Gray Wolf Population’s Effect on Deer Population in Northern Minnesota

Gloria AngellEnvironmental Studies Major

St. Cloud State UniversitySt. 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

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

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

Graph 1

Figure 3

Graph 2

Graph 3

Table 1

Table 2

Results

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.

DiscussionThe 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

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-

K&_user=1822408&_coverDate=07%2F01%2F2001&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1313189565&_rerunOrigin=google&_acct=C000054574&_version=1&_urlVersion=0&_userid=1822408&md5=91b0185964c058166f283119fb53a5bf

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