Chapter 53Chapter 53

• ~ Population ~ Population EcologyEcology

Changes to Changes to population sizepopulation size

• Adding & removing Adding & removing individuals from a individuals from a populationpopulation– birthbirth

– deathdeath

– immigrationimmigration

– emigremigrationation

Population characteristicsPopulation characteristics

• DensityDensity~ # of individuals per unit of area~ # of individuals per unit of area •counts•counts •sample size estimate •sample size estimate •indirect indicators •indirect indicators •mark-recapture•mark-recapture

• DispersionDispersion~ pattern of spacing~ pattern of spacing •random•random~ unpredictable, patternless ~ unpredictable, patternless

spacing (a)spacing (a) •clumped•clumped~ patchy aggregation (b)~ patchy aggregation (b) •uniform •uniform~ even spacing (c)~ even spacing (c)

DemographyDemography:: factors that affect growth & decline of populationsfactors that affect growth & decline of populations

• BirthrateBirthrate (natality, fecundity)~ # of offspring produced(natality, fecundity)~ # of offspring produced

• Death rateDeath rate (mortality) (mortality)

• Age structureAge structure~ relative number of individuals of each age~ relative number of individuals of each age

• Survivorship curveSurvivorship curve~ plot of numbers still alive at each age~ plot of numbers still alive at each age

Population Growth ModelsPopulation Growth Models

• Exponential model (red)Exponential model (red) • idealized population in an • idealized population in an unlimited environment (J-unlimited environment (J-curve); r-selected species curve); r-selected species (r=per capita growth rate)(r=per capita growth rate)

• Logistic model (blue)Logistic model (blue) •carrying capacity (•carrying capacity (KK): ): maximum population size that a maximum population size that a particular environment can support particular environment can support (S-curve); K-selected species(S-curve); K-selected species

Carrying capacityCarrying capacity• Can populations continue to grow Can populations continue to grow

exponentially?exponentially?– of course NOT!of course NOT!

– what sets limit?what sets limit?• resources, predators, parasitesresources, predators, parasites

• Carrying Capacity (K)Carrying Capacity (K)– maximum population maximum population

size that environment size that environment can support with no degradation of can support with no degradation of habitathabitat• not fixed; varies with not fixed; varies with

changes in resourceschanges in resources

2005-2006

Model of growthModel of growthDecrease in rate of growth as reach Decrease in rate of growth as reach carrying capacitycarrying capacity

Population life history “strategies”Population life history “strategies”

• r-selected r-selected (opportunistic)(opportunistic)

• Short maturation & Short maturation & lifespanlifespan

• Many (small) Many (small) offspring; usually 1 offspring; usually 1 (early) reproduction; (early) reproduction; no parental careno parental care

• High death rateHigh death rate

• K-selected K-selected (equilibrial)(equilibrial)

• Long maturation & Long maturation & lifespanlifespan

• Few (large) offspring; Few (large) offspring; usually several (late) usually several (late) reproductions; reproductions; extensive parental careextensive parental care

• Low death rateLow death rate

2005-2006

Different life strategiesDifferent life strategies• K-selectionK-selection

• r-selectionr-selection

K-selection

r-selection

mortality constant

Population limiting factorsPopulation limiting factors

• Density-dependent factorsDensity-dependent factors •competition•competition •predation •predation •stress/crowding •stress/crowding •waste accumulation •waste accumulation

• Density-independent factorsDensity-independent factors •weather/climate•weather/climate •periodic •periodic disturbancesdisturbances

2005-2006

Age structureAge structure• Relative number of individuals of Relative number of individuals of

each ageeach ageWhat do the data imply about population growth in these countries?

2005-2006

Human populationHuman population

What factors have contributed to this exponential What factors have contributed to this exponential growth pattern? growth pattern?

1650500 million

20056 billion

Is the human population reachingcarrying capacity?