Population Dynamics

Objectives

The student will investigate and understand dynamic equilibrium within populations, communities, and ecosystems.

Key concepts include:

• interactions within and among populations including carrying capacities, limiting factors, and growth curves;

Population Dynamics

Population: all the individuals of a species that live together in an area

Demography: the statistical study of populations, make predictions about how a population will change

3 Key Features of Populations

•Size

•Density

•Dispersion (clumped, even/uniform, random)

3 Key Features of Populations

1. Size: number of individuals in an area

Growth RateBirth Rate (natality) - Death Rate (mortality)

How many individuals are born vs. how many die

Birth rate (b) − death rate (d) = rate of natural increase (r).

3 Key Features of Populations

Immigration

Emigration

Natality MortalityPopulation+

+

-

-

Factors That Affect Future Population Growth

Popu

latio

n Dy

nam

icsAddition of individuals

to populations

Removal of individuals from populations

3 Key Features of Populations

2. Density: measurement of population per unit area or unit volume

Formula: Dp= N

Pop. Density = # of individuals ÷ unit of space

S

Factors that Affect Density

Immigration- movement of individuals into a population

Emigration- movement of individuals out of a population

Factors that Affect Density

Density-dependent factors- Biotic factors in the environment that have an increasing effect as population size increases

  Ex. disease competition parasites

Humans Are Not Exempt from Nature’s Population ControlsIreland

Potato crop in 1845

Bubonic plagueFourteenth century

AIDSGlobal epidemic (pages 161-162)

Factors that Affect Density

Density-independent factors- Abiotic factors in the environment that affect populations regardless of their density

  Ex. temperature storms

habitat destruction drought

Density-Independent Factors (e.g., weather)

Good Times!(in Australia)

3 Key Features Populations

3. Dispersion: describes their spacing relative to each other

• clumped

• even or uniform

• random

clumped

even (uniform)

random

Clumped Dispersion of Population

Clumped dispersion implies some sort of cohesive force, e.g., either individuals seek

other individuals out, or individuals are limited in where then can reside

Uniform Dispersion of Population

Uniform dispersion implies some sort of

antagonistic interaction, e.g., either individuals

actively repel other individuals

Random Dispersion of Population

Random dispersion implies a minimum of

interspecific interactions that impact where individuals reside

Other Factors That Affect Population Growth

Limiting factor- any biotic or abiotic factor that restricts the existence of organisms in a specific environment.

EX.- Amount of water Amount of food

Temperature

Many organisms

present

Few organisms present

Few organisms present

None None

Limiting Factor- Zone of Tolerance

Other Factors that Affect Population Growth

Carrying Capacity- the maximum population size that can be supported by the available resources

There can only be as many organisms as the environmental resources can support

No Population Can Continue to Increase in Size Indefinitely

Biotic Potential = Intrinsic growth rate: Maximum potential for growth –occurs where there is unlimited resources

Logistic Growth of a Sheep Population on the Island of Tasmania, 1800–1925

Oscillations about K (the carrying capacity)_

Exponential Growth, Overshoot, and Population Crash of a Reindeer

Irruptive Population Curve

Population Cycles for the Snowshoe Hare and Canada Lynx

Boom and Bust Population Curve

2 Life History Patterns

r Strategists short life span small body size reproduce quickly have many young little parental care Ex: cockroaches,

weeds, bacteria

2 Life History Patterns

K Strategists long life span large body size reproduce slowly have few young provides parental

care Ex: humans,

elephants

Idealized Survivorship curves

Survivorship Curves Three types of survivorship curveslate loss (Type I) Example: Humans constant loss (Type II) Examples: Birds, Fishearly loss (Type III) Example: Mice

How is Population Data Gathered?

Births minus Deaths Immigration and Emigration 1,345 – 645= 700 natural increase Age structure Diagrams

o o Tag and

Recapture

The Human Population Define the following vocabulary a. Total fertility level b. Replacement level fertility c. Infant mortality rate d. Doubling time e. Zero population growth

The Human PopulationWho was Thomas Malthus and what did he

predict?

Human Population Growth

Human Population Growth

World Human Population

http://www.census.gov/ipc/www/worldpop.html

Year Population %

1990 5,284,679,123 1.58 84,130,498 1991 5,368,809,621 1.56 84,182,087 1992 5,452,991,708 1.49 81,942,247 1993 5,534,933,955 1.44 80,547,532 1994 5,615,481,487 1.43 80,781,974 1995 5,696,263,461 1.38 79,253,622 1996 5,775,517,083 1.37 79,551,074 1997 5,855,068,157 1.32 78,019,039 1998 5,933,087,196 1.29 76,861,716 1999 6,009,948,912 1.25 75,529,866

U.S. Human Population

http://eire.census.gov/popest/archives/pre1980/popclockest.txt

Year Population % 1990 249,464,396 1.07 2,442,810 1991 252,153,092 1.08 2,464,396 1992 255,029,699 1.14 2,555,035 1993 257,782,608 1.08 2,425,296 1994 260,327,021 0.99 2,476,255 1995 262,803,276 0.95 2,544,413 1996 265,228,572 0.92 2,752,909 1997 267,783,607 0.96 2,876,607 1998 270,248,003 0.92 2,688,696 1999 272,690,813 0.90 2,645,166

Time unit Births DeathsNatural increase

Year 130,013,274 56,130,242 73,883,032

Month 10,834,440 4,677,520

6,156,919

Day 356,201 153,781 202,419

Hour 14,842 6,408 8,434

Minute 247

107 141

Second 4.1 1.8 2.3

-http://www.ibiblio.org/lunarbin/worldpop

Growth RateWhat is the formula

for finding growth rate?r = b – dr = 26/1000 - 5/1000r = 0.026 – 0.005 = 0.021

or 2.1% per year

OR (the easy way)

r = 26/10 - 5/10 r = 2.6 - .5 = 2.1 or 2.1% per year

Doubling TimeRule of 70 – determines the number of years

it will take a country’s population to double. Doubling time = 70/%growth rate Growth rate = 70/doubling time

Let’s practice: A country’s growth rate is 1.5%. How many

years will it take that country’s population to double? 70/1.5 = 46.7 years

How do population pyramids help us learn

about population?

Population pyramids are used to show information about the age and gender of people in a specific country.

Male Female

Population in millions

In this country

there is a high Birth

Rate

There is also a high

Death Rate.

This population pyramid is typical of countries in poorer parts of the

world (LEDCs.)

In some LEDCs the government is

encouraging couples to have smaller

families. This means the birth rate has

fallen.

Male Female

Population in millions

In this country the number of people in each age group is

about the same.

The largest category of

people were born about 40

years ago.

In this country there is a low Birth Rate and a low Death Rate.

This population pyramid is typical of countries in the richer parts of the

world (MEDCs.)

Population in millions

Male Female

In this country the birth rate is decreasing.

In the future the elderly people will

make up the largest section of the

population in this country.

This is happening more and more in

many of the world’s richer

countries.

Male Female

Population in thousands

This country has a large number of temporary

workers. These are people who migrate here

especially to find a job.

Population pyramid for Mozambique.

Population pyramid for Iceland.

What happens next?

What is going to happen to Japan’s population in the future?Why does this matter?

?

?

?

PRE-REPRODUCTIVE

REPRODUCTIVE

POST-REPRODUCTIVE

Age-Structure Pyramids

Rectangle = Cohort = group of individuals of the same age

Note sex ratios are not always 1:1

You decide!

Developed vs. Developing Countries

Developed1.Examples of Countries2.Rate of population

growth3.Birth rates4.Infant mortality rate5.Life expectancy6.GNI7.Literacy

Developing1.Examples of Countries2.Rate of population

growth3.Birth rates4.Infant mortality rate5.Life expectancy6.GNI 7.Literacy

Read page 173 and make a list of characteristics comparing developing and developed countries

What is the Demographic Transition?

The shift from highhigh to low mortality and fertility

A sign of socio-economic progress?

Time

Naturalincrease

Birth rate

Death rate

Note: Natural increase is produced from the excess of births over deaths.

Demographic TransitionRead pages 174 – 175

What is the definition of demographic transition?

Identify the characteristics of each stage. Stage DescriptionFirst Stage – Pre IndustrialSecond Stage -- TransitionalThird Stage -- IndustrialFourth Stage – Post Industrial

Demographic Transition in Sweden and Mexico

Sources: B.R. Mitchell, European Historical Statistics 1750-1970 (1976): table B6; Council of Europe, Recent Demographic Developments in Europe 2001 (2001): tables T3.1 and T4.1; CELADE, Boletin demografico 69 (2002): tables 4 and 7; Francisco Alba-Hernandez, La poblacion de Mexico (1976): 14; and UN Population Division, World Population Prospects: The 2002 Revision (2003): 326.

0

10

20

30

40

50

60

1775 1800 1825 1850 1875 1900 1925 1950 1975 2000

SwedenBirth Rate

Death Rate

MexicoBirth Rate

Death Rate

Births/Deaths per 1,000

1750