IV. Predator Prey Relationships
Assume that the population of one herbivore species in your ecosystem is roughly 2000 animals. Your ecosystem has
excellent vegetation for feeding, but the food supply obviously has limits. Thus, the 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 herbivore population. It was hoped that natural predation would keep the deer population
from becoming too large and also increase the herbivore quality (or health), as predators often eliminate the weaker
members of the herd. Ten new carnivores were placed into your ecosystem. The results of this program are shown in the
following table.
Directions:
Using the information provided in the chart and the formulas provided to fill in the last two columns for each year. The first
year has been calculated for you.
Formulas:
Predation + Starvation = Total Herbivores Dead
Herbivore Offspring – Total Herbivore Dead = Herbivore Population Change
Year
Carnivore
Population
Herbivore
Population
Herbivore
Offspring
Predation
Starvation
1
10
2000
800
400
100
2
12
2300
920
480
240
3
16
2500
100
640
500
4
22
2360
944
880
180
5
28
2224
996
1120
26
6
24
2094
836
960
2
7
21
1968
788
840
0
8
18
1916
766
720
0
9
19
1952
780
760
0
10
19
1972
790
760
0
Total
Herbivore
Dead
Herbivore
Population
Change
500
+300
Data Analysis:
1. Graph the herbivore and carnivore populations using LoggerPro and attach the graph to this page.
2. Describe what happened to the herbivore population over the course of these 10 years.
3. Describe what happened to the carnivore population over the course of these 10 years.
4. Is a relationship between herbivore and carnivore populations evident? Cite Evidence!
5. Form a Hypothesis: What would have happened to the herbivores on the island had carnivores not been
introduced?
6. Would you be willing to introduce a new predator into your ecosystem a means of controlling another population?
a. Is death by predators more natural or better than death by starvation?
b. How would you determine if your ecosystem is in balance?