Activity 1: Population Growth
Name: ________________________________
PSI Biology
Part I Fruit Flies
You are studying fruit flies in the lab in order to obtain data on fruit fly population growth patterns. You
start with ten flies in a vial and continue to count the flies every five days, adding a set amount of food
every day. You record your data below.
Days
0
Population Size
10
Growth Rate
--
5
25
3
10
100
15
250
20
350
25
365
30
380
35
390
40
395
45
400
50
400
1. Growth rate is calculated by taking the change in population size and dividing it by the change in
time. For example, on day 5, the growth rate would be (25-10) / (5-0) = 3 flies per day. Calculate
the growth rates for the remainder of the chart.
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2. Using the data, draw a graph illustrating the growth of the fruit fly population.
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Part II Deer
The office next to yours is occupied by an ecologist who is studying a population of rabbits that was
released into the wild. One parameter that she follows is population size. Via tag and release methods,
she observes the rabbit population in their natural environment. This particular population of rabbit
lives in a community in which there are no predators and a vast amount of vegetation (food). Her
population data is below:
Generation
0
Population Size
10
10
250
20
600
30
1,200
40
1,500
50
2,500
60
3,800
70
6,000
80
9,000
90
12,000
100
15,000
Growth Rate
--
3. Calculate the growth rates for the data.
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4. Using the data, draw a graph illustrating the growth rate of the rabbit population.
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Analysis
1. What type of growth pattern is the fruit fly population following? Explain the conditions that
cause this type of growth.
2. What type of growth pattern is the rabbit population following? Explain the conditions that
cause this type of growth.
3. Which population has a carrying capacity? What is that carrying capacity?
4. Explain why the growth rates vary between the two populations.
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Answer Key – 20 points
Fruit Flies
2 points
Days
0
5
10
15
20
25
30
35
40
45
50
Population Size
0
25
100
250
350
365
380
390
395
400
400
Growth Rate
-3
15
30
20
3
3
2
1
1
0
2 points
Fruit Fly Population Growth
450
400
Population
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
Days
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Rabbits
2 points
Generation
0
10
20
30
40
50
60
70
80
90
100
Population Size
10
250
600
1,200
1,500
2,500
3,800
6,000
8,500
11,500
15,000
Growth Rate
-24
35
20
30
100
130
220
250
300
350
2 points
RabbitPopulation Growth
16000
14000
Population
12000
10000
8000
6000
4000
2000
0
0
20
40
60
80
100
120
Generation
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Analysis
1. 3 points
The fruit fly is following logistic growth. At first, there were unlimited resources and the
population grew exponentially. But when resources became limited, the population approached
a carrying capacity.
2. 3 points
The rabbit population is growing exponentially. The population keeps increasing at a dramatic
rate due to a lack of predators and abundant food.
3. 2 points
The fruit fly population has a carrying capacity of 400 because it is following logistic growth.
4. 4 points
The growth rate of the fruit fly at first increases but then decreases until it reaches zero. The
growth rate slows as it reaches limited resources and its carrying capacity. The growth rate of
the rabbit population continually increases due to exponential growth. No predators and
abundant food allows the population to keep growing.
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