Presentation 1&2 of Chapter 2

8/3/2019 Presentation 1&2 of Chapter 2

1/35


2/35

Understandingpopula0ongrowth


3/35

SpeciesandPopula/on

Organism Species:gene/callysimilarorganismsthat

reproduce Popula/on:allmembersofaspeciesinan

area


4/35

Population Growth and Natural Hazards

In question: Population growth as a cause fornatural disasters

Under debate: Population as a direct trigger forsome natural disasters, e.g., floods, landslides

In certainty: Population growing into danger zones,e.g., floodplains

In quest: Artificially controlling some naturalhazards


5/35

Populations What is a

population?

When we talkabout

populations what

in general do wemean?

A group of organisms of the samespecies that live in a specific

geographical area and interbreed.

usually breed with members of their

own population.

The group in general and the size ofthe population, or the number of

individuals in it.


6/35

Properties of Populations What properties are

used to describe

populations and

predict changes

within them?

What is Density?

What isDispersion?

Size, density, dispersion, and otherproperties

Densityis the number of individualsof the same species in that live in a

given unit of area.

Dispersionis the pattern ofdistribution of organisms in a

population. A populations dispersion

may be even, clumped, or random.


7/35

What factors affectthe size of a

population?

How does apopulation change?

Births, Deaths, Immigration andEmigration

Immigration- individuals moveinto a population

Emigration- Individuals leave apopulation

Populations grow when there aremore births than deaths or when

individuals move into the

population

Populations decline when thereare more deaths than births orwhen individuals leave the

population .


8/35

Fer/lityandBirthRates

CrudeBirthRateNumberofbirthsinayearperthousand.(Notadjustedforpopula/on

characteris/cs)

TotalFer/lityRateNumberofchildrenborntoanaveragewomaninapopula/onduringherlife.

ZeroPopula/onGrowthOccurswhenbirthsplusimmigra/oninapopula/onjustequaldeathsplus

emigra/on.


9/35

What is growthrate?

Overtime, thegrowth rates ofpopulations changebecause birth rates

and death rates

increase ordecrease.

Growth rateis an expression ofthe increase in the size of anorganism or population over a

given period of time.

Growth rate = birth rate - deathrate.

Growth rates can be positive,negative, or zero


10/35

What must occur forthe growth rate equalzero?

What does zeropopulation growthmean?

Write an Example:

How does negativepopulation growthoccur?

For the growth rate to be zero,the average number of birthsmust equal the averagenumber of deaths.

A population would remain thesame size.

If each pair of adults producedexactly 2 offspring, and eachof those offspring survived toproduce 2 offspring.

If the adults in a populationare not replaced by newbirths, the growth rate will benegative and the populationwill shrink.


11/35

Populations usually stay about the samesize from year to year because variousfactors, like competition and predation kill

many individuals before they can

reproduce.

These factors control the sizes ofpopulations.

In the long run, the factors also determinehow the population evolves.


12/35

MortalityandDeathRates

CrudeDeathRateNumberofdeathsper

thousandpersonsinagivenyear.

Poorcountriesaverageabout20whilewealthiercountriesaverageabout10.Somerapidlygrowingcountrieshave

verylowcrudedeathratescomparedto

slowergrowingcountries,duetoa

higherpropor/onofyoungpeopleinthepopula/on.


13/35

Popula/onGrowthRates

NaturalIncrease(CrudeBirthRateCrudeDeathRate)

TotalGrowthRateIncludesimmigra/onandemigra/on


14/35


15/35

HumanPopula/onHistory


16/35


17/35

DYNAMICSOFPOPULATIONGROWTH

Exponen/alGrowthGrowthataconstantrateofincreaseperunit/me.(Geometric)

Arithme/c(Logis/c)GrowthGrowthataconstantamountperunit/me.


18/35

What isExponential

growth?

Give anExample.

Exponential growthis wherepopulation numbers increase by a

certain factor in each successive time

period.

Occurs in nature only when populationshave plenty of food and space, and

have no competition or predators. For example, population explosions

occur when bacteria or molds grow on a

new source of food.


19/35

Exponential Growth Draw the graph. In exponential

growth, a large

number of individualsis added to the

population in each

succeeding time

period.


20/35

Logistic Growth

What LimitsPopulation

Growth?

Natural conditions are neitherideal nor constant, populationscannot grow forever.

Eventually, resources are usedup or the environment

changes, and deaths increase

or births decrease.


21/35

In the early 1970s, Paul Ehrlich and John Holdren

developed a model summarized as:

Impact = Population * Affluence * Technology

Envronmental impact of a populaton


22/35

Theworldpopula0onincreasedfrom3billionin1959to6billionby1999,adoublingthatoccurredover4years.TheCensus

Bureau'slatestprojec0onsimplythatpopula0ongrowthwillcon0nueintothe21stcentury,althoughmoreslowly.Theworld

popula0onisprojectedtogrowfrom6billionin1999to9billionby244,anincreaseof5percentthatisexpectedtorequire45

years


23/35

Popula0onOscilla0ons


24/35

What is carryingcapacity?

Why are carryingcapacities difficult topredict or calculate?

How is carryingcapacity estimated?

Carrying capacityis the largestpopulation that an environment cansupport at any given time.

A population may increase beyondthis number but it cannot stay at thisincreased size.

Because ecosystems change overtime therefore the population alsochanges

By looking at average populationsizes or by observing a populationcrash after a certain size has been

exceeded.


25/35

Carrying Capacity


26/35

Resource Limits

What is a limitingresource or factor?

What does the supplyof the most severely

limited resource

determine?

That natural resource is thencalled a limiting resource.

Limited resources determines thecarrying capacity of an

environment for a particular

species at a particular time.

A species reaches its carrying capacity when itconsumes a particular natural resource at the samerate at which the ecosystem produces the resource.


27/35

GrowthtoaStablePopula0on

Logis/cGrowthGrowthslowsasthepopula0onapproachescarryingcapacity.


28/35

CarryingCapacityofEarth

SolarEnergyabout10,000/mesglobalenergyuse

Globalenergyuse=sunlighton20,000squaremiles

Globallyabout13ofarablelandisusedforcrops

IfU.S.(5%ofpopula/on)uses25%ofresources,willtake5/mesearthsresourceoutputtoraiseeveryonetoourlevel


29/35

Limi/ngFactors

EnvironmentalResistanceDensityDependentFactorsMortalityrates

increaseasthedensityofthepopula/on

increases.

Disease,Stress,Preda/onDensityIndependentFactorsEffectonmortality

rateisindependentofpopula/ondensity.

Abio/ccondi/ons.


30/35

Popula/onGrowth

Formostofhumanhistory,humanshavenotbeenverynumerouscomparedtoother

species.

Ittookallofhumanhistorytoreach1billion.150yearstoreach3billion.12yearstogofrom5to6billion.

Humanpopula/ontripledduringthetwen/ethcentury.


31/35

Two Types of Population Regulation

Density independent factors are factorsthat affect all populations regardless of

their size ex. Unusual weather

Natural disastersSeasonal cyclesHuman activities

Cutting down forests, damming rivers,etc.


32/35

Two Types of Population Regulation

Density dependant factors are thosefactors that limit or decrease a

population due to the number of

individuals in a population

Examples: CompetitionPredationParasitismDisease


33/35

Population Regulation When a cause of death in a population is

density dependent, deaths occur more quickly ina crowded population than in a sparsepopulation.

This type of regulation happens whenindividuals of a population are densely packedtogether.

Limited resources, predation and disease resultin higher rates of death in dense populationsthan in sparse populations.


34/35

Population Regulation When a cause of death is density independent, a

certain proportion of a population may dieregardless of the populations density.

This type of regulation affects all populations in ageneral or uniform way.

Severe weather and natural disasters are oftendensity independent causes of death.


35/35

POPULATIONGROWTH

Un0ltheMiddleAges,humanpopula0onswereheldincheckbydiseases,faminesandwars,and

thusgrewveryslowly.

Documents

Presentation 1&2 of Chapter 2