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Population Ecology Chapter 39. Ecology - Definition The science of the relationships between organisms and their environments.The science of the relationships.

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Presentation on theme: "Population Ecology Chapter 39. Ecology - Definition The science of the relationships between organisms and their environments.The science of the relationships."— Presentation transcript:

1 Population Ecology Chapter 39

2 Ecology - Definition The science of the relationships between organisms and their environments.The science of the relationships between organisms and their environments.or The interactions that organisms have with other organisms and with their environment.

3 Population A group of individuals of the same species occupying a given area Can be described by demographics –Vital statistics such as size, density, distribution, and age structure

4 Population Age Structure Divide population into age categories –Pre-reproductive –Reproductive –Post-reproductive Population’s reproductive base includes members of the reproductive and pre- reproductive age categories

5 Density & Distribution Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data clumped nearly uniform random

6 Determining Population Size Direct counts are most accurate but seldom feasible Can sample an area, then extrapolate Capture-recapture method is used for mobile species

7 Capture-Recapture Method Capture, mark, and release individuals Return later and capture second sample Count the number of marked individuals and use this to estimate total population

8 Assumptions in Capture-Recapture Marking has no effect on mortality Marking has no effect on likelihood to being captured There is no immigration or emigration between sampling times

9 Changes in Population Size Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals

10 Zero Population Growth Interval in which number of births is balanced by number of deaths Assume no change as a result of migration Population size remains

11 Exponential Growth Population size expands by ever increasing increments during successive intervals The larger the population gets, the more individuals there are to reproduce

12 Biotic Potential Maximum rate of increase per individual under ideal conditions Varies between species In nature, biotic potential is rarely reached

13 Biotic Potential Which has greater biotic potential, Elephants or frogs? Elephants or rhinos? Indian Elephant or African Elephant?

14 Limiting Factors Any essential resource that is in short supply All limiting factors acting on a population dictate sustainable population size

15 Carrying Capacity (K) Maximum number of individuals that can be sustained in a particular habitat Logistic growth occurs when population size is limited by carrying capacity

16 Logistic Growth As size of the population increases, rate of reproduction decreases When the population reaches carrying capacity, population growth ceases

17 Density-Dependent Controls Logistic growth equation deals with density-dependent controls Limiting factors become more intense as population size increases Disease, competition, parasites, toxic effects of waste products

18 Density-Independent Controls Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike

19 Human Population Growth Population now exceeds 6 billion Rates of increase vary among countries Average annual increase is 1.26 percent Population continues to increase exponentially

20 Side-Stepping Controls Expanded into new habitats Agriculture increased carrying capacity; use of fossil fuels aided increase Hygiene and medicine lessened effects of density-dependent controls

21 Future Growth Exponential growth cannot continue forever Breakthroughs in technology may further increase carrying capacity Eventually, density-dependent factors will slow growth

22 Population Growth Curve Estimated size by 10,000 years ago 5 million By 1804 1 billion By 1927 2 billion By 1960 3 billion By 1974 4 billion By 1987 5 billion By 1999 6 billion Projected for 2050 8.9 billion Human Population Growth

23 Fertility Rates Total fertility rate (TFR) is average number of children born to a woman Highest in developing countries, lowest in developed countries

24 Fertility Rates Compared U.S. – brown bar Brazil – red bar Nigeria – gold bar

25 Age Structure Diagrams Show age distribution of a population

26 Age Structure Diagrams: 1997

27 Population Momentum Lowering fertility rates cannot immediately slow population growth rate Why? There are already many future parents alive If every couple had just two children, population would still keep growing for another 60 years

28 Slowing Growth in China World’s most extensive family planning program Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization Since 1972, TFR down to 1.8 from 5.7

29 Effects of Economic Development Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries When individuals are economically secure, they are under less pressure to have large families

30 Demographic Transition Model Based on historical data from western Europe Postulates that as countries become industrialized, first death rates drop, then birth rates drop

31 Demographic Transition Model Stage 1 Preindustrial Stage 2 Transitional Stage 3 Industrial Stage 4 Postindustrial births deaths relative population size lowincreasingvery highdecreasinglowzeronegative

32 Immigration

33 Resource Consumption United States has 4.6 percent of the world’s population Americans have a disproportionately large effect on the world’s resources Per capita, Americans consume more resources and create more pollution than citizens of less developed nations, or any other country by far!

34 Projecting Human Population Size


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