Biology Case Study
Populations and Communities
Name
Date
Period
Using Predators to Manage Populations
In 1970, the deep population of an island forest reserve about 518 square kilometers in size was
about 2000 animals. Although the island has 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 and, 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
Year
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
Wolf
Population
10
12
16
22
28
24
21
18
19
19
Deer
Population
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
100
240
500
180
26
2
0
0
0
0
Population
Change
+300
+200
─140
─116
─150
─126
─52
+46
+20
+30
Questions
1.
On a separate sheet of paper, plot the fluctuations in the deer and wolf population on a graph for
the 10-year study period.
2.
Would it have been better for the ecosystem if more wolves had been introduced in 1971? Why?
3.
Explain why the wolf population declined after 1975.
4.
In which year was deer starvation greatest? From your data and knowledge of ecology, explain
why so many deer died.
2
5.
Predict what might have happened if hunters had been allowed to kill half of the wolf population
in 1974.
6.
Is wolf predation a limiting or a controlling factor on this reserve? What other factors control or
limit a deer population?
7.
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 populations?
8.
If the deer population is to remain steady at 2000 and the number of deer offspring is 1000 in
1981, how many deer would 25 wolves have to eat in a year?
Table 2
Age
0─1
1─2
2─3
3─4
4─5
9.
Number of Deer
860
345
262
168
105
Age
5─6
6─7
7─8
8─9
9─10
Number of Deer
88
68
56
42
6
From the data that describe the herd in 1980 (Table 2), plot a survivorship curve. Which stages
in the life of the deer have the highest mortality? Suggest environmental factors that might make
this so.
10. Use the data from 1980 (Table 2) to draw an age pyramid for the deer population. What
percentage of the population is fawns? Suppose the percentage of fawns was 65 percent.
What would that indicate about the growth of the herd? Would the population be increasing?
3
11. How could knowledge of survivorship curves and age pyramids aid in the management of the
herd population?