involving wolves, ungulates, and riparian vegetation. We additionally present conceptual models of vegetation recovery, illustrating differences in plant height responses to behaviorally and density-mediated trophic cascades. Northern Yellowstone’s “experiment in time,” whereby wolves were removed and then reintroduced, provides new insights regarding how top predators can influence the structure and biodiversity of terrestrial ecosystems. Restoration ecologists and policymakers should consider the potential benefits of large predators as an option for helping restore degraded ecosystems.

Recoupling fire and aspen recruitment after wolf reintroduction in Yellowstone National Park, USA

We report on the recent growth of upland aspen ( Populus tremuloides Michx.) thickets in northwestern Yellowstone National Park, USA following wolf ( Canis lupus L.) reintroduction in 1995. We compared aspen growth patterns in an area burned by the 1988 fires to aspen growth patterns in an adjacent unburned area. Elk ( Cervus elaphus L.) are the principal ungulates that use this area to meet foraging needs. Within a 2 m × 6 m belt transect established in each aspen thicket, we measured aspen densities and recorded annual browsing and height information on the three tallest post-1988 aspen stems. We found greater densities ( p < 0.01) in the burned area relative to the unburned area. A decline in the percentage of stems browsed in the burned area began in 1997, with no measured browsing occurring since 2001. In contrast, the percentage of stems browsed in the unburned area began declining in 2002, with 41% of stems still being browsed in 2004. We hypothesize that the combined effect of fire and a subsequent decrease in herbivory following wolf reintroduction facilitated aspen growth. We further propose that, in addition to any changes in elk density in recent years, a recoupling of fire with increased predation risk from wolves may create a positive feedback loop that improves aspen recruitment.

Safe from the Wolf: Biosecurity, Biodiversity, and Competing Philosophies of Nature

By using the example of the reintroduction of wolves to the southern French Alps, this paper explores the competing ‘philosophies of nature’ that are revealed when agendas of biodiversity enhancement and protection conflict with notions of biosecurity. Tracing the shifting status of wolves as threat and hazard to emblems of reconstituted naturality, I argue that the reintroduction of wolves disturbs notions of both biodiversity and biosecurity, making unified strategies of management increasingly difficult and problematic. More significantly, the reintroduction of these classically ‘wild’ predators into seminatural and domesticated spaces challenges otherwise simplistic classifications not only of wild and domestic but also of human and nonhuman.