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The National Park Service Created

The National Park Service, created in 1916, is a federal agency of the United States that helps manage and preserve national monuments, parks and a variety of species found within its land. Yellowstone National Park, located in Wyoming and Montana, is home to gray wolves (Canis lupus), one of the most crucial keystone species in an ecosystem. Gray wolves are natural wildlife managers, by regulating prey species, allowing other species of wildlife to flourish in healthy populations. Gray wolves were exterminated out of Yellowstone park by the early 40’s and their absence resulted in the prevalence and abundance of other wildlife to fluctuate out of control, resulting in unhealthy ecosystems throughout the park. The reintroduction of Canis lupus, Gray Wolves to Yellowstone National Park was crucial to regaining healthy ecosystems, evidently seen through the trophic cascade that helped regain natural management which regulated overpopulated species and helped return long-term stability to the park.

Gray Wolves have a unique history within Yellowstone National Park, unlike any other wildlife species that has resided within the park. Yellowstone park was established in 1872, however illegal poaching occurred up into the 1880’s, the slaughter of many large game animals threatened multiple species of wildlife including deer, antelope, moose bison and wolves (Yellowstone National Park, 1990). The westward expansion at the time brought humans and their livestock into the direct contact with the wolves. As management, predator control through poisoning was used to eradicate the wolves and help protect domestic livestock. “Poison played a major role in the eradication of the wolf in the west” (Fitzgerald,2015). In Montana alone, roughly eighty-one thousand wolves were killed from the early 1880’s until 1913. The future of wolves in Yellowstone was looking bleak. In 1933, the National Park Service policy stated, “no native predator shall be destroyed on account of its normal utilization of any other park animal.” (Yellowstone National Park,1990) Unfortunately for the wolves this law came too late, by the 1930’s 136 wolves, the last pack, were killed in Yellowstone (National Park Service, 2017). The gray wolf was listed as an endangered species across the United States, except in Minnesota, in 1978 (Grooms, 2005). The future for gray wolves was beginning to look up.

The reintroduction of the gray wolves into Yellowstone was a slow and controversial process that took twenty years of studies and planning to complete. Following their enlistment on the endangered species act, seventeen years later action begun to help reintroduce the wolves. In 1992, congress directed the U.S Fish and Wildlife Service (USFWS), the National Park Service (NPS) and the US Forest Service (USFS) to develop an Environmental Impact Statement (EIS) that covered the reintroduction of gray wolves to Yellowstone. Once the EIS was completed it received more than one-hundred sixty thousand public comments, which at the time was the largest quantity of comments on any federal proposal on record. (Smith, 1996) Between 1995 and 1997, thirty-one wolves were relocated from Canada to Yellowstone. The reintroduction of the wolves was done strategically. The original thirty-one wolves were placed in pens for ten weeks, then slowly released into the wild under close monitoring. The wolves began to breed and by the end of 1995 there were 21 wolves composing three packs; by the end of 1996 there were 51 wolves composing nine packs (Smith, 1996). In 1997, ten wolves were relocated from northeastern Montana to Yellowstone. These would be the last of the wolves reintroduced into Yellowstone National Park. After the three reintroductions of wolves into the park, the wolves began to prey on primarily elk, although moose, deer and a few other large game species were also preyed upon.

A decade later after the reintroduction of the gray wolves, the species began to flourish. In 2008, the wolf populations in Montana, Wyoming and Idaho were removed from the endangered species list.

How wolves in Yellowstone have changed the ecosystem, more specifically caused a trophic cascade is an ever-evolving story. As Yellowstone’s keystone species, the wolves have a disproportionately large responsibility when compared to other species. As an apex predator, the hunting patterns and diets of wolves are key to understanding the basic stepping stones of the trophic cascade they caused.

Wolves as apex predators, also known as top predators, are predators at the top of their food chain. In terms of a trophic pyramid, it is key to know that wolves occupy the highest trophic level. Wolves hunt and live in packs of six to ten animals and have carnivorous diets. ”There are just two or three good hunters in the pack,” (Robbins, 2003).Gray wolves located in Yellowstone are known to roam large distances, expanding their hunting grounds. It is possible for them to travel twelve miles in one day (National Geographic, 2018). Wolves are social animals, meaning they cooperate with one another to hunt and kill their preferred prey. Gray wolves consume a variety of foods within their diets. Larger animals such as deer, elk and moose are preferred, but gray wolves are also known for eating smaller mammals, as well as lizards, snakes, birds and in some cases, fruit. When wolf packs are successful, wolves do not eat in moderation. A single wolf may consume up to twenty pounds of meat in one sitting (National Geographic, 2018).

Elk make up ninety-two percent of wolves’ winter diet. As well as a primary food source for wolves, elk are an essential food source for grizzly bears. Prior to the wolf reintroduction, grizzly populations were rising in Yellowstone. With the reintroduction of the wolves, the predation of elk available for the grizzlies declined (Dobson,2014). Grizzly populations began to decrease. Elk populations began highly threatened after the 1995 reintroduction of wolves. With the double threat of bears and wolves, elk in Yellowstone began to decrease dramatically. Before the reintroduction of the gray wolf, elk populations in the park were around 17,000 in the winter of 1995; by the winter of 2004, after the reintroduction, elk populations decreased nearly fifty percent to 8,335.

In the wolves seventy-year absence, elk became accustom to grazing willows along stream banks without predation risk. Dude to the increase in elk populations, in combination with their new grazing locations, elk contributed to the decrease of many species, including beavers, songbirds and deciduous vegetation the elk grazed on. Changes in willow and aspen growth along river banks changed occurred in the late 1990’s after the reintroduction of the wolves. Increased height in aspen stands along river banks have been associated with the reintroduction of the wolves (Smith, 2003). With new vegetation growing and flourishing subtle changes in river and stream morphology lead to important changes. Aspen and willows, species that were once grazed by the elk, continued to grow. Due to the wolves’ reintroduction, elk no longer grazed in open areas that they used to previously (Gonchar,2014). With these new plant species growing, the rivers and streams began to have less erosion than they did previously; wolves brought back healthy stream and river ecosystems.

With river morphology changing, and vegetation no longer being over grazed, species that were once endangered due to the elks overgrazing began to appear once more and flourish. With aspen and willow trees beginning to grow, a variety of songbirds increased in Yellowstone because their habitat was growing once more. Beavers, a primary consumer just like the elk returned as well. Beavers consume trees such as willow, aspen and cottonwood; when the elk were no longer overgrazing the beaver’s food source, they were able to increase in population size once more. Beavers, being ecosystem engineers, they natural create niches for other species. After their comeback, the beaver’s dams provided habitats for otters, muskrats, and ducks. Species of fish, reptiles and amphibians were even able to bounce back because of the beaver’s dams (Steyn,2014).

Wolves helped regulate elk populations and bring back healthy ecosystems to rivers, but they also caused subtle changes in Yellowstone that are not discussed as frequently. Wolves, which are competitors with the coyotes living in Yellowstone, began to wipe out small numbers of coyotes. The drop-in coyote population lead to an increase in mice and rabbitat populations (Steyn,2014.) Increased mice and rabbitat numbers lead to more eagles, foxes, badgers and weasels. While the bear population did decrease originally due to the wolves consuming elk, the wolves ended up helping the bears as well. More berries began to grow along the river banks, providing the bears a food source that was not available prior. Yellowstone’s biodiversity was changed dramatically after the reintroduction of the gray wolves.

The reintroduction of gray wolves to Yellowstone National Park caused a trophic cascade starting with an apex predator, helping regenerate healthy ecosystems, and wildlife populations within the park. With the reintroduction of the keystone species, wolves naturally helped manage the park in ways no human ever could. Regulating elk populations lead to a domino effect that resulted in the increase of an abundance of wildlife species, as well as allowing overgrazed vegetation to grow. Without the wolves, Yellowstone would be lacking the biodiversity is has today, and provides the world a great example of how removing one species can change an entire ecosystem in under a century.