The Wolves of Yellowstone National Park
A chronicle about keystone species extinction and ecological restoration
The gray wolf (Canis lupus) originally occupied all terrestrial habitats in North America above 20 ° N latitude, but during the 1900–1930 period, there was a deliberate extermination campaign to prevent livestock predation that practically wiped out the species from the United States by 1960 [1].
Perceptions about wolves in North America during the 18th and 19th centuries weren’t good at all [2]. To the pioneer American, the wolf was despised as emblematic of the wilderness and was considered both, a perceived threat to personal safety and livestock and an impediment to progress and civilization.
Certain animals such as wolves, rattlesnakes, cougars (Felis concolor), coyotes (Canis latrans), and lynx (Lynx canadensis) were seen as “vermin”, “murderers” or “gangsters”, and their elimination was perceived as progress [2].
However, beginning in the late 1950s and 1960s, several long-term studies eventually portrayed wolves as something different than “wanton beasts”. These studies aided a change in public attitudes about the environment that eventually cleared the way for the Endangered Species Act (ESA).
In 1973, the gray wolf was officially listed as an endangered species that should be restored [3].
The reintroduction of wolves in Yellowstone National Park
Wolves were present in Yellowstone National Park (YNP) at the time it was established in 1872, but they were eradicated in 1926 [4].
Even after a new awareness and appreciation of wildlife emerged at the beginning of the 20th century, predators continued to bear this historical stigma, and therefore, the reintroduction of wolves could not occur until several decades after the ESA.
The elk (Cervus elaphus) population began to rise following carnivore removal and over the next few years, environmental conditions at the YNP started to decline drastically.
The elk were multiplying inside the park and deciduous, woody species such as aspen and cottonwood suffered from overgrazing that had impacts on the entire ecosystem.
The growing concern about soil erosion and plant death resulted in the agency’s control of elk in the early 1930s. Elk control prevented further degradation but didn’t improve its overall condition.
By 1968, the increase in the elk population spawned a renewed debate about restoring wolves.
Environmental groups began to push to restore wolves and create strongly competing human values, but wolf restoration was always controversial since its eradication was locally perceived as a successful solution to livestock depredation. The controversy lasted for decades [4].
Ultimately, and despite litigation from both pro-wolf (wanting more legal protection) and anti-wolf groups (wanting no action), 66 wolves were captured in Canada, and 10 in Montana, and transported into Idaho and the YNP in 1995 and 1996.
Ecological impacts of top predators in the Yellowstone National Park ecosystem
From an ecological perspective, it was important to restore wolves to the YNP because they are keystone predators.
Top predators have a central role in the functioning of ecosystems and the maintenance of local biodiversity because they regulate prey populations and restrict smaller predators. This, in turn, allows a greater number of different species in an ecosystem to coexist at the same time [5].
Top predators usually are keystone species because they tend to have a disproportionately large effect on their ecosystem relative to its abundance (or biomass). It is particularly important to conserve keystone species because their extinction can lead to dramatic changes in natural systems [6].
Wolves indirectly affect the presence, abundance, and productivity of a wide array of species in the YNP because they directly regulate opportunist or predominant species such as elk and coyotes.
The decline in the elk population resulted in changes in flora, most specifically willows, cottonwoods, and aspens along the fringes of heavily timbered areas. This also has facilitated the recovery of beavers (Castor canadensis) in the YNP (another species that humans decimated in the 1800s).
After wolves were removed from the park, competition for willow (the preferred food, and construction material of beavers) with elk became intense [6]. Although beavers had been protected since the early 1920s and beaver reintroduction efforts were underway, competitive pressure from the elks suppressed its recovery [8].
The presence of wolves seems to have diminished the pressure of elk on stands of willow, and consequently, the beaver population could rise again.
The renewed presence of beavers in the ecosystem had substantial effects on hydrological ecosystem processes. Beaver dams counter erosion and create new ponds and marsh habitats for different species like otters, mink, wading birds, waterfowl, fish, and amphibians [9].
Wolves also diminished the coyote population, which in turn benefited other smaller predators, rodents, and birds of prey. Together, these changes alter plant communities and therefore, can potentially modify the water cycle and other ecosystem processes.
Finally, the carcasses produced by the wolves provide a food resource to scavengers [1]. Almost every wolf kill also attracts a wide array of animals, including (but not limited to): magpies, bald eagles, golden eagles, ravens, wolverines, grizzly bears, black bears, jays, and martens [1,4].
Yes, this story sounds like an alternative version of Disney’s Lion King “Circle Of Life”.
Perhaps the Lion King is exploring a hypothetical case where lions regulate the hyena population and allow other species to coexist (in a Shakespearean way).
The reintroduction of wolves was controversial, and it was a complex process that involved politics, economics, ecology, and society. In the end, it is not only about preserving a single species; it’s about preserving ecological function because we directly depend on it to survive.
Today there are still debates about the ecological role and conservation status of wolves in the United States [10, 11, 12, 13], but that is a topic for another Medium story.
If you want to know more about the reintroduction of wolves in Yellowstone, check out these links [4, 14] and this video [15].
Let me know your opinion in the comments.
If you enjoy reading stories like these and want to support me as a writer, consider signing up to become a Medium member.
See also:
