Biology 12

524 MHR • Unit 5 Population Dynamics

and fertilization, replenish the size and genetic

diversity of populations. Disturbance and succession

are among the natural processes that maintain

ecosystem diversity.

Finally, there are non-renewable resources. This

group includes resources that cannot be replenished

by Earth’s natural processes, as well as those that

are replaced by processes that require very long

periods of time (often thousands or millions of

years). These include metallic minerals (such as

copper, iron, and aluminum), non-metallic

minerals (phosphates), and fossil fuels (including

oil and coal).

Population growth and increased per capita

consumption has placed considerable strain on

all types of resources. But according to the 1998

United Nations Human Development Report, the

problems with non-renewable resources are not as

serious as some researchers predicted several years

ago. Human use of non-renewable resources has

slowed in recent years, and fears that supplies

of materials like oil and minerals might run out

have not materialized. New reserves have been

discovered, efficiency has improved, and recycling

has been introduced. As well, per capita use of

materials such as copper and steel has stabilized

in many countries and declined in others.

Instead, the most urgent problem today is the

deterioration of renewable resources as a result of

overuse or because of environmental degradation,

which reduces the ability of Earth’s natural processes

to replenish supplies. This deterioration happens

not only as a result of the more industrialized

countries overconsuming resources and producing

excessive waste (much of it toxic), but also as a

result of the poverty experienced in less developed

nations. As many have noted, people who have

difficulty finding enough food to feed their families

are unlikely to have the time or desire to learn

about environmental concerns. Although ecologists

realize that cutting down rain-forest trees simply to

supply charcoal for cooking fires is detrimental to

ecosystems, the practice continues because this is

the only way for people to obtain the money they

need to survive. What is needed is a better balance

between economic requirements and ecological

concerns — in all parts of the world.

Such a balance is the goal of proponents of

sustainable development. As defined by the World

Commission on Environment and Development

(also known as the Bruntland Commission) in 1987,

sustainable developmentis development that meets

the needs of the present without compromising the

ability of future generations to meet their own

needs. This seems like common sense. However,

there are many examples of rapid and excessive

exploitation of resources that have provided only

short-term gain and have had serious environmental

costs, as you can see in Figure 15.16. In contrast,

sustainable development — which provides long-

term gain and does not harm the environment —

requires making difficult economic and political

Figure 15.16(A) Much of Bangladesh is traversed by

tributaries of the Ganges River, downstream of India.

(B) Long ago, half of India was forested. Cutting the trees for

timber and firewood, and clearing the land for agricultural

purposes, has reduced the forests to 14 percent of the

country’s area. As a result, the water holding capacity of the

soil is significantly reduced and soil erosion is a serious

problem. Much of this soil, along with high levels of

pollutants (including chemicals from leather tanning and

large amounts of raw sewage), ends up in the Ganges River.

This pollution, coupled with the natural tendency of this river

to flood, has disastrous consequences for Bangladesh.

Arabian Sea Bay of Bengal

Kanpur

GangesRiver

Sri Lanka

Afghanistan

Pakistan

China

Myanmar

India

Allahabad(Benares)Varanasi

Calcutta

Mouth of

the Ganges

Bangladesh

Nepal Bhutan

A B