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White-Tailed Deer Population Model for the Adirondack Ecosystem

Introduction

In addition to being one of the most well-known and well-studied animals in the Adirondacks, the white-tailed deer is an important component of the Adirondack ecosystem. The biology, behavior and population dynamics of the white-tailed deer all reflect its integral ties with an often inhospitable Adirondack environment.

The Adirondack deer model is designed primarily to be a learning tool. Through use of the model, one will become familiar with the many factors influencing Adirondack deer populations and will develop an understanding and appreciation of the intricacy, variability and uncertainty that exists in the Adirondack white-tailed deer's world. The model also allows the user to see the effects of alternative deer management practices and harvest strategies on the virtually managed deer herd.

The model moves the simulated Adirondack deer population through the four seasons of the year, exposing it to the influences of an always changing and challenging Adirondack environment. The user can set up scenarios to explore the influences of different factors or varying combinations of factors on the deer population (a guide is provided in the model to assist in this process). The model will output the resulting deer population (seasonally or annually over the time period specified) based upon the input information.

The Adirondack deer model is the result of nearly 50 years of research on Adirondack deer at the SUNY College of Environmental Science and Forestry 's Adirondack Ecological Center in Newcomb, NY. The key components, environmental conditions and data driving this model directly reflect what we have learned about the biology, behavior and population responses of white-tailed deer in the Adirondack ecosystem over this extended period of time.

Although the learning experiences associated with using the Adirondack deer model have universal applicability, the actual outputs generated by the model are most appropriate to the dynamics of deer populations inhabiting northern forested environments where agricultural influences are minimal.

Instructions

In order to use the deer population model, the file must be downloaded onto the user's computer, along with a run-time version of STELLA. The run-time version of STELLA allows the user to view and use the model, as well as change values of the variables. However, the user cannot change the structure of the model nor save an altered version. Also included is an Excel file, directly linked to the deer model, which provides extra graphics.

1. Download a copy (right mouse click, "save Link as" ) of The White-tailed Deer Population Model (or download Zip version)

2. Download a run-time version (click on "Stella Demo Kit" on the HPS site) of

3. Open STELLA and then the population model. When opening deer.xls, click on yes in the linking dialogue box which should appear upon opening.

To learn more about STELLA and High Performance Systems, Inc., click on the image to go to their home page.

Guide for Using the Adirondack Deer Model

The following sequence of questions is designed as a guide for exploring the wide range of factors affecting Adirondack deer population dynamics. In order for these simulations to be most informative, start with the initial spring deer population shown below. We will call this population the "experimental" population for our simulations. On a 25 square mile management unit, this population represents a deer density of approximately 10 deer / sq. mile.

Experimental Initial Spring Population:

Female adults = 110

Male adults = 70

Female yearlings = 35

Male yearlings = 35

The Effects of Winter

What is the trend in the deer population when the number of days of winter equals 25, 75 or 120?

25 days:     up     down     even
75 days:     up     down     even
120 days:   up     down     even

Note: For each run use the experimental spring population values; habitat = 1.0; predation = 1.0; adult and yearling male hunting = 5.0; female hunting = 1.0. Hold all input factors constant for runs #2 & #3, except for days of winter. Before each run, you will have to set days of winter for each of the 10 years to the above values.

The Effects of Habitat Quality

How does improving habitat quality affect deer population growth?

habitat = 1.0, winter = 25: population trend =

up down even

habitat = 1.5, winter = 25: population growth =

faster slower

Note: Use the experimental spring population values; predation = 1.0; adult and yearling male hunting = 5.0; female hunting = 1.0. Run the model with habitat set at 1.0 and days of winter set at 25 for all years. Rerun the model with all values the same except change habitat quality to 1.5.

Can improving habitat quality offset the impact of a severe Adirondack winter?

yes no

habitat = 1.0, days of winter = 120: population trend =

up down even

habitat = 1.5, days of winter = 120: population trend =

up down even

Note: Repeat the above simulation using days of winter = 120 for all years.

The Effects of Predation

How does predation by black bears and coyotes affect Adirondack deer population growth over time?

reduces increases no effect

Note: For run #1, use the default values for all parameters. Rerun the model changing the predation value to 0 while holding all other values constant.

How does predation affect the length of time (# years) it takes for the deer population to recover from the impact of severe winters?

recovery period without predation =

_______ years

recovery period with predation =

_______ years

Note: Change the days of winter values to 25 for all years except year 2 and 3; set year 2 and 3 equal to 120 days. Set predation = 1.0 and set the initial population, all hunting parameters and habitat to the default values. Run the model. Then rerun the model with predation set at 0. After each run count the number of years it takes for the deer population to return to its year 2 (pre-severe winter) level.

On average, a severe winter occurs every 3-4 years in the central Adirondacks. Using what you have learned from the model so far, what effect could the combination of recurring severe winters and the influences of predation have on deer hunter success rates in this region?

A. minor ups and downs but generally increasing over time
B. periodic declines followed by prolonged periods of recovery
C. dramatic drop followed by a rapid and sustained recovery

The Effects of Harvesting Female Deer

How does the harvest of females effect the deer population?

reduce increase unchanged

Note: Run #1 - use the “experimental” deer population values; set days of winter to the default values; habitat = 1.0; predation = 1.0; adult and yearling male harvest = 5; female harvest = 1. Run #2 - hold all values the same except change female harvest to 9 (In run #1 you are harvesting 5% of the adult female deer; in run #2 45%).

Which harvest rate maintains a higher deer population level overall, 5% or 45%?

Which harvest rate allows for a faster recovery in the deer population after a severe winter, 5% or 45%?

How would the female harvest rate have to be adjusted in order to maintain the same deer population if predation rates doubled?

upward downward

How would the female harvest rate have to be adjusted in order to maintain the same deer population if habitat quality increased?

upward downward

The Effects of “Bucks Only” Hunting

How does a “ bucks only” hunting regulation effect deer population growth when compared with a hunting program that harvests both males and females?

increase decrease no effect

How does the sex ratio (# adult bucks vs. # adult does) in the fall deer population change over time under a “bucks only” hunting regulation?

What happens to the adult male population over time when the harvest of yearling males is increased?

up down unchanged

Note: Set up your own scenarios to determine the answers to these questions. Use the deer.xls file to view seasonal age and sex composition graphs.

Questions?

Contact Charlotte L. Demers at cdemers@esf.edu or 518-582-4551

Model developed by Richard W. Sage Jr., Associate Director, Adirondack Ecological Center, SUNY ESF

Model produced by Paulette Salmon, Technical Consultant

Acknowledgments: We extend our sincere appreciation to all the students and scientists at the Adirondack Ecological Center over the past 50 years who have added to the knowledge base used to develop this model. Also, a special thanks to Charlotte Demers for helping put this work on the web

Funding for model production provided through the Roosevelt Wild Life Program, SUNY College of Environmental Science and Forestry
Last updated: August 28, 2003

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