Transcript 08_HumanPop - School of Life Sciences

Announcements
September 11, 2006
Study Abroad Program
Africa/Asia/Middle East Open House
Wednesday, Sept. 13
3:30 - 5:30 PM
101 International Studies Building
Announcements
September 11, 2006
New handout available for students taking the
course for honor’s credit.
(additional assignment choice added)
Make sure you come talk to me before starting your
assignment!
Announcements
September 11, 2006
Schedule for next week:
Monday (Sept 18th) - brief review of what you
need to know for first exam.
Wednesday (Sept 20th) - first exam
Friday (Sept 22) - no class
Which of these age distributions has a Type III
survivorship curve?
A
B
C
Type III survivorship curve
Very high mortality among the young
Which of these age distributions has a Type III
survivorship curve?
A
Type III survivorship curve
Very high mortality among the young
Type I survivorship curve
Survival is high until old age
Examples:
• Dall sheep
• Humans in
developed
countries
Type II survivorship curve
Mortality is spread evenly among all age
groups
Example:
•Many
species of
birds
Type 2 or 3
Type 1
Type 1
Carrying Capacity —Number of individuals of a species that can be
indefinitely sustained in a given area.
Environmental Resistance
• Environmental Resistance—Any factor
(limiting factor) in the environment
influencing carrying capacity. Four main
factors:
–
–
–
–
Raw material availability
Energy availability
Waste accumulation and disposal
Organism interaction
Logistic Equation
Note: This equation is provided only to
help. You do not need to memorize it.
You will not be asked about the
equation on a test.
dN
N

 rN 1  
dt
 K
Causes of population crashes
• Population size can sometimes overshoot
carrying capacity
• Environmental resistance factors can
change, lowering carry capacity
When population > carrying capacity,
death rates > birth rates
Population crashes!!
Example 1: bacterial population crash due to
toxic waste accumulation
Example 2: Population cycling due to organism
interaction
Hare population:
birth rate limited by food
availability
death rate determined by
predators, food
Lynx population:
birth and death rate determined
by food availability (hares)
Example 2: Population cycling due to organism
interaction
Start: both have low population density
• Hares – high food, low predators = pop increase over
next generations
• Lynx – as hares increase, more food = pop increase
• Hares – when high pop density, increased
competition for food and increased predation = low
birth rate & high death rate = sharp pop decrease
• Lynx – when high pop density and few hares, low
food = low birth rate & high death rate = sharp pop
decrease
• Back to start
Population Cycles
Remember: Several factors influence population
growth rate:
Birthrate
Death rate
Sex Ratio
Age Distribution
Immigration
Emigration
But, there are also additional things about the
individuals that influence how the population grows
Life history traits – characteristics of an individual
that influence survival and reproduction
Age at maturity
House Mouse
African elephant
2 months
11 - 20 years
Atlantic Salmon
3-6 years
Life history traits – characteristics of an individual
that influence survival and reproduction
Number of offspring produced
House Mouse
5-8 young every
month
African elephant
1 calf every
3-8 years
Atlantic Salmon
1,500 to 8,000
eggs once
Life history traits – characteristics of an individual
that influence survival and reproduction
Number of reproductive events
House Mouse
African elephant
~6-12
~3 - 10
Atlantic Salmon
1
Life history traits – characteristics of an individual
that influence survival and reproduction
Lifespan
House Mouse
~2 years
African elephant
60 - 70 years
Atlantic Salmon
3-6 years
How do the following life history traits affect the
rate of reproduction?
Age at
maturity
#
offspring
# reprod.
events
life span
2 mo
many
one
long
2 yr
few
many
short
2 mo
many
many
long
2 yr
many
many
long
Reproductive strategies and population fluctuations
• K-strategists:
•long lived
•produce few
offspring
•parental care
Remember
that “K” is
Carrying
Capacity
Reproductive strategies and population fluctuations
K-strategists:
•stable populations at
carrying capacity (K)
•examples: humans (in
theory), deer, lions
–controlled by density-dependent limiting factors
factors more severe as population increases
example: food
Reproductive strategies and population fluctuations
r-strategists:
•small
•short life
•many offspring
Gypsy moth caterpillars
Remember that “r” is population growth rate
r=b-d
Reproductive strategies and population fluctuations
r-strategists:
•rarely reaches K
•little or no parental
care
Gypsy moth caterpillars
Reproductive strategies and population fluctuations
r-strategists:
•controlled by
density-independent
limiting factors:
weather, pond
drying
Gypsy moth caterpillars
–good at using temporarily abundant resources
Points to know:
Understand the three types of survivorship curves.
What factors influence population growth rates?
What are some life history traits?
Know the difference between K- and r- strategists and
what kind of limiting factors each has.
Human Population Issues I
Lecture Objectives
• Understand past and current human
population growth trends and their impacts
• Understand the factors that affect human
population growth
• Understand how social and political issues
influence these factors
Human population growth
• Long lag phase, then exponential growth
Currently…
• 6.2 billion humans on Earth
– tripled since 1900; 7.8 billion expected by 2025
• Overall, 1.3% annual growth rate
– 54 years to double population if not decreased
Currently…
• Countries vary greatly in actual growth rate
Why should we care about human
population growth rates?
Human population growth contributes to:
• Famine
• Economic disparities increase, leading to
increased political unrest
• Environmental degradation
• Water & air pollution
• Extinction of species
• Carrying capacity of Earth???????
What factors influence human
population growth?
Same as for other species:
• Birth rate
• Death rate
• Sex ratio
• Age distribution
• Immigration/emigration
• Density
Study of these for humans called demography
Birth rates and Death rates
Sex Ratio
• Humans have roughly 1:1 sex ratio
• Total Fertility Rate – number of children a
woman has during lifetime
• Replacement Fertility = 2.1
children/female/lifetime (leads to zero
population growth in long term)
Age Distribution
If total fertility rate
immediately = 2.1,
population would still
increase for 20 years!
“Aging population”
fewer young,
productive workers
U.S. Age Distribution over time
• “Baby boom” changes major societal concerns
Housing,
schools,
supplies for
children
Child care,
luxury items,
productive
working
years
University
education,
large young
workforce
Retirement,
elderly heath
care
Immigration/Emigration
• Of 1.1 % increase in U.S. pop, 0.5% is due
to immigration
• Mexico loses an estimated 250,000 people
per year to emigration
• Millions of people want to emigrate from
war-torn, poverty-stricken countries to more
stable, developed countries
Population Density
• Number of people per unit land area
• As density increases, more severe impacts
on environment
Density (people per sq mile*)
India
733.2
China
320.9
US
68.7
Russia
22.7
*not all square miles equally productive
Population Density
• Distribution of people within countries also
important.
• 47% of world’s population in cities,
expected to increase to 60% by 2025
• Problems with dense populations in cities:
–
–
–
–
–
Water transported long distances
Wastes difficult to get rid of
Decreased air quality
Large burden on local environment
Social unrest due to economic disparity
NYTimes:
A Greener Globe, Maybe
By ANDR EW C. REVKIN , Augu st 29, 2004
Globalization, often po rtrayed as an environmental vil lain, may
help, so me experts say, becau se multinational corporations, setting
up factories in poor countries, tend to set higher envi ronmental
standards, prompting loc al commun ities to dem and similar
standards for home-grown industries. China, far and away the
most important of the deve loping economies, is already pushing to
reduce sooty emissions.
Increasing urbanization shou ld also help the envi ronment. Almost
all of the extra three billion or so people expe cted by midcentury
will live in or around cities, according to studies by the United
Nations and the N ational Ac ademy o f Sciences. City dwellers tend
to use energy and other resources more efficiently, and have less
direct impact on untrammeled landscapes like forests.
Social & political factors influence
human population growth
• What determines how many children a
woman has?
• What policies do countries have on
population growth? Immigration?
Major social factors affecting birth rates
1. Cultural role/status of women
– In male-dominated societies, traditional role of
women is to marry & have children
– Women not educated, encouraged to marry young
– Lack of education makes women dependent on
husband, children
Women in developed countries educated, have
option to delay marriage or not marry
Major social factors affecting birth rates
1. Cultural role/status of women, cont.
– Early marriage = more child-bearing years = more
children
– % of births by 15-19 year olds:
• Africa 17%
• Latin America 16%
• All developed countries 3%
Major social factors affecting birth rates
2. Desires of women & access to birth control
– Women in less-developed countries have more
children than they want
– Often little access to birth control, education on
how to use
– Religious views on birth control
(http://www.cnn.com/2004/LAW/03/01/church.contraceptives.ap/index.h
tml)
However, women in less-developed countries want
more children than women in developed countries.
WHY?
Economic value of children
In less-developed countries:
• Guard against high infant
mortality
• Security in old age
• Labor force
In developed countries:
• High probability of
survival
• Large economic
expenditure not put into
retirement plan
• Increase labor by parents
= desire for more children
= desire for less children
Most important factors affecting
population growth rates
1. Development of/access to modern birth
control
2. Education of women
Political policies on population growth
• Encouraged in some countries (U.S.,
European) by subsidies:
–
–
–
–
–
Paid maternity leave
Guaranteed jobs
Childcare
Tax deductions
Birth bonus (Canada)
Need younger workers to support aging
populations
Political policies on population growth
• Discouraged in other countries with varying
degrees of success
China:
1. Due to slow economic growth, PRC began first
population control measures in 1955
2. Campaign begun in 1971
- Raised legal age of marriage to 23 for women, 25 for
men in rural areas and 25,28 in urban areas
3. One child limit started in 1978
4. Contraception and abortion readily available and
widely used.
Result: Current total fertility rate of 1.8
Political policies on population growth
India:
1. Little government intervention until recently
2. Emphasizing improving quality of life
- Decrease infant mortality to decrease desire
- Encourage education for women
Result: Current total fertility rate of 3.2 children
(goal of 2.1 by 2010)
Effect of different policies
Pop size (mil)
China 1280.7
India 1049.5
% growth rate
# added/year (mil)
0.7
1.7
8.96
17.84
This is not an endorsement of the methods used by
PRC to reduce births!!
Political policies on immigration
• Countries with low birth rates (European,
Japan, China) may face shortage of workers
without immigration
• Emigrants want to move to developed
countries to improve standard of living
– Tremendous pressure on Europe and N.
America to accept immigrants
– Significant numbers of immigrants can strain
social systems
How many total children do you
want to have?
1) 0-1
2) 2-3
3) 4-5
4) > 5
Points to know
1. Know the past, present, and projected future world
population of humans
2. Know the human issues for each of the 6 factors that
affect population growth rate
3. Why do women have more children in male-dominated
societies and less children in developed countries?
4. What two changes have caused/will cause the greatest
decrease in population growth rates?
5. How have political policies in China and India changed
their population growth rates?
6. How do political policies on immigration affect growth
rates? Why do many people want to emigrate?