Biology 12

520 MHR • Unit 5 Population Dynamics

produced fertilizers and pesticides, and genetically

modified crops. The Green Revolution, which

began in the 1950s, consisted of an international

effort to transfer the farming methods and crop

varieties used so successfully in the more developed

countries to less developed nations. Applying these

highly mechanized, high-input methods in Africa,

Asia, and Latin America dramatically increased

yields. Worldwide rice production, for example,

increased over 300 percent from 140 000 000 t in

1948 to 471 600 000 t in 1991, while the land being

tilled increased only 71 percent. These increases

have had costs, including environmental damage

caused by chemicals and increased soil erosion.

There has also been a loss of genetic diversity in

the crop types used, which may make it more

difficult to select new, insect- or drought-resistant

strains in the future and may increase the

susceptibility of a crop to disease. Therefore, it is

probably unwise to assume that technology can solve

all our problems without introducing new ones.

The Fewer Forks Approach

A second method of dealing with problems arising

from human population growth has been called the

fewer forks approach. This involves slowing or

reducing population growth, most often by lowering

fertility rates. Many methods of achieving this have

been advocated and shown to have some success,

including lowering infant mortality rates, increasing

the economic well-being of families, improving

the status and educational level of women, and

promoting contraception. Most of these strategies

move the population into a later stage of the

demographic transition process, in which birth

rates decline. Which of these will be the most

successful or should be attempted in a particular

area depends on many factors, including cultural

values and the availability of economic opportunities.

The Better Manners Approach

Third, there is the better manners approachof

dealing with the impact of population growth, which

advocates improving how people interact. When

individuals use the environment as a source(a

supply house of specific materials) or as a sink

(a substance or site that absorbs and holds on to

materials, often for a long period), their actions have

consequences for others. Ignoring these consequences

has been referred to as the tragedy of the commons.

This tragedy has been repeated over and over again

all over the world, as groups — for example, nations,

regional interests, or families — scramble to obtain

a portion of a theoretically open resource, often

preventing others from having their share. Without

careful planning, such use may deplete or damage

the resource. Therefore, this approach is not

sustainable for the group that has access to the

resource or for others who want access to it.

Many examples exist of resources becoming

damaged. Overgrazing by cattle and logging without

appropriate replanting on crown land (in Canada,

this is land owned by the federal government)

reduces the value of the land for other species as

well as for humans. It also makes it more difficult

for the land itself to recover and be available for

the future. Overhunting of whales and overfishing

by certain countries and/or segments of the fishing

industry has depleted stocks of some species to the

point where they may be unable to recover, as

shown in Figure 15.14. In the mid-1950s, fishers in

Atlantic Canada caught approximately 240 000 t of

northern cod (Gadus morhua) per year. Shortly

afterward, they began increasing their take of this

species; in 1968, about 800 000 t were caught. After

this, the amount fishers were able to catch declined

steadily. By the 1970s, it was apparent that the

species had been overfished and its numbers had

declined. Many methods of fishing, such as using

large nets dragged near the ocean bottom, have also

damaged the ocean environment such that it is less

able to support populations of different organisms.

Figure 15.14As shown in this graph, the biomass of fish

aged 6 years or more decreased from a peak of 1 500 000 t

to less than 300 000 t in 1975. At this time, Canada acted

to limit foreign fishing in the area, and the fish stock

rebounded for a time. But it declined again due to poor

environmental conditions and overfishing. A complete

moratorium on cod fishing was in effect from 1992 to 1999.

(Data from the Canadian Department of Fisheries and Oceans.)

195519601965197019751980198519901995

200 000

400 000

600 000

800 000

1 000 000

1 200 000

1 400 000

1 600 000

Biomass (age 6

+)

(tonnes)

Year