CHAPTER 52CHAPTER 52

POPULATION ECOLOGYPOPULATION ECOLOGY

CharacteristicsCharacteristics

DensityDensity DistributionDistribution Size Size Age StructureAge Structure

DensityDensity

Direct Counts- Direct Counts- – Larger, less numerous organismsLarger, less numerous organisms

Plankton Population SamplingPlankton Population Sampling– Time x velocity x diameter = MTime x velocity x diameter = M33

– Total # of plankton/ MTotal # of plankton/ M3 3 = # plankton per M= # plankton per M33

– 75 plankton/0.5 M75 plankton/0.5 M33 = 150/M = 150/M33

Mark & Recapture- many animalsMark & Recapture- many animals Aerial Surveys – Aerial Surveys –

– Line transects etc.Line transects etc.– observe large areas, large animals by sightobserve large areas, large animals by sight

Mist nets for migrating birdsMist nets for migrating birds

Mark & RecaptureMark & Recapture

# marked in 1# marked in 1stst catch catch = = # recaptures in 2# recaptures in 2ndnd catch catch

Population total total # in 2Population total total # in 2ndnd catch catch

OR:OR:

N = N = # marked in 1# marked in 1stst catch x total # in 2 catch x total # in 2ndnd catch catch # of recaptures in 2# of recaptures in 2ndnd catch catch

# marked = 50 Total in 2# marked = 50 Total in 2ndnd catch = 100 # catch = 100 # recaptures = 10recaptures = 10

N = 50 x 100/10 N = 500N = 50 x 100/10 N = 500

DispersionDispersion

How the individuals are arranged in the How the individuals are arranged in the landscape.landscape.

Uniform – Uniform – – all parts of the habitat suitable, but has intra-all parts of the habitat suitable, but has intra-

specific competitionspecific competition Random Random

– all parts of habitat suitableall parts of habitat suitable Clumped-Clumped-

– Habitat is patchy orHabitat is patchy or– Social behaviorsSocial behaviors

DispersionDispersion

Population SizePopulation Size

Starting size of populationStarting size of population Add: Births and immigrationAdd: Births and immigration Subtract: Deaths and emigrationSubtract: Deaths and emigration Gives the New population size, Gives the New population size,

Population GrowthPopulation Growth

TimeTime # Females# Females Eggs/FemaleEggs/Female # Flies# Flies

11 11 100100 100100

22 5050 100100 5,0005,000

33 2,5002,500 100100 250,000250,000

44 125,000125,000 100100 12,500,00012,500,000

55 6,250,0006,250,000 100100 625,000,000625,000,000

66 312,000,000312,000,000 100100 31,250.000,00031,250.000,000

77 15,625,000,00015,625,000,000 100100 1,563,500,000,0001,563,500,000,000

Growth curve for fieldMice in a cornfield

Exponential Exponential GrowthGrowth

Fig. 9.4, p. 201

Time (t)

Po

pu

lati

on

siz

e (N

)

Exponential Growth

Exponential GrowthExponential Growth

Biotic Potential – Pop. Biotic Potential – Pop. Grows as fast as Grows as fast as physiology allows.physiology allows.

Unlimited resourcesUnlimited resources No pollution build upNo pollution build up Ideal conditionsIdeal conditions Short lived periodShort lived period Often quickly die out, Often quickly die out,

colonize new areascolonize new areas R selected speciesR selected species

Logistic GrowthLogistic Growth

Time (t)P

op

ula

tio

n s

ize

(N)

K

Logistic Growth

Logistic GrowthLogistic Growth Slower initial Slower initial

growthgrowth Long –term stable Long –term stable

pop. At carrying pop. At carrying capacity (K).capacity (K).

K is size of pop. K is size of pop. Area can sustain.Area can sustain.

Growth slowed by Growth slowed by limiting factorslimiting factors

Fig. 32.2Fig. 32.2

Population Limiting FactorsPopulation Limiting Factors Density dependent Density dependent

factorsfactors– CompetitionCompetition– PredationPredation– Stress/crowdingStress/crowding– Waste accumulationWaste accumulation– DiseaseDisease– SpaceSpace– ResourcesResources

Density independent Density independent factorsfactors– Weather/climateWeather/climate– Periodic disturbancesPeriodic disturbances

Population Life History StrategiesPopulation Life History Strategies

R

K

Type I vs Type IIIType I vs Type III

Type III Type III (R selected)(R selected)– Short maturation & Short maturation &

lifespanlifespan– Many offspringMany offspring– No parental careNo parental care– High death rateHigh death rate

Type I Type I (K selected)(K selected)– Long maturation & Long maturation &

lifespanlifespan– Few offspringFew offspring– Extensive parental Extensive parental

carecare– Low death rateLow death rate

Fewer, larger offspringHigh parental care and protection of offspringLater reproductive ageMost offspring survive to reproductive ageLarger adultsAdapted to stable climate and environmental conditionsLower population growth rate (r)Population size fairly stable and usually close to carrying capacity (K)Specialist nicheHigh ability to competeLate successional species

elephant saguaro

K-Selected Species

r-Selected Species

cockroach dandelion

Many small offspringLittle or no parental care and protection of offspringEarly reproductive ageMost offspring die before reaching reproductive ageSmall adultsAdapted to unstable climate and environmental conditionsHigh population growth rate (r)Population size fluctuates wildly above and below carrying capacity (K)Generalist nicheLow ability to competeEarly successional species

European KestralsEuropean Kestrals

r selectedr selected– Population grows at Population grows at

biotic maxbiotic max– Lots of offspringLots of offspring– Little parental careLittle parental care– Reproduce early, Reproduce early,

oftenoftenK selectedK selected– Population adapted Population adapted

to being at carrying to being at carrying capacitycapacity

– Few offspringFew offspring– Lots of parental careLots of parental care– Reproduce late, Reproduce late,

infrequentlyinfrequently

TestingTestingaa

hypothesishypothesis

Human Population GrowthHuman Population Growthoror

Go Forth and MultiplyGo Forth and Multiply

Human Population growthHuman Population growth For most of our history a logistic curve.For most of our history a logistic curve. Currently exponential growthCurrently exponential growth

– Not uniform around the globeNot uniform around the globe– Developing nations growing fastest Developing nations growing fastest

What has made the change possible?What has made the change possible?– Drop in death rate. Birth rate has fallen, not Drop in death rate. Birth rate has fallen, not

increased.increased. How long will this be sustainable?How long will this be sustainable? Future predictions for growth?Future predictions for growth?

Human Population GrowthHuman Population Growth

World – Wide Trend??World – Wide Trend??

Growth rates differ within and Growth rates differ within and between countries:between countries:

Births per woman

< 2

2-2.9

3-3.9

4-4.9

5+

Data notavailable

Births per woman

Infant deaths per 1,000live births

<10

10-35

36-70

71-100

100+Data notavailable

Infant deaths

Fig. 11.3, p. 240

<1%

1-1.9%

2-2.9%

3+%

Data notavailable

Annual worldpopulation growth

Population Growth

GNP per capita, 1998

Low income (Under $1,000)

Middle income ($1,000–$10,000)

High income (Above $10,000)

Fig. 1.5, p. 9

Income and country

Rapid Growth Slow Growth Zero Growth Negative Growth

General age structure diagrams

Canada United States

India Australia

Mexico China

Males Females Males Females

Age

Females Males

1955

20

20

Millions24

24

1985

Millions24

24

2035

Millions

2015

24

24

Millions

Yellow= Baby BoomersYellow= Baby Boomers

USA age structure DiagramsUSA age structure Diagrams

NOW WHAT?NOW WHAT?

Where we are:Where we are:

1930, 2 billion1930, 2 billion September 1999, 6 billionSeptember 1999, 6 billion

– 3 people every second3 people every second– 250,000 every day250,000 every day– 87 million every year87 million every year

–12 billion by 2050 12 billion by 2050 –8 Billion- if slower rate8 Billion- if slower rate

Influence on environmentInfluence on environment More land for agriculture, resource More land for agriculture, resource

exploitationexploitation More land for cities, roadways, suburbsMore land for cities, roadways, suburbs Less fish in the sea for the food chainLess fish in the sea for the food chain DeforestationDeforestation Oil, gas won’t last foreverOil, gas won’t last forever Pollution builds upPollution builds up Better “green” technologies?Better “green” technologies? Heightened awareness, concern?Heightened awareness, concern? Better understanding of ecosystems?Better understanding of ecosystems?

Human disturbance

Tropic of Capricorn

Equator

Predominantly naturalPartially disturbedHuman dominated

AntarcticCircle

Tropic ofCancer

ArcticCircleArcticCircle

Human domination of landscape

Every second… 5 people are born

and 2 people die,

a net gain of 3 people.

Improved medical care has dramatically reduced infant mortality and mortality of

women during labor.

Demographic transitionDemographic transition

Larger urban families cost more, birth rate Larger urban families cost more, birth rate dropsdrops

Population now much larger, slows its growth Population now much larger, slows its growth raterate

Influence of other (cultural, religious) pressures Influence of other (cultural, religious) pressures can slow birth rate declinecan slow birth rate decline

Women often lack freedom to determine family Women often lack freedom to determine family size, education employment opportunitiessize, education employment opportunities

Demographic transitionDemographic transition Death rate (infant mortality) drops firstDeath rate (infant mortality) drops first Birth rate remains constantBirth rate remains constant Population increases quicklyPopulation increases quickly Economy transitions from agriculture to urbanEconomy transitions from agriculture to urban

Stage 1 Preindustrial

Stage 2 Transitional

Stage 3 Industrial

Stage 4 Postindustrial

births

deaths

relative population

size

low increasing very high

decreasing low zero negative

3230282624222018161401910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010B

irth

s p

er t

ho

usa

nd

po

pu

lati

on

Demographictransition Depression Baby boom Baby bust Echo baby boom

World War II

Year

USA demographic transition & population size

4.0

3.5

3.0

2.5

2.02.1

1.5

1.0

0.5

01920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Bir

ths

per

wo

man

Total fertility rates in USA 1917-2000

Baby Boom(1946-64)

1975 on ….Below native replacement rate- immigration keeps population growing

19071914New laws restrict immigration

Great Depression

Legal immigration to the United States between 1820 and 1997