CHECKS AND BALANCES 5 OVERVIEW Students become managers of a herd of animals in a paper-pencil, discussionbased activity. BACKGROUND White Tailed Deer White-tailed deer have always been a part of the forest community in Pennsylvania. Their numbers and their affects on Pennsylvania s forests have varied. Although there is no way to know for sure, it is estimated that when Europeans came to Pennsylvania, deer density was somewhere between 5 15 deer per square mile. Deer were hunted by the Native Americans and later the European settlers. They hunted the deer for meat as well as for their hides. During the heaviest logging years in Pennsylvania, deer were hunted particularly hard in order to supply meat for logging camps. Hunting was unrestricted and deer meat was in high demand. By the late l890s deer were all but extirpated from Pennsylvania. The Pennsylvania Game Commission was established in 1895. Its primary responsibility was to protect the few deer that remained. A bucks only law was passed in l907. A few years later a hunting license law was enacted in order to raise money. Some of the money raised from the license fees was used to purchase and restock deer in Pennsylvania. In addition to deer being nearly extirpated, so were many of the predators of the deer. Once laws were established to protect the deer, the lack of natural predators allowed deer numbers to increase rapidly. In addition, the vast acreage of recently cut forests provided optimal deer forage. Deer densities went from nearly zero just before l900 to 40 deer per square mile by l930. In just over 30 years Pennsylvania went from a state with almost no deer, to a state with far too many deer. Their population levels have remained high in many parts of Pennsylvania. Most resource managers agree that ideally deer densities should not exceed 20 deer per square mile. When they do, a variety of negative changes occur in the forest community. The change in forest plants affects a change in the animal species present. Since the shrub and ground layer is nearly eliminated, favorable habitat for wildlife species such as grouse, rabbits, turkey and various other mammals and birds is reduced. Researchers in Pennsylvania found that at deer densities over 20 per square mile, habitat for songbirds that nest from the ground to about 25 feet above the ground had been greatly reduced. Some species are no longer found at all in the forest community. Researchers also found that the abundance of songbirds in general (regardless of nesting preference) was reduced by about 20 percent. Excessive browsing by deer is the primary factor responsible for regeneration failures after harvesting. Stands that do regenerate successfully usually contain large numbers of advance seedlings before cutting and do not have a high number of competing plants, such as ferns and grasses. If the numbers of deer are high enough, the deer can suppress and/or destroy advance regeneration of trees (those seedlings already present when the stand is cut), as well as new seedlings that develop after harvesting. Perhaps the most critical issue facing our forests is how to ensure the renewal of healthy and productive forested ecosystems. Our forests are dependent on natural regeneration for their existence. In many areas of Pennsylvania the forest floor is nearly devoid of small tree seedlings that may be critical if a forest is to renew itself. Many factors may inhibit natural forest regeneration, including poor seed production, competing vegetation, insects and diseases. The white-tailed deer has been recognized as a key factor in the diminishment of forest regeneration. As a result, forests have not adequately regenerated to acceptable biological communicates in many parts of the GRADE LEVELS: Grades 6 10 OBJECTIVES: Students will (1) evaluate hypothetical wildlife management decisions and (2) identify at least four factors that can affect the size of a wildlife population. PENNSYLVANIA PROPOSED ENVIRONMENT & ECOLOGY STANDARDS ADDRESSED: 4.7.7 A. Describe diversity of plants and animals in ecosystems. B. Explain how species of living organisms adapt to their environment. C. Explain natural and human actions in relation to the loss of species. 4.8.7 A. Describe how the development of civilization relates to the environment. C. Explain how human activities may affect local, regional and national environments. 4.9.7 A. Explain the role of environmental laws and regulations. 4.7.10 A. Explain the significance of diversity in ecosystems. B. Explain how structure, function and behavior of plants and animals affect their ability to survive. C. Identify and explain why adaptations can lead to specialization. 4.8.10 A. Analyze how society s needs relate to the sustainability of natural resources. C. Analyze how human activities may cause changes in an ecosystem. 4.9.10 A. Explain why environmental laws and regulations are developed and enacted. ESTIMATED DURATION: One to two 45-minute periods MATERIALS NEEDED: Paper and pencils; card sheets; dice one per student Checks and Balances 45
Commonwealth following natural and human-caused disturbances (Penn s Woods, p.9). The impacts of high numbers of deer are not limited to our forest ecosystems. Agricultural crop damage, damage to garden and landscaping plants, and deer-vehicle collisions also increase with higher numbers of deer. In addition, it is thought that the increase in deer population has likely contributed to the spread of Lyme Disease since deer are a host of the tick that transmits the bacterium causing Lyme Disease in humans. Various methods have been tried to protect the forest from over-browsing by deer including fencing, fertilization (to stimulate rapid height growth in seedlings) and other methods. While some of these methods can be somewhat effective, they are too costly to apply to large forest communities. Deer feed heavily on the woody twigs and leaves within their reach. In time, the forest structure is substantially altered. Browse lines devoid of vegetation become evident from the ground level to the height deer are able to reach while feeding (about 6 feet or 2 meters). In forests where deer densities exceed 20 per square mile, the biodiversity of the forest community is negatively affected. There is a decrease in species richness (the number of species present), a decrease in species abundance (the number of individuals present) and an alteration of species composition with regard to wildflowers, shrubs, and tree seedlings. These forests often move toward dense fern cover. Since deer prefer not to eat ferns, these low, dense plants grow thickly and block out much of the light that seedlings and other plants need to grow. PROCEDURES 1. Each student is asked to be the manager of a white-tailed deer (or other animal) population. The carrying capacity of the habitat is 100 animals. The point of the activity is to end up with a viable population after nine rounds, simulating nine years. If at any time the student s population drops to less than 10 or rises to more than 200 individual animals, that student no longer has a viable herd and watches the other students until the conclusion of the activity. 2. Each student has a beginning population of 100 animals. Separate the cards into three decks for a total of 36 cards: a condition deck (18 cards), a reproduction deck (9 cards) and a management deck (9 cards). Shuffle the cards within each deck. (See instructions for making cards at the end of this activity.) Explain that cards will be drawn in the following sequence: condition card, reproduction card, condition card, management card. This sequence of draw will be repeated, each repetition representing an annual cycle (the students may think of each draw as representing a different season, e.g., autumn, winter, spring, summer). As each card is drawn it is read aloud to the entire class. Each student then rolls his or her die and follows the instructions on the card to determine his or her herd population s new size. Some computations will result in fractions; numbers may be rounded to the nearest whole. NOTE: Students may object to the use of dice to determine the impact of decisions made for wildlife management purposes. Their concerns are appropriate; wildlife management is based on more than the chance elements reflected in the use of dice. However, chance has its impacts as well, as in the case of weather conditions in a given year, food supply, etc. Encourage students to discuss and consider what is realistic and what is unrealistic about the impact of dice in this activity encouraging the recognition that wildlife management is far more complex than can be represented through this activity. 3. Wrap up the activity with a class discussion. Include topics such as: identify and describe what appeared to be the impacts of the condition, reproduction and management card; given one of the objectives of this activity to evaluate hypothetical management decisions what seemed to be the benefits and/or liabilities, if any, of management decisions made? Did populations managed under different strategies by different students show different trends? How do these compare? Would students manage differently if given a second chance? What aspects of this activity seemed realistic? Which didn t? What are examples of ways that habitat can be 46 Checks and Balances
improved? Short term? Long term? Is human management of wildlife populations necessary? Beneficial? Why or why not? For people? For the animals? EXTENSION OR VARIATION Add a monetary aspect to the above activity. Students allowing for hunting might have more available revenue for projects like habitat enhancement based on income from sales of hunting licenses. Other expenses might include salaries of wildlife managers, funds for research, feeding animals in severe conditions, relocation, etc. ASSESSMENT Have students name four factors that can affect the size of a wildlife population. explain what might be meant by the phrase some wildlife managers have said that wildlife management involves more management of people than wildlife. Instructions for making cards Make the following cards, according to three categories: Reproduction Cards, Condition Cards, and Management Cards. There are 36 cards in total. The number in parentheses indicates how many of each card should be made. NOTE: the number of cards and the suggestions for numerical manipulations, e.g., three times the roll, are relatively arbitrary. They are designed for students to recognize that a number of diverse factors can affect wildlife; the numerical weight should not be interpreted literally. As the cards are read aloud, be certain to note differences in decreasing or increasing herd size by percentage or by number. (After using these cards once, students may want to experiment with making additional cards, or changing these cards. Students may also want to make additional complete sets of cards for use by small groups or individual students.) NOTE CONCERNING REPRODUCTION CARDS: The rate of reproduction is designed to vary with population density. The method of determining your population s rate of reproduction at a particular population size is derived from a number of assumptions. One of them is that carrying capacity is 100 individuals. As your population drops below 100, the potential rate of reproduction increases reaching a peak at just above 50 individuals. The effect mimics the potential for rapid population growth many herbivore populations can exhibit when population levels are well below carrying capacity; in other words, food resources are readily available for reproduction effort, given that other environmental factors prove favorable. Below 10 individuals, reproduction is not allowed, reflecting severe reduction in reproductive activity observed at very low population levels because of, for example, imbalance sex ratios, the inability to find suitable mates, or the disruption of social and mating systems. As the population grows above 100 individuals, the reproduction rate steadily decreases reflecting the increasing activity of limiting factors as the population exceeds carrying capacity. Adapted from Project Wild, Council for Environmental Education, 1996, Checks and Balances. Checks and Balances 47
REPRODUCTION Reproduction Card Average Year (6) This has been an average reproduction year. Increase your herd by (100/your current population size) times three times your roll, if your current population is over 50 individuals. If your population is between 50 and 10, increase your population by three If your population is under 10, don t reproduce. REPRODUCTION Reproduction Card Excellent Year (3) This has been an excellent reproduction year. Increase your herd by (100/your current population size) times five times your roll, if your current population is over 50 individuals. If your population is between 50 and 10, increase your population by the number equal to five times your roll. If your population is under 10, you may not reproduce. Weather Card (2) has had a serious negative impact on the survival of the herd. Decrease your herd by the percentage equal to five Habitat Alteration Card (2) _ what) has occurred, altering critical habitat. Increase or decrease (students choose which before rolling die) herd by the percentage equal to three Weather Card (2) has had a dramatic positive impact on the survival of the herd. Increase your herd by the percentage equal to five Habitat Improvement Card (1) _ what) has occurred, improving critical habitat. Increase herd by five Habitat Destruction Card (2) has occurred, destroying critical habitat. Decrease herd size by the number five Research Card (1) what) research has been successfully accomplished. Increase or decrease (students choose which before rolling the die) herd by two times your roll. Predator Card (1) Predation has occurred, affecting the herd size. Decrease herd size by the percentage equal to your roll. Law Enforcement Card (1) what) law enforcement activities have protected the herd against illegal actions like poaching. Increase herd by the percentage equal to two Habitat Degradation Card (4) (Students need to specify what) has occurred, damaging critical habitat. Decrease herd by the number equal to three times your roll. Education Card (1) what) education activities have led to increased understanding of wildlife and habitat. Increase or decrease (students choose which before rolling the die) herd by the percentage equal to two times your roll, or by two 48 Checks and Balances
Disease Card (1) Disease has struck the herd. Decrease herd by the percentage equal to your roll. Habitat Acquisition Card (1) Habitat acquisition has increased the area of available and suitable habitat. Increase herd size by five Habitat Loss Card (5) (Students need to specify what) has resulted in a loss of critical habitat for the herd. Decrease herd by the number equal to five Hunting Card (1) A request for a hunting season has been made. Do you wish to allow hunting in your area? If yes, decrease your herd by the percentage equal to five If no, record no change in the size of your herd. Poaching Card (1) Poaching illegal killing of animals has reduced the size of the herd. Decrease herd by the number equal to two Habitat Restoration Card (1) what) has occurred, restoring critical habitat. Increase herd by the percentage equal to five Checks and Balances 49