ObjectiveObjective Explain how population sizes are Explain how population sizes are
regulated.regulated.
Key TermsKey Terms
PopulationPopulation
DispersionDispersion
Growth rateGrowth rate
Reproductive potentialReproductive potential
Carrying capacityCarrying capacity
What Is a Population?What Is a Population? Group of organisms of the same speciesGroup of organisms of the same species
live in the same area live in the same area interbreedinterbreed
Organisms usually breed with members Organisms usually breed with members of their own population.of their own population.
PopulationsPopulations ““Population” refers to the group as a Population” refers to the group as a
whole or the size - number of whole or the size - number of individuals (members) in the group.individuals (members) in the group.
PopulationsPopulations Population DensityPopulation Density - number of - number of
members that live in a specific area.members that live in a specific area.
PopulationsPopulations Dispersion - Dispersion -
distribution of distribution of organisms in a organisms in a populationpopulation ClumpedClumped UniformUniform RandomRandom
Growth RateGrowth Rate Population change over time can be Population change over time can be
represented by:represented by:
Growth RateGrowth Rate Changes when birth rates and death Changes when birth rates and death
rates increase or decrease. rates increase or decrease. Can be positive, negative, or zero.Can be positive, negative, or zero.
Growth RateGrowth Rate Positive – average number Positive – average number
of births of births >> average average number of deathsnumber of deaths
Negative - average number Negative - average number of births of births << average average number of deathsnumber of deaths
Zero - average number of Zero - average number of births = average number births = average number of deathsof deaths
Population sizes usually stay Population sizes usually stay the samethe same
Certain factors control the Certain factors control the sizes of populations (limiting sizes of populations (limiting factors).factors).
• spacespace• diseasedisease• immigration/emigrationimmigration/emigration• predators and parasitespredators and parasites
Growth RateGrowth Rate
Reproductive PotentialReproductive Potential The maximum number of offspring a The maximum number of offspring a
specific organism can produce.specific organism can produce. Depends upon Depends upon
fecundityfecundity fertilityfertility gestationgestation
Reproductive PotentialReproductive Potential Increases when individuals Increases when individuals
produce more offspring at a timeproduce more offspring at a time reproduce more oftenreproduce more often reproduce earlier in lifereproduce earlier in life
• shortens generation time – average age of shortens generation time – average age of reproductionreproduction
Reproductive PotentialReproductive Potential Small organisms have short Small organisms have short
generation times generation times can reproduce after few hours/few dayscan reproduce after few hours/few days populations grow quicklypopulations grow quickly
Reproductive PotentialReproductive Potential Large organisms reach reproductive Large organisms reach reproductive
age after years age after years have a much lower reproductive have a much lower reproductive
potentialpotential populations grow slowlypopulations grow slowly
Exponential GrowthExponential Growth A large number of A large number of
individuals is added individuals is added to the population to the population each generation. each generation.
Numbers increase Numbers increase by a certain factor by a certain factor (usu. 2).(usu. 2).
Occurs in nature Occurs in nature with plenty of with plenty of resources and no resources and no predators.predators.
Only the best adapted members of a Only the best adapted members of a population will survive and population will survive and reproduce. reproduce.
Characteristics of a population may Characteristics of a population may evolve over time.evolve over time.
Limits to Population GrowthLimits to Population Growth
Carrying CapacityCarrying Capacity Largest population an environment Largest population an environment
can support at any time.can support at any time. Population can increase beyond this Population can increase beyond this
number but cannot stay elevatednumber but cannot stay elevated
Carrying CapacityCarrying CapacityEstimated by average population Estimated by average population sizes or by observing population sizes or by observing population crashes after a certain size has been crashes after a certain size has been exceeded.exceeded.
Resource LimitsResource Limits
Resource LimitsResource Limits Carrying capacity is reached when Carrying capacity is reached when
species consume a resource at the species consume a resource at the same rate that the resource is same rate that the resource is produced.produced. resource consumption = resource creationresource consumption = resource creation
That natural resource is called a That natural resource is called a limiting resource.limiting resource. FoodFood WaterWater LightLight
Resource competition Resource competition increases as increases as population population approaches carrying approaches carrying capacity.capacity.
Competition within a Competition within a population is part of population is part of the pressure of the pressure of natural selection.natural selection.
Competition Within a Competition Within a PopulationPopulation
Members of a species may compete Members of a species may compete indirectly for social dominance or for a indirectly for social dominance or for a territory.territory.
A territory is an area defended by one or A territory is an area defended by one or more individuals against other individuals.more individuals against other individuals. space space sheltershelter foodfood matesmates breeding sitesbreeding sites
Competition Within a Competition Within a PopulationPopulation
Causes of death in a population may Causes of death in a population may be density dependent or density be density dependent or density independent.independent.
Population RegulationPopulation Regulation
Population RegulationPopulation Regulation
Density dependent Density dependent cause of death - cause of death - deaths occur more deaths occur more quickly in a quickly in a crowded population crowded population than in a sparse than in a sparse population.population. Limiting factorsLimiting factors PredationPredation EmigrationEmigration
Population RegulationPopulation Regulation
Population RegulationPopulation Regulation Density independent cause of death Density independent cause of death
– some of the population can die – some of the population can die regardless of the population’s regardless of the population’s density.density. Severe weather Severe weather Natural disastersNatural disasters
Do Now/Objective – separate Do Now/Objective – separate paper…Hand In (4 min)paper…Hand In (4 min)
Do all living organisms interact in the Do all living organisms interact in the same way?same way?
List the different ways organisms List the different ways organisms interact with each other.interact with each other.
NicheNiche Ecological role of an organismEcological role of an organism
where it makes its homewhere it makes its home resources it needs to surviveresources it needs to survive how it interacts with other organismshow it interacts with other organisms
A niche includes an organism’s A niche includes an organism’s habitat. habitat. habitat is an area within an ecosystem.habitat is an area within an ecosystem.
Niche MapNiche Map
All organisms use their habitats in a unique way.All organisms use their habitats in a unique way.
Think about your niche (where you fit into your Think about your niche (where you fit into your community) and answer:community) and answer:
• Where do you gather your favorite resources?Where do you gather your favorite resources?
• Who do you compete or cooperate with?Who do you compete or cooperate with?
• Where do you live and where do you hang out?Where do you live and where do you hang out?
• Do you spend certain parts of the day in certain places?Do you spend certain parts of the day in certain places?
Draw a niche bubble map that shows how your use Draw a niche bubble map that shows how your use your habitat. INCLUDE 4+ interactions and your habitat. INCLUDE 4+ interactions and describedescribe those interactions on your maps. those interactions on your maps.
Key TermsKey Terms
NicheNiche
CompetitionCompetition
PredationPredation
ParasitismParasitism
MutualismMutualism
ComensalismComensalism
SymbiosisSymbiosis
Species InteractionSpecies Interaction Five main types of interactions:Five main types of interactions:
• CompetitionCompetition• PredationPredation• ParasitismParasitism• MutualismMutualism• CommensalismCommensalism
CompetitionCompetition Organisms try to use the same Organisms try to use the same
limited resourcelimited resource Members of the same species Members of the same species
competecompete they require the same resources they require the same resources they occupy the same niche they occupy the same niche
Indirect CompetitionIndirect Competition
Species can compete Species can compete even if they never even if they never come into direct come into direct contact with each contact with each other.other.
Adaptations to CompetitionAdaptations to Competition Members of different species Members of different species
sometimes compete (niche overlap)sometimes compete (niche overlap) each species use some of the same each species use some of the same
resources in a habitat.resources in a habitat.
Adaptations to CompetitionAdaptations to Competition
Law of Competitive ExclusionLaw of Competitive Exclusion No two species can occupy the same No two species can occupy the same
niche (competing for the same niche (competing for the same resources) at the same time indefinitelyresources) at the same time indefinitely
Adaptations to CompetitionAdaptations to CompetitionThe species will often divide up the The species will often divide up the niche niche
by areaby area
by time of useby time of use
Adaptations to CompetitionAdaptations to Competition Niche restriction - each species uses Niche restriction - each species uses
less of the niche than they are less of the niche than they are capable of using. capable of using. Actual niche may be smaller than Actual niche may be smaller than
potential niche.potential niche.
Adaptations to CompetitionAdaptations to Competition
PredationPredation One species kills and eats the other One species kills and eats the other
speciesspecies predatorpredator preyprey
PredatorsPredators
Some predators Some predators eat only specific eat only specific types of prey.types of prey. sizes of both sizes of both
populations have a populations have a direct relationshipdirect relationship
ParasitismParasitism
An organism lives An organism lives in or on another in or on another organism to feed organism to feed on the other on the other organism organism parasiteparasite host host
Parasitism vs. PredationParasitism vs. Predation Parasites depend on their hosts; Parasites depend on their hosts;
usually don’t kill them.usually don’t kill them. The host is often weakened or The host is often weakened or
diseased by the parasite.diseased by the parasite.
SymbiosisSymbiosis Relationship where two different Relationship where two different
organisms benefit from each otherorganisms benefit from each other MutualismMutualism CommensalismCommensalism
MutualismMutualism
Relationship between two species where Relationship between two species where both species benefit.both species benefit.
CommensalismCommensalism Relationship between two organisms Relationship between two organisms
where one organism benefits and the where one organism benefits and the other is unaffected.other is unaffected.
CoevolutionCoevolution Can occur with species in symbiotic Can occur with species in symbiotic
relationships. relationships. species may evolve adaptations that species may evolve adaptations that
improve the benefits to each member.improve the benefits to each member.
Species InteractionsSpecies InteractionsInteractioInteractio
n Typen TypeSpecies Species
AA
(harmed (harmed or or
benefitebenefited)d)
Species BSpecies B
(harmed (harmed or or
benefitedbenefited))
DescriptionDescription Your own Your own exampleexample
1.1. CompetitionCompetition
HarmedHarmed HarmedHarmed Both parties Both parties struggle for a struggle for a
limited resourcelimited resource
Coyote and kit fox Coyote and kit fox both hunting both hunting kangaroo ratkangaroo rat
2.2.
3.3.
4.4.
5.5.