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Chapter 4 Population Chapter 4 Population EcologyEcology

4.1 Population Dynamics4.1 Population Dynamics

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Population CharacteristicsPopulation Characteristics

Population Density: number of organisms per Population Density: number of organisms per unit areaunit area

Spatial distribution: the dispersion or pattern Spatial distribution: the dispersion or pattern of spacing of organismsof spacing of organisms

UNIFORM CLUMPEDRANDOM

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Principles of Population GrowthPrinciples of Population Growth

Population growth rate: explains how fast a Population growth rate: explains how fast a given population grows.given population grows.

Population growth measured in different ways:Population growth measured in different ways: Microorganisms- how fast population grows in Microorganisms- how fast population grows in

tube or bottletube or bottle Plants/animals- how fast population grows in a Plants/animals- how fast population grows in a

new environment with plenty of resourcesnew environment with plenty of resources

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How Fast Do Populations GrowHow Fast Do Populations Grow

Usually not linearUsually not linear

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How Fast Do Populations GrowHow Fast Do Populations Grow

Usually slow at firstUsually slow at first Called a “J”-shaped Called a “J”-shaped

curvecurve Slow at first because Slow at first because

number of reproducing number of reproducing organisms is smallorganisms is small

Called exponential Called exponential growth: as a population growth: as a population gets larger it grows gets larger it grows fasterfaster

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Limits of the EnvironmentLimits of the Environment

Population growth usually stops due to lack of Population growth usually stops due to lack of resourcesresources FoodFood WaterWater ShelterShelter Space Space

Population growth usually stops due to build Population growth usually stops due to build up of waste products which poison the up of waste products which poison the organismsorganisms

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Carrying CapacityCarrying Capacity

Number of organisms of one species that an Number of organisms of one species that an environment can supportenvironment can support

““S”-shaped growthS”-shaped growth

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Carrying CapacityCarrying Capacity

Fluctuations above and below carrying capacity are normal

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Patterns of Population GrowthPatterns of Population Growth

Do population have a “J”-shaped population Do population have a “J”-shaped population growth pattern or a ”S”-shaped population growth pattern or a ”S”-shaped population growth pattern?growth pattern?

Depends on organism’s reproductive patternDepends on organism’s reproductive pattern

In nature there is a continuum (range) of In nature there is a continuum (range) of population growth patterns from “J”-shaped population growth patterns from “J”-shaped population growth pattern to ”S”-shaped population growth pattern to ”S”-shaped population growth patternpopulation growth pattern

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““J”-shaped population growth J”-shaped population growth patternpattern

Also called “r” strategistsAlso called “r” strategists Mosquito, bacteriaMosquito, bacteria Reproduce very rapidly, produce many off Reproduce very rapidly, produce many off

spring in short period of timespring in short period of time Environment unpredictable and change rapidlyEnvironment unpredictable and change rapidly Small body size, mature rapidly, reproduce Small body size, mature rapidly, reproduce

early, short life spanearly, short life span Populations increase rapidly then declinePopulations increase rapidly then decline

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””S”-shaped population growth patternS”-shaped population growth pattern

Also called “Also called “kk” strategists” strategists Slow rate of reproduction, produce few Slow rate of reproduction, produce few

offspringoffspring Elephants, bears, whales, redwood trees, cactiElephants, bears, whales, redwood trees, cacti Live in stable environmentLive in stable environment Large, reproduce and mature slowly, long-Large, reproduce and mature slowly, long-

livedlived Maintain population size near carrying Maintain population size near carrying

capacitycapacity

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Environmental Limits to Population Environmental Limits to Population GrowthGrowth

Limiting Factors: biotic or abiotic factors that Limiting Factors: biotic or abiotic factors that regulate size of a populationregulate size of a population

Two types of limiting factorsTwo types of limiting factors Density dependent factorsDensity dependent factors Density independent factorsDensity independent factors

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Density Dependent FactorsDensity Dependent Factors

Increasing effect as population size increasesIncreasing effect as population size increases DiseaseDisease CompetitionCompetition ParasitesParasites FoodFood

The more dense the population the faster The more dense the population the faster disease can spreaddisease can spread Big problem in agricultural cropsBig problem in agricultural crops

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Density Independent FactorsDensity Independent Factors

Affect all populations regardless of their Affect all populations regardless of their densitydensity

Most are abiotic factorsMost are abiotic factors TemperatureTemperature FloodsFloods StormsStorms DroughtDrought Habitat destructionHabitat destruction PollutionPollution

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Organisms Limit Their Population Organisms Limit Their Population SizeSize

Predation affects population sizePredation affects population size Predator prey relationships often show a cycle Predator prey relationships often show a cycle

of population increases and decreases over of population increases and decreases over timetime

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Predator Prey RelationshipsPredator Prey Relationships

Hare

Lynx

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Predator Prey RelationshipsPredator Prey Relationships

Important for health of natural population Important for health of natural population Usually young, old or injured are caughtUsually young, old or injured are caught

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Effects of CompetitionEffects of Competition

Competition for food, Competition for food, water, territory are water, territory are density dependent density dependent factorsfactors

Only the best suited to Only the best suited to the environment survivethe environment survive

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Effects of Crowding and StressEffects of Crowding and Stress

Crowding causes stressCrowding causes stress AggressionAggression Decrease in parental careDecrease in parental care Decease in fertilityDecease in fertility Decrease in resistance to Decrease in resistance to

diseasedisease Can lead to decrease in Can lead to decrease in

population sizepopulation size

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Chapter 4 Population Chapter 4 Population BiologyBiology

4.2 Human Population4.2 Human Population

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Demographic TrendsDemographic Trends

Human Population

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Human PopulationHuman Population

Demography: study of human population Demography: study of human population growth characteristicsgrowth characteristics

Humans keep pushing up the carrying capacity Humans keep pushing up the carrying capacity by:by: eliminating competing organisms eliminating competing organisms increasing food production increasing food production controlling disease organismscontrolling disease organisms

What is the carrying capacity for humans?What is the carrying capacity for humans?

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Effects of Birth and Death RatesEffects of Birth and Death Rates

Population growth = birth rate – death ratePopulation growth = birth rate – death rate Demographic transition is when there has been Demographic transition is when there has been

a change from high birth rate and death rates a change from high birth rate and death rates to low birth rates and death rates.to low birth rates and death rates.

In many industrialized nations decreasing In many industrialized nations decreasing death rates are more a factor than increasing death rates are more a factor than increasing birth rates (life expectancy keeps increasing)birth rates (life expectancy keeps increasing)

Zero population growth exists when birthrate Zero population growth exists when birthrate equals death rate.equals death rate.

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Age Affects Population GrowthAge Affects Population Growth

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Age Structure DiagramsAge Structure Diagrams

Used to predict population growthUsed to predict population growth

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Mobility and Human Population Mobility and Human Population GrowthGrowth

Immigration: movement of individuals into a Immigration: movement of individuals into a populationpopulation

Emigration: movement of individuals out of a Emigration: movement of individuals out of a populationpopulation

Immigration and emigration have no change in Immigration and emigration have no change in world population but can change numbers of world population but can change numbers of individuals in nations, regions or citiesindividuals in nations, regions or cities

Useful for planningUseful for planning