Population EcologyPopulation Ecology

Elizabeth PetrieElizabeth Petrie

Jill StittleburgJill Stittleburg

Sherry WiedmanSherry Wiedman

Today’s objectives:Today’s objectives:

• Define carrying capacityDefine carrying capacity

• Describe how and why population Describe how and why population growth rates change as the growth rates change as the population approaches carrying population approaches carrying capacitycapacity

• Discuss the “sixth extinction” and Discuss the “sixth extinction” and measurement of extinction ratesmeasurement of extinction rates

• Analyze human causes of extinctionAnalyze human causes of extinction

Changes in Population SizeChanges in Population Size

• What causes populations to change in What causes populations to change in size?size?

• What are some factors that may limit What are some factors that may limit population growth?population growth?

• Is there a point at which the population Is there a point at which the population cannot grow anymore? Why or why not?cannot grow anymore? Why or why not?

• Population growth is a function of birth Population growth is a function of birth rate and death rate-rate and death rate-

If birth rate > death rate, population If birth rate > death rate, population increasesincreasesIf death rate > birth rate, population If death rate > birth rate, population

decreasesdecreases

If birth rate = death rate, then the If birth rate = death rate, then the population population stablizesstablizes

Limiting Factors-Limiting Factors-

• An environmental factor that prevents a An environmental factor that prevents a population from increasing.population from increasing.

Lack of :

food

water

shelter

space

There are 2 types of limiting There are 2 types of limiting factors:factors:

• Density dependent factorsDensity dependent factors

• Density independent factorsDensity independent factors

Density- dependent factorsDensity- dependent factors• Limiting factors that increase in Limiting factors that increase in

intensity as the population increases in intensity as the population increases in size.size.

• Will reduce birth rates or increase death Will reduce birth rates or increase death ratesrates

Ex. limited food suppliesEx. limited food supplies

increased risk of infectious increased risk of infectious diseasedisease

toxins due to increased waste toxins due to increased waste levelslevels

Density-independent factorsDensity-independent factors

• Influence population rates regardless Influence population rates regardless of their densityof their density

Ex. weather events: drought, Ex. weather events: drought,

floods, extreme floods, extreme temperaturestemperatures

human interventionshuman interventions

Carrying capacityCarrying capacity

• The maximum population that can be The maximum population that can be supported indefinitely in a given supported indefinitely in a given environmentenvironment

• Populations that are experiencing Populations that are experiencing exponential growth eventually reach exponential growth eventually reach carrying capacitycarrying capacity

Fruit Fly Population Growth

Population GrowthPopulation Growth

• When conditions are good, a When conditions are good, a population can grow exponentiallypopulation can grow exponentially

• The effects of declining resources The effects of declining resources gradually slow growth rategradually slow growth rate

• Growth rate declines to zero as it Growth rate declines to zero as it approaches carrying capacityapproaches carrying capacity

• If a population grows beyond the If a population grows beyond the carrying capacity, a population crash carrying capacity, a population crash may occurmay occur

14.1: The Sixth Extinction14.1: The Sixth Extinction

• VocabularyVocabulary– Extinction: complete loss of a speciesExtinction: complete loss of a species– Biodiversity: entire variety of living Biodiversity: entire variety of living

organismsorganisms– Endangered Species Act: law passed in Endangered Species Act: law passed in

1973 with the purpose of protecting and 1973 with the purpose of protecting and encouraging the population growth of encouraging the population growth of threatened and endangered speciesthreatened and endangered species

Endangered Species Act Endangered Species Act (ESA)(ESA)• Written and passed because humans Written and passed because humans

seemed to be triggering the rapid rate at seemed to be triggering the rapid rate at which species were being lostwhich species were being lost

– Ex: passenger pigeon, whooping crane, bald Ex: passenger pigeon, whooping crane, bald eagles, elephant sealseagles, elephant seals

• Critics of ESA say that saving all species Critics of ESA say that saving all species is unrealistic goal because extinction is a is unrealistic goal because extinction is a natural processnatural process

– The 10 million species living today represent The 10 million species living today represent only 1% of all species that have ever existedonly 1% of all species that have ever existed

Measuring Extinction Rates Measuring Extinction Rates • Earth’s history highlighted by 5 mass extinctions Earth’s history highlighted by 5 mass extinctions

thus farthus far– Mass extinction: period of a few thousand or Mass extinction: period of a few thousand or

few hundred years in which 50%-90% of living few hundred years in which 50%-90% of living species lostspecies lost

From http://www.jkaneart.com/massextinctiongraph.htm

Causes of Mass ExtinctionCauses of Mass Extinction

• First five thought to be caused by First five thought to be caused by natural global changes: changes in sea natural global changes: changes in sea level and climate fluctuations, changes level and climate fluctuations, changes in ocean and land forms—continental in ocean and land forms—continental drift, asteroid impactdrift, asteroid impact

• The sixth mass extinction (that The sixth mass extinction (that scientists currently believe we are scientists currently believe we are experiencing) is being caused by human experiencing) is being caused by human activityactivity

Human causes of extinction:Human causes of extinction:

• Habitat DestructionHabitat Destruction

• Habitat FragmentationHabitat Fragmentation

• Introduced SpeciesIntroduced Species

• OverexploitationOverexploitation

• PollutionPollution