Graphing Change
s
in Population
Changes in a popula-
tion’s size can be
d
ispla
y
e
d
on a line graph. Figure 7 sho
w
s a
graph of the changes in a rabbit population. The vertical axis
sho
w
s the numbers of rabbits in the population,
w
hile the hori-
zontal axis sho
w
s time. The graph sho
w
s the size of the popula-
tion over a ten-
y
ear perio
d
.
If birth rate
death rate, population size increases.
If death rate
birth rate, population size decreases.
Inequalities
The population statement is
an example of an inequality.
An inequality is a mathemati-
cal statement that compares
two expressions. Two signs
that represent inequalities are
<
(is less than)
>
(is greater than)
For example, an inequality
comparing the fraction to the
decimal 0.75 would be written
Practice Problems
Write an
inequality comparing each
pair of expressions below.
1.
5
■
6
2.
0.4
■
3.
2
(
8)
■
7
1.5
1
2
--
0.75
3
5
--

Differentiated Instruction
Calculating Growth Rate
Materials
none
Time
5 minutes
Focus
Review with students the definitions
of
birth rate
and
death rate.
TeachAsk: Suppose 1,600 snow geese died in the same year that 1,400 were born. What would the growth rate be for that year?(Tell students that birth rate – death rate = growth rate: b – d = g.1,400 −1,600 = growth rate of −200 geese for that year) What does a negative growth rate mean?(The population is declining.)
ApplyAsk: What might account for a death rate that is higher than the birth rate? (Possible answers: Disease; not enough food; being eaten by other animals; unfavorable environmental conditions)learning modality: logical/mathematicalChangesin a Rabbit Population
For:
Changes in Population Activity
Visit:
PHSchool.com
Web Code:
cep-5012
Students investigate the factors
influencing changes in population size.
Gifted and Talented
Calculating Growth Rate
Tell students
that ecologists use the birth and death rates
to calculate a population’s growth rate, the
rate at which the population is changing.
The birth rate
(b)
minus the death rate
(d)
L3
equals the growth rate
(g): b
−
d = g.
Have
students use this formula to calculate the
growth rate of rabbits discussed in the text.
(600 births
−
400 deaths = a growth rate of
200 rabbits per year)
learning modality:
logical/mathematical
Monitor Progress
L2
Writing
Have each student write a
paragraph explaining how birth rate
and death rate affect the size of a
population. Students can save their
paragraphs in their portfolios.
Answer
Figure 7
Fourth year of the study; about
850
L2
Year of Study
Number of Rabbits
(thousands)
0
1
2
3
4
5
6
7
8
9
10
900
800
700
600
500
400
300
200
100
From Year 4 to Year 8, more
rabbits left the population
than joined it, so the
population decreased.
F
IGURE
7
This line graph shows how the
size of a rabbit population
changed over a ten-year period.