Announcements September 11, 2006 Study Abroad Program Africa/Asia/Middle East Open House Wednesday,...

Announcements

September 11, 2006

Study Abroad ProgramAfrica/Asia/Middle East Open House

Wednesday, Sept. 133:30 - 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 curveSurvival 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 1 Type 1Type 2 or 3

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

⎟⎠⎞

⎜⎝⎛ −=

KN

rNdtdN

1

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.

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 availabilitydeath 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

11 - 20 years 3-6 years

Atlantic SalmonAfrican elephant

2 months

House Mouse


Atlantic SalmonAfrican elephantHouse Mouse

1 calf every 3-8 years

1,500 to 8,000 eggs once

5-8 young every month

Number of offspring produced



Number of reproductive events

~3 - 10 1~6-12



Lifespan

60 - 70 years 3-6 years~2 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

• K-strategists:

Remember that “K” is Carrying Capacity

•long lived•produce few offspring•parental care

Reproductive strategies and population fluctuations

–controlled by density-dependent limiting factors

factors more severe as population increases

example: food

K-strategists:•stable populations at carrying capacity (K)•examples: humans (in theory), deer, lions


Gypsy moth caterpillars

Remember that “r” is population growth rate

r = b - d

r-strategists:•small•short life•many offspring



r-strategists:•rarely reaches K•little or no parental care



–good at using temporarily abundant resources

r-strategists:•controlled by density-independent limiting factors:

weather, pond drying


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

University education,

large young workforce

Child care, luxury items,

productive working

years

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 environmentDensity (people per sq mile*)

India 733.2China 320.9 US 68.7Russia 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

Globalization, often portrayed as an environmental villain, mayhelp, some experts say, because multinational corporations, settingup factories in poor countries, tend to set higher environmentalstandards, prompting local communities to demand similarstandards for home-grown industries. China, far and away themost important of the developing economies, is already pushing toreduce sooty emissions.

Increasing urbanization should also help the environment. Almostall of the extra three billion or so people expected by midcenturywill live in or around cities, according to studies by the UnitedNations and the National Academy of Sciences. City dwellers tendto use energy and other resources more efficiently, and have lessdirect impact on untrammeled landscapes like forests.

NYTimes:A Greener Globe, MaybeBy ANDREW C. REVKIN , August 29, 2004

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


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%


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.html)

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

= desire for more children

In developed countries:• High probability of

survival• Large economic

expenditure not put into retirement plan

• Increase labor by parents

= 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 successChina:1. Due to slow economic growth, PRC began first

population control measures in 19552. 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 19784. 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) % growth rate # added/year (mil)

China 1280.7 0.7 8.96

India 1049.5 1.7 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 know1. 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?

Announcements September 11, 2006 Study Abroad Program Africa/Asia/Middle East Open House Wednesday,...

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