DEER: PREDATION OR STARVATIONNAME:

In 1970 the deer population of an island forest reserve of about 518 Km2 in size was about 2,000 animals. Although the island had excellent vegetation for feeding, the food supply obviously had limits. The forest management personnel feared that overgrazing might lead to mass starvation of the deer and depletion of the vegetation on the island. Because the area was too remote for hunters, the wild life service decided to bring in natural predators to control the deer population. It was hoped that, eventually, natural predation would maintain a stable deer population and at the same time improve the quality of the heard by eliminating the weaker deer. In 1971, 10 wolves were flown to the island. The results of this natural predator program are presented on the chart below.

YEAR / WOLF POPULATION / DEER POPULATION / DEER BIRTHS / DEATH BY PREDATION / DEATH BY STARVATION / POPULATION CHANGE
1971 / 10 / 2,000 / 800 / 400 / 100 / +300
1972 / 12 / 2,300 / 920 / 480 / 240 / +200
1973 / 16 / 2,500 / 1,000 / 640 / 500 / -140
1974 / 22 / 2,360 / 944 / 880 / 180 / -116
1975 / 28 / 2,244 / 996 / 1,120 / 26 / -150
1976 / 24 / 2,094 / 836 / 960 / 2 / -126
1977 / 21 / 1,968 / 788 / 840 / 0 / -52
1978 / 18 / 1,916 / 766 / 720 / 0 / +46
1979 / 19 / 1,952 / 780 / 760 / 0 / +20
1980 / 19 / 1,972 / 790 / 760 / 0 / +30

QUESTIONS: Answer on a separate paper.

  1. Plot the deer population and the wolf population. Graph both populations on the same graph. NOTE: you will have to use two different scales for each population on the vertical axis. Set up your scales so that the deer line and the wolf line cross.
  2. In the 2nd sentence above we are told the food supply “obviously” had limits. Why is this so?
  3. Why did the researchers only introduce 10 wolves to the island in 1971? Would 20 have been a better starting number for the wolves?
  4. Why did the wolf population decline after 1975?
  5. Why did so many deer starve in 1973? What would have happened if the wolves were not there?
  6. The deer population is controlled by the wolves? Is the wolf population controlled by the deer? Explain your answer.
  7. What other population on the island controls both the wolf (indirectly) and the deer (directly)?
  8. What is your estimate of the carrying capacity of the deer on this island? The wolves? Why?
  9. Does your graph in #1 follow the pattern of a predator/prey graph?
  10. Plot a survivorship curve from the deer census of 1982 below. Age is on the horizontal axis and number of deer on the vertical. When is the population changing the most? What is the most dangerous age for a deer on the island?

AGE / # OF DEER
0-1 / 860
1-2 / 345
2-3 / 262
3-4 / 168
4-5 / 105
5-6 / 88
6-7 / 68
7-8 / 56
8-9 / 42
9-10 / 6
Total / 2000