Download Predator-Prey Interactions Predation is a density

Predator-Prey Interactions
Predation is a density-dependent limiting factor; it is affected by the number of individuals in a
given area. For example, the population of a predator can be limited by the amount of prey available.
The opposite is true as well. The population of a prey species can be affected by changes in its
predator population. If the predator population declines, the population of the prey may increase as a
result of less pressure from predators.
Scientists have been studying predator-prey interactions for many years, collecting data about
both the predator and prey populations over time. In some cases, a cyclical pattern of rising and
falling population numbers emerges between a predator and its prey.
Scientists have found that this pattern exists in as many as 30 percent of predator-prey
populations studied. In some cases, the cycle may occur over a long period, such as ten years. In other
cases, one cycle of both populations rising and falling may take only months.
In this lab, you will graph and analyze population data for a predator and its prey that was
collected previously under laboratory conditions. You will also graph and analyze data collected for a
prey population in which the predator was removed.
Problem
How do predator-prey interactions affect population numbers of both the predator and the prey?
Scenario
Two species of mites, one which preys on the other, were housed together in a laboratory experiment,
along with a realistic amount of food for the prey. The numbers of both populations were monitored.
Table 1 contains population data for both Eotertranychus sexmaculatus (prey) and Typhlodromus
occidentalis (predator).
Procedure
1. Use the data in Table 1 to construct a line graph with two y-axes that shows the changes in the
Eotertranychus and Typhlodromus populations. Be sure to correctly label both the x-axis and each y
axis. Label x-axis as “Days” and the left y-axis as “Prey”; the right y-axis as “Predator”. Use the
following intervals to set up your graph.
“Prey” y-axis = 100 mites
“Predator” y-axis = 2 mites
“Days” x-axis = 5 days
2. Use a BLUE color pencil to draw a line on the graph representing the Eotertranychus population.
3. Use a GREEN color pencil to draw a line on the graph representing the Typhlodromus population.
4. Table 2 contains data about a population of Kaibab mule deer in Arizona in which all predators were
removed. Use the data in Table 2 to construct a new graph that shows the changes in the
population.
Label the x-axis “Year” and the y-axis “# of mule deer (thousands)”. Use the following intervals to
set up your graph.
x-axis = 2.5 years
y-axis = 5,000 mule deer
Table 1. MITE POPULATIONS
Table 2. KAIBAB MULE DEER
Day
Eotertranychus
(prey)
Typhlodromus
(predator)
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
100
200
600
1100
1400
800
600
280
200
200
220
225
250
300
410
500
875
1590
1800
1900
2100
1750
1350
850
500
500
600
750
700
800
1200
1800
1900
1770
1700
1800
1675
1320
610
200
50
0
0
2
4
12
28
38
29
18
15
9
8
7
3
2
2
4
6
6
17
19
21
29
25
36
22
6
5
12
5
1
1
1
1
2
3
8
19
30
47
31
9
0
Year
# of mule deer
1900
1905
1910
1915
1920
1923
1930
1935
1940
2,900
8,000
20,000
42,500
79,000
100,000
10,000
6,200
5,000
Name: __________________________________________________________ Date: ____________________________ Period: _______
Predator-Prey Interactions
1. Mites Graph
2. Kaibab Deer Graph
3. How did the population of Typhlodromus change in relation to the population of Eotertranychus?
Approximately how long is one cycle of rising, failing, and rising again (a) in population number and
(b) in this predator-prey interaction?
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
4. How would the following changes affect the population numbers in the TyphlodromusEotertranychus system:
(a) the addition of another predator species that also preys on Eotertranychus
(b) the addition of another species that Typhlodromus will also eat
(c) cutting the Eotertranychus food source in half
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
5. What type of graph does the graph for Kaibab deer show? Why did the population crash?
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________
______________________________________________________________________________________________________________________