1. Gray Wolf Population’s Effect on Deer Population in Northern Minnesota
Gloria Angell
Environmental Studies Major
St. Cloud State University
St. Cloud, MN 56301
Abstract: In 2007, the Gray wolf was downgraded from endangered species to threatened
species in Minnesota. Since then the Gray wolf population has continued to grow. Since the Gray
wolf has no real predators in the area the continued growth of the gray wolf has some
agriculturalists and hunters worried that their growth will continue undisturbed until they become
a problem. The objective is to generate a model using STELLA to determine if the current
population trend will continue and if the wolf population will disturb the deer population in
Minnesota.
Introduction
“Who’s afraid of the big bad wolf?” Answer: everyone. The wolf has a had an extreme
amount of bad publicity in the past. Everyone has heard countless children’s stories that paint the
wolf as the bad guy or watched movies or read books that involve a wolf terrorizing somebody.
All of this negative propaganda coupled with the wolf’s main source of food being large game is
largely to blame for the wolves near extinction. In 1849 a wolf bounty was put into effect which
gave people $3 for every wolf carcass they brought in. This bounty grew over the next century to
$35 in 1965 when the bounty ended. However, by this time the wolf population had dwindled to
less than 750 wolves in just the northeast corner of Minnesota and it was still legal to hunt and
trap wolves. Then in 1974 wolves were listed on the endangered species list in Minnesota and
were finally allowed to repopulate Minnesota.
Minnesota is currently the only state in America to have down listed the wolf from
endangered species to threatened species. Today there are about 3,000 wolves in Minnesota
alone. In order to ensure that the wolf doesn’t become an endangered species again, Minnesota
has put into effect a wolf management plan. The wolf management plan regulates Population
Monitoring, Population Management, Public Safety, Wolf Damage Management, Enforcement,
Information and Education, Research and Staffing. Through this regulation Minnesota hopes to
stabilize the wolf population in coming years. The average male gray wolves weigh 79 pounds
and are anywhere from 4.3 to 6.6 ft from nose to the tip of the tail. They are also sexually
dimorphic with female wolves generally being 20% than the average male. They travel in pacts
of anywhere from 2-8 wolves and generally mate for life. They can run at speeds of 35 miles per
hour and jump 12 feet.
Deer hunting is a much honored tradition in Minnesota. It began as any other type of
hunting, as a means of feeding ones family, and has continued as a much celebrated past time.
Deer hunting occurs every fall and last for a few weeks. The average hunter spends five days
afield during Minnesota’s firearms deer season and last year’s total deer harvest was 222,000, the
eighth highest on record. In total, 832,860 deer hunting licenses and permits (all types) were sold
in 2008 with 98 percent of deer licenses are sold to Minnesota residents. A male whitetail deer
2. generally weighs between 130 to 300 pounds. The female (doe) usually weighs from 90 to 200
pounds. Length ranges from 62 to 87 inches, including the tail, and the shoulder height is 32 to
40 inches. In order for this cherished past time to continue it’s important to keep the deer
population in check. Currently there are 1,113,000 deer in MN, according to DNR estimates.
Last year wolves killed an estimated 43,000 deer which is an average of 15 deer per wolf per
year.
Methods
The population model was created using STELLA software. All of the
information used in the model was found on the internet using various websites and statistics.
Figure 1 and 2 are the original model. Graph 1 represents the deer and wolf populations over a
fifty year span. Figure three is the equations that were used to make the models. The model is
split up into two sectors in order to make it easier to understand, Wolf population and Deer
population. The first sector is wolf population and is made up of one stock containing the total
wolf population in MN with the initial population starting at 3,000. There are two flows
connected to the stock, births leading in and deaths leading out. There are three converters
connected to the birth flow including female wolves, births per female and pup survival rates.
The female wolf converter is based on the percentage of female wolves that are of reproductive
age. The births per female is made up of the female wolf population multiplied by 2 to account
for the average litter size a wolf has. The pup survival rate is based on the percentage of pups
that survive past 10 months which is about 50% (elyminnesota.com). There is just one converter
connected to the death flow, natural deaths. This is the only converter included because it is
currently illegal to hunt or trap wolves in MN and there isn’t very much data regarding other
wolf deaths.
The second sector is a model of the deer population in Minnesota. It contains one stock of
the total deer population with the initial deer population starting at 1,113,000. Connected to the
stock are two flows, deer births, leading in, and deer deaths, leading out. There is just one
converter connected to the deer births flow, female deer. The deer deaths flow has 4 converters
connected to it. They are: car accidents, hunting, deaths due to humans and natural death. The car
accidents converter is taken from the average of car accidents involving deer in MN (MN DNR).
The hunting converter is the average percentage of deer killed by hunters a year
(elyminnesota.com). The car accident and hunting converters are added together to form the
deaths due to humans converter. The natural deaths converter is the average amount of deer that
die due natural deaths a year. The goal of this model was to be able to sustain the amount of
wolves and deer together.
The next model (Figure 3) was designed to determine if the number of wolves, left
uncontrolled, would affect the deer population. The wolf population model is the same as above
except there is an additional converter attached to wolf deaths. It’s called the starvation converter
and it is linked between wolf death’s and total deer population. If the deer population drops
below 500,000 then 10% of the wolves will die, if the deer population drops below 250,000 then
20% of the deer will die, and if the deer population becomes 0 then 90% of the wolves will die.
The deer population model has an additional converter and a ghost of the wolf population. The
converter is called death by wolf and uses the wolf ghost to account for the number of deer killed
3. each year per wolf. It multiplies the number of wolves at any time by 15, which is the number of
deer killed yearly per wolf (MN DNR). Then it is added to the natural deaths and human caused
deaths to make up the total amount of deer deaths a year.
Figure 1
Figure 2
7. The total deer population and wolf population over a fifty year period is shown in graph
2. The total number of deer and wolf deaths over a fifty year period is shown in Graph 3.As it
shows in graph 2 the wolf population began at 3,000 wolves and by the end of the 50 year time
period dropped below 100. The deer population began at 1,113,000 deer and by the end of the
fifty years was about 300,000. The equations for figure 1 are listed in table and the equations for
figure 2 are listed in table 2. The results of the model turned out to be more extreme than what
was expected. While the growth and death patterns are very close to what was expected, the
numbers grew and dropped at pretty extreme degrees.
Discussion
The model can’t take everything into account so it isn’t an exact representation of what
will happen over the coming fifty years. One short coming is that within the next five years
people will be able to begin hunting and trapping wolves on a limited basis. Since this hasn’t
started yet, no data was found on how many wolves affect per year. This could drastically change
the model and account for any over abundance of wolves that occurs.
An additional inaccuracy in the model was the deer births expected every year. While it
was possible to find statistics regarding how many fawns were born a year, it was much more
difficult to find an accurate statistic for the expected survival rate of a fawn. For this step an
estimate was used instead of actual data. The deer population that was used in this model was the
total amount of deer in MN, while the wolf population is only located in one small section in
northeast MN. In order for this model to be more accurate the data found should be centralized to
the same area.
This model would be a helpful tool in considering how to further protect both deer and
wolf populations. However it could be more accurate if more data could be collected from
different sections in Minnesota. This way people could identify what is working or not working
for each individual section of MN regarding both wolf and deer populations.
Works Cited
8. MN DNR, (2002, November 8). Car Deer Accidents. Retrieved April 25th, 2010 from the MN
DNR website: http://www.dnr.state.mn.us/radiobite/script_023.html
Timberjay, (2006). Deer Population At Record Levels. Retrieved April 26th, 2010 from the Ely
Minnesota website:
https://www.elyminnesota.com/index.php?option=com_content&view=article&id=53:de
er-population-at-record-levels&catid=22:nature-articles&Itemid=100
Jensen, A. L. and Miller, D.H. (2000, November 14). Age structured matrix predation model for
the dynamics of wolf and deer populations. Retrieved April 25th, 2010 from
ScienceDirect website:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBS-43N738T-
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Mech, David L. and Nelson, Michael E. (2000, March) Do Wolves Affect White-Tailed Buck
Harvest In Northeastern Minnesota. Retrieved April 28th , 2010 from Minnesotans for
Sustainability website:
http://www.mnforsustain.org/wolf_mech_and_nelson_wolves_deer_harvest.htm
