ecology population growth –any organism provided ideal growing conditions will experience rapid...

EcologyEcology

Population GrowthPopulation Growth

Population GrowthPopulation Growth

– Any organism provided ideal growing Any organism provided ideal growing conditions will experience rapid conditions will experience rapid population growthpopulation growth

– Larger it gets, faster it grows – Larger it gets, faster it grows – exponential growth curveexponential growth curve

– Darwin calculated if all the offspring Darwin calculated if all the offspring of 1 pair of elephants were to survive of 1 pair of elephants were to survive and reproduce, after 750 yrs there and reproduce, after 750 yrs there would be 19 million elephantswould be 19 million elephants

Why doesn’t exponential Why doesn’t exponential growth happen for long?growth happen for long?

Sooner or later, you will run out of Sooner or later, you will run out of resources.resources.

Competition for resources Competition for resources – deer population for exampledeer population for example

Logistic GrowthLogistic Growth

– Lets introduce a few animals to a new Lets introduce a few animals to a new environmentenvironment

– at first the population begins to grow at first the population begins to grow slowly slowly

– Soon the population grows rapidly –Soon the population grows rapidly –few die, many producedfew die, many produced

– Population growth begins to slow – Population growth begins to slow – growing still, but slower – why is this growing still, but slower – why is this happening?happening?

Carrying Capacity

Carrying CapacityCarrying Capacity

The largest # of The largest # of individuals an individuals an environment can environment can supportsupport


– When birthrate and deathrate are When birthrate and deathrate are equal, population growth stopsequal, population growth stops

– Steady state – population size stays Steady state – population size stays the same (averages out)the same (averages out)


– Draw a line through the middle of Draw a line through the middle of steady state – carrying capacitysteady state – carrying capacity

– Carrying capacity is the average of Carrying capacity is the average of the steady statethe steady state

– Factors at this point keep the Factors at this point keep the population from getting any bigger – population from getting any bigger – food, overcrowding, competitionfood, overcrowding, competition


Occurs when resources become less Occurs when resources become less available (Slows population growth available (Slows population growth rate)rate)

Slow population growth rate due to Slow population growth rate due to

1.1. Decrease in birthrateDecrease in birthrate

2.2. Increase in deathrateIncrease in deathrate

3.3. Immigration decreasesImmigration decreases

4.4. Emigration increasesEmigration increases

Density Dependent Density Dependent Limiting FactorsLimiting Factors

– factors that control population size factors that control population size operate more strongly on large operate more strongly on large populations than small onespopulations than small ones

– Competition, predation, parasitism, Competition, predation, parasitism, and crowdingand crowding

CompetitionCompetition– struggle for food, water, & spacestruggle for food, water, & space


PredationPredation– Just about every species serves as Just about every species serves as

food for some other speciesfood for some other species– Predators vs. PreyPredators vs. Prey


Prey – defensesPrey – defenses– Poison chemicalsPoison chemicals– ShellsShells– Poison skinsPoison skins– CamouflageCamouflage– Behaviors such as mimicryBehaviors such as mimicry

PoisonPoison

Batesian mimicryBatesian mimicry

Monarch Monarch butterfly or butterfly or viceroy viceroy butterfly?butterfly?

Mertensian mimicry Mertensian mimicry (Warning coloration)(Warning coloration)

Coral snake or King Coral snake or King snake?snake?

Camouflage in natureCamouflage in nature

Industrial Industrial melanism of melanism of the peppered the peppered mothmoth

Shells as Shells as DefenseDefense

Slime as DefenseSlime as Defense

Limiting FactorsLimiting Factors

Growth of many species is Growth of many species is controlled by density dependent controlled by density dependent and density independent limiting and density independent limiting factors.factors.


CounterdefensesCounterdefenses– Monarch butterfly caterpillars have Monarch butterfly caterpillars have

evolved the ability to avoid certain evolved the ability to avoid certain plant poisonsplant poisons

– Predator population varies with prey Predator population varies with prey populationpopulation

Large # of prey = large # predators = Large # of prey = large # predators = small # preysmall # prey


Symbiosis means living togetherSymbiosis means living together– Parasitism – one benefits, one is hurt Parasitism – one benefits, one is hurt

– Commensalism – one benefits, one Commensalism – one benefits, one

not affected not affected – Mutualism - both benefit Mutualism - both benefit


Crowding and StressCrowding and Stress– crowding helps parasites travel from crowding helps parasites travel from

host to hosthost to host– Most animals have built in need for Most animals have built in need for

certain amount of space – hunting, certain amount of space – hunting, nesting, territory (fish for example)nesting, territory (fish for example)

– Increase fighting = decrease breedingIncrease fighting = decrease breeding Make Love Not WarMake Love Not War

Limits to population growthLimits to population growth

Limiting Factor – causes population growth to decreaseLimiting Factor – causes population growth to decrease Density Dependent Limiting FactorsDensity Dependent Limiting Factors Factors which work best with a large dense populationFactors which work best with a large dense population Interspecific competitionInterspecific competition Intraspecific competitionIntraspecific competition PredationPredation DiseaseDisease ParasitismParasitism Density Independent Limiting FactorsDensity Independent Limiting Factors Tornado, hurricane, drought, temperatureTornado, hurricane, drought, temperature Human disturbance (Clear-cutting forests or damming Human disturbance (Clear-cutting forests or damming

rivers)rivers)

CompetitionCompetition

Competitive exclusion principleCompetitive exclusion principle No two species can occupy the same No two species can occupy the same niche in the same habitat at the same niche in the same habitat at the same timetime

InterInterspecific competition occurs specific competition occurs between two species for similar between two species for similar resourcesresources

IntraIntraspecific competition occurs within specific competition occurs within a species for similar resourcesa species for similar resources

Why Competition?Why Competition?

Limited resourcesLimited resources FoodFood WaterWater SpaceSpace ShelterShelter MatesMates SunlightSunlight

PredationPredation

Prey have evolved defense mechanisms Prey have evolved defense mechanisms to prevent predationto prevent predation

Poison (Monarch butterflies & Dart Poison (Monarch butterflies & Dart frogs)frogs)

MimicryMimicry CamouflageCamouflage ShellsShells SlimeSlime

Density Independent Density Independent Limiting FactorsLimiting Factors

Because population size does not Because population size does not matter in these instances, these matter in these instances, these natural occurances are called natural occurances are called density-independent limiting density-independent limiting factorsfactors..


Long hot dry weatherLong hot dry weather FrostsFrosts Happen regardless of how large Happen regardless of how large

the population isthe population is


Boom and Bust Growth CurvesBoom and Bust Growth Curves– Populations grow exponentially then Populations grow exponentially then

crash, then back again crash, then back again Aphids feed on plant buds that can be Aphids feed on plant buds that can be

washed away in a rain stormwashed away in a rain storm

Human Population GrowthHuman Population Growth

Exponential growth due to:Exponential growth due to: AgricultureAgriculture IndustryIndustry Better healthcare / medicineBetter healthcare / medicine Reduced death rateReduced death rate High birth rateHigh birth rate

Human Population GrowthHuman Population Growth

Human populations tend to increase Human populations tend to increase over timeover time– About 500 years ago, human About 500 years ago, human

population began growing population began growing exponentially.exponentially.

– Today, it has slowed in the US and Today, it has slowed in the US and parts of Europe, but not in most of the parts of Europe, but not in most of the rest of the worldrest of the world

– China, India, Africa, and Latin AmericaChina, India, Africa, and Latin America

DemographyDemography

The scientific study of human The scientific study of human populationspopulations

BirthratesBirthrates DeathratesDeathrates Age structureAge structure

U.S. Age DistributionU.S. Age Distribution

South Africa Age South Africa Age DistributionDistribution

South Africa and U.S.South Africa and U.S.

ecology population growth –any organism provided ideal growing conditions will experience rapid...

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