THINKING LAB
The Carrying Capacity
of the Food Supply
Background
Imagine that food is the most important factor limiting the
growth of the human population. If you knew how much
land was required to support an individual, you could
estimate how many people Earth could sustain — as long
as they all ate the same amount as this standardindividual.
In this lab, you will take the first steps toward making such
an estimate.
You Try It
1.The table shows the average amount of energy
contained in human food that could be produced per
square metre of land per year. For example, 1 m^2 of a
field of wheat yields a number of kernels that, when
converted to bread, will provide approximately 2720 kJ
of energy per year. The same area would yield enough
corn to produce 540 kJ of energy in beef when fed
to cattle.
2.Many experts recommend that active teenage males
should each consume about 11 720 kJ of energy
per day. For an active teenage female, this figure is
9 200 kJ per day. From the list of food types in the
table, select the foods that you might eat in one day.
Using the labels shown on food packages or other
nutritional information, determine the amount of energy
you might obtain from each type of food in a day. Many
food labels give the amount of energy contained in a
single serving in calories (Cal or Kcal). To convert this
to kJ, multiply by 4.184.
3.Multiply your results by 365 to obtain the amount of
food energy you would consume in a year.
4.Determine the area of land required to support your
yearly requirement of each food type by dividing
consumption (step 2) by yield (from the table). Sumthese values over all food types to obtain the amount
of land that would be needed to support you for a year.
5.Assuming that you represent the typical male or female
in your class, determine how much land it would take
to grow enough food to feed all of your class for a year.
How much would it take to feed the population of the
entire school?
6.How much land would it take to support six billion
people for a year assuming this consumption pattern?
Do you think this is a reasonable assumption? Explain
your answer.
7.What else would you need to know in order to determine
the carrying capacity of Earth? Would this figure remain
the same from year to year, or even day to day?
8.Did the amount of land needed to sustain an individual
for a year vary among people in your class? Explain the
source of this variation.Type of foodYield
(kJ/m^2 /yr)
bread
oranges and
grapefruit
peanut butter
rice or rice cereal
potatoes
carrots
apples
pears or peaches
margarine2720
4200
3850
5230
6700
3400
6300
3750
1250
Average amount of energy contained in human food that
could be produced per square metre of land per yearType of foodYield
(kJ/m^2 /yr)
cane sugar
cornmilk
cheese
eggs
chicken
beef
fish14 640
1050
1760
170
840
800
540
8
Chapter 15 Human Ecology • MHR 519some indication that the human population may
be coming close to what many people perceive
as its limit.
In summary, we cannot currently predict (with
any level of confidence) how many people Earth
can support. We do know that it depends on more
than simply the availability of resources. We also
know that regardless of what the actual carrying
capacity may be, we are already at the point where
the human population has had a substantial impact
on environmental quality. Researchers in various
fields have suggested three general approaches to
reduce this impact: the bigger pietheory, the fewer
forksapproach, and the better mannersapproach.
The Bigger Pie Theory
First, some suggest that the carrying capacity can
be increased to whatever is needed by improving
technology. This has been called the bigger pie
theory. This theory suggests that Earth can be made
to sustain any number of people — we just need to
grow more food, improve energy technology, and
so on.
The discovery of how to grow crops and
domesticate animals is certainly an example of
increasing the carrying capacity by increasing the
food supply. Many more inventions followed, from
the hand plough to the steam engine, commercially