Biology 12

THINKING LAB

Comparing the Growth of

Different Populations

Background

Although they may not live in unlimited environments

(a topic for the next chapter), many human populations

currently appear to be growing exponentially. Since

populations in different parts of the world face varying

environmental conditions, their per capita birth and death

rates (and thus their growth rates) also vary. In this lab, you

will compare the growth rates for several different human

populations to see the effect the growth rate has on the

shape of their growth curves.

You Try It

1.The table shows the number of births and deaths

that occur annually for each 1000 people in different

populations. Prepare a table that will allow you to

include the following columns of calculated data:

(a)per capita birth rate (b)

(b)per capita death rate (d)

(c)growth rate (r) for each population

Using a spreadsheet program or a calculator, determine

the values for each of the listed populations and

complete your table.

2.Design another table in which you can record the

current size of each population as well as its size 10,

20, 50, 75, 100, and 200 years from now. Using the

exponential growth equation and either a spreadsheet

program or a calculator, determine the size of each

population at each time interval listed.

3.Graph the results you obtained on a graph or graphs

like the one shown in Figure 14.10.

4.Describe the relationship between the steepness of the

curve and the value of r.

5.Does the size of the starting population have an effect

on the shape of the curve?

6.What causes the value of rto be less than one? What

happens to the curve if ris negative?

Country

2001

population size

(in millions)

Sweden

Bulgaria

Tunisia

Senegal

Greece

Nigeria

Honduras

8.9

8.1

9.7

9.7

10.9

126.6

6.7

Number of

births per 1000

individuals

Number of

deaths per 1000

individuals

10

9

19

41

10

41

33

11

14

6

13

10

14

6

476 MHR • Unit 5 Population Dynamics

represents the current population size, rthe growth

rate of the population, and tthe number of time

units in the future, the size of the population at

this time (Nt) is:

Nt=N 0 ×ert

In this formula, eis a constant (representing the

base of natural logarithms) that is approximately

2.71828. So if the current size of a population is

1000 individuals (N 0 = 1000 ) and the growth rate

is 0.05 (r=0.05), the size of this population five

years from now (t= 5 ) will be:

N 5 = 1000 ×2.718280.05×^5 =1284.025individuals

As is true for populations with non-overlapping

generations, a graph of population size versus time

for this population would be J-shaped.

As you know, as long as ris positive, a population

is growing. Does the shape of the growth curve

change with different values of r? What does it look

like if ris negative? The Thinking Lab below will

give you an opportunity to examine these questions.

Population Growth in

Limited Environments

Imagine that the bacteria shown in Figure 14.11

continue to reproduce exponentially. After 20 hours,

there would be 1.1× 1012 individuals. Within four

days the mass of this single bacterial population

would be greater than that of Earth (assuming this

species is typical of most bacterial species in terms

of mass)! But there are no bacterial populations

this size on the planet, despite the fact that both

the growth rate and the generation time of our

http://www.mcgrawhill.ca/links/biology12

If you would like to analyze data from different human

populations, or include more countries in your analysis in the

Thinking Lab: Comparing the Growth of Different Populations,

the information you need is available on the Internet. Go to

the web site above, and click on Web Linksto find out where

to go next.

WEB LINK