Managing Our Natural Resources, 6e, Camp - 35

CHAPtER 3

Concepts in Natural Resources Management

35

Carrying Capacity
A population level can be defined as the number of a given species of plant or
animal in a given area at a particular point in time. Carrying capacity refers to
the maximum population level for which an ecosystem can provide ongoing food
and shelter. The population level of any species cannot long exceed the carrying
capacity of the ecosystem.
Carrying capacities are affected by the food webs that include the species in
question. Here is an example: Quail eat insects and plant seeds. A covey of quail
must have an adequate supply of food to thrive and reproduce-even to survive.
The population level of quail in a given area cannot exceed the carrying capacity
for that area.
Population levels are also affected by water availability, shelter, and predators.
All these factors, as well as diseases and parasites, help keep populations of each
species at an acceptable level in the "balance" of nature. Chapter 24 deals with
this concept in more detail. When a population exceeds its ecosystem's carrying
capacity, diseases, predators, or starvation will inevitably reduce the population
level. That is the way of nature.
In a previous section, we discussed the concept of actions in one part of
an ecosystem affecting other parts of the system. The most profound effect by
humans on the ecosystem has been from the advent of agricultural production
of food and fiber. Farming has drastically increased the carrying capacity of the
world for humans by increasing the amount of food that can be produced on
the land. Intensive crop and livestock production have enhanced that aspect of
the ecosystem. At the same time, we cannot so drastically alter one aspect of the
ecosystem without also affecting other parts of the system.
We are learning that we cannot long ignore or bypass ecological principles.
For instance, when we harvest crops, we remove much of the organic matter that
would normally be returned to the soil by decomposition. In the long term, this
has a drastic effect on the ecosystem. Thus, modern conservation practices such
as incorporating crop residues and green manure crops into the soil are direct
applications of ecological principles.

tABLE 3-1 estimated
past and projected World
population over 8,000 Years
Years

HUMAn POPULAtiOn
Earlier in this chapter, it was pointed out that the human population has grown
over the years. At about the time of the birth of Christ, the world's human population was about 300 million. That figure was a great increase over the estimated
10 million at about 6,000 BCE, and the rate of increase has jumped in the past
few centuries to unbelievable levels (Table 3-1).
Those figures are startling. As late as 1800, there were fewer than 1 billion
living humans. The number had grown to 1.6 billion by 1900. It had skyrocketed
to 4.3 billion in 1979 and surpassed 6 billion in 1999 and 7 billion in 2011. It is
even more astonishing to see this information on a graph (Figure 3-10).
The United Nations provides the most widely used projections of future
human population.i Populations projections require scientists to make certain assumptions about the future birth rate and mortality rate. The United
Nations, provides projections based on a "best guess" that results in what the
report refers to as the "medium" projection. That "best guess" projection is
shown in Table 3.1. The UN report also provides alternative projections based
on a high growth rate (increased birth rate and lower mortality) and a low

Population
(in Billions)

6000BC

0.01

AD 1

0.30

1000

0.31

1250

0.40

1500

0.50

1750

0.79

1800

0.98

1850

1.26

1900

1.65

1950

2.52

2000

6.07

2050*

8.92

2100*

9.06

2150*

8.49

2200*

8.50

2250*

8.75

2300*

8.97

* these projections represent the
"medium" growth estimate. actual
estimates range from 5.49 to 14.08 billion
in 2100 and 3.16 to 21.24 billion in 2200,
depending on the assumptions made
regarding birth and mortality rates.
Sources:
Prior to 1950, World Resources Institute, http://www
.wri.org/
Starting with 1950, United Nations, http://www.un.org/
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http://www.wri.org/ http://www.wri.org/ http://www.un.org/

Table of Contents for the Digital Edition of Managing Our Natural Resources, 6e, Camp

Contents
Managing Our Natural Resources, 6e, Camp - Cover1
Managing Our Natural Resources, 6e, Camp - Cover2
Managing Our Natural Resources, 6e, Camp - i
Managing Our Natural Resources, 6e, Camp - ii
Managing Our Natural Resources, 6e, Camp - iii
Managing Our Natural Resources, 6e, Camp - iv
Managing Our Natural Resources, 6e, Camp - v
Managing Our Natural Resources, 6e, Camp - Contents
Managing Our Natural Resources, 6e, Camp - vii
Managing Our Natural Resources, 6e, Camp - viii
Managing Our Natural Resources, 6e, Camp - ix
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Managing Our Natural Resources, 6e, Camp - xi
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