Population Dynamics and Population Dynamics and Human PopulationHuman Population

Part I:Part I:Population DynamicsPopulation Dynamics

Population DynamicsPopulation Dynamics

1. Size (# of individuals)1. Size (# of individuals) 2. Density (# of individuals in a certain space)2. Density (# of individuals in a certain space) 3. Dispersion (spatial pattern of individuals)3. Dispersion (spatial pattern of individuals) 4. Age distributions (proportion of individuals 4. Age distributions (proportion of individuals

by age in a population)by age in a population)

These may change in response to These may change in response to environmental stresses and changes in environmental stresses and changes in environmental conditions.environmental conditions.

What governs population size?What governs population size?

BirthsBirths DeathsDeaths ImmigrationImmigration EmigrationEmigration

Population change = (births + immigration) - Population change = (births + immigration) - (deaths + emigration)(deaths + emigration)

Biotic PotentialBiotic Potential All populations vary in their ability to grow.All populations vary in their ability to grow. The The intrinsic rate of increaseintrinsic rate of increase ( (rr) is the rate at ) is the rate at

which a population would grow if there were no which a population would grow if there were no limits on resources.limits on resources.

Organisms with high biotic potential tend to:Organisms with high biotic potential tend to: Reproduce early in lifeReproduce early in life Have short generation times (time between generations)Have short generation times (time between generations) Reproduce many timesReproduce many times Have large numbers of offspring each timeHave large numbers of offspring each time

Limits on Biotic PotentialLimits on Biotic Potential

No population can grow indefinitely!No population can grow indefinitely! There are limiting factors in the environment which There are limiting factors in the environment which

put a halt to population growth (put a halt to population growth (environment environment resistanceresistance).).

The actual population size is determined by the The actual population size is determined by the relationship between the biotic potential and the relationship between the biotic potential and the environmental resistance. This is known as the environmental resistance. This is known as the carrying capacitycarrying capacity ( (KK) of an organism (the number of ) of an organism (the number of individuals of a species that can be sustained individuals of a species that can be sustained indefinitely in a given location)indefinitely in a given location)

Minimum viable population Minimum viable population (MVP)(MVP)

Typically the intrinsic rate of increase for a Typically the intrinsic rate of increase for a population requires a certain minimum population requires a certain minimum population size be present. population size be present.

If notIf not Individuals may not be able to find matesIndividuals may not be able to find mates Interbreeding may occurInterbreeding may occur Genetic diversity may be too low to allow for Genetic diversity may be too low to allow for

adaptations to environmental changes.adaptations to environmental changes.

Exponential GrowthExponential Growth Populations with few resource limitations in the Populations with few resource limitations in the

environment will grow exponentially.environment will grow exponentially. The population size starts to grow slowly at first The population size starts to grow slowly at first

ant then grows faster as the population increases.ant then grows faster as the population increases. J shaped curveJ shaped curve

Logistic Growth CurveLogistic Growth Curve

There is exponential growth when the There is exponential growth when the population is small enough and hasn’t population is small enough and hasn’t encountered significant environmental encountered significant environmental resistance, but the growth decelerates and resistance, but the growth decelerates and levels off as it reaches the carrying capacity.levels off as it reaches the carrying capacity.

S shaped curve.S shaped curve.

Exceeding Carrying CapacityExceeding Carrying Capacity

Sometimes a species will overshoot the Sometimes a species will overshoot the carrying capacity. Typically because of a carrying capacity. Typically because of a reproductive lag time. reproductive lag time.

This results in a dieback or crash in the This results in a dieback or crash in the population.population.

Carrying capacity is notCarrying capacity is not

a fixed value.a fixed value.

Population Growth and DensityPopulation Growth and Density

Density independent population controlsDensity independent population controls - - control the population regardless of densitycontrol the population regardless of density Floods, fires, hurricanes, habitat destructionFloods, fires, hurricanes, habitat destruction

Density dependent population controlsDensity dependent population controls - - have a greater affect on the population as the have a greater affect on the population as the density increasesdensity increases Competition, predation, parasitism, diseaseCompetition, predation, parasitism, disease Ex. Bubonic plagueEx. Bubonic plague

Population fluctuationsPopulation fluctuations

StableStable - population usually remains about the - population usually remains about the samesame

IrruptiveIrruptive - population size is maintained, but - population size is maintained, but suddenly goes up and crashes back to a suddenly goes up and crashes back to a slightly lower levelslightly lower level

IrregularIrregular - population size goes up and down - population size goes up and down for no known reasonfor no known reason

CyclicCyclic- population goes through regular - population goes through regular increases and crashes over time.increases and crashes over time.

Reproductive StrategiesReproductive Strategies

r-selected species or opportunistsr-selected species or opportunists Reproduce rapidly when conditions are favorable or when Reproduce rapidly when conditions are favorable or when

a disturbance opens up an new opportunitya disturbance opens up an new opportunity Tend to be found in early stages of succession and are more Tend to be found in early stages of succession and are more

successful when there are disturbances.successful when there are disturbances. K-selected species or competitorsK-selected species or competitors

Do well in competitive situations when the population size Do well in competitive situations when the population size is near the carrying capacityis near the carrying capacity

Typically follow a logistic growth curveTypically follow a logistic growth curve May be more prone to extinctionMay be more prone to extinction Do better in stable environmentsDo better in stable environments

Characteristics of r strategistsCharacteristics of r strategists Many small offspringMany small offspring Small adultsSmall adults Early age of reproductionEarly age of reproduction Short generation timesShort generation times Little or no parental careLittle or no parental care Short livedShort lived Most offspring die before reaching reproductive ageMost offspring die before reaching reproductive age Population fluctuates wildly around KPopulation fluctuates wildly around K GeneralistsGeneralists Not competitiveNot competitive Adapted to changes in environmental conditionsAdapted to changes in environmental conditions Early successional speciesEarly successional species High biotic potentialHigh biotic potential

Characteristics of K strategistsCharacteristics of K strategists Fewer, larger offspringFewer, larger offspring Larger adultsLarger adults Later reproductive ageLater reproductive age Longer generation timesLonger generation times More parental careMore parental care Longer livedLonger lived Most offspring survive to reproductive ageMost offspring survive to reproductive age Population fairly stable around KPopulation fairly stable around K SpecialistsSpecialists CompetitiveCompetitive Better suited to stable environmentsBetter suited to stable environments Late succesional speciesLate succesional species Low biotic potentialLow biotic potential

The availability of suitable The availability of suitable habitat for individuals of a habitat for individuals of a population in a particular population in a particular area is what determines its area is what determines its ultimate population size.ultimate population size.

Survivorship Curves - Survivorship Curves - show the show the number of survivors of each age group number of survivors of each age group

for a particular speciesfor a particular species

Late loss curvesLate loss curves - most organisms survive - most organisms survive through their reproductive years and die off through their reproductive years and die off later. Examples: most K strategists.later. Examples: most K strategists.

Early loss curvesEarly loss curves - most organisms die off - most organisms die off before their reproductive years. Examples: before their reproductive years. Examples: most r strategists.most r strategists.

Constant loss curvesConstant loss curves - organisms die off at a - organisms die off at a fairly steady rate regardless of age. Examples: fairly steady rate regardless of age. Examples: songbirds, lizards, and small mammals. songbirds, lizards, and small mammals.

Life TablesLife Tables

Show the numbers of individuals at each age Show the numbers of individuals at each age from a survivorship curve. from a survivorship curve.

Show the probable life expectancy at each age.Show the probable life expectancy at each age. Life insurance companies rely on these to set Life insurance companies rely on these to set

prices.prices.

Conservation Biology - Conservation Biology - uses best uses best available information to preserve species and available information to preserve species and

ecosystems.ecosystems. Seeks to answer:Which species are in danger of Seeks to answer:Which species are in danger of

extinction?extinction? What functions in ecosystems are of the greatest value to What functions in ecosystems are of the greatest value to

us and other species?us and other species? What can we do to sustain and manage species and What can we do to sustain and manage species and

ecosystems?ecosystems? Assumes:Assumes:

Biodiversity is necessary for all life.Biodiversity is necessary for all life. Humans should not be the cause of loss of biodiversity.Humans should not be the cause of loss of biodiversity. Preserve biodiversity through intact and sufficient land in Preserve biodiversity through intact and sufficient land in

ecosystems.ecosystems.

Human Impacts on EcosystemsHuman Impacts on Ecosystems

Fragmentation and degradation of habitat.Fragmentation and degradation of habitat. Simplification of ecosystems often resulting in Simplification of ecosystems often resulting in

monocultures.monocultures. Overusing/wasting/destroying earth’s net primary Overusing/wasting/destroying earth’s net primary

productivity.productivity. Eliminating some predators.Eliminating some predators. Introduction of exotic species.Introduction of exotic species. Over harvesting natural resources.Over harvesting natural resources. Altering chemical cycles and energy flows.Altering chemical cycles and energy flows. Creating resistant pest species and bacteria.Creating resistant pest species and bacteria.

Part II:Part II:Human population dynamicsHuman population dynamics

Factors affecting human Factors affecting human population sizepopulation size

Population change = (births+immigration) - (deaths + Population change = (births+immigration) - (deaths + emigration)emigration)

Birth rate (crude birth rate) - the number of live births per 1000 Birth rate (crude birth rate) - the number of live births per 1000 people in a population per year.people in a population per year.

Death rate (crude death rate) - the number of deaths per 1000 Death rate (crude death rate) - the number of deaths per 1000 people in a population per year. people in a population per year.

Annual rate of natural population change (%) =Annual rate of natural population change (%) = birth rate - death ratebirth rate - death rate

1010

Rule of 70 (Doubling time) = 70 / (% increase)Rule of 70 (Doubling time) = 70 / (% increase)

Definitions of fertilityDefinitions of fertility

Replacement level fertility - the number of Replacement level fertility - the number of children a couple must have to replace children a couple must have to replace themselves.themselves. 2.1 in developed countries2.1 in developed countries Up to 2.5 in developing countriesUp to 2.5 in developing countries

Total fertility rate - an estimate of the average Total fertility rate - an estimate of the average number of children a woman will have during number of children a woman will have during her reproductive years.her reproductive years.

Factors affecting birth and Factors affecting birth and fertility ratesfertility rates

Importance of children to the workforceImportance of children to the workforce UrbanizationUrbanization Cost of raising and educating childrenCost of raising and educating children Educational and employment opportunites for womenEducational and employment opportunites for women Infant mortality rateInfant mortality rate Average age of marriageAverage age of marriage Availability of pensionsAvailability of pensions Availability of legal abortions and birth control Availability of legal abortions and birth control

methodsmethods Religious beliefs, traditions, and culturesReligious beliefs, traditions, and cultures

Factors affecting death ratesFactors affecting death rates

Availability of foodAvailability of food NutritionNutrition Public healthPublic health Sanitation and personal hygieneSanitation and personal hygiene Safety of water suppliesSafety of water supplies

Indicators of healthIndicators of health

Life expectancy - average number of years a newborn Life expectancy - average number of years a newborn can expect to livecan expect to live Life expectancy has increased in developed and many Life expectancy has increased in developed and many

developing countriesdeveloping countries Life expectancy is dropping in the world’s poorest nationsLife expectancy is dropping in the world’s poorest nations

Infant mortality rate - number of babies out of every Infant mortality rate - number of babies out of every 1000 born who die before their first birthday1000 born who die before their first birthday Single most important indicator of a society’s quality of lifeSingle most important indicator of a society’s quality of life High infant mortality indicatesHigh infant mortality indicates

UndernutritionUndernutrition MalnutritionMalnutrition Infectious diseaseInfectious disease

Age structure diagrams - Age structure diagrams - show the show the proportion of a population by sex at each age proportion of a population by sex at each age

levellevel Age CategoriesAge Categories

PrereproductivePrereproductive ReproductiveReproductive PostreproductivePostreproductive

Types of PyramidsTypes of Pyramids Rapid growthRapid growth

Guatemala, Nigeria, Saudi ArabiaGuatemala, Nigeria, Saudi Arabia Slow growthSlow growth

U.S., Canada, AustraliaU.S., Canada, Australia Zero growthZero growth

Spain, Austria, GreeceSpain, Austria, Greece Negative growthNegative growth

Germany, Bulgaria, SweedenGermany, Bulgaria, Sweeden

Population PyramidsPopulation Pyramids

Pros and cons of reducing birthsPros and cons of reducing births

Opponents of slowing growth:Opponents of slowing growth: Life expectancy is longer than at any time in Life expectancy is longer than at any time in

historyhistory The world can still support billions more peopleThe world can still support billions more people We are the world’s most valuable resourceWe are the world’s most valuable resource

Proponents of slowing growth:Proponents of slowing growth: If we do nothing, will cause more deathsIf we do nothing, will cause more deaths Cause more environmental harmCause more environmental harm

Demographic Transition - Demographic Transition - as as countries become more industrialized, first countries become more industrialized, first

their death rates, and then birth rates declinetheir death rates, and then birth rates decline Preindustrial stagePreindustrial stage

Little population growth because conditions are harsh and Little population growth because conditions are harsh and birth rates and death rates are highbirth rates and death rates are high

Transitional stageTransitional stage Industrialization begins, food production and health care Industrialization begins, food production and health care

improve so death rates drop, but birth rates remain highimprove so death rates drop, but birth rates remain high Industrial stageIndustrial stage

Birth rates begin to drop and population growth slowsBirth rates begin to drop and population growth slows Postindustrial stagePostindustrial stage

Birth rates continue to decline until they equal or become Birth rates continue to decline until they equal or become less than death ratesless than death rates

Demographic TransitionDemographic Transition

Demographic TrapDemographic Trap

Rapid growth rate in developing countries Rapid growth rate in developing countries could cause them to become stuck in stage 2 as could cause them to become stuck in stage 2 as rising population surpasses the ability of the rising population surpasses the ability of the country to provide for adequate healthcare and country to provide for adequate healthcare and outweighs any economic benefits.outweighs any economic benefits.

May cause countries to revert to stage 1.May cause countries to revert to stage 1. Also resources available to today’s developing Also resources available to today’s developing

nations are not the same as those once nations are not the same as those once available.available.

What can help reduce birth rates What can help reduce birth rates and population size?and population size?

Family planning programsFamily planning programs Empowering womenEmpowering women Economic incentivesEconomic incentives Improved health careImproved health care Access to educationAccess to education Eradicating povertyEradicating poverty Greater involvement of men in child-rearing and birth Greater involvement of men in child-rearing and birth

controlcontrol Reduction of unsustainable use of resourcesReduction of unsustainable use of resources

Part III:Part III:Case StudiesCase Studies

ThailandThailand Adopted policy in 1971 to reduce population growth. Adopted policy in 1971 to reduce population growth.

(Growth rate 3.2% and avg. of 6.4 children by 2002 growth (Growth rate 3.2% and avg. of 6.4 children by 2002 growth rate 0.8% and 1.8 kids)rate 0.8% and 1.8 kids)

What they tried to do?What they tried to do? Creative family planning methods supported by the governmentCreative family planning methods supported by the government High literacy and advances for womenHigh literacy and advances for women Better health care for women and childrenBetter health care for women and children Openness of Thai people for new ideasOpenness of Thai people for new ideas Support of family planning by religious leadersSupport of family planning by religious leaders

Still room for improvementStill room for improvement High levels of air pollutionHigh levels of air pollution Need to improve public healthNeed to improve public health

United StatesUnited States Population is growing faster than any other developed nation (1.2%)Population is growing faster than any other developed nation (1.2%) Higher birth rate than death rate accounts for 60% of increase, but also Higher birth rate than death rate accounts for 60% of increase, but also

large immigration rate.large immigration rate. Birth rates decreased between 1910 to 1930 as industrialization took hold Birth rates decreased between 1910 to 1930 as industrialization took hold

and women became more important in the work force. Remained low and women became more important in the work force. Remained low through the 30’s.through the 30’s.

Rose sharply between 1946 and 1964 - baby boom.Rose sharply between 1946 and 1964 - baby boom. Declined from 1965 to 1976 and then has increased again.Declined from 1965 to 1976 and then has increased again. High infant mortality rates in U.S. compared to other developed nationsHigh infant mortality rates in U.S. compared to other developed nations

Inadequate health care for poor women and their infantsInadequate health care for poor women and their infants Drug addictionDrug addiction High teen pregnancy ratesHigh teen pregnancy rates

In 2002, lower than since 1940In 2002, lower than since 1940 Still the highest teen pregnancy rate of developed nations.Still the highest teen pregnancy rate of developed nations.

United States Population United States Population PyramidsPyramids

ChinaChina Between 1972 and 2002, TFR has been cut from 5.7 to 1.8 Between 1972 and 2002, TFR has been cut from 5.7 to 1.8

childrenchildren Forced to do something or face mass starvationForced to do something or face mass starvation Has the most strict population control program in the worldHas the most strict population control program in the world

Couples urged to postpone age of marriage and only have one Couples urged to postpone age of marriage and only have one childchild

Married couples have easy access to birth control methods and Married couples have easy access to birth control methods and abortionsabortions

Married couples who pledge to have no more than one child Married couples who pledge to have no more than one child receive benefits such as extra food, free medical care, but breaking receive benefits such as extra food, free medical care, but breaking the pledge forfeits the benefits.the pledge forfeits the benefits.

Population should begin declining in 2042 (amend the proposals Population should begin declining in 2042 (amend the proposals then?)then?)

ChinaChinaPopulation PyramidsPopulation Pyramids

2100 Projected for 2050

IndiaIndia World’s first national family planning program in 1952, World’s first national family planning program in 1952,

but in 2002 still second most populous country.but in 2002 still second most populous country. Big problems with poverty, malnutrition, and Big problems with poverty, malnutrition, and

environmental conditions.environmental conditions. Half the labor force is unemployed or has only occasional workHalf the labor force is unemployed or has only occasional work 53% of children suffer from malnutrition53% of children suffer from malnutrition Has 16% of world’s pop, but only 2.3% of land and 2% of Has 16% of world’s pop, but only 2.3% of land and 2% of

forestsforests Half of cropland is degradedHalf of cropland is degraded 70% of water is seriously polluted70% of water is seriously polluted Still have an average of 3.2 children per woman. Most couples Still have an average of 3.2 children per woman. Most couples

believe that they need many children to do work and care for believe that they need many children to do work and care for them in old age. Cultural preference for boys; often keep them in old age. Cultural preference for boys; often keep having children until a boy is born. having children until a boy is born.

Comparing India’s growth to Comparing India’s growth to China’sChina’s

AfricaAfrica Has most of the world’s poorest countries with an average life Has most of the world’s poorest countries with an average life

expectancy of only 55 years.expectancy of only 55 years. Serious hunger and malnutrition in infants and children, but Serious hunger and malnutrition in infants and children, but

losing high number of young adults due to AIDSlosing high number of young adults due to AIDS HIV/AIDS epidemic is ravaging Africa (6000 people a day HIV/AIDS epidemic is ravaging Africa (6000 people a day

die). die). Life expectancy may drop to 35 or 40 yearsLife expectancy may drop to 35 or 40 years High number of orphans (40 million by 2010)High number of orphans (40 million by 2010) Loss of labor forceLoss of labor force Drop in food productionDrop in food production

Reduce spread of HIVReduce spread of HIV EducationEducation Health careHealth care Family planningFamily planning

African nationsAfrican nations

Zimbabwe:Zimbabwe: from 65 to 39 years from 65 to 39 years Bostwana:Bostwana: 62 to 40 62 to 40 Republic of Congo: Republic of Congo: 57 to 4757 to 47 Congo: Congo: 54 to 4954 to 49 Ethiopia:Ethiopia: 51 to 41 51 to 41 Ivory Coast:Ivory Coast: 57 to 46 57 to 46 Kenya:Kenya: 66 to 48 66 to 48 Namibia:Namibia: 65 to 42 65 to 42 Nigeria:Nigeria: 58 to 54 58 to 54 Rwanda:Rwanda: 54 to 42 54 to 42 South Africa:South Africa: 65 to 56 65 to 56 Swaziland:Swaziland: 58 to 39 58 to 39 Tanzania:Tanzania: 55 to 46 55 to 46 Uganda:Uganda: 54 to 43 54 to 43