Ecology of Ecology of PopulationsPopulations

Chapter 46Chapter 46

Chapter OutlineChapter Outline Scope of EcologyScope of Ecology Population Density and DistributionPopulation Density and Distribution Population Growth ModelsPopulation Growth Models Survivorship CurvesSurvivorship Curves Age DistributionsAge Distributions Regulation of Population SizeRegulation of Population Size Life History PatternsLife History Patterns Human Population GrowthHuman Population Growth

Environmental ImpactEnvironmental Impact

Scope of EcologyScope of Ecology

EcologyEcology – what is it? – what is it? Definitions:Definitions:

Habitat Habitat - Place where an organism lives.- Place where an organism lives. PopulationPopulation - All the organisms within an - All the organisms within an

area belonging to the same species.area belonging to the same species. CommunityCommunity - All various populations - All various populations

interacting at same locale.interacting at same locale. EcosystemEcosystem – A collection of communities – A collection of communities

Ecological LevelsEcological Levels

Density and Density and Distribution of Distribution of

PopulationsPopulations Population DensityPopulation Density - Number - Number

of individuals per unit area or of individuals per unit area or volume.volume.

Population DistributionPopulation Distribution - - Pattern of dispersal of Pattern of dispersal of individuals within the area of individuals within the area of interest.interest.

Uniform DistributionUniform Distribution

Random DistributionRandom Distribution

Clumped DistributionClumped Distribution

Characteristics of Characteristics of PopulationsPopulations

They tend to growThey tend to grow Intrinsic Rate of Natural Intrinsic Rate of Natural

Increase (Increase (rr))

Population Growth Population Growth ModelsModels

Exponential GrowthExponential GrowthBiotic PotentialBiotic Potential Environmental ResistanceEnvironmental Resistance

Exponential Growth CurveExponential Growth Curve

Logistic GrowthLogistic Growth

Logistic growth—indicated by an S-Logistic growth—indicated by an S-shaped curveshaped curve

Difference between logistic and Difference between logistic and exponential due to environmental exponential due to environmental resistanceresistance

Logistic GrowthLogistic Growth

Carrying CapacityCarrying Capacity

Carrying Capacity is the maximum Carrying Capacity is the maximum number of individuals of a given number of individuals of a given species the environment can support.species the environment can support. The closer the population to the carrying The closer the population to the carrying

capacity, the greater the environmental capacity, the greater the environmental resistance.resistance.

Biotic potential is having full effect and Biotic potential is having full effect and birthrate is a maximum during exponential birthrate is a maximum during exponential growth.growth.

St. Paul Island Reindeer Population

Mortality PatternsMortality Patterns CohortCohort --- all the members of a --- all the members of a

population born at the same time.population born at the same time. SurvivorshipSurvivorship---the probability of ---the probability of

newborn individuals of a cohort newborn individuals of a cohort surviving to particular ages.surviving to particular ages.

Illustrated by Survivorship CurvesIllustrated by Survivorship Curves

Survivorship CurvesSurvivorship Curves

Survivorship CurvesSurvivorship Curves

Age DistributionsAge Distributions

What proportion of What proportion of population is in each population is in each cohort? cohort?

Age Structure DiagramsAge Structure Diagrams

U.S. Age Distributions U.S. Age Distributions

Regulation of Population Regulation of Population SizeSize

Density - Dependent Density - Dependent FactorsFactors

Density - Independent Density - Independent FactorsFactors

Factors That Affect Population Size

Density Dependent Factors

1. Competition Intraspecific Interspecific

2. Predation

3. Parasitism

4. Disease

Factors That Affect Population Size

Density Independent Factors

1. Abiotic factors

2. Unpredictable, catastrophic

events

Life History PatternsLife History Patterns r r - Strategists - Strategists

(Opportunistic)(Opportunistic) Remember Remember

r=reproductionr=reproduction

Life History PatternsLife History Patterns k k - Strategists (Equilibrium)- Strategists (Equilibrium)

Remember k=Karrying Remember k=Karrying kapacitykapacity

Human Population GrowthHuman Population Growth

Human population has had an Human population has had an exponential growth pattern.exponential growth pattern. Doubling time currently estimated at 53 Doubling time currently estimated at 53

years.years. Population SizePopulation Size

1800 1800 1 Billion1 Billion 1930 1930 2 Billion2 Billion 196019603 Billion3 Billion 200020006 Billion6 Billion

World Population GrowthWorld Population Growth

Country Country DevelopmentDevelopment More-Developed Countries More-Developed Countries

(MDCs) GR=0.1%(MDCs) GR=0.1% Less-Developed Countries Less-Developed Countries

(LDCs) GR= 1.6%(LDCs) GR= 1.6% LDC population expected to LDC population expected to increase from 5-8b by 2050increase from 5-8b by 2050

Age DistributionsAge Distributions Age Structure DiagramsAge Structure Diagrams

divide populations into divide populations into three age groups.three age groups.Pre-ReproductivePre-ReproductiveReproductiveReproductivePost-ReproductivePost-Reproductive

The Demographic The Demographic TransitionTransition

Stage I: high birthrates and death Stage I: high birthrates and death ratesrates

Stage II: continued high birthrates, Stage II: continued high birthrates, declining death ratesdeclining death rates

Stage III: falling birthrates and death Stage III: falling birthrates and death rates, eventually stabilizingrates, eventually stabilizing

More-Developed CountriesMore-Developed Countries

Less-Developed CountriesLess-Developed Countries

Population Structures by Age and Sex, 2005 Millions

300 100 100 300300 200 100 0 100 200 300

Less Developed Regions

More Developed Regions

Male Female Male Female

80+ 75-79 70-74 65-69 60-64 55-59 50-54 45-49 40-44 35-39 30-34 25-29 20-24 17-19 10-16

5-90-4

Age

Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003.

Age Distribution of the World’s Age Distribution of the World’s PopulationPopulation

Figure 7.2Figure 7.2 World World Population Distribution by Population Distribution by

Region, 1998 and 2050Region, 1998 and 2050

Environmental ImpactEnvironmental Impact

Measured in terms of:Measured in terms of:Population SizePopulation SizeResource Consumption Resource Consumption Per Capita Per Capita

Resultant PollutionResultant Pollution

Environmental ImpactEnvironmental Impact

ReviewReview Scope of EcologyScope of Ecology Population Density and DistributionPopulation Density and Distribution Population Growth ModelsPopulation Growth Models Survivorship CurvesSurvivorship Curves Age DistributionsAge Distributions Regulation of Population SizeRegulation of Population Size Life History PatternsLife History Patterns Human Population GrowthHuman Population Growth

Environmental ImpactEnvironmental Impact