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Chapter 20 POPULATIONS. 20.1 Understanding Populations As the human population grows, the population of other species declinesAs the human population.

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Presentation on theme: "Chapter 20 POPULATIONS. 20.1 Understanding Populations As the human population grows, the population of other species declinesAs the human population."— Presentation transcript:

1 Chapter 20 POPULATIONS

2 20.1 Understanding Populations As the human population grows, the population of other species declinesAs the human population grows, the population of other species declines Population: a group of organisms that belong to the same species and live in a particular place at the same timePopulation: a group of organisms that belong to the same species and live in a particular place at the same time

3 Population Size The actual population size can be difficult to measureThe actual population size can be difficult to measure Individuals can be too abundant, too widespread, or too mobile to be easily countedIndividuals can be too abundant, too widespread, or too mobile to be easily counted

4 Sampling a Population When it isn’t possible to count every member of the population, a sample is takenWhen it isn’t possible to count every member of the population, a sample is taken From that sample, the population can be estimatedFrom that sample, the population can be estimated

5 Population Density Measures how crowded a population isMeasures how crowded a population is Expressed as the number of individuals per unit of area or volumeExpressed as the number of individuals per unit of area or volume Estimates are calculated for the total land areaEstimates are calculated for the total land area

6 Dispersion The spatial distribution of individuals within a populationThe spatial distribution of individuals within a population Clumped: clustered togetherClumped: clustered together Even: separated by the same amount of spaceEven: separated by the same amount of space Random: no patternRandom: no pattern

7 Clumped Distribution Food or living space may be clumpedFood or living space may be clumped Social behavior (herds)Social behavior (herds) Flocking behaviorFlocking behavior

8 Even Distribution Social interactionsSocial interactions Colonial nesting behaviorColonial nesting behavior V-pattern in flight (waterfowl migration)V-pattern in flight (waterfowl migration)

9 Random Distribution Results from seed dispersal by wind or by birdsResults from seed dispersal by wind or by birds Example: forests or a field of wildflowersExample: forests or a field of wildflowers

10 Population Dynamics Birth rate: the number of births occurring over a certain period of timeBirth rate: the number of births occurring over a certain period of time Death rate/mortality rate: the number of deaths over a period of timeDeath rate/mortality rate: the number of deaths over a period of time Life expectancy: how long an individual is expected to live (the average life span)

11 Age Structure Shows the distribution of individuals in different age groups in a populationShows the distribution of individuals in different age groups in a population Populations with a higher percentage of younger individuals will tend to have rapid growthPopulations with a higher percentage of younger individuals will tend to have rapid growth

12 Patterns of Mortality Survivorship curves: show the likelihood of survival at different ages throughout the life of an organismSurvivorship curves: show the likelihood of survival at different ages throughout the life of an organism Type I, II, or IIIType I, II, or III

13 Types of Survivorship Curves Type I: the chance of dying is smallType I: the chance of dying is small until late in life until late in life Type II: the chance of dying is the same regardless of ageType II: the chance of dying is the same regardless of age Type III: the chance of dying whileType III: the chance of dying while young is great young is great

14 20.2 Measuring Populations Growth Rate: the amount by which a population changes size in a given amount of time Depends on birth, death, emigration and immigration Birth rate – death rate = growth rate

15 Immigration vs. Emigration Immigration: movement INTO a populationImmigration: movement INTO a population Emigration: movement OUT OF a populationEmigration: movement OUT OF a population

16 The Exponential Model Describes a population that increases rapidly after only a few generationsDescribes a population that increases rapidly after only a few generations The larger the population gets, the faster it growsThe larger the population gets, the faster it grows J-shaped curveJ-shaped curve Will become limited by notWill become limited by not enough food and too much enough food and too much wastes (limiting factors) wastes (limiting factors)

17 The Logistic Model Describes a population that becomes stable at the carrying capacityDescribes a population that becomes stable at the carrying capacity Carrying capacity: the number of individuals the environment can support over a long period of timeCarrying capacity: the number of individuals the environment can support over a long period of time S-shaped curveS-shaped curve

18 Population Regulation Density-independent factors: reduce a population regardless of the population size (weather, natural disasters, fire)Density-independent factors: reduce a population regardless of the population size (weather, natural disasters, fire) Density-dependent factors: the higher the population, the more organisms that are affected (food, territory, nest sites)Density-dependent factors: the higher the population, the more organisms that are affected (food, territory, nest sites)

19 Population Fluctuation Populations can fluctuate due to environmental changesPopulations can fluctuate due to environmental changes Example: population cycle of the snowshoe hare and the lynxExample: population cycle of the snowshoe hare and the lynx

20 Perils of Small Populations Small populations are at risk of extinctionSmall populations are at risk of extinction Vulnerable to inbreeding, disease, environmental disturbances, etc.Vulnerable to inbreeding, disease, environmental disturbances, etc. Inbred offspring have shorter life spans, decreased genetic variability, and are more susceptible to diseasesInbred offspring have shorter life spans, decreased genetic variability, and are more susceptible to diseases

21 20.3 Human Population Growth Early human populations lived in small nomadic groups and obtained food by hunting and gatheringEarly human populations lived in small nomadic groups and obtained food by hunting and gathering Had a high mortality rate, especially among infants and childrenHad a high mortality rate, especially among infants and children

22 The Agricultural Revolution 10,000 years ago, humans domesticated animals and cultivated plants10,000 years ago, humans domesticated animals and cultivated plants Agriculture increased the available food supplyAgriculture increased the available food supply Human population began to grow fasterHuman population began to grow faster

23 The Industrial Revolution After the Middle Ages, 25% of the humanAfter the Middle Ages, 25% of the human population in Europe died due to the bubonic plague population in Europe died due to the bubonic plague The industrial revolution began around 1780 when there was a shift to using machinery and burning fossil fuelsThe industrial revolution began around 1780 when there was a shift to using machinery and burning fossil fuels Improvements in hygiene and inImprovements in hygiene and in health care led to population growth health care led to population growth

24 Developed Countries Developed countries: modern, industrialized areas with better health care, longer life expectancies, but lower population growthDeveloped countries: modern, industrialized areas with better health care, longer life expectancies, but lower population growth Examples: U.S., Japan, Canada, Russia, Germany, AustraliaExamples: U.S., Japan, Canada, Russia, Germany, Australia Includes only 20% of the world’s population, but uses 75% of all fossil fuels!

25 Developing Countries Developing countries: poorer areas, lower life expectancy, but higher population growthDeveloping countries: poorer areas, lower life expectancy, but higher population growth Examples: Central America, South America, Mexico, AfricaExamples: Central America, South America, Mexico, Africa Includes 80% of the world’s population, but uses only 25% of the fossil fuels globally

26 Human Population Explosion By 2020, the human population could be as high as 12.5 billionBy 2020, the human population could be as high as 12.5 billion Will Earth be able to sustain thatWill Earth be able to sustain that amount of people or will the amount of people or will the human population reach its human population reach its carrying capacity? carrying capacity?


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