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Name_______________ Graphing

Deer: Predation or Starvation?

In 1970 the deer population of an island forest reserve about 518 square kilometers in size was about 2,000 animals. Although the island had excellent vegetation for feeding, the food supply obviously had limits. Thus the forest management personnel feared that overgrazing might lead to mass starvation. Since the area was too remote for hunters, the wildlife service decided to bring in natural predators to control the deer population. It was hoped that, eventually, natural predation would eliminate the weakest deer, thereby preventing the herd from becoming too large while, at the same time, increasing the quality of the herd. In 1971, 10 wolves were flown into the island. The results of this natural predator program are presented in Table 1.

Table 1: Natural Predator Program Results Year 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 Wolf pop. 10 12 16 22 28 24 21 18 19 19 Deer pop. 2000 2300 2500 2360 2244 2094 1968 1916 1952 1972 Deer offspring 800 920 1000 944 996 836 788 766 780 790 Predation 400 480 640 880 1120 960 840 720 760 760 Starvation Pop. changes 100 +300 240 +200 500 -140 180 -116 26 -150 2 -126 0 -52 0 +46 0 +20 0 +30

Questions:

1. Plot the fluctuations in the deer and wolf population on a graph for the tenyear study period. (Don!t forget to label your x and y axis and give your graph a title).

2. Would it have been better for the ecosystem if more wolves had been introduced in 1971? Why or why not?

3. In which year was deer starvation greatest?

From your data and knowledge of ecology, explain why so many deer died.

4. Does the number of wolves limit or control the number of deer in this ecosystem?

Explain your answer.

5. How does the size of the deer population influence the number of wolves on the island?

If no hunting is allowed, what natural mechanisms will control the wolf population?

6. Which stages in the life of the deer have the highest mortality?

Suggest environmental factors which might make this so.

7. Draw a line graph which compares the number of individuals in the deer population versus their age. This is called an "Age Structure" graph. (Be sure to label your X and Y axis and give your graph a title).

Age 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 Total

Number of deer in the population 860 345 262 168 105 88 68 56 42 6 2000

8. How could knowledge of an age structure graph be helpful in determining the management of herd populations?

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