Chapter 8Chapter 8Population ChangePopulation Change

Principles of Population Principles of Population EcologyEcology Population EcologyPopulation Ecology

Study of populations and why their Study of populations and why their numbers change over timenumbers change over time

Population densityPopulation density The # individuals of a species/area or The # individuals of a species/area or

volume at a given timevolume at a given time

Studying PopulationsStudying Populations

How to Study Populations:How to Study Populations: QuadratsQuadrats TransectsTransects Capture-recapture methodsCapture-recapture methods

Bird bands

Change in Population SizeChange in Population Size

Growth Growth raterate

Birth Birth raterate

Death Death raterate

Immigration Immigration raterate

Emigration Emigration raterate

r = (b – d) + (i – e) r = (b – d) + (i – e)

Calculating Population Calculating Population ChangeChange

Maximum Population Maximum Population GrowthGrowth Intrinsic Rate of GrowthIntrinsic Rate of Growth

Growth rate under ideal conditionsGrowth rate under ideal conditions J- Shaped Curve (exponential growth)J- Shaped Curve (exponential growth)

Logistic GrowthLogistic Growth

Population CrashPopulation Crash

Overshooting carrying capacity can Overshooting carrying capacity can lead to population crashlead to population crash

Factors That Affect Factors That Affect Population SizePopulation Size

Density Density Dependent Dependent FactorFactor Factor whose Factor whose

effect on effect on population population changes as pop. changes as pop. density changesdensity changes

Examples:Examples:

Food Food ShelterShelter

Boom-Or-Bust Population Boom-Or-Bust Population CyclesCycles

Case Study- Predator Prey Case Study- Predator Prey Dynamics on Isle RoyaleDynamics on Isle Royale As wolf population increases, moose As wolf population increases, moose

population decreases (and vice population decreases (and vice versa)versa)

Factors That Affect Factors That Affect Population SizePopulation Size Density Independent FactorsDensity Independent Factors

Factors that affect population size, but Factors that affect population size, but are not influenced by changes in are not influenced by changes in population densitypopulation density

Examples:Examples: Killing frostKilling frost Severe blizzardSevere blizzard FireFire

Reproductive StrategiesReproductive Strategiesr-selected speciesr-selected species-Small body size-Small body size- Early maturity- Early maturity- Short life span- Short life span- Large broods- Large broods- Little or no parental - Little or no parental

carecare- Probability of long Probability of long

term survival is term survival is lowlow

- Mosquitoes and Mosquitoes and DandelionsDandelions

k-selected speciesk-selected species- Small broodsSmall broods- Long life spanLong life span- Slow developmentSlow development- Large body sizeLarge body size- Late reproductionLate reproduction- Low reproductive Low reproductive

raterate- Redwood trees and Redwood trees and

human beingshuman beings

SurvivorshipSurvivorship

Some populations fit two Some populations fit two curvescurves

Herring GullsHerring Gulls Type III & Type III &

Type IIType II

MetapopulationsMetapopulations

A set of local populations among A set of local populations among which individuals are distributed in which individuals are distributed in distinct habitat patches across a distinct habitat patches across a landscapelandscape

Source habitatsSource habitats Sink habitatsSink habitats

MetapopulationsMetapopulations

Human PopulationHuman Population DemographyDemography

Science of population structure and Science of population structure and growthgrowth

Human Population since 1980 is J-Human Population since 1980 is J-shaped curveshaped curve

Population Increase in Population Increase in MexicoMexico

Demographics of CountriesDemographics of Countries

Demographic StagesDemographic Stages

Fertility Changes in Select Fertility Changes in Select CountriesCountries

Age Structure DiagramsAge Structure Diagrams

Worldwide Worldwide

29% of human population is under 29% of human population is under age 15age 15

Could cause large increase in birth Could cause large increase in birth ratesrates