Population EcologyPopulation Ecology

Population EcologyPopulation Ecology

Certain ecological principles govern the Certain ecological principles govern the

growth and sustainability of all growth and sustainability of all

populations--including human populations--including human

populations populations

Ecological Principles Apply to All Ecological Principles Apply to All SpeciesSpecies

Humans, Palms, Crabs, Seagulls, algae, etc.

Limits to GrowthLimits to Growth

A population’s growth depends on A population’s growth depends on

the resources of its environmentthe resources of its environment

Deer introduced to Angel Island Deer introduced to Angel Island

– Population outstripped resourcesPopulation outstripped resources

Angel IslandAngel Island

Angel Island 1Angel Island 1 A. Angel Island is a game reserve in San A. Angel Island is a game reserve in San

Francisco Bay near Sausalito Francisco Bay near Sausalito  B. In the early 1900's well-meaning nature B. In the early 1900's well-meaning nature

lovers introduced deer to the islandlovers introduced deer to the island C. With no natural predators to control C. With no natural predators to control

them the population quickly rose to a level them the population quickly rose to a level much higher than the island could supportmuch higher than the island could support

D. Well meaning people brought food to D. Well meaning people brought food to the island to feed the deer, causing the the island to feed the deer, causing the population to further increasepopulation to further increase

Angel Island 2Angel Island 2

E. Eventually the population grew to E. Eventually the population grew to over 300, much too large for the over 300, much too large for the island to supportisland to support

F. As the deer began to starve they F. As the deer began to starve they ate most of the native vegetation. ate most of the native vegetation. Without vegetation the soil started Without vegetation the soil started washing away and the island washing away and the island environment rapidly deterioratedenvironment rapidly deteriorated

Angel Island - 3Angel Island - 3

G. It was proposed that hunters kill some G. It was proposed that hunters kill some of the deer and/or that coyotes, the deer’s of the deer and/or that coyotes, the deer’s natural predators, be introduced to the natural predators, be introduced to the island. However many people objected island. However many people objected because they viewed both alternatives as because they viewed both alternatives as cruelcruel

H. Eventually two thirds of the population H. Eventually two thirds of the population was rounded up and moved to the was rounded up and moved to the mainland, at a cost of $3,000 per deermainland, at a cost of $3,000 per deer

Angel Island - 4Angel Island - 4 I. However, tracking studies revealed that I. However, tracking studies revealed that

the majority of the deer moved to the the majority of the deer moved to the mainland were killed by cars, dogs, mainland were killed by cars, dogs, coyotes and hunters within 60 dayscoyotes and hunters within 60 days

J. The story of Angel Island illustrates a J. The story of Angel Island illustrates a basic ecological principle: a population's basic ecological principle: a population's growth is dependent on the resources of growth is dependent on the resources of its environment. Human intervention could its environment. Human intervention could only postpone, not prevent the inevitableonly postpone, not prevent the inevitable

Angel Island - 5Angel Island - 5 K. Many environmental problems are simply the K. Many environmental problems are simply the

result of a lack of understanding of basic result of a lack of understanding of basic ecological principles by politicians, lawyers, ecological principles by politicians, lawyers, economists, the general public and even well economists, the general public and even well intentioned "environmentalists". Human intentioned "environmentalists". Human ignorance of simple ecological principles often ignorance of simple ecological principles often leads to disastrous resultsleads to disastrous results

From: From: http://arnica.csustan.edu/boty1050/Ecology/ecolohttp://arnica.csustan.edu/boty1050/Ecology/ecology.htmgy.htm

Human Population ProblemsHuman Population Problems

Over 6 billion people aliveOver 6 billion people alive

About 2 billion live in povertyAbout 2 billion live in poverty

Most resources are consumed by the Most resources are consumed by the

relatively few people in developed relatively few people in developed

countries countries

Population GrowthPopulation Growth

For most of human history, humans For most of human history, humans have not been very numerous have not been very numerous compared to other species.compared to other species.– It took all of human history to reach 1 It took all of human history to reach 1

billion.billion.– 150 years to reach 3 billion.150 years to reach 3 billion.– 12 years to go from 5 to 6 billion.12 years to go from 5 to 6 billion.

Human population tripled during the Human population tripled during the twentieth century.twentieth century.

Human Population HistoryHuman Population History

U.S. POPClock ProjectionU.S. POPClock Projection

According to the U.S. Bureau of the Census, the According to the U.S. Bureau of the Census, the resident population of the United States, resident population of the United States, projected to 03/21/05 at 17:04 GMT (EST+5) is projected to 03/21/05 at 17:04 GMT (EST+5) is

295,707,750295,707,750 COMPONENT SETTINGSCOMPONENT SETTINGS One birth every.................................. 7 seconds One birth every.................................. 7 seconds

One death every.................................. 11 seconds One death every.................................. 11 seconds One international migrant (net) every............ 24 One international migrant (net) every............ 24 seconds Net gain of one person seconds Net gain of one person every..................... 12 seconds every..................... 12 seconds

PopulationPopulation

A group of individuals of the same species A group of individuals of the same species

occupying a given area during a particular occupying a given area during a particular

period of timeperiod of time

Can be described by demographicsCan be described by demographics

– Vital statistics such as size, density, Vital statistics such as size, density,

distribution, and age structuredistribution, and age structure

Population Age StructurePopulation Age Structure

Divide population into age categoriesDivide population into age categories

Population’s reproductive base Population’s reproductive base

includes members of the reproductive includes members of the reproductive

and pre-reproductive age categoriesand pre-reproductive age categories

Population Age Structure DiagramPopulation Age Structure Diagram

Density & DistributionDensity & Distribution

Number of Number of individuals in some individuals in some specified area of specified area of habitathabitat

Crude density Crude density information is more information is more useful if combined useful if combined with distribution with distribution

datadata

clumped

nearly uniform

random Figure 45.2

Page 808  

Clumped DistributionClumped Distribution

Determining Population SizeDetermining Population Size

Direct counts are most accurate but Direct counts are most accurate but seldom feasibleseldom feasible

Can sample an area, then extrapolateCan sample an area, then extrapolate

Capture-recapture method is used for Capture-recapture method is used for mobile speciesmobile species

Population EstimatePopulation Estimate

How could you determine the How could you determine the population size of the students in population size of the students in Robinson Hall? Robinson Hall?

The number of revelers on the beach?The number of revelers on the beach?

Does Time and Place Make a Does Time and Place Make a Difference?Difference?

Daytona Beach

Hilton Head

Capture-Recapture MethodCapture-Recapture Method

Capture, mark, and release Capture, mark, and release individualsindividuals

Return later and capture second Return later and capture second samplesample

Count the number of marked Count the number of marked individuals and use this to estimate individuals and use this to estimate total populationtotal population

Example:Example:Capture - RecaptureCapture - Recapture

In 1970, naturalists wanted to estimate In 1970, naturalists wanted to estimate the number of pickerel fish in Dryden Lake the number of pickerel fish in Dryden Lake in central New York State. They in central New York State. They captured captured 232 pickerel232 pickerel, put a mark on their fins, , put a mark on their fins, and returned the fish to the lake. Several and returned the fish to the lake. Several weeks later, another weeks later, another sample of 329 sample of 329 pickerelpickerel fish were captured. Of this fish were captured. Of this second sample, second sample, 16 had marks on their 16 had marks on their fins.fins. (Chaterjee in Mosteller et al. (Chaterjee in Mosteller et al. Statistics by Example: Finding ModelsStatistics by Example: Finding Models).).

Chain PickerelChain Pickerel

How Many Pickerel Were in the How Many Pickerel Were in the Lake?Lake?

N = total number of pickerel in lakeN = total number of pickerel in lake NM = total number of marked pickerel NM = total number of marked pickerel

(232)(232) RC = Number of recaptured pickerel (16)RC = Number of recaptured pickerel (16) NS = number of fish in sample (329)NS = number of fish in sample (329)

NM/N = RC/NSNM/N = RC/NS N = (NM x NS)/RCN = (NM x NS)/RC

Solution Solution

N = (232 x 329)/16N = (232 x 329)/16

N = 4770N = 4770 pickerel in the lake pickerel in the lake (estimate)(estimate)

This is an example of how the This is an example of how the “Capture/Recapture” method works.“Capture/Recapture” method works.

AssumptionsAssumptions

The sampling is randomThe sampling is random The marked organisms will not be harmed The marked organisms will not be harmed

by the capture and markingsby the capture and markings The marked organisms will not avoid The marked organisms will not avoid

recapturerecapture The samples are statistically large enough The samples are statistically large enough

to avoid problems with sampling errorto avoid problems with sampling error No significant emigration/immigration No significant emigration/immigration

occursoccurs The sampling is done promptlyThe sampling is done promptly

Changes in Population SizeChanges in Population Size

Immigration adds individualsImmigration adds individuals

Emigration subtracts individualsEmigration subtracts individuals

Births add individualsBirths add individuals

Deaths subtract individualsDeaths subtract individuals

Zero Population GrowthZero Population Growth

Interval in which number of births Interval in which number of births

is balanced by number of deathsis balanced by number of deaths

Assume no change as a result of Assume no change as a result of

migrationmigration

Population size remains stablePopulation size remains stable

Per Capita RatesPer Capita Rates Rates per individualRates per individual

Total number of events in a time Total number of events in a time

interval divided by the number of interval divided by the number of

individualsindividuals

Per capita birth rate per month =Per capita birth rate per month =

Number of births per month Number of births per month

Population sizePopulation size

rr

Net reproduction per individual per unit Net reproduction per individual per unit

time (Intrinsic rate of natural increase) time (Intrinsic rate of natural increase)

a constant the units are inverse timea constant the units are inverse time

Variable combines per capita birth and Variable combines per capita birth and

death rates (assuming both constant)death rates (assuming both constant)

Can be used to calculate rate of growth Can be used to calculate rate of growth

of a populationof a population

Exponential Growth EquationExponential Growth Equation

GG = = rNrN

GG is population growth per unit time is population growth per unit time rr is net reproduction per individual is net reproduction per individual

per unit timeper unit time NN is population size is population size

Exponential GrowthExponential Growth

Population size Population size expands by ever expands by ever increasing increasing increments during increments during successive intervalssuccessive intervals

The larger the The larger the population gets, the population gets, the more individuals more individuals there are to there are to reproducereproduce

Figure 45.4Page 810

(r) Strategies(r) Strategies

Short lifeShort life Rapid growthRapid growth Early maturityEarly maturity Many small offspring.Many small offspring. Little parental care.Little parental care. Little investment in individual offspring.Little investment in individual offspring.

Adapted to unstable environment.Adapted to unstable environment. Pioneers, colonizersPioneers, colonizers Niche generalistsNiche generalists PreyPrey Regulated mainly by extrinsic factors.Regulated mainly by extrinsic factors. Low trophic level.Low trophic level.

Weedy Species – “r Strategists”Weedy Species – “r Strategists” Opportunistic Species - Quickly appear when opportunities Opportunistic Species - Quickly appear when opportunities

arise.arise.– Many weeds.Many weeds.

Pioneer Species - Can quickly colonize open, disturbed, or Pioneer Species - Can quickly colonize open, disturbed, or bare ground.bare ground.

Effect of DeathsEffect of Deaths

Population grows exponentially as long as per Population grows exponentially as long as per capita death rates are lower than per capita birth capita death rates are lower than per capita birth

ratesrates

25% mortality

between divisions

Figure 45.5Page 811

Biotic PotentialBiotic Potential

Maximum rate of increase per Maximum rate of increase per

individual under ideal conditionsindividual under ideal conditions

Varies between speciesVaries between species

In nature, biotic potential is rarely In nature, biotic potential is rarely

reachedreached

Limiting FactorsLimiting Factors

Any essential resource that is in Any essential resource that is in

short supplyshort supply

All limiting factors acting on a All limiting factors acting on a

population dictate sustainable population dictate sustainable

population sizepopulation size

Carrying Capacity (Carrying Capacity (KK))

Maximum number of individuals that Maximum number of individuals that

can be sustained in a particular habitatcan be sustained in a particular habitat

Logistic growth occurs when Logistic growth occurs when

population size is limited by carrying population size is limited by carrying

capacitycapacity

Logistic Growth EquationLogistic Growth Equation

G = rG = rmaxmax N ((K-N)/K)N ((K-N)/K)

G = G = population growth per unit timepopulation growth per unit time

rrmaxmax = = maximum population growth rate maximum population growth rate

per unit timeper unit time

N = N = number of individualsnumber of individuals

K = K = carrying capacitycarrying capacity

Logistic GrowthLogistic Growth

As size of the population increases, As size of the population increases, rate of reproduction decreasesrate of reproduction decreases

When the population reaches carrying When the population reaches carrying capacity, population growth ceasescapacity, population growth ceases

Figure 45.6Page 812

initial carrying capacity

new carrying capacity

Logistic Growth GraphLogistic Growth Graph

K StrategistsK Strategists

Long lifeLong life Slower growthSlower growth Late maturityLate maturity Fewer large offspring.Fewer large offspring. High parental care and protection.High parental care and protection. High investment in individual High investment in individual

offspring.offspring.

More on K StrategistsMore on K Strategists

Adapted to stable environment.Adapted to stable environment.Later stages of succession.Later stages of succession.Niche specialistsNiche specialistsPredators (often, but not always)Predators (often, but not always)Regulated mainly by intrinsic Regulated mainly by intrinsic

factors.factors.High trophic level.High trophic level.

Top PredatorsTop Predators

Overshooting CapacityOvershooting Capacity

Population may Population may temporarilytemporarily increase above increase above carrying capacitycarrying capacity

Overshoot is Overshoot is usually followed by usually followed by a crash; dramatic a crash; dramatic increase in deathsincrease in deaths

Figure 45.6Page 812

Reindeer on St. Matthew’s Island

Density-Dependent ControlsDensity-Dependent Controls

Logistic growth equation deals with Logistic growth equation deals with

density-dependent controlsdensity-dependent controls

Limiting factors become more Limiting factors become more

intense as population size intense as population size

increasesincreases

Disease, competition, parasites, Disease, competition, parasites,

toxic effects of waste productstoxic effects of waste products

Density-Independent ControlsDensity-Independent Controls

Factors unaffected by population Factors unaffected by population

densitydensity

Natural disasters or climate changes Natural disasters or climate changes

affect large and small populations affect large and small populations

alikealike

A Hurricane is an Example of a A Hurricane is an Example of a Density Independent FactorDensity Independent Factor

Earth Quakes and TsunamisEarth Quakes and Tsunamis

Life History PatternsLife History Patterns

Patterns of timing of reproduction Patterns of timing of reproduction

and survivorshipand survivorship

Vary among speciesVary among species

Summarized in survivorship Summarized in survivorship

curves and life tablescurves and life tables

Life TableLife Table

Tracks age-specific patterns Tracks age-specific patterns

Population is divided into age Population is divided into age

categoriescategories

Birth rates and mortality risks are Birth rates and mortality risks are

calculated for each age categorycalculated for each age category

Survivorship CurvesSurvivorship Curves

Graph of age-specific survivorship Graph of age-specific survivorship

Figure 45.8Page 815

Type IType I

Large animals, few offspring, much Large animals, few offspring, much parental care, live to an old ageparental care, live to an old age

Type IIType II

Birds are good examples……Birds are good examples……

Intermediate number of offspring, Intermediate number of offspring, some parental care, fairly constant some parental care, fairly constant survival rate over a lifesurvival rate over a life

time.time.

Type IIIType III

These are typical “r strategists”, These are typical “r strategists”, weedy species, pesky…..weedy species, pesky…..

Short life, many offspring, little Short life, many offspring, little parental care, high parental care, high

mortality of themortality of the

young…young…

Predation and Life History Predation and Life History

Guppy populations vary in life history Guppy populations vary in life history

characteristics and morphologycharacteristics and morphology

Differences have genetic basisDifferences have genetic basis

Variation seems to be result of directional Variation seems to be result of directional

selection by predatorsselection by predators

Human Population Growth Human Population Growth

Population now exceeds 6 billionPopulation now exceeds 6 billion

Rates of increase vary among countriesRates of increase vary among countries

Average annual increase is 1.26 percentAverage annual increase is 1.26 percent

Population continues to increase Population continues to increase

exponentiallyexponentially

Side-Stepping ControlsSide-Stepping Controls

Expanded into new habitats Expanded into new habitats

Agriculture increased carrying capacity; Agriculture increased carrying capacity;

use of fossil fuels aided increaseuse of fossil fuels aided increase

Hygiene and medicine lessened effects Hygiene and medicine lessened effects

of density-dependent controlsof density-dependent controls

Future GrowthFuture Growth

Exponential growth cannot continue Exponential growth cannot continue

foreverforever

Breakthroughs in technology may Breakthroughs in technology may

further increase carrying capacity further increase carrying capacity

Eventually, density-dependent Eventually, density-dependent

factors will slow growthfactors will slow growth

Fertility Rates Fertility Rates

Worldwide, average annual rate of Worldwide, average annual rate of

increase is 1.26%increase is 1.26%

Total fertility rate (TFR) is average Total fertility rate (TFR) is average

number of children born to a womannumber of children born to a woman

Highest in developing countries, lowest Highest in developing countries, lowest

in developed countriesin developed countries

Age Structure DiagramsAge Structure Diagrams

Show age distribution of a populationShow age distribution of a population

Rapid Growth

Slow Growth

Zero Growth

Negative Growth

Figure 45.14Page 821

Population MomentumPopulation Momentum

Lowering fertility rates Lowering fertility rates cannotcannot immediately slow population growth immediately slow population growth raterate

Why? There are already Why? There are already many future many future parents aliveparents alive

If every couple had just two children, If every couple had just two children, population would still keep population would still keep growing growing for another 60 yearsfor another 60 years

Projected Human PopulationsProjected Human Populations

Life Expectancy and IncomeLife Expectancy and Income

Slowing Growth in ChinaSlowing Growth in China

World’s most extensive family World’s most extensive family

planning program planning program

Government rewards small family Government rewards small family

size, penalizes larger families, size, penalizes larger families,

provides free birth control, abortion, provides free birth control, abortion,

sterilizationsterilization

Since 1972, TFR down to 1.8 from 5.7Since 1972, TFR down to 1.8 from 5.7

Effects of Economic Effects of Economic Development Development

Total fertility rates (TFRs) are highest in Total fertility rates (TFRs) are highest in

developing countries, lowest in developing countries, lowest in

developed countriesdeveloped countries

When individuals are economically When individuals are economically

secure, they are under less pressure to secure, they are under less pressure to

have large familieshave large families

Sweat Shop, IndiaSweat Shop, India

http://www.mcps.k12.md.us/curriculum/socialstd/grade7/india/Sweatshop.html

Shop size = 2m x 5m. How many people can you count?

Population Sizes in 2001Population Sizes in 2001

Asia 3.7 billion

Europe 727 million

Africa 816 million

Latin America 525 million

North America 316 million

Oceania 31 million

Demographic Demographic Transition ModelTransition Model

Based on historical data from Based on historical data from

western Europewestern Europe

Postulates that as countries become Postulates that as countries become

industrialized, first death rates drop, industrialized, first death rates drop,

then birth rates dropthen birth rates drop

Demographic Demographic Transition ModelTransition Model

Stage 1 Preindustrial

Stage 2 Transitional

Stage 3 Industrial

Stage 4 Postindustrial

births

deaths

relative population

size

low increasing very high decreasing low zero negativeFigure 45.16

Page 822

Resource ConsumptionResource Consumption

United States has 4.7 percent of the United States has 4.7 percent of the world’s populationworld’s population

Americans have a disproportionately Americans have a disproportionately large effect on the world’s resourceslarge effect on the world’s resources

Per capita, Americans consume more Per capita, Americans consume more resources and create more pollution resources and create more pollution than citizens of less developed than citizens of less developed nationsnations