1 human population how many people can the earth sustain? how big will the world population get?
TRANSCRIPT
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Human Population
• How many people can the Earth sustain?• How big will the world population get?
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Population Dynamics
• Dynamics of Population Growth• Factors that Increase or Decrease
Populations• Factors that Regulate Population Growth
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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
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Fig. 9.1 Exponential growth: Nt = N0ert, where r=growth rate
Only possible under ideal conditions!
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CS Fig. 6.4
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JLag
Rapid Growth
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CS Fig. 7.2
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As observed in movie in lab!
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SExamples:Mice, Bacteria inPetri dish
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CS Fig. 6.5
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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
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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
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Fig. 9.6
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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
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CS Fig. 7.9
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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
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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
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CS Fig. 7.13
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DevelopingDeveloped
3636
3737
Projected as moreof world becomesdeveloped
CS Fig. 7.10
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Fig. 7.8
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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
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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
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Long-term UN population projections
CS Fig. 7.17
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United NationsCS p. 128
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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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The End.
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