Biology 12

Chapter 15 Human Ecology • MHR 523

15.3 Negative Effects on Carrying Capacity

To survive and achieve a condition of well-being,
people consume manufactured goods and natural
resources (such as water and food). Of course, the
manufacture of goods also involves the use of
natural resources. These resources provide the
material from which the items are made or
the energy that drives the manufacturing and
distribution processes. Consumption in itself is not
a bad thing. The problem arises when the rate of
consumption is more than can be sustained by
limited resources.
Some of the things we use as resources are not
actually limited, at least from the perspective of the
human time scale. Called perpetual resourcesby
many, these include energy from the Sun, wind,
and tides, as illustrated in Figure 15.15. The supply
of these is essentially inexhaustible.
Other resources (including air, water, and soil)
are referred to as renewable resources. The major
difference between perpetual and renewable
resources is that human influence cannot deplete
perpetual resources. Biodiversity can also be
considered a renewable resource.
The concept of biodiversityencompasses species
diversity (the variety of plants, animals, and other
organisms on Earth), the genetic diversity that
exists within each of these species, and the diversity
of ecosystems (ecosystem diversity) of which these
species are a part. A diversity of ecosystems is
integral to the functioning of the biosphere. For
example, marsh ecosystems filter and purify water,
while ocean and forest ecosystems act as sinks for
excess carbon dioxide in the atmosphere. Of
course, each of these ecosystems — and each of the
other types as well — plays many roles, providing
a home and services for a diversity of species,
including humans.

Having a diversity of species within communities

tends to stabilize ecosystems and make them more

resilient to degradation. Genetic variability within

a species also has many advantages. For example, it

provides the potential for evolutionary change. If

alleles exist that confer an advantage in a changed

environment, the species may adapt as a result of

natural selection, rather than going extinct.

Figure 15.15Natural resources can be grouped into three

main categories when considered on a human time scale:

perpetual, renewable, and non-renewable. Given that fossil

fuels are derived from the bodies of dead plants and animals,

why do you think they are classified as non-renewable?

Just because these resources are described as

renewable does not mean that supplies are unlimited

and everlasting. Air and water can be polluted, soil

can become depleted, and populations can get so

small that species go extinct. For the most part,

however, these resources can be renewed or

replenished by Earth’s natural processes — as long

as they are not used up too quickly. Some of these

processes are part of biogeochemical cycles, such

as the decomposition and carbon fixation that are

part of the carbon cycle. These cycles tend to cleanse

and recycle air, water, and soil. Other processes

that are part of biological cycles, including meiosis

natural resources

perpetual renewable non-renewable

solar energy

wind

tides

clean air

drinking water

fertile soil

biodiversity

fossil fuels

metallic

minerals

non-metallic

minerals

EXPECTATIONS

Distinguish among perpetual, renewable, and non-renewal resources.

Describe why clean air, drinkable water, fertile soil, and biodiversity are vital

renewable resources.

Describe the effects of human population growth on the environment and

quality of life, including the effects of growth on future generations.

Describe differences in rates of consumption that exist among rich and poor

segments of the world’s population.