presentation 1&2 of chapter 2
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8/3/2019 Presentation 1&2 of Chapter 2
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Understandingpopula0ongrowth
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SpeciesandPopula/on
Organism Species:gene/callysimilarorganismsthat
reproduce Popula/on:allmembersofaspeciesinan
area
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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
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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.
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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.
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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 .
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Fer/lityandBirthRates
CrudeBirthRateNumberofbirthsinayearperthousand.(Notadjustedforpopula/on
characteris/cs)
TotalFer/lityRateNumberofchildrenborntoanaveragewomaninapopula/onduringherlife.
ZeroPopula/onGrowthOccurswhenbirthsplusimmigra/oninapopula/onjustequaldeathsplus
emigra/on.
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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
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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.
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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.
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MortalityandDeathRates
CrudeDeathRateNumberofdeathsper
thousandpersonsinagivenyear.
Poorcountriesaverageabout20whilewealthiercountriesaverageabout10.Somerapidlygrowingcountrieshave
verylowcrudedeathratescomparedto
slowergrowingcountries,duetoa
higherpropor/onofyoungpeopleinthepopula/on.
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Popula/onGrowthRates
NaturalIncrease(CrudeBirthRateCrudeDeathRate)
TotalGrowthRateIncludesimmigra/onandemigra/on
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HumanPopula/onHistory
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DYNAMICSOFPOPULATIONGROWTH
Exponen/alGrowthGrowthataconstantrateofincreaseperunit/me.(Geometric)
Arithme/c(Logis/c)GrowthGrowthataconstantamountperunit/me.
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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.
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Exponential Growth Draw the graph. In exponential
growth, a large
number of individualsis added to the
population in each
succeeding time
period.
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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.
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In the early 1970s, Paul Ehrlich and John Holdren
developed a model summarized as:
Impact = Population * Affluence * Technology
Envronmental impact of a populaton
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Theworldpopula0onincreasedfrom3billionin1959to6billionby1999,adoublingthatoccurredover4years.TheCensus
Bureau'slatestprojec0onsimplythatpopula0ongrowthwillcon0nueintothe21stcentury,althoughmoreslowly.Theworld
popula0onisprojectedtogrowfrom6billionin1999to9billionby244,anincreaseof5percentthatisexpectedtorequire45
years
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Popula0onOscilla0ons
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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.
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Carrying Capacity
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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.
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GrowthtoaStablePopula0on
Logis/cGrowthGrowthslowsasthepopula0onapproachescarryingcapacity.
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CarryingCapacityofEarth
SolarEnergyabout10,000/mesglobalenergyuse
Globalenergyuse=sunlighton20,000squaremiles
Globallyabout13ofarablelandisusedforcrops
IfU.S.(5%ofpopula/on)uses25%ofresources,willtake5/mesearthsresourceoutputtoraiseeveryonetoourlevel
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Limi/ngFactors
EnvironmentalResistanceDensityDependentFactorsMortalityrates
increaseasthedensityofthepopula/on
increases.
Disease,Stress,Preda/onDensityIndependentFactorsEffectonmortality
rateisindependentofpopula/ondensity.
Abio/ccondi/ons.
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Popula/onGrowth
Formostofhumanhistory,humanshavenotbeenverynumerouscomparedtoother
species.
Ittookallofhumanhistorytoreach1billion.150yearstoreach3billion.12yearstogofrom5to6billion.
Humanpopula/ontripledduringthetwen/ethcentury.
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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.
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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
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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.
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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.
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POPULATIONGROWTH
Un0ltheMiddleAges,humanpopula0onswereheldincheckbydiseases,faminesandwars,and
thusgrewveryslowly.
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