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Population Dynamics. Objectives The student will investigate and understand dynamic equilibrium within populations, communities, and ecosystems. Key concepts.

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Presentation on theme: "Population Dynamics. Objectives The student will investigate and understand dynamic equilibrium within populations, communities, and ecosystems. Key concepts."— Presentation transcript:

1 Population Dynamics

2 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;

3 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

4 3 Key Features of Populations Size Density Dispersion (clumped, even/uniform, random)

5 3 Key Features of Populations 1. Size: number of individuals in an area

6 Growth Rate Birth 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

7 Immigration Emigration Natality Mortality Population + + - - Factors That Affect Future Population Growth

8 Population Dynamics Addition of individuals to populations Removal of individuals from populations

9 3 Key Features of Populations 2. Density: measurement of population per unit area or unit volume Formula: D p = N Pop. Density = # of individuals ÷ unit of space S

10 Factors that Affect Density Immigration- movement of individuals into a population Emigration- movement of individuals out of a population

11 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

12 Humans Are Not Exempt from Nature’s Population Controls Ireland Potato crop in 1845 Bubonic plague Fourteenth century AIDS Global epidemic

13 Factors that Affect Densi ty Density-independent factors- Abiotic factors in the environment that affect populations regardless of their density Ex. temperature storms habitat destruction drought

14 Density-Independent Factors (e.g., weather) Good Times! (in Australia)

15 3 Key Features Populations 3. Dispersion: describes their spacing relative to each other clumped even or uniform random

16 clumped even (uniform) random

17 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

18 Uniform Dispersion of Population Uniform dispersion implies some sort of antagonistic interaction, e.g., either individuals actively repel other individuals

19 Random Dispersion of Population Random dispersion implies a minimum of interspecific interactions that impact where individuals reside

20 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

21 Many organisms present Few organisms present None Limiting Factor- Zone of Tolerance

22 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

23 No Population Can Continue to Increase in Size Indefinitely Biotic Potential = Intrinsic growth rate: Maximum potential for growth –occurs where there is unlimited resources

24 Logistic Growth of a Sheep Population on the Island of Tasmania, 1800–1925 Oscillations about K (the carrying capacity)_

25 Exponential Growth, Overshoot, and Population Crash of a Reindeer Irruptive Population Curve

26 Population Cycles for the Snowshoe Hare and Canada Lynx Boom and Bust Population Curve

27 2 Life History Patterns  r Strategists  short life span  small body size  reproduce quickly  have many young  little parental care  Ex: cockroaches, weeds, bacteria

28 2 Life History Patterns  K Strategists  long life span  large body size  reproduce slowly  have few young  provides parental care  Ex: humans, elephants

29 Idealized Survivorship curves

30 Survivorship Curves Three types of survivorship curves late loss (Type I) Example: Humans constant loss (Type II) Examples: Birds, Fish early loss (Type III) Example: Mice



33 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

34 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

35 The Human Population Who was Thomas Malthus and what did he predict?

36 Human Population Growth s_main s_main


38 Human Population Growth

39 -

40 Growth Rate What is the formula for finding natural increase (growth rate)? r = b – d r = 26/1000 - 5/1000 r = 0.026 – 0.005 = 0.021 0.021 X 100 = 2.1% per year OR (the easy way) r = 26/10 - 5/10 r = 2.6 -.5 = 2.1 or 2.1% per year

41 Doubling Time Rule 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

42 How do population pyramids help us learn about population?


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

45 In some LEDCs the government is encouraging couples to have smaller families. This means the birth rate has fallen.

46 MaleFemale 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.)

47 Population in millions MaleFemale 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.

48 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.

49 Population pyramid for Mozambique. Population pyramid for Iceland.

50 What happens next?


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

53 ?

54 ?

55 ?

56 You decide!



59 What is the Demographic Transition? high The shift from high to low mortality and fertility A sign of socio-economic progress? Time Natural increase Birth rate Death rate Note: Natural increase is produced from the excess of births over deaths.

60 Demographic Transition Read pages 210-211 What is the definition of demographic transition? Identify the characteristics of each stage. Stage Description First Stage – Pre Industrial Second Stage -- Transitional Third Stage -- Industrial Fourth Stage – Post Industrial

61 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. Births/Deaths per 1,000 1750

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