population ecology

Population EcologyPopulation Ecology

Study of the factors that affect the Study of the factors that affect the population dynamics of any species!population dynamics of any species!

Current Population ClockCurrent Population Clock

http://www.ibiblio.org/lunarbin/worldpop

Overview of Chapter 8Overview of Chapter 8 Principles of Population EcologyPrinciples of Population Ecology Reproductive StrategiesReproductive Strategies The Human PopulationThe Human Population Demographics of CountriesDemographics of Countries Demographics of United StatesDemographics of United States

Principles of Population EcologyPrinciples of Population Ecology Population EcologyPopulation Ecology

– Study of populations and why their numbers change Study of populations and why their numbers change over timeover time

– Important forImportant for Endangered speciesEndangered species Invasive speciesInvasive species

PopulationPopulation– Group of individuals of same species living in the Group of individuals of same species living in the

same geographic area at the same timesame geographic area at the same time

Population Dynamics:Population Dynamics: Several factors are included:Several factors are included: Population densityPopulation density Birth rateBirth rate Death rateDeath rate Growth rateGrowth rate Age structureAge structure Resources (quantity, type, quality)Resources (quantity, type, quality)

How a Population Responds to the Environment Depends Upon Several

Interactions:

• How individuals compete for food• How disease, predation, and other environmental

pressures affect population• Reproductive success (or failure)• Management of populations for ecosystem health

and/or human needs• forestry management – tree populations, • agronomy – pest and crop populations• wildlife management – animal and fish populations

Population DensityPopulation Density the number of individuals of a species per unit the number of individuals of a species per unit

of area or volume at a given timeof area or volume at a given time Population density can change dramatically in Population density can change dramatically in

different habitats, or in the same habitat over a different habitats, or in the same habitat over a short distanceshort distance

Population density can indicate a potential Population density can indicate a potential pollution source in a river or streampollution source in a river or stream

Population DensityPopulation Density Population densityPopulation density

– The number of individuals of a species per unit area The number of individuals of a species per unit area or volume at a given timeor volume at a given time

– Ex: minnows per Liter of pond waterEx: minnows per Liter of pond water

Ovals below have same population, and Ovals below have same population, and different densitiesdifferent densities

Birth RateBirth Rate the rate at which individuals produce offspringthe rate at which individuals produce offspring Birth rate in humans: (b) = the number of Birth rate in humans: (b) = the number of

births per 1000 people per year (human terms)births per 1000 people per year (human terms)

Death RateDeath Rate

= the rate at which organisms die= the rate at which organisms dieDeath rate in humans: (d) = the Death rate in humans: (d) = the number of deaths per 1,000 people number of deaths per 1,000 people per yearper year

Growth RateGrowth Rate the rate of change (increase or decrease) in a the rate of change (increase or decrease) in a

population; population;

Formula: Growth rate (r) = b-d Formula: Growth rate (r) = b-d Growth rate in humans is also called the Growth rate in humans is also called the “natural increase” in the population“natural increase” in the population

Example Growth Rate Problem:Example Growth Rate Problem:

Population of 40,000 people; 800 births per Population of 40,000 people; 800 births per year; 400 deaths per yearyear; 400 deaths per year– b = 800/40,000 = 0.02b = 800/40,000 = 0.02– d = 400/40,000 = 0.01d = 400/40,000 = 0.01– r = 0.02 – 0.01 = 0.01 or 1.0% per year population r = 0.02 – 0.01 = 0.01 or 1.0% per year population

growth rategrowth rate

r is positive if people are born faster than they r is positive if people are born faster than they die; r is negative is people die faster than they die; r is negative is people die faster than they are bornare born

DispersalDispersal the movement of individuals from one location the movement of individuals from one location

to another, which affects the population at to another, which affects the population at either locationeither location

Immigration (i) – individuals entering a Immigration (i) – individuals entering a populationpopulation

Emigration (e) – individuals leaving a Emigration (e) – individuals leaving a populationpopulation

Global Populations vs. Local Global Populations vs. Local Populations…Populations…

Global populations depend purely on birth and Global populations depend purely on birth and death ratesdeath rates

Local populations depend on birth and death Local populations depend on birth and death rates plus immigration and emigration ratesrates plus immigration and emigration rates

Example Growth Rate Problem 2:Example Growth Rate Problem 2: Population of 250,000; 1400 births per year; Population of 250,000; 1400 births per year;

900 deaths per year; 100 immigrants and 200 900 deaths per year; 100 immigrants and 200 emigrants yearlyemigrants yearly

b = 1,400/250,000 = 0.0056b = 1,400/250,000 = 0.0056 d = 900/250,000 = 0.0036d = 900/250,000 = 0.0036 i = 100/250,000 = 0.0004i = 100/250,000 = 0.0004 e = 200/250,000 = 0.0008e = 200/250,000 = 0.0008 r = b – d + i –e = 0.0056 – 0.0036 + 0.0004 – r = b – d + i –e = 0.0056 – 0.0036 + 0.0004 –

0.0008 = 0.00160.0008 = 0.0016 **Note: This is equivalent to 0.16% growth**Note: This is equivalent to 0.16% growth

Birth Rate & Death Rate Birth Rate & Death Rate Calculations…Points to ConsiderCalculations…Points to Consider

NOTE: Sometimes birth and death rates are NOTE: Sometimes birth and death rates are simply given as percentages, which indicates simply given as percentages, which indicates how many people were born (or died) out of how many people were born (or died) out of 100. Either way of reporting (rate or number 100. Either way of reporting (rate or number per 1,000 living) is acceptable. per 1,000 living) is acceptable.

Example: Birth rate of 1.1% means 1.1 people Example: Birth rate of 1.1% means 1.1 people were born for every 100 people living in area were born for every 100 people living in area under consideration.under consideration.

Typically reported as 11 births per 1,000 Typically reported as 11 births per 1,000 people living.people living.

Example Growth Rate Problem 3: Example Growth Rate Problem 3: Note: NOT on your packet…Note: NOT on your packet…

Birth rate = 1.1% (NOTE: this would be 1.1 per Birth rate = 1.1% (NOTE: this would be 1.1 per 100; or 11 per 1,000)100; or 11 per 1,000)

Death rate = 0.8%Death rate = 0.8% Immigration = 0.08%Immigration = 0.08% Emigration = 0.04%Emigration = 0.04% Growth rate = 1.1 – 0.8 + .08 - .04Growth rate = 1.1 – 0.8 + .08 - .04 = 0.34%= 0.34%This means that 0.34 people are added to the This means that 0.34 people are added to the

population for every 100 living; or 3.4 people population for every 100 living; or 3.4 people per 1,000 living.per 1,000 living.

Calculating Future PopulationsCalculating Future Populations Extending population growth into the future utilizes a Extending population growth into the future utilizes a

physical constant e = 2.7183physical constant e = 2.7183 Formula:Formula:

Population Population (final)(final) = Population = Population (initial)(initial) x e x e (r * t)(r * t)

PPff = P = Pi i x e x e (r * t)(r * t)

Where r is the growth rate IN PERCENT expressed in Where r is the growth rate IN PERCENT expressed in DECIMAL form, and t is the time (number of years)DECIMAL form, and t is the time (number of years)

NOTE: On a calculator, you plug in the r x t first, then raise NOTE: On a calculator, you plug in the r x t first, then raise 2.7183 to that number, then multiply result by the initial 2.7183 to that number, then multiply result by the initial population!population!

Calculating Future PopulationsCalculating Future Populations EXAMPLE: EXAMPLE:

– 2002 Pakistan population = 143.5 million2002 Pakistan population = 143.5 million– Pakistan population growth rate is 2.1%Pakistan population growth rate is 2.1%– 2010 population:2010 population:

P = 143.5 million x 2.7183 P = 143.5 million x 2.7183 (.021 x 8 yrs)(.021 x 8 yrs)

P = 143.5 million x 2.7183 P = 143.5 million x 2.7183 (0.168)(0.168)

P = 143.5 million x 1.182937939P = 143.5 million x 1.182937939 P = 169.8 millionP = 169.8 million

Estimating Animal Populations:Estimating Animal Populations: Most of the time, determining animal Most of the time, determining animal

populations in an ecosystem setting is difficult populations in an ecosystem setting is difficult unless the animal is sessile (immobile) and unless the animal is sessile (immobile) and easy to count.easy to count.

Tag & Recapture is often the preferred method Tag & Recapture is often the preferred method used to estimate animal populationsused to estimate animal populations– Works by catching an initial sample, “tagging” with Works by catching an initial sample, “tagging” with

some identification mark or tag, releasing them, and some identification mark or tag, releasing them, and recapturing them later.recapturing them later.

– A simple ratio is used to determine final population.A simple ratio is used to determine final population.

Biotic Potential:Biotic Potential: the maximum rate at which a population can the maximum rate at which a population can

increaseincrease Life History Characteristics that Influence Life History Characteristics that Influence

biotic potential:biotic potential:– Age at which reproduction beginsAge at which reproduction begins– Amount of life that reproduction is possibleAmount of life that reproduction is possible– Number of reproductive periods per lifetimeNumber of reproductive periods per lifetime– Number of offspring per reproductive eventNumber of offspring per reproductive event

Larger organisms generally have smallest Larger organisms generally have smallest biotic potential, while microorganisms have the biotic potential, while microorganisms have the highesthighest

Life history traits – characteristics of an individual that influence survival and reproduction

Age at maturity

11 - 20 years 3-6 years

Atlantic SalmonAfrican elephant

2 months

House Mouse


Atlantic SalmonAfrican elephantHouse Mouse

1 calf every 3-8 years

1,500 to 8,000 eggs once

5-8 young every month

Number of offspring produced



Number of reproductive events

~3 - 10 1~6-12



Lifespan

60 - 70 years 3-6 years~2 years

Exponential Population Exponential Population Growth:Growth:

Populations with a constant Populations with a constant reproductive rate will have an reproductive rate will have an accelerating population growth accelerating population growth under optimal conditions under optimal conditions

doubling of population occurs in doubling of population occurs in successively shorter intervalssuccessively shorter intervals

Numbers of Bacteria During 10 hour Numbers of Bacteria During 10 hour Period (growing exponentially!)Period (growing exponentially!)

Environmental Resistance:Environmental Resistance: limits to exponential population growth occur limits to exponential population growth occur

when population reaches a size that allows when population reaches a size that allows environmental limits to take effectenvironmental limits to take effect

Environmental limits include:Environmental limits include:– SpaceSpace– FoodFood– Exposure to toxins, etc.Exposure to toxins, etc.– Increase in population of predatorsIncrease in population of predators

Carrying Capacity:Carrying Capacity: Carrying Capacity (K) = the largest population Carrying Capacity (K) = the largest population

that can be maintained for an indefinite period that can be maintained for an indefinite period of time in a particular environmentof time in a particular environment

Carrying capacity changes with changes in the Carrying capacity changes with changes in the environment, either natural or artificialenvironment, either natural or artificial– Droughts, pollution, excess rainfall, etc.Droughts, pollution, excess rainfall, etc.

Carrying CapacityCarrying Capacity

S-Shaped Population Curves…S-Shaped Population Curves… Graphs of populations influenced by Graphs of populations influenced by

environmental limitations show a characteristic environmental limitations show a characteristic S shape curveS shape curve

Shows an initial exponential growth, followed Shows an initial exponential growth, followed by slowed growth and then a flattening of the by slowed growth and then a flattening of the curve as environmental limits are reachedcurve as environmental limits are reached

S-Shaped Growth Curve (paramecia):S-Shaped Growth Curve (paramecia):

Example 1: bacterial population crash due Example 1: bacterial population crash due to toxic waste accumulationto toxic waste accumulation

Reproductive Strategies:Reproductive Strategies: Nature forces organisms to make tradeoffs in Nature forces organisms to make tradeoffs in

the expenditure of energythe expenditure of energy Only some energy can be used for Only some energy can be used for

reproduction, since each organism must reproduction, since each organism must uptake nutrients to grow, hunt for food, etc.uptake nutrients to grow, hunt for food, etc.

““r-selected” and “k-selected” species have r-selected” and “k-selected” species have developed over time in response to energy developed over time in response to energy requirementsrequirements

r – Selected Species:r – Selected Species:

Those species that have traits that favor Those species that have traits that favor growth rate strategies (“r-strategists)growth rate strategies (“r-strategists)

Typical r-selected strategies:Typical r-selected strategies:– Small body sizeSmall body size– Early maturityEarly maturity– Short life spanShort life span– Large broodsLarge broods– Minimal required parental careMinimal required parental care– Live in unpredictable or temporary environmentsLive in unpredictable or temporary environments– Opportunists (like mosquitos, insects, weeds, etc.)Opportunists (like mosquitos, insects, weeds, etc.)

K-Selected SpeciesK-Selected Species

• Called “K-strategists”

• Species that try to maximize the chances of survival, especially in environments where the number of individuals (N) is near the carrying capacity (K) of the environment

K-Selected Strategies…K-Selected Strategies…

• Long life span, slow development

• Late reproduction

• Large body size

• Low reproductive rate

• Examples: redwood trees, animals requiring long parental care (Tawny owls pair for life!)

Survivorship:Survivorship:

• Life tables are constructed by ecologists to indicate the relative chances of survival at any time during the life of the organism

• Each organism is classified as a Type I, Type II, or Type III Survivorship organism

Survivorship = the probability that a given individual Survivorship = the probability that a given individual in a population will survive to a particular age.in a population will survive to a particular age.

Type I Survivorship: the Type I Survivorship: the young and those at young and those at reproductive age have reproductive age have a high chance of livinga high chance of living

Type II Survivorship: the Type II Survivorship: the probability of survival probability of survival does not change with does not change with ageage

Type III Survivorship: the Type III Survivorship: the probability of death probability of death greatest early in life, greatest early in life, those that survive have those that survive have high survival rate until high survival rate until old ageold age

Factors That Affect Population Factors That Affect Population SizeSize

Density-Dependent Factors: Density-Dependent Factors: A change in population density initiates A change in population density initiates

some factor, which subsequently has a some factor, which subsequently has a counter-effect on the population counter-effect on the population

Examples of D-D Factors:Examples of D-D Factors:Disease, predation, competition for resourcesDisease, predation, competition for resources

Predator-prey relationships involve Predator-prey relationships involve dynamics of density-dependent factors.dynamics of density-dependent factors.

Predator-Prey on Isle Royale…Predator-Prey on Isle Royale…

From 1960 to the mid 1980’s…this is a simple predator-prey dynamic relationshipFrom 1960 to the mid 1980’s…this is a simple predator-prey dynamic relationship Mid 1980’s the wolf population crashed…later confirmed to be the result of a deadly Mid 1980’s the wolf population crashed…later confirmed to be the result of a deadly

canine parvovirus disease…canine parvovirus disease… This allowed moose to flourish…but by mid-1990’s there were so many that they This allowed moose to flourish…but by mid-1990’s there were so many that they

literally overgrazed their main food source (ash and aspen)…which led to a sudden literally overgrazed their main food source (ash and aspen)…which led to a sudden collapse, which then triggered a die-off of the already struggling wolves by 1998 collapse, which then triggered a die-off of the already struggling wolves by 1998 (only 14 individuals were counted!)(only 14 individuals were counted!)

Population Cycles – Hares/Lynx Example

Example 2: Population cycling due Example 2: Population cycling due to organism interactionto organism interaction

Start: both have low population densityStart: both have low population density Hares – high food, low predators = pop increase Hares – high food, low predators = pop increase

over next generationsover next generations Lynx – as hares increase, more food = pop Lynx – as hares increase, more food = pop

increaseincrease Hares – when high pop density, increased Hares – when high pop density, increased

competition for food and increased predation = low competition for food and increased predation = low birth rate & high death rate = sharp pop decreasebirth rate & high death rate = sharp pop decrease

Lynx – when high pop density and few hares, low Lynx – when high pop density and few hares, low food = low birth rate & high death rate = sharp pop food = low birth rate & high death rate = sharp pop decreasedecrease

Back to startBack to start

Population Cycles

Density-Independent Density-Independent Factors…Factors…

Any environmental factor that Any environmental factor that affects the size of a population but affects the size of a population but is not influenced by changes in is not influenced by changes in population densitypopulation density

Usually Usually abioticabiotic factors, such as factors, such as random severe weather, fires, random severe weather, fires, timing & severity of winter season, timing & severity of winter season, etc.etc.

Cause distress to a populationCause distress to a population

Human PopulationHuman Population

Right now at over 6.6 billion and counting…Right now at over 6.6 billion and counting… Scientific advances have enabled us to Scientific advances have enabled us to

improve the productivity of the land…so food improve the productivity of the land…so food production has kept pace…not a limiting production has kept pace…not a limiting factor for much of the worldfactor for much of the world

However, have we reduced the ability of the However, have we reduced the ability of the land to sustainably feed future generations? land to sustainably feed future generations?

Exponential Exponential growth so fargrowth so far

Should “level Should “level out” out” sometime sometime during the during the 2121stst century century

S-curve may S-curve may be be developing developing alreadyalready

What will What will cause the S-cause the S-curve????curve????

The Human Population Clock…The Human Population Clock…

100 million more people from 2009 to 100 million more people from 2009 to 2010…let’s see why:2010…let’s see why:

Increase is NOT due to a rise in the birth rate Increase is NOT due to a rise in the birth rate (b). (b). World birth rate has declined slightly.World birth rate has declined slightly.

Increase is due to a DRAMATIC decrease in Increase is due to a DRAMATIC decrease in the death rate (d).the death rate (d).– Greater food productionGreater food production– Better medical careBetter medical care– Improvements in water quality and sanitationImprovements in water quality and sanitation

World Growth RateWorld Growth RateActually has started to decline!Actually has started to decline!

Growth Rate (r) was at 2.2% in 1960’s, Growth Rate (r) was at 2.2% in 1960’s, now estimated at 1.2% (2006)now estimated at 1.2% (2006)

S-curve coming soon…S-curve coming soon…

Zero Population Growth: when the birth Zero Population Growth: when the birth rate = death rate; should occur by the rate = death rate; should occur by the end of the 21end of the 21stst century (2100) century (2100)

Role of the U.N. (United Nations)Role of the U.N. (United Nations)

UN periodically provides estimates of UN periodically provides estimates of population growth rates in each country, population growth rates in each country, including factors influencing births and including factors influencing births and deaths. deaths. UN estimates that human population will UN estimates that human population will most likely be 9.1 billion by 2050. (range most likely be 9.1 billion by 2050. (range between 7.7 and 10.6 billion)between 7.7 and 10.6 billion)Earth’s “carrying capacity” unknown…but Earth’s “carrying capacity” unknown…but studies by Van Den Bergh and Rietveld studies by Van Den Bergh and Rietveld (Netherlands) suggest 7.7 billion is our upper (Netherlands) suggest 7.7 billion is our upper limit!limit!Will humans slow down pop. growth, or will Will humans slow down pop. growth, or will there be widespread human suffering and there be widespread human suffering and death as Earth becomes uninhabitable????death as Earth becomes uninhabitable????

DemographicsDemographicsBranch of sociology that deals with Branch of sociology that deals with population statistics population statistics

Separates countries into categories Separates countries into categories based on stage of development, which based on stage of development, which relates to population growth potentialrelates to population growth potential

Highly Developed, Developing, Less-Highly Developed, Developing, Less-Developed nationsDeveloped nations

Demographics…Demographics…Highly Developed Countries include:Highly Developed Countries include:– U.S., Germany, Canada, France, Sweden, U.S., Germany, Canada, France, Sweden,

Australia, Japan, U.K., etc.Australia, Japan, U.K., etc.– Highly industrializedHighly industrialized– Low birth ratesLow birth rates– Very low infant mortality ratesVery low infant mortality rates– Longer life expectanciesLonger life expectancies

Demographics…Demographics…Developing Countries – includes moderately Developing Countries – includes moderately developed and less-developeddeveloped and less-developed

Moderately developed countries include:Moderately developed countries include:– Thailand, Mexico, Turkey, Peru, Brazil, Chile, Thailand, Mexico, Turkey, Peru, Brazil, Chile,

etcetc– Moderate birth ratesModerate birth rates– Moderate infant mortality ratesModerate infant mortality rates– Moderate level of industrializationModerate level of industrialization

Demographics…Demographics…Less Developed Nations Include:Less Developed Nations Include:– Cambodia, Bangladesh, Ethiopia, Niger, etc.Cambodia, Bangladesh, Ethiopia, Niger, etc.– Highest birth ratesHighest birth rates– Highest infant mortality ratesHighest infant mortality rates– Shortest life expectanciesShortest life expectancies– Lowest average per-capita GNI PPP’s Lowest average per-capita GNI PPP’s (gross (gross

national income in purchasing power party divided by midyear national income in purchasing power party divided by midyear population)population)

Doubling Time:Doubling Time:

Doubling Time = amount of time it takes for Doubling Time = amount of time it takes for the population to double in sizethe population to double in size– Usually calculated for each countryUsually calculated for each country

Formula for Doubling Time (Formula for Doubling Time (ttdd))

– ttd d = 70/r= 70/r

Shorter the doubling time, the less developed Shorter the doubling time, the less developed the country likely isthe country likely is

Typical Doubling Times:Typical Doubling Times:– Laos = 30 yrs.; Laos = 30 yrs.; Ethiopia = 28 yrs.Ethiopia = 28 yrs.– France = 175 yrs.;France = 175 yrs.; Turkey = 47 yrs.Turkey = 47 yrs.

Fertility:Fertility:

Replacement-Level Fertility = the number of Replacement-Level Fertility = the number of children a couple must produce in order to children a couple must produce in order to “replace” themselves “replace” themselves (usually considered 2.1, since (usually considered 2.1, since some infants & children die before reaching maturity) some infants & children die before reaching maturity)

Total Fertility Rate is currently 2.8 worldwideTotal Fertility Rate is currently 2.8 worldwide

Demographic Stages:Demographic Stages:

Four stages are observed, based Four stages are observed, based upon European historyupon European history

1.1. Pre-industrial stagePre-industrial stage

2.2. Transitional stageTransitional stage

3.3. Industrial stageIndustrial stage

4.4. Postindustrial stagePostindustrial stage

Pre-industrial stagePre-industrial stage

High birth and death ratesHigh birth and death rates Modest population growthModest population growth High infant mortality rateHigh infant mortality rate Famines, plagues, wars commonFamines, plagues, wars common

Transitional StageTransitional Stage

Lowered death rate due to advances Lowered death rate due to advances in health care, better food supply, in health care, better food supply, water sanitation measureswater sanitation measures

Birth rate still highBirth rate still high Population grows rapidlyPopulation grows rapidly

Industrial StageIndustrial Stage

Decline in birth rates, still relatively Decline in birth rates, still relatively low death ratelow death rate

Population growth rate slows a bitPopulation growth rate slows a bit Increase in wealth usually Increase in wealth usually

accompanies a decrease in birth accompanies a decrease in birth ratesrates

Postindustrial StagePostindustrial Stage

Low birth and death ratesLow birth and death rates Better educated and more affluent Better educated and more affluent

population…tend to desire smaller population…tend to desire smaller familiesfamilies

Examples: U.S.A., Canada, Australia, Examples: U.S.A., Canada, Australia, Japan, EuropeJapan, Europe

Demographic Stages based on Demographic Stages based on birth and death rates…birth and death rates…

Age Structure of CountriesAge Structure of Countries

Age structure = the number and Age structure = the number and proportion of people at each age in a proportion of people at each age in a populationpopulation

Age structure helps in determining Age structure helps in determining future growth ratesfuture growth rates

Age structure diagrams provide a quick Age structure diagrams provide a quick way to look at figures, and determine way to look at figures, and determine what is happening to a populationwhat is happening to a population

Age Structure Diagrams:Age Structure Diagrams:

Nigeria, United States, and Nigeria, United States, and Germany Age Structure Germany Age Structure

Diagrams:Diagrams:

United States Population United States Population Issues:Issues:

Largest population of all “highly developed” Largest population of all “highly developed” nationsnations

U.S. is over-populated due ONLY to immense U.S. is over-populated due ONLY to immense over-consumptionover-consumption of resources by individuals of resources by individuals

Immigration rate is among the highest, adding Immigration rate is among the highest, adding to population growth well beyond birth rateto population growth well beyond birth rate

1 million legal immigrants yearly, plus illegal 1 million legal immigrants yearly, plus illegal immigrants estimated at 300,000 yearly immigrants estimated at 300,000 yearly (conservative estimate…)(conservative estimate…)

No formal population policy exists (as it does in No formal population policy exists (as it does in China and other countries, for example)China and other countries, for example)

United States Population United States Population Issues:Issues:

Immigration and Nationality Act (1952) Immigration and Nationality Act (1952) now called the Immigration Reform and now called the Immigration Reform and Control Act (IRCA):Control Act (IRCA): Abolished national quotas on immigrationAbolished national quotas on immigration Gives preference to those with family Gives preference to those with family

members already here, those who can fill members already here, those who can fill vacant jobs, and refugees seeking asylumvacant jobs, and refugees seeking asylum

Most immigrants now come from Mexico, Most immigrants now come from Mexico, Phillipines, Vietnam, Dominican Republic, Phillipines, Vietnam, Dominican Republic, and Chinaand China

Many immigrants are poor, have few skillsMany immigrants are poor, have few skills

Education of Immigrants into Education of Immigrants into USUS

Immigration & Environmental Immigration & Environmental Questions Questions

Arguments/Questions in favor of immigration restrictions:Arguments/Questions in favor of immigration restrictions: Is population of U.S. already too large?Is population of U.S. already too large? More immigrants means more pollution, less literate public, More immigrants means more pollution, less literate public,

resource depletion?resource depletion? Immigrants adopt the polluting lifestyle of current U.S. Immigrants adopt the polluting lifestyle of current U.S.

residents?residents? Immigrants generally do not get involved in the political Immigrants generally do not get involved in the political

process…creates a more apathetic populationprocess…creates a more apathetic population Arguments/Questions against immigration restrictions:Arguments/Questions against immigration restrictions:

Morally unacceptable to refuse immigrants?Morally unacceptable to refuse immigrants? Immigrants typically lead simpler lifestyles, so they contribute Immigrants typically lead simpler lifestyles, so they contribute

only marginally to environmental stress?only marginally to environmental stress? Creates a global consciousness & more diverse populationCreates a global consciousness & more diverse population Immigrants will gladly work in jobs most Americans would Immigrants will gladly work in jobs most Americans would

prefer not to…so they are necessary to some degree????prefer not to…so they are necessary to some degree???? Where do you stand????Where do you stand????

population ecology

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