Transcript Unit_3_population

Population Change
Overview of Chapter 8
o
o
o
o
o
Principles of Population Ecology
Reproductive Strategies
The Human Population
Demographics of Countries
Demographics of United States
Principles of Population Ecology
o
Population Ecology
•
•
Study of populations and why their numbers
change over time
Important for
•
•
o
Endangered species
Invasive species
Population
•
Group of individuals of same species living in
the same geographic area at the same time
Population Density
o
Population density
•
•
o
The number of individuals of a species per unit
area or volume at a given time
Ex: minnows per Liter of pond water
Ovals below have same population, and
different densities
Change in Population Size
Change in Population Size
Principles of Population Ecology
o
o
How Do Populations Change in Size?
Global scale:
Growth rate
Death rate
r= b–d
Birth
rate
*remember that when
calculating growth rates you
always use per 1000 individuals
in the population unless
specifically stated otherwise!
Practice Problem: “Global
Population Change”
o
You have a human population of 10, 000
where there are 200 births per year and
100 deaths per year. Calculate the natural
growth rate of this population (Hint: remember
that we always calculate per 1000…reduce!)
o
Use r = b – d
Answer
o
200/10,000 = 20/1000 = 0.02
o
100/10,000 = 10/1000 = 0.01
o
R = b – d = 0.02 – 0.01 = 0.01
o
More examples can be found at the end of chapter 8
or 1% per year
Calculating Population Change:
“Local Population”
Growth
rate
Death
rate
Emigration
rate
r = (b – d) + (i – e)
Birth
rate
Immigration
rate
Birth (b), Death (d), Immigration (i) and Emigration
(e) are calculated per 1000 people
Practice Calculating Local
Population Growth
o
Calculate the growth of a population of 10,
000, that has 100 births, 50 deaths, 10
immigrants, and 100 emigrants
o
Use equation: r = (b - d) + ( i – e )
REDUCE!
o
Answer
o
o
o
o
o
o
b =100/10,000 = 10/1000 = .010
d =50/10,000 = 5/1000 = 0.005
i =10/10,000 = 1/1000 = 0.001
e = 100/10,000 = 10/1000 = 0.01
So, r = (0.010 – 0.005) + (0.001 – 0.010)
r = 0.005 – 0.009 = -0.004, or -0.4% per year
Maximum Population Growth
o
Intrinsic Rate of Growth (Biotic Potential)
•
•
Growth rate under ideal conditions
J- Shaped Curve (exponential growth)
Environmental Resistance
o
Environmental limits (resistance)
•
•
o
Prevent indefinite reproduction
Unfavorable food, water, shelter, predation, etc.
Carrying Capacity (K)
•
•
•
Maximum # of individuals an environment can
support
Causes leveling off of exponential growth
S- shaped curve of logistic population growth
Population Crash
o
Overshooting carrying capacity can lead to
population crash
•
Abrupt decline in population density
Factors That Affect Population Size
o
Density Dependent Factor
•
•
Factor whose effect on population changes as
population density changes
Examples:
•
•
•
•
Predation
Disease
Competition
Sometimes cause Boom-or-Bust Population
Cycles
Boom-Or-Bust Population Cycles
Case Study- Predator Prey Dynamics on
Moose and Wolf Isle Royale
o
As wolf population increases, moose
population decreases (and vice versa)
Factors That Affect Population Size
o
Density Independent Factors
•
•
Factors that affects population size, but is not
influenced by changes in population density
Examples:
•
•
•
Killing frost
Severe blizzard
Fire
Reproductive Strategies
r-selected species
k-selected species
-Small body size
-Small broods
- Early maturity
-Long life span
- Short life span
-Slow development
- Large broods
-Large body size
- Little or no parental
-Late reproduction
care
-Low reproductive rate
- Probability of long term -Redwood trees and
survival is low
human beings
- Mosquitoes and
Dandelions
Survivorship
Some populations fit two curves
o
o
Herring Gulls
Type III (as
chicks) & Type
II (as adults)
Human Population
o
Demography
•
o
Science of
population structure
and growth
Human Population
since 1980 is Jshaped curve
(exponential)
Population experts believe
that this graph will level out
during the 21 century and
represent an S-shaped curve.
When this happens which
individuals will be those dying
and which will be those
surviving???
Human Population
1 Billion
1800
2 Billion
1930
3 Billion
1960
4 Billion
1975
5 Billion
1987
6 Billion
1999
6.6 Billion
2006
Population Increase in Mexico
High D.R. due
to Mexican
revolution
Analysis: death rate declined much more than
the birth rate so there was a high population
growth during the 20th century
Doubling Time
o
o
o
o
o
One Way to express population growth of
a country is to determine it’s doubling time
Doubling Time = The amount of time it
takes for a population to double in size
(assuming that it’s growth rate (r) doesn’t change)
Doubling time can identify a country as highly, moderate, or less
developed.
The shorter the doubling time the less developed the country!
Formula (simplified): TD (time double) or DT (doubling time) = 70/r
Replacement Level Fertility
o
o
o
Replacement-level-fertility: The number of
children that a couple must produce in
order to “replace” themselves
It usually given as 2.1 children
The number is greater than 2 b/c some
children die before they hit reproductive
age
Total Fertility Level (global)
o
o
o
Total-Fertility-Level: The global average
number of children born to each woman
Currently we are at 2.8!
This is way above the replacement level
fertility rate!
Projecting Future
Global Human
Populations
o
o
o
Population is increasing
Growth rate (r) has
started to decline
Projections for 2050
•
•
•
Low = 7.7 billion
High = 10.6 billion
Most likely = 9.1 billion
Demographics of Countries
Demographic Stages
o
Pre-industrial Stage
•
•
o
Transitional Stage
•
•
o
Lowered death rate
Rapid population growth
Industrial Stage
•
•
o
Birth and death rates high
Modest population growth
Birth rate decline
Population growth slow
Post Industrial Stage
•
•
Low birth and death rates
Population growth very slow
Demographic Stages
Age Structure Diagrams (or
Pyramids) Explained
o
o
o
A countries age structure helps us predict
the future growth of a country
The number of males/females at each age
from birth to death is represented
It is especially important to look at the
pre-reproductive and reproductive years
(generally speaking if they are larger then
the population is expanding
Age Structure Diagrams
o
The number and proportion of people at
each age in a population
Demographics of Specific Countries
World-wide
Population Statistics
o
o
o
29% of human
population is under
age 15
The higher the %
the higher the
likelihood of growth
Could cause large
increase in birth
rates
Education of Immigrants into US
See envirobrief on pg. 179 of your text
Addressing Population Issues
Women in
Egypt learning
about family
planning.
Egypts TFR’s
declined to
3.5, which was
at 7.0 in the
1960’s
Overview
o
Population and Quality of Life
•
•
o
Reducing the Total Fertility Rate
•
•
•
o
Culture and Fertility
Social and Economic Status of Women
Family Planning Services
Government Policies and Fertility
•
o
Population and Chronic Hunger
Economic Effects of Population Growth
China, India, Mexico, Nigeria, Europe
Achieving Population Stabilization
Population and Quality of Life
o
o
Difficult to meet basic needs in developing
countries
Problems associated with overpopulation:
•
•
•
•
•
•
Environmental degradation
Hunger
Persistent poverty
Economic stagnation
Urban deterioration
Health issues
Carrying Capacity
o
Carrying Capacity (K)
•
o
o
The maximum number of individuals of a given
species that a particular environment can
support for an indefinite period, assuming no
changes in the environment
Overuse of land can cause a decrease in
carrying capacity
Uncertain what the carrying capacity of
the earth is for humans
Population and Chronic Hunger
o
Food security
•
o
Condition in which people live with chronic hunger
and malnutrition
Effects of Chronic Hunger
•
•
Weakened immune
system
Increased susceptibility to
illness and disease such as
•
•
•
•
Malaria
Measles
Diarrhea
Acute respiratory illness
Population and Chronic Hunger
o
Ways to Help Solve the Food Problem
•
•
•
Control population growth
Promote economic development of developing
countries without adequate food supplies
Provide access to food and land resources to
those who live in areas without them
Areas with Greatest Food Problems
Economic Effects of Population Growth
o
Two viewpoints from economists:
•
•
o
o
Population growth stimulates economic
development and technological innovation
Rapidly expanding hampers developmental
efforts
Most observations support the second
viewpoint
Developmental efforts are also hampered
by debt from past development attempts
Reducing the Total Fertility Rate
Three major influences on total fertility rate
1. Cultural traditions
2. Social & economic status of women
3. Family planning (or the lack of)
Cultural
Traditions
o
o
o
Culture influences and
controls individuals’
behaviors
Marriage age
Couple is expected to
have large number of
children
•
o
Children often work in
family business
•
o
Due to high infant and child
mortality rates
Provide support for aging
parents
Religious values
Social & Economic Status of Women
o
o
Gender inequality is common worldwide
Disparities
•
•
•
•
•
•
•
Political participation
Social status
Economic status
Health status
Legal rights
Education
Employment and
earnings
Illiteracy in 2002
Single most important factor affecting high total fertility rates is
low status of women
Educational Opportunities and Fertility
o
Women with more education
•
•
Marry later
Have fewer children
Family Planning Services
o
o
In many countries men make reproductive
decisions regarding contraceptives
Family planning services offer information
to both men and women on:
•
•
•
•
Sexuality
Contraception
STDs
Parenting
Contraceptive Use Among Married
Women of Reproductive Age
Government Policies and FertilityChina
o
o
Largest population in the world
Controversial Family Planning Policy
•
•
1971- Chinese Government pursued birth
control seriously
1979- Incentives to promote later marriages
and one-child families
•
•
Medical care, schooling for child, preferential
housing, retirement funds
Brought about rapid and drastic decrease in
fertility
Government Policies and FertilityChina
o
Law – controversial and unpopular
•
•
•
Compromised freedom of choice
Social pressure to abort a second child
Pressure to abort/kill female first child
•
o
More boys than
girls in China
Law more
relaxed in rural
China
Government Policy and Fertility- India
o
Severe population pressure
•
1950- first country with governmentsponsored family planning
•
•
1976- introduced incentives and compulsory
sterilization
•
•
Did not work due to language/cultural barriers
Unpopular and failure
Recent years- government focused on
education
•
Much more effective, but TFR still above
replacement level (currently at 3.4)
Government Policy and FertilityMexico
o
Young age structure
•
Huge potential for population growth: 33% of
population is under age 15
•
o
Positive growth momentum
1974- government imparted educational
reform, family planning, health care
•
Very successful
Government Policy and FertilityNigeria
o
Population challenge
•
o
o
Largest population of any African country
Very high reproductive potential: 43% of
population is less than age 15
Current National Population Policy
•
•
Improving health care
Population education
Government Policy and Fertility- Europe
o
Population concern
•
•
o
Proportion elderly people
in population is increasing
Due to low TFR
Decrease in population
could cause decrease
economic growth
Achieving Population Stabilization
o
How can developing country governments help?
•
•
•
Increase $$ allotted to pubic health and family
planning services
Education on affordable, safe, effective methods of
birth control
Increase average level of education
•
o
Especially for women
How can developed country governments help?
•
•
Provide financial support
Supporting research and development of new birth
control methods