The Ecological Importance of the Gray Wolf and it’s Reintroduction to Colorado
Gray wolves, or Canis lupus, historically inhabited the state of Colorado until the mid-20th century, when hunters nearly annihilated the species from most of the lower 48 states. The historical range of the wolf once covered over two-thirds of the United States, yet today gray wolves only inhabit certain regions of Alaska, northern Michigan, northern Wisconsin, western Montana, northern Idaho, northeast Oregon, and the
Yellowstone
area of Wyoming. Wolves can thrive in a diversity of habitats from the tundra to woodlands, forests, grasslands and deserts if there are high enough densities of suitable prey. The gray wolf is now an extirpated species, meaning they no longer exist in their historical habitat, but still exist elsewhere. Gray wolves are listed as an Endangered species under the Endangered Species Act and are under management authority of the U.S Fish and Wildlife service. According to the IUCN Red List, the historical range of the grey wolf has been reduced primarily in developed areas of Europe, Asia, Mexico, and the United States by poisoning and hunting due to predation on livestock and concern for public safety. However, due to strong conservation efforts, the gray wolf has been reintroduced to some of its former habitat and as their populations increase, a ripple of environmental effects follow. Without enough natural predators in Colorado to maintain healthy population dynamics, populations of native ungulates have become so abundant they are harming vegetation and the equilibrium of many ecosystems. Predator-prey relationship dynamics are extremely important to the health of an ecosystem as they keep the populations of both species in balance. Ungulates have great impact on vegetative species and can influence the survival and abundance of birds and insects, and an overpopulated density of ungulates may even have influence on natural biogeochemical cycles, such as water and nitrogen cycles. Predators create stability in an ecosystem and are an essential part of maintaining healthy equilibrium in an environment. The management of Colorado's ungulate species relies on the reintroduction and management of the gray wolf and is critical in efforts to restore Colorado’s natural ecosystems and to establish ecological balance and abundance in the environment.
The gray wolf plays a vital role in the overall health and functioning of ecosystems. Once introduced to Yellowstone National Park in 1995 and 1996, the wolf population grew rapidly. At the time, the elk population was at an all-time high and provided a large supply of prey, which influenced wolf reproduction. Significant research and evidence suggests that elk changed their feeding habits in response to the presence of wolves, avoiding areas where they could be easily seen and ambushed. This allowed for the vegetation in riparian areas to recover and replenish itself. The research journal “Restoring Yellowstone’s Aspen with Wolves” by authors William Ripple and Robert Beschta displays photographs taken at a variety of locations which showed considerable recovery of aspen in areas where it was once overgrazed when elk were over-abundant. The article also includes demographics on the relationship between wolf populations, elk populations, the percentage of browsed aspen, and the mean aspen heights in Yellowstone’s northern range (515-519) to demonstrate that much of the aspen growth observed in riparian areas after the reintroduction of wolves appears to have been due to reduced browsing by elk. Although these riparian areas cover only a small area of the ecosystem, the park was witnessing the first significant growth of aspen in nearly half a century. More recent data, such as a study from Oregon State University College of Forestry, suggests that similar recoveries are being seen in cottonwoods and willows. Ripple and Beschta concluded that areas along streams became heavily browsed and eventually suppressed following the removal of wolves, apparently due to unhindered browsing by elk. However, after the reintroduction of wolves in 1996, browsing intensity on willows lessened in some areas and it was hypothesized that browsing reflects terrain developments, which then influence predation risk and consequently lower elk densities. This significant growth of vegetative species has led to an increase in the abundance and diversity of riparian bird species. All of this evidence highlights the importance of species interaction between predator and prey, and suggests that wolves have a strong top-down effect on the trophic structure of an ecosystem.
The presence of wolves may even help reduce the number of sick and/or injured individuals of a population, such as ungulates with chronic wasting disease (CWD). Thompson Hobbs (2006) developed a model that suggested that the presence of just 20 wolves would eradicate chronic wasting disease from elk in the Rocky Mountain National Park in two to three decades. His scholarly article “A Model Analysis of Effects of Wolf Predation on Prevalence of Chronic Wasting Disease in Elk Populations of Rocky Mountain National Park” uses a simple mathematical model to evaluate the potential for selective predation by wolves to reduce or eradicate chronic wasting disease in populations of elk in Rocky Mountain National Park. Hobbs demonstrates that increasing mortality rates in diseased populations can set back disease transmission and reduce disease prevalence. Increasing mortality rates slow the transmission of CWD by reducing the average life expectancy of infected individuals, which can flatten the time in which animals are infectious, thereby reducing the spread of infections. Hobbs demonstrates that if the number of new infections produced per infected individual is less than one, then the disease will eventually be eradicated from the population. The reintroduction of gray wolves affects the abundance, distribution, and behavior of other animals through interspecific interactions and will help manage disease control of other species.
Wolves strongly influence ecosystem components, such as structure and processes. More wolves generally results in fewer ungulates, which leads to greater plant biomass and diversity. Comparatively, fewer wolves results in more ungulates, which in turn reduces plant biomass and diversity and has echoed effects on food webs and trophic levels. Terrestrial ecosystems are naturally maintained and balanced by top-down effects, which directly influence prey and then descend down to lower trophic levels, and bottom-up effects which directly influence plant life, then ascend up the food chain. In ecosystems that support abundant populations of ungulates, top–down control by predators may be particularly important due to the biogeochemical linkages of ungulate prey with plants and soil microbes. Grazing intensity in ecosystems with high ungulate populations is much higher in comparison to other terrestrial ecosystems. Additionally, wolves influence the distribution, behavior, and foraging of the surviving ungulates, which also have effect on vegetative matter. For example, in Yellowstone National Park, reintroduced wolves created an “ecology of fear,” whereby elk reduce the amount of time they spend browsing on woody vegetation, allowing for replenishment of that vegetative species (Ripple and Beschta 2004). Yet, the effects of wolves go far beyond predator-prey-plant interactions. For example, wolf predation on ungulates influences the abundance and behavior of scavengers by providing them a source of carrion (Smith and Bangs 2009). Wolves can influence the abundance of other species as well and can reduce the abundance of coyotes, which directly influences other animal populations too.
Although many benefits are associated with the reintroduction of the gray wolf to Colorado, there are many factors to consider in such large scale conservation efforts. According to a case study concluded by Iowa State University on the reintroduction of the gray wolf to Yellowstone National Park, the costs of the reintroduction efforts to YNP in 1996 was $267,000 with seventeen gray wolves introduced that year. U.S Fish and Wildlife services stated that initial recovery costs were lower than predicted primarily because reintroduction objectives were met in 2 years rather than in the predicted 3-5 years. The cost of using wolves as an ecosystem stewardship tool should be carefully compared with other alternatives to reduce overpopulated ungulates and conserve ecosystems, such as fertility control, and building fences to exclude herbivores from vegetation. The U.S Fish and Wildlife services also say the gray wolf now roams free in nine states and is stable and healthy throughout its current range, therefore the success of this recovery started a proposal to remove all gray wolves from protection under the Endangered Species Act. Wolves are necessary not only to restore ecosystem health, but to encourage biodiversity conservation efforts. Small populations of wolves, even single packs, could be restored to relatively small natural areas for purposes of ecosystem restoration and stewardship. However, even with small scale efforts we must acknowledge the complications and challenges involved in such an effort, but also understand that the benefits could be substantial. In order for conservation efforts to be successful, we need to obtain an enhanced understanding of the ecological niche of the wolf, change public attitudes and perceptions, and provide an opportunity for wolf conservation and ecosystem restoration of Colorado’s Rocky Mountains.
Works Cited
A Model Analysis of Effects of Wolf Predation on Prevalence of Chronic Wasting Disease in Elk
Populations of Rocky Mountain National Park
www.researchgate.net/publication/2406158
87 A Model Analysis of Effects of Wolf Predation on Prevalence of Chronic Wasting
Disease in Elk Populations of Rocky Mountain National Park
Dobson, Andy P. “Yellowstone Wolves and the Forces That Structure Natural Systems.” PLoS
Biology, vol. 12, no. 12, 2014, doi:10.1371/journal.pbio.1002025
Hobbs, N. Thompson, and David J. Cooper. “11 Have Wolves Restored Riparian Willows in
Northern Yellowstone?” Yellowstones Wildlife in Transition,
doi:10.4159/harvard.9780674076419.c15
Licht, Daniel S., et al. “Using Small Populations of Wolves for Ecosystem Restoration and
Stewardship.” BioScience, vol. 60, no. 2, 2010, pp. 147–153. JSTOR,
www.jstor.org/stable/10.1525/bio.2010.60.2.9. Accessed 28 Apr. 2020
“Reintroduction of the Gray Wolf to Yellowstone National Park: A Case Study.” ISU Bioethics
Outreach--Gray Wolf in Yellowstone, www.bioethics.iastate.edu/classroom/graywolf.html.
Ripple, William J., and Robert L. Beschta. “Restoring Yellowstone’s Aspen with Wolves.”
Biological Conservation, vol. 138, no. 3-4, 2007, pp. 514–519.,
doi:10.1016/j.biocon.2007.05.006
Ripple, William J., and Robert L. Beschta. “Wolves, Elk, Willows, and Trophic Cascades in theUpper Gallatin Range of Southwestern Montana, USA.” Forest Ecology andManagement, vol. 200, no. 1-3, 2004, pp. 161–181., doi:10.1016/j.foreco.2004.06.017
Service, U.S. Fish and Wildlife. “Wolves of the Northern Rocky Mountains: U.S. Fish and
Wildlife Service.” Official Web Page of the U S Fish and Wildlife Service,
www.fws.gov/mountain-prairie/es/species/mammals/wolf/annualrpt01/2001report.htm.
Smith, Douglas W., and Edward E. Bangs. “Reintroduction of Wolves to Yellowstone National
Park: History, Values and Ecosystem Restoration.” Reintroduction of Top-Order Predators,
pp. 92–125., doi:10.1002/9781444312034.ch5