Chapter 52: Population EcologyChapter 52: Population EcologyPopulation ecologyPopulation ecologyStudy of populations in relationship to the Study of populations in relationship to the environmentenvironmentIncludes environmental influences on Includes environmental influences on population density, distribution, age population density, distribution, age structure, & sizestructure, & size

PopulationPopulationIndividuals of one species simultaneously Individuals of one species simultaneously occupying the same general area, utilizing occupying the same general area, utilizing the same resources, & influences by similar the same resources, & influences by similar environmental factorsenvironmental factors

Characteristics of populationsCharacteristics of populations Population densityPopulation density

Number of individuals per unit areaNumber of individuals per unit area Measuring densityMeasuring density

Count all individuals in a representative sample areaCount all individuals in a representative sample area Estimates based on indirect indicators such as nest, burrows, Estimates based on indirect indicators such as nest, burrows,

droppings, or tracksdroppings, or tracks Mark-recapture methodMark-recapture method

Population dispersionPopulation dispersion The pattern of spacing among individuals within the designated The pattern of spacing among individuals within the designated

geographic boundariesgeographic boundaries TypesTypes

ClumpedClumped Individuals are aggregated in patchesIndividuals are aggregated in patches Most commonMost common

UniformUniform Spacing of individuals is evenSpacing of individuals is even Rare but territoriality is often the reasonRare but territoriality is often the reason

RandomRandom Varies in an unpredictable wayVaries in an unpredictable way Occurs in absence of strong attractions/repulsions of individualsOccurs in absence of strong attractions/repulsions of individuals Rare Rare Ex. Windblown dandelionsEx. Windblown dandelions

DemographyDemography Study of factors that affect the growth & decline Study of factors that affect the growth & decline

of populationsof populations Age structure & sex ratioAge structure & sex ratio

Age structureAge structure Relative number of individuals of each age in the populationRelative number of individuals of each age in the population

Birth rate/fecundityBirth rate/fecundity Death rateDeath rate Generation timeGeneration time

The average span of time between birth of individual & the The average span of time between birth of individual & the birth of their offspringbirth of their offspring

Sex ratioSex ratio Proportion of individuals of each sex found in a populationProportion of individuals of each sex found in a population

Life Tables & survivorship curvesLife Tables & survivorship curves Type IType I

Death rate increases in elderly but is flat for other agesDeath rate increases in elderly but is flat for other ages Type IIType II

Death rate constant throughout all age spansDeath rate constant throughout all age spans Type IIIType III

Death rate high in young & elderly Death rate high in young & elderly

Life HistoryLife History Traits affecting organism’s schedule of reproduction & Traits affecting organism’s schedule of reproduction &

survivalsurvival Life histories are highly diverse but exhibit patternsLife histories are highly diverse but exhibit patterns Includes:Includes:

When reproduction beginsWhen reproduction begins How often an individual reproducesHow often an individual reproduces How many offspring an individual producesHow many offspring an individual produces

Limited resources mandate tradeoffs between Limited resources mandate tradeoffs between investment in reproduction vs. own survivalinvestment in reproduction vs. own survival SemelparitySemelparity

Organism invests most of their energy into growth & development Organism invests most of their energy into growth & development then expends all energy into a single reproductive effort before then expends all energy into a single reproductive effort before dyingdying

Ex. Annual plants, salmon, bambooEx. Annual plants, salmon, bamboo Favored in highly variable, unpredictable environments with low Favored in highly variable, unpredictable environments with low

offspring survival ratesoffspring survival rates IteroparityIteroparity

Organism produces fewer offspring at a time but over several Organism produces fewer offspring at a time but over several reproductive seasonsreproductive seasons

Favored in dependable environments with high competition for Favored in dependable environments with high competition for resourcesresources

Population Growth ModelsPopulation Growth Models Exponential model Exponential model

Idealized population in an unlimited Idealized population in an unlimited environmentenvironment

Logistic modelLogistic model Incorporates the concept of carrying capacity Incorporates the concept of carrying capacity

(K)(K) Carrying capacity= maximum population size Carrying capacity= maximum population size

an environment can supportan environment can support

Regulation of Population GrowthRegulation of Population Growth Intra-specific competitionIntra-specific competition

2 or more individuals of the same species rely on 2 or more individuals of the same species rely on a limited resource. a limited resource.

Density-dependant factorsDensity-dependant factors intensify as the population increasesintensify as the population increases Competition for resourcesCompetition for resources TerritorialityTerritoriality Health (i.e. disease)Health (i.e. disease) PredationPredation Toxic waste Toxic waste Intrinsic factors (i.e. stress syndrome in white Intrinsic factors (i.e. stress syndrome in white

footed mice)footed mice)

Population DynamicsPopulation Dynamics Study of the interactions between biotic & Study of the interactions between biotic &

abiotic factors that cause variations in abiotic factors that cause variations in population sizepopulation size

Some populations have regular boom & Some populations have regular boom & bust cyclesbust cycles Small herbivoresSmall herbivores lemmings show a 3-5 year lemmings show a 3-5 year

cyclecycle Large herbivoresLarge herbivores snowshoe hare shows a 9- snowshoe hare shows a 9-

11 year cycle11 year cycle InsectInsect Cicada show a 13-17 year cycle Cicada show a 13-17 year cycle In some species crowding effects the In some species crowding effects the

endocrine system=reduced fertilityendocrine system=reduced fertility

Human Population GrowthHuman Population Growth For centuries humans have appeared to grow For centuries humans have appeared to grow

exponentially…exponentially… Agricultural revolutionAgricultural revolution increased birth rate & increased birth rate &

decreased death ratedecreased death rate Industrial revolutionIndustrial revolution improved sanitation, nutrition, improved sanitation, nutrition,

& health care& health care Can not grow indefinitely….Can not grow indefinitely….

Population ecologists do not agree on the human Population ecologists do not agree on the human carrying capacity carrying capacity

Age structure within each country causes variations in Age structure within each country causes variations in population growthpopulation growth

Humans can consciously control reproduction through Humans can consciously control reproduction through contraception or government sponsored family planningcontraception or government sponsored family planning

Agricultural & industrial technology has increased carrying Agricultural & industrial technology has increased carrying capacitycapacity

Social changes, individual choice, government intervention Social changes, individual choice, government intervention and/or increased mortality due to environmental limitations and/or increased mortality due to environmental limitations will cause the human population to stop growingwill cause the human population to stop growing