Biology 12

15.2 What Is Earth’s Carrying Capacity?

516 MHR • Unit 5 Population Dynamics

In 1679, Anton van Leeuwenhoek, the Dutch

scientist whose main contribution to science

involved improving the microscope and studying

microscopic organisms, estimated that the

maximum number of people the world could

support was 13.4 billion. He calculated this figure

by multiplying the population of the Netherlands

by the ratio of Earth’s total inhabited land area to

the area of the Netherlands. These numbers were,

of course, estimates. At that time, there were no

reliable census data available for the Netherlands

or any other country. In addition, parts of the world

were poorly mapped, so the amount of inhabitable

land was uncertain.

Many more estimates of Earth’s carrying capacity

for humans have followed van Leeuwenhoek’s.

These have ranged from less than one billion people

to over one trillion, and they are getting more

scattered over time, as illustrated in Figure 15.12.

There has been no clear trend since 1679 for the

estimates to get increasingly larger or smaller, or

even to move closer together. In fact, Figure 15.12

shows that the spread between the highest and

lowest estimates has increased with time. This

indicates that trying to determine the value of K

(the carrying capacity) for humans is a difficult task.

It also suggests that we may be aiming at a moving

target — perhaps the carrying capacity is not

constant but changes or fluctuates over time. This

should not be surprising given that the carrying

capacity depends on many variables, including the

condition of the environment, which itself changes

over time.

Methods of Estimating

Carrying Capacity

A few theorists who have estimated human

population limits have based their assertions

on little or no evidence or logic. However, most

estimates have been based on some sort of data

and have been calculated using one of a variety of

methods. Some researchers analyzing this question

have divided the terrestrial portions of Earth into

regions and specified a maximum density of

population that each of these regions could support.

They have then multiplied these maximum densities

by the area of each region and taken the sum to

obtain the total number of people that could be

supported on Earth. The difficulty with this method

lies in determining the densities for each region.

Few researchers used objective, repeatable methods

to do this. In addition, they assumed that these

densities would not change over time, which is

unlikely given that environmental conditions change.

Figure 15.12This graph gives an indication of the extent

of variation in estimates of the human carrying capacity. It

also illustrates how the scatter in estimates has increased

over time. Notice how the estimates do not seem to be

converging on a single true value. In fact, the largest

estimate ever made (published in 1964) would be off the

scale of this diagram and therefore has been omitted.

1650 1700 1750 1850

10

100

1000

1800 1900 1950 2000

Maximum population (billions)

Year

EXPECTATIONS

Evaluate the carrying capacity of Earth and relate the carrying capacity to

the growth of populations and their consumption of natural resources and

advances in technology.

Explain why it is difficult to determine human carrying capacity.