Chapter 8Population Change

Overview of Chapter 8

• Principles of Population Ecology• Reproductive Strategies• The Human Population• Demographics of Countries• Demographics of United States

Principles of Population Ecology

• Population Ecology– Study of populations and why their numbers change over

time– Important for• Endangered species• Invasive species

• Population– Group of individuals of same species living in the same

geographic area at the same time

Population Density

• Population density– The number of individuals of a species per unit area or

volume at a given time– Ex: minnows per Liter of pond water

Change in Population Size

Change in Population Size

Calculating Population Change

CRUDE BIRTH/DEATH RATE are calculated per 1000 people

Growth Growth raterate

Birth Birth raterate

Death Death raterate

Immigration Immigration raterate

Emigration Emigration raterate

r = (b – d) + (i – e) r = (b – d) + (i – e)

Maximum Population Growth• Intrinsic Rate of Growth (Biotic Potential)– Growth rate under ideal conditions– J- Shaped Curve (exponential growth)

Environmental Resistance

• Environmental limits (resistance)– 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

Check for understanding• 4 - I can explain to my peers why populations

cant grow in size forever.• 3 - I understand what limits populations from

growing in size unstopped. • 2 - I understand carrying capacity, but need

more practice.• 1 - huh? Exponential growth? Carrying

capacity?

Population Crash• Overshooting carrying capacity can lead to

population crash– Abrupt decline in population density

Factors That Affect Population Size

• 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 Isle Royale

• As wolf population increases, moose population decreases (and vice versa)

Factors That Affect Population Size

• Density Independent Factors– Factors that affects population size, but is not

influenced by changes in population density– Examples:• Killing frost• Severe blizzard• Fire

Check for understanding• 4 - I can explain to my peers different ways that

populations increase in size and factors that limit uncontrollable population growth.

• 3 - I understand different ways that populations grow and limitations to their growth.

• 2 - I understand how exponential growth, boom and bust, and carrying capacity, but I need more practice.

• 1 - I am lost population growth.

Reproductive Strategies

r-selected speciesr-selected species k-selected speciesk-selected species

-Small body size-Small body size

- Early maturity- Early maturity

- Short life span- Short life span

- Large broods- Large broods

- Little or no parental - Little or no parental carecare- Probability of long Probability of long term survival is lowterm survival is low- Mosquitoes and Mosquitoes and DandelionsDandelions

-Small broodsSmall broods-Long life spanLong life span-Slow developmentSlow development-Large body sizeLarge body size-Late reproductionLate reproduction-Low reproductive rateLow reproductive rate-Parental careParental care-Redwood trees and Redwood trees and human beingshuman beings

Survivorship

Some populations fit two curves

• Herring Gulls • Type III (young)

& Type II

Check for understanding• 4 - I can explain to my peers how

reproductive strategies vary from survivorship types.

• 3 - I understand how reproductive strategies vary from survivorship types .

• 2 - I understand, I think, but need to review my notes on reproductive strategies and survivorship types.

• 1 - Aren’t all organisms the same????

Human Population• Demography– Science of population

structure and growth

• Human Population is J-shaped curve

• Thomas Malthus – food for people??

famine & disease!!!• better crop yields

Human Population

1 Billion1 Billion 18001800

2 Billion2 Billion 19301930

3 Billion3 Billion 19601960

4 Billion4 Billion 19751975

5 Billion5 Billion 19871987

6 Billion6 Billion 19991999

6.6 Billion6.6 Billion 20062006

Population Increase in Mexico

Projecting Future Populations

• Population is increasing; why is death rate going down?

• Growth rate (r) has started to decline• Zero-population growth: birth rate

and death rate are equal (S –shaped curve)

• Projections for 2050 – variation due to fertility rate of less developed countries– Low = 7.7 billion– High = 10.6 billion– Most likely = 9.1 billion

Demographics of Countries

• Highly developed countries – Ex: US, Japan, Germany – – low birth rates, low infant mortality rates (6% US;

54% world), long life expectancy (77 US, 67 world), high per-capita GNI PPP ($34,000, $7,000)

• Developing countries: – moderately developed countries (Ex: Mexico,

Thailand) – high infant mortality/birth rates, but declining

– less developed countries (Bangladesh, Niger, Ethiopia)

Growth rate

• Doubling time!! – amount of time for an area to double = 70/r (r = growth rate as %)– Which type of country has shorter doubling time?

• Replacement-level fertility – typically 2.1 children– Total fertility rate (world) is above replacement

level (about 2.5)– Impacting factors: infant mortality rate, population

momentum by ## of young females, need/lack of need for children to work (rural), education (especially of women!!)

Check for understanding

• 4 - I can explain to my peers zero population growth, total fertility rate, replacement level fertility, and doubling time.

• 3 - I understand zero population growth, total fertility rate, replacement level fertility, and doubling time.

• 2 - I understand, I think, but need to review my notes on zero population growth, total fertility rate, replacement level fertility, and doubling time

• 1 - I understand some of the terms, but not all.

Demographic Stages• Pre-industrial Stage

– Birth and death rates high – poor medical care, limited food supply– Modest population growth

• Transitional Stage– Lowered death rate – higher education/improved conditions– Rapid population growth

• Industrial Stage– Birth rate decline – urbanization decreases economic reason for

many kids, women educated/work, retirement safety nets reduce it– Population growth slow

• Post Industrial Stage– Low birth and death rates– Population growth very slow

Demographic Stages

Age Structure

• The number and proportion of people at each age in a population

Demographics of Specific Countries

World-wide

• 29% of human population is under age 15

• Could cause large increase in birth rates

Check for understanding• 4 - I can explain to my peers all the different

demographic stages, why they occur AND how to read age structure graphs. I should just drop out of HS now .

• 3 - I understand all the different demographic stages, why they occur AND how to read age structure graphs .

• 2 - I understand demographic transition and age structure graphs, BUT…..

• 1 - I am lost and need to hear it all again.