Bears will attempt to chase the wolves away, and are usually successful. Many other animals—from eagles to invertebrates—consume the remains. One fascinating discovery involves coat color. About half of wolves in Yellowstone are dark black in color, with the other half mostly gray coats. The presence of black coats was due to a single gene a beta defensin gene termed CBD or the K-locus , with all black coated individuals carrying a mutation linked to this coat color - a mutation believed to have originated in domestic dogs of the Old World.
The origin of the K-locus in wolves likely came from hybridization between dogs and wolves in northwest North America within the last 7, years as early humans brought domestic dogs across the Bering Land Bridge.
In Yellowstone, this discovery set the stage for studies that explored the link between coat color, reproduction, survival, and behavior. It was found that the K-locus gene is involved in immune function in addition to causing black coat color, suggesting an additional role in pathogen defense.
For example, black wolves have greater survivorship during distemper outbreaks. Another study found gray wolves to be more aggressive than black colored wolves during territorial conflict, as well as have higher reproductive success. During breeding season, there is also greater mate choice between opposite color male and female pairs compared to same colored pairs.
Together, these data suggest fitness trade-offs between gray and black coat color, evidence for the maintenance of the black coat color in the population.
That ratio reversed from to , indicating changes in prey vulnerability and availability. Although elk is still the primary prey, bison has become an increasingly important food source for wolves. While there is some predation on bison of all age classes, the majority of the consumption comes from scavenging winter-killed prey or bison dying from injuries sustained during breeding season.
The discovery of these changes emphasizes the importance of long-term monitoring to understand predator-prey dynamics. Changes in wolf predation patterns and impacts on prey species like elk are inextricably linked to other factors, such as other predators, management of ungulates outside the park, and weather e. Weather patterns influence forage quality and availability, ultimately impacting elk nutritional condition. Consequently, changes in prey selection and kill rates through time result from complex interactions among these factors.
Current National Park Service NPS research focusses on the relative factors driving wolf predation over the past 25 years. Occupying just 10 percent of the park, it is winter range for the biggest elk herd in Yellowstone and is arguably the most carnivore-rich area in North America. Early management of predators caused dynamic changes to the ecosystem. The reappearance of carnivores on the landscape has had significant and sometimes unexpected impacts on the resident grazers and their habitat.
In the first years following wolf restoration, the population grew rapidly as the newly formed packs spread out to establish territories with sufficient prey.
The wolves have expanded their population and range, and now are found throughout the GYE. Disease periodically kills a number of pups and old adults. Outbreaks of canine distemper occurred in , , and In , distemper killed twothirds of the pups within the park. Infectious canine hepatitis, canine parvovirus, and bordetella have also have been confirmed among Yellowstone wolves, but their effects on mortality are unknown.
Sarcoptic mange, an infection caused by the mite Sarcoptes scabiei , reached epidemic proportions among northern range wolves in By the end of , the epidemic had mostly subsided; however, the infection is still present at lower prevalences throughout the park. Wolf packs are highly territorial and communicate with neighboring packs by scent-marking and howling.
Occasionally packs encounter each other, and these interactions are typically aggressive. Larger packs often defeat smaller groups, unless the small group has more old adult or adult male members.
Sixty-five percent of collared wolves are ultimately killed by rival packs. Most of the decrease has been in packs on the northern range, where it has been attributed primarily to the decline in the elk population and available territory. Canine distemper and sarcoptic mange have also been factors in the population decline. Each year, park researchers capture a small proportion of wolves and fit them with radio tracking and GPS collars.
These collars enable researchers to gather data on an individual, and also monitor the population as a whole to see how wolves are affecting other animals and plants within the park. Groups included breeding adults and younger wolves one to two years old. Each wolf was radio-collared as it was captured in Canada. While temporarily penned, the wolves experienced minimal human contact. Approximately twice a week, they were fed elk, deer, moose, or bison that had died in and around the park.
They were guarded by law enforcement rangers who minimized how much the wolves saw humans. The pen sites and surrounding areas were closed to visitation and marked to prevent unauthorized entry. Biologists checked on the welfare of wolves twice each week, using telemetry or visual observation while placing food in the pens. Although five years of reintroductions were predicted, no transplants occurred after because of the early success of the reintroductions.
Some people expressed concern about wolves becoming habituated to humans while in the acclimation pens. However, wolves typically avoid human contact. Confinement was also a negative experience for them and reinforced their dislike of human presence.
Preliminary data from studies indicate that wolf recovery will likely lead to greater biodiversity throughout the GYE. Wolves have preyed primarily on elk, and these carcasses have provided food to a wide variety of other animals, especially scavenging species.
Wolves are increasingly preying on bison, especially in late winter. Grizzly bears have usurped wolf kills almost at will, contrary to predictions and observations from other areas where the two species occur. Wolf kills, then, provide an important resource for bears in low-food years. Aggression toward coyotes initially decreased the number of coyotes inside wolf territories, which may have benefited other smaller predators, rodents, and birds of prey.
So far, data suggest wolves are contributing to decreased numbers of elk calves surviving to adulthood and decreased survival of adult elk. Wolves may also be affecting where and how elk use the habitat. Some of these effects were predictable but were based on research in relatively simple systems of one to two predator and prey species.
Such is not the case in Yellowstone, where four other large predators black bears, grizzly bears, coyotes, and cougars prey on elk—and people hunt the elk outside the park.
Thus, interactions of wolves with elk and other ungulates have created a new degree of complexity that makes it difficult to project long-term population trends. The effect of wolf recovery on the dynamics of northern Yellowstone elk cannot be generalized to other elk populations in the GYE.
The effects depend on complex factors including elk densities, abundance of other predators, presence of alternative ungulate prey, winter severity, and—outside the park—land ownership, human harvest, livestock depredations, and human-caused wolf deaths.
A coalition of natural resource professionals and scientists representing federal and state agencies, conservation organizations and foundations, academia, and land owners is collaborating on a comparative research program involving three additional wolf-ungulate systems in the western portion of the GYE.
Results to date indicate the effects of wolf predation on elk population dynamics range from substantial to quite modest. Several lawsuits were filed to stop the restoration on a variety of grounds. These suits were consolidated, and in December , the judge found that the wolf reintroduction program in Yellowstone and central Idaho violated the intent of section 10 j of the Endangered Species Act because there was a lack of geographic separation between fully protected wolves already existing in Montana and the reintroduction areas in which special rules for wolf management apply.
The Justice Department appealed the case, and in January the decision was reversed. The biological requirements for removing the wolf from the endangered species list have been achieved: at least wolves and three consecutive years of at least 30 breeding pairs across three recovery areas. The FWS approved wolf management plans in Idaho and Montana, and in it delisted wolves in these two states and in Yellowstone and Grand Teton national parks.
Several environmental groups sued to stop the delisting, however. They successfully argued that the Wyoming wolf management plan was flawed and that genetic connectivity had not been established between the GYE and the other recovery areas. A court decision required the wolf to be listed again as an endangered species. A legal challenge resulted in the Northern Rocky Mountain wolf population being returned to the federal endangered species list.
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