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The Ecological Impacts of Removing the Gray Wolf (Canis Lupus) from the Endangered Species List in the Yellowstone/ Idaho Area.
Adam Meyer
ENVS 190
13 May 2014
Canis lupus Credit: Gary Kramer / USFWS
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Table of Contents:
Acronym list:……………………………………………………………………………………………………………2
Abstract:…………………………………………………………………………………………………………………..3
Introduction:…………………………………………………………………………………………………………….3
Methods:…………………………………………………………………………………………………………………..9
Analysis:…………………………………………………………………………………………………………………...10
Discussion:……………………………………………………………………………………………………………….17
References:………………………………………………………………………………………………………………19
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Acronym list:
ESA: Endangered Species Act
NPS: National Park Service
USFWS: United States Fish & Wildlife
YNP: Yellowstone National Park
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Abstract:
The goal of this project is to evaluate the ecological impacts of removing the gray
wolf (Canis lupus) from the endangered species list in the Yellowstone/ Idaho area.
Removing a keystone species has proven detrimental to ecosystems. In June 2013, the
United States Fish & Wildlife [USFWS] has proposed to remove the gray wolf off the
endangered species list. This decision is backed with scientific research that has proven
that the gray wolf has grown outside their historic range and the reintroduction has proven
successful. As of now, the gray wolf is preying on a lot of livestock which is causing issues
with many livestock ranchers. Because of these reasons, the ranchers also want the gray
wolves delisted.
Introduction:
Gray wolves were eradicated from the Yellowstone/ Idaho area in the 1940-‐1970’s
(http://www.nps.gov/yell/naturescience/wolfrest.htm). After the recognition of the wolf
as a keystone species in the 1970’s, the United States added the gray wolf to the federal
endangered species list. Following the listing of the gray wolf, Yellowstone National Park
was in desperate need of a top predator to restore its ecosystem, and in the spring of 1995
the gray wolf was reintroduced to the park
(http://www.nps.gov/yell/naturescience/wolfrest.htm). After close to 20 years of careful
conservation practices, the gray wolf is now flourishing in the Yellowstone/ Idaho area.
Currently, the gray wolf is still protected under the federal Endangered Species Act. This
act protects the wolf from hunting and trapping; however, there are people that want the
gray wolf delisted in North America. After several comprehensive studies, it has been
determined that the gray wolf has outgrown its historic range and has proven the recovery
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methods effective. The USFWS has proposed to have the gray wolf delisted from the
endangered species list because of these reasons.
The gray wolf is a member of the dog family. Gray wolves are the ancient ancestors
to our domesticated dogs and are related to the coyote (Canis latrans) and several other
wild dog species. Like many other dog species the gray wolf is a pack hunter; however, it is
not uncommon for an individual wolf to break from a pack and form its own pack
(http://www.nps.gov/yell/naturescience/wolfinfo.htm). These individual wolves may
remain alone from days to years before they can find a mate. Although wolves are pack
hunters, an individual is still a highly efficient hunter. The gray wolf in most ecosystems is
the top predator. There are several populations of gray wolf; however this study focuses on
the Idaho/ Yellowstone population. The Yellowstone/ Idaho population of wolves is a
larger than average wolf; males weigh between 100-‐130 pounds and females weigh
between 80-‐110 pounds (http://www.nps.gov/yell/naturescience/wolves.htm). The
average life span of these wolves is 5 years; however, they can live up to 12 years in the
wild (http://www.nps.gov/yell/naturescience/wolves.htm). The average pack size in this
area is 2-‐11 individuals. The pack size varies under a number of conditions including food
availability, disease, wolf mortality from other packs, and poaching
(http://www.nps.gov/yell/naturescience/wolfinfo.htm). They mate in February and give
birth to average of five pups in April. Each pack has its own unique structure, with some
individuals being an alpha male or female and some members being subordinate
(http://www.nps.gov/yell/naturescience/wolves.htm). Each member has its role in the
pack. Packs mark their territory by urinating around the boundary and howling. A wolf
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caught crossing another wolf’s territory is most likely to be greeted with a fight
(http://www.nps.gov/yell/naturescience/wolves.htm).
The reason why the gray wolf is considered a keystone species is because of its role
as a top predator. In most ecosystems, a top predator is needed for the ecosystem to
function properly. Although the Yellowstone/ Idaho area does contain grizzly and black
bears, these bears cannot kill large prey such as elk or deer on a regular basis. The gray
wolf primarily feeds on ungulates where as a bear’s diet might contain berries and other
plants. By feeding on these ungulates, the gray wolf effectively controls these species from
over grazing an area. After making a kill, the wolves also contribute to several other species
that prey on the carcass (http://www.nps.gov/yell/naturescience/wolfinfo.htm). Unlike
mountain lions and grizzly bears, wolves abandon their prey after feeding on the carcass.
Abandoning the carcass leaves much needed meat for scavengers, which include the
coyote, bald eagle, golden eagle, grizzly bear, black bear, raven, magpie, and red fox
(http://www.nps.gov/yell/naturescience/wolfinfo.htm). This extra food source for
scavengers is essential in hard winters when other food sources are unavailable.
During the early 1800’s, the native people worshipped and idolized the wolf; man
and wolf lived harmoniously. That story would change however, westward expansion
brought settlers from the east. Many settlers staked out a claim in what is now Idaho,
Montana, and Wyoming (http://www.nps.gov/yell/naturescience/wolfrest.htm). These
settlers made a living however they could, and many of them chose livestock ranching as a
means to get ahead. Their livestock overgrazed many areas causing local wildlife to have a
shortage on food. This shortage would cause a ripple effect, local wildlife would soon starve
Meyer | 6 Figure 1: (Zmyj 1996)
and populations would drop. The wolves that would prey on the local wildlife would also
need to find a way to eat. It is believed that because the wolf is such an efficient hunter that
it invokes fear in us. This meant preying on the livestock that replaced the local wildlife.
Losing livestock to a predator was not
something taken lightly, and men would poison,
trap, and shoot any wolf that was viewed as a
threat (Zmyj 1996). “Between 1914 and 1926,
at least 136 wolves were killed in the park; by
the 1940s, wolf packs were rarely reported. By the mid-‐1900s, wolves had been almost
entirely eliminated from the 48 states
(http://www.nps.gov/yell/naturescience/wolfrest.htm)”. It was not only the wolf being
poisoned and trapped, any predator viewed as a threat to livestock or “more desirable”
wildlife like elk or deer were also hunted. This meant the death of many bears, coyotes,
foxes, and cougars (Wilmers 2003).
The 1950’s & 1960’s marked a harsh time for the wolves; more accurate rifles,
"In those days we had never heard of passing up a chance to kill a wolf. In a second we were pumping lead into the pack, but with more excitement than accuracy…" ~Aldo Leopold
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stronger poisons, and more lethal traps were available to hunters and ranchers9 (Zmyj
1996). [Figure 1, shows some of inhumane methods some of the ranchers used to capture/
eradicate the wolves]. During this time, white men set out on a mission to eradicate the
wolf and create a predator free ecosystem. The U.S. government even implemented a
nationwide wolf control policy. This wolf control policy was highly effective; an intensive
survey conducted in the 1970s found no evidence of a wolf population in Yellowstone
(http://www.nps.gov/yell/naturescience/wolfrest.htm).
This hunting free-‐ for-‐ all would soon come to a halt in 1973 when the Endangered
Species Act [ESA] was passed (Perry 2012). The ESA would protect any plant or animal
facing extinction. Under the Act a “threated” or “endangered” species will have a significant
amount of its habitat protected in order for the species to fully recover. Because of the gray
wolves low numbers, they were listed as an endangered species, and any person caught
poisoning, trapping, or shooting the wolves for no reason would have been penalized
heavily. Two decades after the passing of the ESA marked a controversial time in U.S.
history, and on March 21, 1995, gray wolves were reintroduced back into Yellowstone
National Park (http://www.nps.gov/yell/naturescience/wolfrest.htm). This decision
would prove to be a heavily debated one through the years. Today, many farmers and
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ranchers still do not agree with the reintroduction of the wolves.
Figure 2: http://www.fws.gov/mountain-‐prairie/species/mammals/wolf/annualrpt13/figures/FINAL_Fig7a_Num-‐BP-‐State_2013.pdf
[Figure 2, shows the population trend of the gray wolf from 1982-‐2013. This graph
emphasizes the dramatic population growth following the reintroduction of the wolves.]
Yellowstone
National Park [YNP]
was created as the
first national park in
1872. YNP expands
over 3,472 square
miles. The park
resides 96% in
Figure 3: Map of Yellowstone. Lonely Planet. (2009)
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Wyoming, 3% in Montana, and 1% in Idaho
(http://www.nps.gov/yell/planyourvisit/factsheet.htm). Yellowstone is home to many
species including threatened Canada lynx and grizzly bear, and the endangered gray wolf
(http://www.nps.gov/yell/planyourvisit/factsheet.htm). The history of the park states that
the gray wolves were in the park when it was created
(http://www.nps.gov/yell/naturescience/wolfrest.htm). United States created a
Yellowstone National Park Act of 1872. It states the Secretary of the Interior "shall provide
against the wanton destruction of the fish and game found within said Park
(http://www.nps.gov/yell/naturescience/wolfrest.htm)" Although the wolves resided in
the park, people viewed them as a “wanton destruction of the fish and game”, and the
eradication methods followed. These eradication methods would continue for nearly 200
years until the passing of ESA in 1973. During 1995 to 1997, Yellowstone was designated
as one of three recovery sites for the gray wolves and 41 wild wolves from Canada and
northwest Montana were released in YNP
(http://www.nps.gov/yell/naturescience/wolfrest.htm).
Methods:
The gray wolf is one of the most researched species in the world. I focused on the
research pertaining to the gray wolf as an important species to ecosystems. Many of these
studies compare what the Yellowstone/ Idaho area was like before the reintroduction of
the wolf to what the ecosystem is now, and how the gray wolf has enhanced the area. I will
be utilizing a meta-‐approach style to conduct this study. I will review the current studies
and literature on this topic.
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Analysis:
There have been several studies pertaining to the listing of the gray wolf as an
endangered species, one of which is an analysis conducted by Chris Woolston (2013). He
reviewed the decision of USFWS to delist the gray wolf from the endangered species list.
The USFWS argues that the gray wolf has outgrown its historic range and that the agency
needs to focus on the recovery of the Mexican gray wolf now (Woolston 2013). However,
many scientists and organizations believe that USFWS did not use proper researching
methods for their studies. Without proper research methods, these studies would be
incorrect. This was of particular interest because it shows the misconnection between
scientists and general public. The general public believes that all studies conducted by a
federal branch i.e. USFWS should be truthful and correct. Still many scientists speculate on
the correct population of Canis lupus. Another study conducted by Creel and Rotella (2010)
reviews the scientific justification of the 2009 delisting of the Rocky mountain population
of the gray wolf. The researchers believe that USFWS based their justification on many
social attitudes toward the wolves (Bruskotter et. al 2010). “In general, stakeholders calling
for reductions in wolf numbers are concerned about three issues: livestock losses, effects
on ungulates (particularly elk) and human safety. In 2008 and 2009, Northern Rocky
Mountain wolves were responsible for an average of 203 confirmed kills of cattle (from a
population of approximately 5.9 million cattle) and 538 confirmed kills of sheep (Creel and
Rotella 2010)”. These stakeholders have a huge influence in the law making in the
endangered species list. Creel and Rotella (2010) conclude that the USFWS should
reevaluate their decision and use accurate population surveys to determine if the gray wolf
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is in need of delisting. This study is of particular interest because it solidifies the
importance of “good science” when determining the need for a delisting of a species. Not
only is “good science” a necessity when it comes to delisting an endangered species, it is
severely important to be accurate in population estimates when the species that is in
consideration for delisting is also one of the keystone species of the ecosystem. Another
study conducted in 2009-‐2010 researchers (Ausband, Rich, and Glenn) used surveys from
hunters, howling and sign surveys to help predict wolf population in Idaho. The authors
emphasize the importance of using more than one survey method to improve the accuracy
of the study. The difficulties in
estimating a wolf population is
highlighted in this study, “Methods for
estimating the size of large carnivore
populations are financially and
logistically challenging (Ausband etal.
2014)”. These difficulties could lead to
inaccuracy which could misconstrue
population estimates (Ausband et al.
2014). Since the gray wolf population
is being evaluated for delisting, it is
essential that population estimate surveys are accurate. [Figure 4, shows a team of
researchers taking measurements and fitting a wolf for a radio collar. A lot of data
regarding the species is gathered this way (Smith et. al 2010)] .
Figure 4: Radio-‐collaring a wolf. http://www.nps.gov/yell/naturescience/upload/Wolf_AR_2011.pdf
Meyer | 12
Many other studies have been conducted regarding the wolf’s impacts on other
species. Researches Ripple, Beschta, and Fortin (2014) analyzed the secondary effects of
reintroducing wolves back into YNP. The researchers theorized that the threatened grizzly
bear would benefit from a lower elk population. Lower elk populations would decrease
forging from these ungulates and in turn have more berry-‐producing shrubs for the grizzly
bear to eat (Ripple et. al 2014). Their study on the impacts of ungulates on the threated
grizzly bear population was the first of its kind. Their research and finding were significant
to the importance of the gray wolf in the ecosystem. “We suggest researchers and policy
makers consider wolves, trophic interactions and competition from wild and domestic
ungulates when addressing research and management of grizzly bears (Ripple et. al 2014)”.
This study signifies the importance of the gray wolf on the threatened grizzly bear
population in the YNP. The grizzly bear and the elk are not the only species that the wolf
has had a major impact on. The coyote, one of the parks other canine species had a huge
population change after the reintroduction of the wolf. Before the wolf was reintroduced,
the coyote was largest canine species in the area (Merkle et. al 2009). The study conducted
by Merkle, Stahler, and Smith (2009) investigated the environmental impacts of the wolf on
the coyote. Before the reintroduction of the wolves, the coyotes were over populated.
Coyotes in that area preyed heavily on small mammals and birds (Merkle et. al 2009). This
created an imbalance on the ecosystem. The wolves were documented to kill 25 coyotes
and in 275 interactions wolves chased the coyotes (Merkle et. al 2009). This study suggests
the importance of the wolf to moderate the coyote’s population. By moderating the coyote’s
population, the wolves partially restored the ecosystem back to a natural state. Once again,
this study highlights the importance of the wolf as a keystone species. Not only are coyotes
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and grizzly bears affected by the wolf’s presence, but the endangered Canadian lynx as well.
Ripple, Wirsing, and Beschta (2011) studied the effects of the reintroduction of the wolves
on the endangered Canadian lynx population. The results of their study theorize that the
reintroduction of wolves will do two things, 1) bring the coyote population back to a
healthy population, which will in turn increase the snowshoe hare population. The
snowshoe hare is a primary food source for the lynx. And 2) bring the elk population back
to a healthy population, which will in turn increase the forging sites for the snowshoe hare
(Ripple et. al 2011). They emphasize the importance of little-‐considered trophic and
competitive interactions when attempting to recover an endangered carnivore such as the
lynx (Ripple et. al 2011). This means if more wolves equals less coyotes, then less coyotes
equals less competitive interactions, which in turn would lead to a rebounding lynx
population. This is another study affirming the importance of the wolf to the Yellowstone/
Idaho area. The data from this study helps solidify the need for the wolf in this ecosystem.
Not only do wolves create more prey for lynxes by reducing the number of coyotes, they
also create more carrion for other scavengers. Researchers Wilmers, C.C., and Crabtree
(2003) create an experiment looking at the carrion available to scavengers after the wolves
have made a kill. They conclude that in the presence of the wolf, more large animals are
killed and thus providing more carrion for scavengers. “By partially consuming their prey,
wolves subsidize scavengers with a high calorie resource that may be essential for
metabolic maintenance, growth and/or reproductive success (Wilmers et. al 2003)”.This
carrion is particularly important during winter months when food is scarce for scavengers,
thus creating a need for wolves. For example “Female grizzly bears with reliable high-‐
energy foods, for instance, have been shown to attain larger body size and have bigger litter
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sizes than their counterparts with less reliable and/or lower-‐calorie foods (Wilmers et. al
2003)”. As indicated above, the wolves have provided an essential resource for the threated
grizzly bear; however, not only the grizzly bear benefits from this resource, “increasing the
time over which carcasses are available during the winter, this carrion subsidy may
contribute significantly to the biodiversity of the region (Wilmers et. al 2003)”.
Many studies provided thus far have shown only the importance of the wolf to other
fauna. There have been significant amounts of studies conducted pertaining to the wolf and
its effects on plants. Scientists Beschta, R.L. and Ripple (2012) conducted several studies on
the berry-‐producing shrubs within
YNP’s northern ungulate winter
range. These studies were conducted
15 years after the gray wolves
reintroduction into the park, which
gave the plants ample time to
regrow. The studies have provided
evidence that the gray wolves
predation on the ungulates has
helped to restore berry-‐producing
shrubs stands to recover (Beschta et.
al 2012). The berry-‐producing
shrubs are not only beneficial to
ungulates but other species as well,
Figure 5: (Beschta et. al 2012)
Meyer | 15
and a fully recovered ecosystem is beneficial to all species. The importance and role of the
gray wolf in this ecosystem is highlighted in this study, and in figure 5 [the images show the
differences between the absence of ungulates in area (a) and the presence of ungulates in
an area (b). “Contrasting aspen sites in the northern range of Yellowstone (September
2010): (a) A riparian site that has experienced reduced ungulate browsing pressure in
recent years with resultant increases in the heights of serviceberry and chokecherry
(foreground) as well as increased aspen and mountain alder (Alnus incana) recruitment
(i.e., growth above browse level of elk; background) and (b) an upland site experiencing
continued high levels of ungulate browsing, no increased heights of berry-‐producing
shrubs, and no aspen recruitment. Note the two-‐tiered aspen stand structure comprising an
overstory of mature trees and an understory of young aspen; the missing intermediate
size/age classes occurred over multiple decades when elk herbivory, in the absence of
wolves, prevented aspen recruitment (Beschta et. al 2012)”]. Another study conducted by
Eisenber, Seager, and Hibbs (2013) evaluates the gray wolf and its importance to forest
ecology. This study and Beschta’s 2012 study show the importance of the wolf to forest
ecology. “Trophic cascades driven by apex predators via top-‐down effects have been
identified in ecosystems worldwide (Eisenberg et. al 2013)”. In this study it shows the
effects of the gray wolf on aspen communities. They conclude that the wolves have helped
the aspen groves back to a more natural state. They suggest “applying the precautionary
principle to create healthier, more resilient aspen forests would suggest conserving apex
predators, as feasible, where their ranges coincide with aspen (Eisenberg et. al 2013)”. In
conclusion, the wolves have helped the ecosystem rebound to a more natural state, thus
proving the importance of the wolf as a keystone species.
Meyer | 16
If the gray wolf were to be delisted nationwide, many states would open a hunting
season for the species. Many states that already have a recovered population have already
chosen to use a hunting season as a means of population control. There have already been
some studies on the effects of hunting on wolf populations. One of which, is the study
conducted by Creel and Rotella (2010). Their study shows some of the possible effects of
the delisting of the species. Creel and Rotella (2010) evaluate the impacts of an immediate
hunting season following the delisting of a population of gray wolves in 2009. Idaho and
Montana had a set 20% quota on population elimination, after the season a population
estimate determined that 37% of the population was killed during the year of the delisting.
This evidence is useful when determining the delisting of other wolf populations. If the
entire gray wolf population were to decrease by 37% that could prove detrimental to the
population. If wolves are to be kept on the endangered species list, alternative methods are
available for nuisance control of the wolf. Researches Hawley, Rossler, and Gehring (2013)
studied the likelihood of using electronic shock collars as a management tool for reducing
livestock losses caused by gray wolves. Electronic shock collars could help reduce
negativity towards wolves as well as livestock loss. This device would be an excellent non-‐
lethal management tool. These shock collars are expensive, but these collars would help
ranchers keep wolves off their property (Hawley et. al 2013).
A lot of money and effort has gone into the research of the gray wolves (Way and
Bruskotter 2012). USFWS now wants to shift their efforts to the recovery of the Mexican
wolf population in the Southwest. (http://www.fws.gov/home/wolfrecovery/). “The
Mexican wolf is the rarest subspecies of gray wolf in North America. Once common
throughout portions of the southwestern United States, the Mexican wolf was all but
Meyer | 17
eliminated from the wild by the 1970s
(http://www.fws.gov/southwest/es/mexicanwolf/)”. A mere 83 Mexican wolves roam the
wild today. This number is drastically less than the historic population number. This
subspecies is also an essential species to an ecosystem, and it has shared a similar story to
the gray wolf’s tragic history.
A higher Mexican wolf
population would be needed
for the ecosystem to regain
its natural state. [Figure 6,
shows the home range of the
Mexican gray wolf].
Discussion:
As a top predator and a keystone species, the gray wolf is an important asset to an
area. The results of this discussion should assess the implications of removing the gray wolf
from the endangered species list. I am hoping this research will help students become
familiar with the current issues associated with removing gray wolves from the
endangered species list. Aldo Leopold was an author and leading environmentalist. His
work has inspired many conservationists. Many of his ideas were formed from his work
with the wolf. Aldo was a ranger for USFWS and his job was to increase the deer population
for the hunters. USFWS believed that the best way to increase the population was to
eliminate the wolf and make a predator-‐free ecosystem. "I was young then, and full of
Figure 6: http://www.azgfd.gov/w_c/es/mexican_wolf.shtml
Meyer | 18
trigger-‐itch; I thought that because fewer wolves meant more deer, that no wolves would
mean hunters’ paradise." This belief held true to many scientists and hunters at the time.
This belief has carried on to many hunters and ranchers today. After his realization of his
impacts of removal of the wolf from the mountains he worked, he changed his beliefs and
redirected his career to obtain a more natural ecosystem. "I now suspect that just as a deer
herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer."
Just as Aldo once believed that a predator-‐free landscape was the solution to a flourishing
game population, we too have to change our misconceptions and negativity towards the
wolf. I believe the wolf is an essential species to the Yellowstone/ Idaho ecosystem because
of its impact in helping restore the ecosystem back its natural state. This quality makes the
gray wolf a keystone species to this area. Although there have been many studies
indicating the benefits of the wolf to this ecosystem, there have also been many biased
studies that have proven the wolf’s population higher than what it actually is. This higher
population estimate would lead to a higher hunting quota. An incorrect population
estimate could be detrimental to the wolf’s population (Ausband et al. 2014). I hope USFWS
will reevaluate their studies and methods they used to conduct their population estimates.
Meyer | 19
References:
1) Ausband, D.E., Rich, L.N., Glenn, E.M., Mitchell, M.S., Zager, P., Miller, D.A.W., Waits, L.P., Ackerman, B.B., and Mack, C.M. (2014). Monitoring gray wolf populations using multiple survey methods. Journal of Wildlife Management 78, 335-‐346.
2) Beschta, R.L., and Ripple, W.J. (2012). Berry-‐producing shrub characteristics
following wolf reintroduction in Yellowstone National Park. For. Ecol. Manage. 276, 132-‐138.
3) Bruskotter, J.T., Toman, E., Enzler, S.A., and Schmidt, R.H. (2010). Are Gray Wolves
Endangered in the Northern Rocky Mountains? A Role for Social Science in Listing Determinations. BioScience 60, 941-‐948.
4) Creel, S., and Rotella, J.J. (2010). Meta-‐Analysis of Relationships between Human
Offtake, Total Mortality and Population Dynamics of Gray Wolves (Canis lupus). Volume 5. pp. 1-‐7.
5) Eisenberg, C., Seager, S.T., and Hibbs, D.E. (2013). Wolf, elk, and aspen food web
relationships: Context and complexity. Forest Ecology & Management 299, 70-‐80.
6) Hawley, J.E., Rossler, S.T., Gehring, T.M., Schultz, R.N., Callahan, P.A., Clark, R., Cade, J., and Wydeven, A.P. (2013). Developing a New Shock-‐Collar Design for Safe and Efficient Use on Wild Wolves. Wildlife Society Bulletin 37, 416-‐422.
7) Merkle, J.A., Stahler, D.R., and Smith, D.W. (2009). Interference competition between
gray wolves and coyotes in Yellowstone National Park. Canadian Journal of Zoology 87, 56-‐63.
8) Perry, S. (2012). The Gray Wolf Delisting Rider and State Management Under the
Endangered Species Act. Ecology Law Quarterly 39, 439-‐473.
9) Ripple, W.J., Beschta, R.L., Fortin, J.K., and Robbins, C.T. (2014). Trophic cascades from wolves to grizzly bears in Yellowstone. Journal of Animal Ecology 83, 223-‐233.
Meyer | 20
10) Ripple, W.J., Wirsing, A.J., Beschta, R.L., and Buskirk, S.W. (2011). Can restoring wolves aid in lynx recovery? , Volume 35. pp. 514-‐518.
11) Smith, D.W., Bangs, E.E., Oakleaf, J.K., Mack, C., Fontaine, J., Boyd, D., Jimenez,
M., Pletscher, D.H., Niemeyer, C.C., Meier, T.J., et al. (2010). Survival of Colonizing Wolves in the Northern Rocky Mountains of the United States, 1982-‐2004. Journal of Wildlife Management 74, 620-‐634.
12) Way, J.G., and Bruskotter, J.T. (2012). Additional considerations for gray wolf
management after their removal from Endangered Species Act protections. Journal of Wildlife Management 76, 457-‐461.
13) Wilmers, C.C., Crabtree, R.L., Smith, D.W., Murphy, K.M., and Getz, W.M.
(2003). Trophic facilitation by introduced top predators: Grey wolf subsidies to scavengers in Yellowstone National Park. Journal of Animal Ecology 72, 909-‐916.
14) Woolston, C. (2013). Grey wolves left out in the cold. Nature 501, 143-‐144.
15) Zmyj, P.M. (1996). A FIGHT TO THE FINISH": THE EXTERMINATION OF THE
GRAY WOLF IN WYOMING, 1890-‐1930. Montana: The Magazine of Western History 46, 14-‐25.
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