Chapter 5
Basics:
-- Population today: about 6 billion
-- annual growth rate today: about 1.5%/yr
-- so about 90 million people will be added this year...equal to about the population of the United States in 1945
-- most of the current growth is in developing countries: 1.9%/yr or doubling time of 35 years... industrialized countries growing at about 1%/yr (doubling time of about 70 years)
Population and technology:
-- human impact on the environment is
Impact = population *impact per individual
... impact per individual is greater in industrialized countries ... impact generally goes up as standard of living goes up
Notes:
-- combination of increasing population and increasing standard of living has resulted in more rapid increase of impact on the environment
-- the addition of people in industrialized countries has a larger environmental impact than the addition of people in non-industrialized countries
-- The Nasty Dilemma: improving the standard of living around the world will likely result in a lower population increase, but it will also increase the impact per individual... the net result is likely no decrease in environmental impact despite a decrease in population growth rate
The History of Human
Four periods:
1. hunters and gatherers... total population of a few million... low population density (1 person per 200 km2)
2. Rise of agriculture: allows higher population density (1 person per 1 km2), total population of 100 million
3. Industrial revolution/Machine Age: rapid increase in population as health care and food supply increase; total population about 1 billion in early 1800’s
4. Current situation: industrialized nations with slow increase, non-industrialized nations with more rapid increase; maximum rate of growth in industrialized/modern era, 2%/year. reached in 1950’s... now its 1.5%/yr.
Definitions:
Population - a group of individuals of the same species living in the same area or interbreeding
Species - all individuals capable of interbreeding (made up of populations)
growth rate - difference between birth rate and death rate
birth rate - number of births per unit time
crude birth rate - number of births per year per 1000 individuals
death rate - number of deaths per unit time
crude death rate - number of deaths per year per 1000 individuals
so... crude growth rate - number of births per year per 1000 individuals minus number of deaths per year per 1000 individuals
More definitions...
Maximum lifetime - genetically determined maximum possible age
Life expectancy - average number of years that an individual can expect to live, given their current age
Doubling time and exponential growth (from Chapter 3)...
An S shaped curve thought to represent population growth over time...
slow early growth,
then leveling off as carrying capacity is reached.
Assumptions are key, and not very reliable...
assume:
The logistic growth curve
The Demographic Transition
A three stage pattern of changes in birth rates and growth rates that has occurred (been observed) in industrialized countries.
(compare with the logistic growth curve... a theory of how populations stabilize and reach carrying capacity)
Three stages in the Demographic Transition...
1. decline in death rate as health and sanitation improve
2. High growth rate due to continuing high birth rates and decline in death rate
3. Birth rate drops as education improves and families place more resources (and value) on each child
Transition from 2 to 3 only occurs if values change and prompt this... this is not a certain outcome...
The Demographic Transition
Note:
-- Possible Stages 4 and 5...
4. Decline in death rate due to medical advances in treating chronic illnesses (heart disease, etc.)... results in increase in population
5. Decline in birth rates to once again reach zero population growth
Future stages?????
Stage 1: Human death rates and the rise of society
Crude death rate in Switzerland: 9
Crude death rate in Bangladesh: 17
Improvement in the death rate due to medical advances
Two basic types of diseases:
- chronic: always present, affects small but roughly constant percentage of population (heart disease, cancers...)
- acute or epidemic: appears infrequently, but affects large percentage of population when it does occur (influenza, plague, measles...)
medical advances have been made mostly against epidemic diseases, not chronic diseases
deaths due to chronic diseases:
United States 70%
Ecuador 33%
Notes:
-- As epidemic diseases are controlled, percentage of deaths by chronic diseases increases...
... does not mean that chronic diseases are becoming more potent or widespread, just means that less people are dying of epidemic diseases (you gotta die of something...)
-- New epidemic diseases are constantly surfacing (AIDS virus, for example)
-- Old epidemic diseases can become immune to current treatments... bacterial infections are now evolving which are resistant to penicillin and other anti biotics...
-- Mobility of humans helps the spread of epidemic diseases
Zero Population Growth....
Predictions of maximum growth are currently based on the logistic curve. But we need to know the inflection point in the curve to know how large the maximum population will be. We don't know this...
Another way to estimate the maximum population is to determine the carrying capacity of the Earth for humans.
This is also not easy as the limiting factors are not constant...
Limiting factors:
-- short term (1-10 years): food disruption by war or climate change, new epidemic disease, major war, release of toxic chemical
-- medium term: climate changes affecting food human life, desertification, pollutants affecting food or human life (acid rain), resource depletion, energy depletion
-- long term: soil erosion affecting crop yields, climate changes affecting food human life, pollutants affecting food or human life, resource depletion, energy depletion
Yet another way to estimate maximum population...
per capita availability: the amount of resources available per person
if this can be estimated, and the resources accurately totaled, then the maximum population can be estimated
this approach depends strongly on values
some researchers think that we have already reached the limit of per capita availability for some resources (for example wood, fish, wool...)
Population Age Structure
... defined as the proportion of the population in each age class
Notes:
-- structure tells us something about population's future... is high, low, or no growth likely?
-- age dependency ratio:
= sum of people over 65 + under 15
sum of people between 15 and 65
... this ratio affects economic conditions....
in non-industrialized societies, the 15 to 65 care for the old, so having more children is desirable.
in industrialized societies, the care of the old is distributed by taxes, so large families are not necessary... however, as the ratio increases, the tax base decreases, so more taxes per individual are required, not a politically good move. (France, for example, encourages couples to have children, in part because of this tax base issue.)
A Common Problem:
short term pressures may force solutions which are bad for the long term
Additional Concepts:
Total fertility rate: number of children expected to be born of a woman in her lifetime
Total fertility rate tends to decline as income increases:
Note that overall, total fertility rate has been dropping in all but the poorest nations...
-- Population momentum (also population lag effect): phenomenon that population will continue to grow even after total fertility rates equal only the replacement rate... due to weighting of age structure towards the young...
... takes time to achieve zero population growth, must maintain replacement fertility for long enough for current generation of women to age past child bearing years... the US total fertility rate is below replacement level, but population is still growing!
Predictions for Future Population:
-- World Bank prediction: (assumptions in the book) 10 to 12 billion, mostly in developing countries (about 90%).
-- higher numbers (20 billion or more) depend largely on food and resource (water, oil, etc.) availability
-- lower numbers (7 to 10 billion) assume factors such as climate change and resource depletion will decrease food supply in developing countries, resulting in large scale starvation
Life expectancy:
Note that the improvement has been in the younger ages... maximum ages have not changed greatly, and have perhaps decreased!
Most effective mechanism is to delay the age of first birth...
... this is tied with education levels and power among women... the higher these are, the later women have children, the lower the fertility rate.
Notes:
-- in undeveloped countries, women work 2/3 of all hours, yet receive only 10% of the wages... women own 0.01% of the world’s property...
-- middle class women in the United States have fertility rates which are much lower than replacement rates... women in poverty in the United States have fertility rates which greatly exceed the replacement rate... 40% of the girls now aged 14 in the United States will be pregnant at least once before they reach the age of 20, most of these living in poor, urban areas...abortion rates exceed live birth rates in these areas...