PopulationsPopulations

Characteristics of Characteristics of PopulationsPopulations

Three important characteristics of a Three important characteristics of a population are its geographic population are its geographic distribution, density, and growth rate.distribution, density, and growth rate.

Geographic distribution describes the Geographic distribution describes the area a population lives inarea a population lives in

Population densityPopulation density is the number of is the number of individuals that live in an areaindividuals that live in an area

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Population GrowthPopulation Growth

Three factors affect population Three factors affect population size: size:

The number of birthsThe number of birthsThe number of deaths The number of deaths The number of individuals that The number of individuals that enter or leave the populationenter or leave the population

Population growthPopulation growth

Populations grow if more individuals Populations grow if more individuals are born than die in any period of timeare born than die in any period of time

ImmigrationImmigration - the movement of - the movement of individuals into an area, can cause a individuals into an area, can cause a population to growpopulation to grow

EmigrationEmigration - the movement individuals - the movement individuals out of a population, can cause a out of a population, can cause a population to decrease in sizepopulation to decrease in size

Exponential GrowthExponential Growth

If a population has unlimited space and If a population has unlimited space and food, and is protected from predators and food, and is protected from predators and disease, then the population size will disease, then the population size will increase exponentiallyincrease exponentially

Exponential growthExponential growth occurs when the occurs when the individuals in a population reproduce at a individuals in a population reproduce at a constant rate.constant rate.

Under ideal conditions with unlimited Under ideal conditions with unlimited resources, a population will grow resources, a population will grow exponentiallyexponentially

Exponential GrowthExponential Growth

Bacteria reproduce by splitting in half, if the Bacteria reproduce by splitting in half, if the bacteria have a doubling time of 20 bacteria have a doubling time of 20 minutes, then within 20 minutes the 1minutes, then within 20 minutes the 1stst bacterium with divide to produce 2 bacteria.bacterium with divide to produce 2 bacteria.

After 20 more minutes the 2 bacteria divide After 20 more minutes the 2 bacteria divide to form 4.to form 4.

After 20 minutes 4 becomes 8, in one hour After 20 minutes 4 becomes 8, in one hour there is 64, in two more hours there is 512, there is 64, in two more hours there is 512, in just one day the colony of bacteria will be in just one day the colony of bacteria will be 4,720,000,000,000,000,000,000 !!!!!!4,720,000,000,000,000,000,000 !!!!!!

Exponential GrowthExponential Growth

A graph of exponential growth forms A graph of exponential growth forms a J-shaped curvea J-shaped curve

Logistic GrowthLogistic Growth

Obviously exponential growth can not Obviously exponential growth can not continue for very long.continue for very long.

As resources become less available, the As resources become less available, the growth of a population slows or stops.growth of a population slows or stops.

Logistic growthLogistic growth occurs when a occurs when a population’s growth slows or stops population’s growth slows or stops following a period of exponential following a period of exponential growthgrowth

Logistic GrowthLogistic Growth

Population growth may slow or stop when Population growth may slow or stop when birthrates and death rates occur at the birthrates and death rates occur at the same rate.same rate.

Population growth will slow when Population growth will slow when immigration decreases, and emigration immigration decreases, and emigration increases, or both.increases, or both.

Carrying capacityCarrying capacity is the largest is the largest number of individuals of a population that number of individuals of a population that a given environment can support a given environment can support

Logistic GrowthLogistic Growth

A graph of logistic growth forms an A graph of logistic growth forms an S-shaped curve.S-shaped curve.

Limits to GrowthLimits to GrowthLimiting FactorsLimiting FactorsDensity-Dependent Density-Dependent

FactorsFactorsDensity-Independent Density-Independent

FactorsFactors

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Limiting FactorLimiting Factor

Any factor that caused population Any factor that caused population growth to decrease.growth to decrease. CompetitionCompetition PredationPredation Parasitism and diseaseParasitism and disease Drought and other climate extremesDrought and other climate extremes Human disturbancesHuman disturbances

Density-dependent Density-dependent factorsfactors

Density-dependent factorsDensity-dependent factors are are limiting factors that depends on limiting factors that depends on population size.population size.

The larger the population the more it is The larger the population the more it is affectedaffected

Examples: competition, predation, Examples: competition, predation, parasitism and diseaseparasitism and disease

Predator-Prey Predator-Prey RelationshipRelationship

The regulation of a population by The regulation of a population by predation predation

Density-independent Density-independent factorsfactors

Density-independent factorsDensity-independent factors affect affect all populations in similar ways, no all populations in similar ways, no matter what the size ismatter what the size is

Examples: weather, natural Examples: weather, natural disasters, seasonal cycles and disasters, seasonal cycles and certain human activitiescertain human activities

Human Population Human Population GrowthGrowth

Just like the populations of many Just like the populations of many other organisms, the human other organisms, the human population is increasing with timepopulation is increasing with time

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DemographyDemography

DemographyDemography is the study of human is the study of human populationspopulations

Birthrates, death rates, and the age Birthrates, death rates, and the age structure of a population help structure of a population help predict why some countries have predict why some countries have high growth rates while other high growth rates while other countries grow more slowlycountries grow more slowly

Demographic transitionDemographic transition

Demographic transitionDemographic transition a dramatic a dramatic change in birth and death rates change in birth and death rates which slows a countries growth ratewhich slows a countries growth rate

Age structure diagramsAge structure diagrams are models are models used to predict future growth of used to predict future growth of countriescountries

Age structure diagramAge structure diagram

Which countries has gone through Which countries has gone through demographic transition?demographic transition?