Chapter 8 NotesChapter 8 NotesPopulation Population DynamicsDynamicsAP Env. ScienceAP Env. Science

Ecocolumn LabEcocolumn Lab

Biosphere 2

POPULATION DYNAMICS?POPULATION DYNAMICS?

Change in…Change in… Population Size: Number of individualsPopulation Size: Number of individuals Population Density: Number of individuals Population Density: Number of individuals

in a certain spacein a certain space What is the population What is the population

density for the bunnies?density for the bunnies?

What is the population What is the population density of students in density of students in this classroom?this classroom? 25

feet

30 feet

POPULATION DYNAMICS?POPULATION DYNAMICS?

Population Dispersion: Distribution of Population Dispersion: Distribution of the individuals of a population within a the individuals of a population within a certain areacertain area

ClumpingClumping Uniform DispersionUniform Dispersion Random DispersionRandom Dispersion

POPULATION DYNAMICS?POPULATION DYNAMICS? Population Dispersion: Distribution of the Population Dispersion: Distribution of the

individuals of a population within a certain individuals of a population within a certain areaarea ClumpingClumping Uniform DispersionUniform Dispersion Random DispersionRandom Dispersion

POPULATION DYNAMICS?POPULATION DYNAMICS? Population Dispersion: Distribution of the Population Dispersion: Distribution of the

individuals of a population within a certain individuals of a population within a certain areaarea ClumpingClumping Uniform DispersionUniform Dispersion Random DispersionRandom Dispersion

LIMITS ON POPULATION GROWTHLIMITS ON POPULATION GROWTH

Population controlled by…Population controlled by… BirthsBirths DeathsDeaths ImmigrationImmigration EmigrationEmigration Formula: Population Δ = Formula: Population Δ = (Births + Immigration) – (Deaths + (Births + Immigration) – (Deaths +

Emigration)Emigration)

These variables depend on various growth and These variables depend on various growth and decrease factorsdecrease factors

INTRINSIC RATE OF INCREASEINTRINSIC RATE OF INCREASE Biotic Potential: Capacity for growthBiotic Potential: Capacity for growth Intrinsic Rate of IncreaseIntrinsic Rate of Increase

““r”r” Rate at which a population would grow if it had Rate at which a population would grow if it had

unlimited resourcesunlimited resources i.e. Under ideal conditions, how fast could the i.e. Under ideal conditions, how fast could the

population growpopulation grow High “r”High “r”

Reproduce early in life / Short generation timesReproduce early in life / Short generation times Can reproduce many timesCan reproduce many times Have many offspring each reproductive cycleHave many offspring each reproductive cycle

Some examples of high “r”•Housefly: 5.6 trillion descendents within about 13 months•Bacteria: 1 billion in 10 hours

ENVIRONMENTAL RESISTANCEENVIRONMENTAL RESISTANCE High “r” is a dreamHigh “r” is a dream

Rarely is/are ideal conditions found in natureRarely is/are ideal conditions found in nature No population can grow indefinitelyNo population can grow indefinitely There are always limits to population growth (see below)There are always limits to population growth (see below)

What restricts a population’s intrinsic rate of What restricts a population’s intrinsic rate of increase, or biotic potential?increase, or biotic potential?

Environmental ResistanceEnvironmental Resistance All those factors that serve to limit a populationAll those factors that serve to limit a population Population in a given place at a given time is the Population in a given place at a given time is the

interplay between biotic potential and environmental interplay between biotic potential and environmental resistanceresistance

Helps to determine carrying capacity (Helps to determine carrying capacity (KK)) Number of individuals of a given species that can be Number of individuals of a given species that can be

sustained indefinitely in a given spacesustained indefinitely in a given space

Growth factors(biotic potential)

Favorable lightFavorable temperatureFavorable chemical environment (optimal level of critical nutrients)

Abiotic

BioticHigh reproductive rate

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmental change

Decrease factors(environmental resistance)

Too much or too little lightTemperature too high or too lowUnfavorable chemical environment (too much or too little of critical nutrients)

Abiotic

BioticLow reproductive rate

Specialized niche

Inadequate food supply

Unsuitable or destroyed habitat

Too many competitorsInsufficient ability to hide from or defend against predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapt to environmental change

TYPES OF POPULATION GROWTHTYPES OF POPULATION GROWTH

EXPONENTIAL GROWTHEXPONENTIAL GROWTH Starts out slowly and proceeds faster and Starts out slowly and proceeds faster and

fasterfaster Occurs when a population has few (if any) Occurs when a population has few (if any)

limitations on it resourceslimitations on it resources Grows at the intrinsic rate of increase (r)Grows at the intrinsic rate of increase (r) J-shaped curveJ-shaped curve Rarely happens (for Rarely happens (for extended extended

period of period of time) in nature time) in nature

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Exponential Growth

TYPES OF POPULATION GROWTHTYPES OF POPULATION GROWTH

LOGISTIC GROWTHLOGISTIC GROWTH Exponential growth followed by a decrease in Exponential growth followed by a decrease in

growth rate as the population reaches its growth rate as the population reaches its carrying capacity (K)carrying capacity (K)

Growth levels off and population stabilizes Growth levels off and population stabilizes around carrying capacityaround carrying capacity

Growth typically fluctuates Growth typically fluctuates around the around the carrying capacitycarrying capacity

S-shaped curveS-shaped curve

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Logistic Growth

AFFECTS OF DENSITY ON GROWTHAFFECTS OF DENSITY ON GROWTH

DENSITY-INDEPENDENT FACTORSDENSITY-INDEPENDENT FACTORS Affect a population’s size regardless of the Affect a population’s size regardless of the

population densitypopulation density ExamplesExamples

FloodsFloods HurricanesHurricanes Unseasonable weatherUnseasonable weather FireFire Habitat destructionHabitat destruction Pesticide sprayingPesticide spraying

AFFECTS OF DENSITY ON GROWTHAFFECTS OF DENSITY ON GROWTH

DENSITY-DEPENDENT FACTORSDENSITY-DEPENDENT FACTORS Factors whose effects on a population change Factors whose effects on a population change

with population densitywith population density Some factors have a greater effect as a Some factors have a greater effect as a

population’s density increasespopulation’s density increases ExamplesExamples

CompetitionCompetition PredationPredation ParasitismParasitism DiseaseDisease

TYPES OF POPULATION CHANGE CURVESTYPES OF POPULATION CHANGE CURVES

In nature, there are four general categories of In nature, there are four general categories of population fluctuationspopulation fluctuations

STABLESTABLE Population fluctuates slightly above and below its carrying Population fluctuates slightly above and below its carrying

capacitycapacity Example: many species found in tropical rain forests where Example: many species found in tropical rain forests where

average temp and rainfall is fairly constantaverage temp and rainfall is fairly constant

IRRUPTIVEIRRUPTIVE Fairly stable population that occasionally explodes, or irrupts to a Fairly stable population that occasionally explodes, or irrupts to a

high peak and then crashes to a more stable lower levelhigh peak and then crashes to a more stable lower level The population explosion may be result of favorable weather, The population explosion may be result of favorable weather,

more food, fewer predatorsmore food, fewer predators

TYPES OF POPULATION CHANGE CURVESTYPES OF POPULATION CHANGE CURVES

IRREGULARIRREGULAR Population demonstrates chaotic behavior with Population demonstrates chaotic behavior with

no recurring pattern to population sizeno recurring pattern to population size

CYCLICCYCLIC Cyclic fluctuations in population size over a Cyclic fluctuations in population size over a

regular period of timeregular period of time Lemming populations rise and fall every 3-4 Lemming populations rise and fall every 3-4

yearsyears Lynx and snowshoe hare populations generally Lynx and snowshoe hare populations generally

rise and fall in a 10-year cyclerise and fall in a 10-year cycle

ROLE OF PREDATORS IN CONTROLLING ROLE OF PREDATORS IN CONTROLLING POPULATION SIZEPOPULATION SIZE

Predator and prey undergo cyclic changes in their Predator and prey undergo cyclic changes in their numbersnumbers TOP-DOWN CONTROL: Hypothesis that predators TOP-DOWN CONTROL: Hypothesis that predators

cause the cyclical rise and fall of prey populationscause the cyclical rise and fall of prey populations We used to think predator periodically reduced prey populationWe used to think predator periodically reduced prey population Thus, predator population would go downThus, predator population would go down Fewer predators = prey population would reboundFewer predators = prey population would rebound

Predators would soon rebound as prey became Predators would soon rebound as prey became more plentifulmore plentiful

1895 1905 1915 1925 1935

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ROLE OF PREDATORS IN CONTROLLING ROLE OF PREDATORS IN CONTROLLING POPULATION SIZEPOPULATION SIZE

BOTTOM-UP CONTROL: Hypothesis that the BOTTOM-UP CONTROL: Hypothesis that the prey cause the cyclical rise and fall of predator prey cause the cyclical rise and fall of predator populationspopulations Some prey that live on islands without predators Some prey that live on islands without predators

also experience boom-and-bust cyclesalso experience boom-and-bust cycles Food supply increases = Rabbits have more to eat Food supply increases = Rabbits have more to eat

= Rabbit population increases= Rabbit population increases Rabbits overuse their food supply = Rabbits can’t Rabbits overuse their food supply = Rabbits can’t

get enough food = Rabbits dieget enough food = Rabbits die Plants then recover, and the process begins againPlants then recover, and the process begins again Predators are affected by this rise and fall of the Predators are affected by this rise and fall of the

rabbit populationrabbit population

TYPES OF REPRODUCTIVE PATTERNSTYPES OF REPRODUCTIVE PATTERNS Opportunists / r-Selected SpeciesOpportunists / r-Selected Species

High intrinsic rate of increase (r)High intrinsic rate of increase (r) Reproduce early and put most of energy into Reproduce early and put most of energy into

reproduction (but not rearing)reproduction (but not rearing) Tend to be OPPORTUNISTSTend to be OPPORTUNISTS

Species with a broad ecological niche; Can live in many Species with a broad ecological niche; Can live in many different places, eat a variety of foods, and tolerate a different places, eat a variety of foods, and tolerate a wide range of environmental conditionswide range of environmental conditions

ExamplesExamples AlgaeAlgae BacteriaBacteria RodentsRodents Annual plantsAnnual plants InsectsInsects

Do well in changing environments / habitatsDo well in changing environments / habitats Go through irregular and unstable boom-and-bust Go through irregular and unstable boom-and-bust

cyclescycles

r-Selected Species

cockroach dandelion•Many small offspring•Little or no parental care and protection of offspring•Early reproductive age•Most offspring die before reaching reproductive age•Small adults•Adapted to unstable climate and environmental conditions•High population growth rate (r)•Population size fluctuates wildly above and below carrying capacity (K)•Generalist niche•Low ability to compete•Early successional species

TYPES OF REPRODUCTIVE PATTERNSTYPES OF REPRODUCTIVE PATTERNS

Competitor / K-Selected SpeciesCompetitor / K-Selected Species Tend to do well in competitive conditions Tend to do well in competitive conditions

where their population is near the carrying where their population is near the carrying capacity (K)capacity (K)

Usually follow a logistic growth curveUsually follow a logistic growth curve Reproduce late, but most of energy into Reproduce late, but most of energy into

nurturing/protecting just a few offspringnurturing/protecting just a few offspring Thrive in ecosystems with fairly constant Thrive in ecosystems with fairly constant

environmental conditionsenvironmental conditions ExamplesExamples

Large mammalsLarge mammals Birds of preyBirds of prey Large and long-lived plantsLarge and long-lived plants

•Fewer, larger offspring•High parental care and protection of offspring•Later reproductive age•Most offspring survive to reproductive age•Larger adults•Adapted to stable climate and environmental conditions•Lower population growth rate (r)•Population size fairly stable and usually close to carrying capacity (K)•Specialist niche•High ability to compete•Late successional species

elephant saguaro

K-Selected Species

SURVIVORSHIP CURVESSURVIVORSHIP CURVES Different reproductive strategies result in different Different reproductive strategies result in different

life expectancieslife expectancies SURVIVORSHIP CURVES: Graph showing the SURVIVORSHIP CURVES: Graph showing the

number of survivors in different age groups for a number of survivors in different age groups for a particular speciesparticular species

Three generalized types of survivorship curvesThree generalized types of survivorship curves Late LossLate Loss

High survivorship to a certain ageHigh survivorship to a certain age Higher mortality rates for older membersHigher mortality rates for older members

Early LossEarly Loss Survivorship is low in early lifeSurvivorship is low in early life Species tend to produce a lot of young, many of which dieSpecies tend to produce a lot of young, many of which die

Constant LossConstant Loss Fairly constant death rate at all agesFairly constant death rate at all ages

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Estimating Animal Estimating Animal PopulationsPopulations Mark-Capture-RecaptureMark-Capture-Recapture

A.K.A. “The Lincoln Index”A.K.A. “The Lincoln Index”