Modeling the Black Bear Population

 Tom Bulka Northern High School Accident, MD Susan Ragan Maryland Virtual High School of Science and Mathematics Silver Spring, MD Managing wildlife populations is often a controversial topic. When deer populations exceed the carrying capacity of a suburban area, residents see the deer roaming in their backyards eating their prized ornamental plantings. Road kill becomes more prevalent as the deer cross highways in search of mates and food. And yet, deer-hunting is often problematic out of concern for human safety and animal cruelty. Now, imagine living in western Maryland in the foothills of the Appalachian Mountains and having too many black bears roaming around. That was the situation in 1995 when Tom Bulka asked his computer programming class to design a computer model that would determine if a hunting season for black bear should be reinstated. Using a variety of resources, the students created a model in the STELLATM programming language and presented their results to the state DNR office. Although nothing happened immediately, nine years later Maryland issued permits for the hunting of 30 black bears in Western Maryland. The story below explains how Tom's class developed their model.
 The outcome of the students' work is illustrated by the graph below, which illustrates the projected adult bear population forty years from now based on no hunting (graph 1), a hunting quota of 5 bear per year (graph 2), and a hunting quota of 10 bear per year (graph 3). The model diagram shows that the student took into account that most bears do not reach adulthood until they are three years old, there are different survival rates for different ages of cubs, and migration rates vary by age. One of the limitations of the model is that there is no provision made for habitat stress nor the increasing encroachment of humans into bear territories.

 General Facts about Maryland Black Bears In 1956 there were only approximately 12 bears in the state. In 1991, the population was estimated to be between 165 and 200. The number being used most often in 1995 was 200. The majority of Maryland bears live west of Cumberland. Some bears make their way to Maryland from other states. When these bears are captured, they are brought to western Maryland. This amounts to 1 bear every 2 to 3 years. Bears have large territories and will move across state lines. There has never been a direct restocking program in the state of Maryland. However, in the late 70's, Pennsylvania stocked areas of southwestern Pennsylvania, and many of these bears migrated to western Maryland. In the mid-80's, West Virginia modified its hunting law so that there was more pressure on male bears and less on females. This increased the number of bears in West Virginia, some of whom made their way into western Maryland. Bears average 3 cubs per litter. Most females breed around 3 years of age; however, 10% or less will breed at 2 years of age. The bears who breed at age 3 are four years old at the time they give birth. There is a two year time period between litters, unless the female loses all of her litter, in which case she will breed again the following year. The loss of an entire litter happens about 1 out of 7 or 8 litters. The ratio of male to female is approximately 60:40. Less than 10% of mature bears die each year. This is generally due to vehicular accidents and illegal poaching, not disease. There is a 50% mortality for first year cubs. Only 30% of cubs reach maturity. Of tagged bears recovered in 1994, 19 were found out of state and 11 were found in state.

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