1

Human Population

• How many people can the Earth sustain?• How big will the world population get?

2

Population Dynamics

• Dynamics of Population Growth• Factors that Increase or Decrease

Populations• Factors that Regulate Population Growth

3

Population Dynamics

• Simple relationship:– The number of individuals in a population

changes with time based on the balance between the number of births and numbers of deaths in the population

N/t = birthrate – death rate

or

dN/dt = birthrate – death rate

4

Fig. 9.1 Exponential growth: Nt = N0ert, where r=growth rate

Only possible under ideal conditions!

55

6

CS Fig. 6.4

6

JLag

Rapid Growth

7

CS Fig. 7.2

7

As observed in movie in lab!

J

88

SExamples:Mice, Bacteria inPetri dish

9

CS Fig. 6.5

9

1010

Examples ofenvironmentalfactors in anaquatic environ-ment that deter-mine the carryingcapacity

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Fig. 9.2 Many Environmental Factors are related to the Population density

1: Population grows when density is low

2: Population density increases

3: Environmental conditions/ resources deteriorate/ decline

4: Population and population density decrease

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Fig. 9.3

1313

Finiteamount offoodavailable!

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Defining Carrying Capacity

• The Carrying Capacity is the“Maximum number of individuals of a population that can be maintained indefinitely by the environmental goods and services that are generated by a given area of the environment”

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Maximum Number of Individuals

• “The Maximum Number of Individuals is determined by the balance between the amount of environmental goods and services that are required by each individual and the quantity of these goods and services that are supplied by the environment.”

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Given Area

• “A given area of the environment is critical to the notion of carrying capacity because the availability of environmental goods and services varies with the type of environment.”

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Maintained Indefinitely

• “Maintained indefinitely refers to the ability of an ecosystem to provide the same quantity and quality of environmental goods and services over time.”

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Fig. 9.4

Pond characteristicsFrog requirements

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Tab. 9.1

Limiting factorFor frog population

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Fig. 9.5

Which pond willbe able to better recycle the frog’swaste?

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Fig. 9.7

22

Fig. 9.6

23

Are Humans Different thanBacteria, Moose, and Frogs?

• To answer question, need to look at human demography

• Are the only two things you can count on Death and Taxes? – No. People will get married, they will have

babies.• Demography is the study of statistical data on

births, deaths, geographical distributions of populations, growth rates and age structures of populations, etc.

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CS Fig. 7.4

24

2525

26

CS Fig. 7.9

26

Most of popchildbearingage or younger

Popmoreevenlydistri-buted

Babyboomers

HighBirth andDeath rates

LowBirth and

Death rates

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US Population Changes

Fig. 9.13

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Growing, Stable, and Shrinking Populations

Fig. 9.12

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Analysis of Population Trends

• Which countries’ populations are growing the fastest?

• Which are stable or shrinking?• Were the countries with stable or shrinking

populations always that way?– No! Clear trend in population growth rates

with level of economic development• Trend called the Demographic Transition

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Similar to CS Fig. 7.14

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Low High

Phase I Phase II Phase III Phase IV

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Fig. 9.15

Noteunits for birthrates

32

Similar toCS Fig. 7.20

32BirthsPer woman

Undeveloped – no transition

Developing – have beguntransition

Developed – completed transition

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Fig.

9.10

The lowerthe fertilityrate, the lower thebirthrate in the population

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Fig. 7.19

35

CS Fig. 7.13

35

DevelopingDeveloped

3636

3737

Projected as moreof world becomesdeveloped

CS Fig. 7.10

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Fig. 7.8

39

Life and Death

• With increasing health care available to world population, life expectancies will increase

• But what controls birthrates?– WOMEN!

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Total Fertility declines as women’s education increases

CS Fig. 7.15

41

UN population prediction

• Based on lowered fertility rates (nearing 3 per woman) they revised their estimates downward

• Still high!– 3 is still more than 2.1– Declining mortality

rates– Population momentum

(from young population structure)

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Fig. 9.9

43

Long-term UN population projections

CS Fig. 7.17

44

United NationsCS p. 128

45

Can the Earth sustain 10 to 15 Billion people?

ORCan we sustain the Earth with 10 to 15

billion humans on it?OR

Can we sustain Earth with 6 billion living an American lifestyle?

Keep this question in mind as we discuss land use, energy use, global warming,

pollution, etc.

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Human Carrying Capacity• “The Maximum Number of Individuals is determined by the

balance between the amount of environmental goods and services that are required by each individual and the quantity of these goods and services that are supplied by the environment.”– This balance has changed throughout human history!

• Human beginnings (~1-2 million years ago) until ~10,000 years ago, humans like other animals on planet: hunting and gathering

– Population less than millions, not billions

• ~10,000 years ago, humans different from other animals on planet: development of agriculture – manipulation of environment

– Population into the many millions

• ~300 years ago: expanded agriculture and industrialization– Population into the hundreds of millions

• ~50 years ago: green revolution!– Population into the many billions

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Human Carrying Capacity

• “A given area of the environment is critical to the notion of carrying capacity because the availability of environmental goods and services varies with the type of environment.”– Humans unique from other animals in that they

“live” in many environments through trade– Trade has expanded and become more efficient

throughout human history

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Human Carrying Capacity

• “Maintained indefinitely refers to the ability of an ecosystem to provide the same quantity and quality of environmental goods and services over time.”

– Humans rely on environment not only for subsistence (like frogs), but for goods that give us quality of life

– Many resources are being used faster than they are replenished by nature

– Humans have found ways to prop up some of these resources, like fisheries and soil fertility, but how indefinite (sustainable) are these methods?

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50

The End.

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