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NIS - BIOLOGY

NIS - BIOLOGY. Lecture 16 Population Dynamics Ozgur Unal. Population Characteristics. Population : the members of a single species that share the same geographic location at teh same time. How can we describe populations ?

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NIS - BIOLOGY

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  1. NIS - BIOLOGY Lecture 16 Population Dynamics OzgurUnal

  2. PopulationCharacteristics • Population:themembers of a singlespeciesthatsharethesamegeographiclocation at tehsame time. • How can wedescribepopulations? • Whataresomeobservationsyou can makeaboutpopulations of insectsoverthecourse of a year? Populations of speciesaredescribedbydensity, spatialdistributionandgrowth rate. Thesecharacteristicsareusedtoclassifyallpopulations of organismsincludingbacteria, animalsandplants.

  3. PopulationDensity Populationdensityis thenumber of organismsperunitarea. Inordertofindtheaveragepopulationdensity, simplydividethe total number of organismsby total area. Figure 4.1 and 4.2!

  4. SpatialDistribution Populationdensitymight not be uniformeverywhere. Dispersionis thepattern of spacing of a populationwithin an area. Mainlythreetypes of dispersion: uniform, clumpedandrandom.

  5. SpatialDistribution • Whatadvantage do smallerfishgainbyformingclumpedgroups? Figure 4.2 Whichtype of populationdistributionallowsyoutopredictmoreaccuratelyhowmanyindividualsreside in a givenarea?

  6. PopulationRanges • Nopopulation (not eventhehumanpopulation) occupiesallhabitats in thebiosphere. • Somespecieshaveverylimitedpopulationrangeordistribution. • Examples: Iiwi, peregrinefalconetc. Whatarethereasonswhysomespeciesare not abletoexpandtheirpopulationrange?

  7. PopulationLimitingFactors • Allspecieshavelimitingfactors, whichkeepthemfromcontinuingtoincreaseindefinitely. • Example: Foodsupply.. • Ifthefoodsupplyincreases, a largerpopulationmightresult. If it decreases a smallerpopulationmightresult. Populationlimitingfactors can be groupedintotwo: density-independentfactorsanddensity-dependentfactors.

  8. PopulationLimitingFactors • Density-independentfactors: • Anyfactor in an environmentthatdoes not depend on thenumber of members in a populationperunitarea is a density-independentfactor. • Thesefactorsareususallyabioticandincludenaturalphenomenasuch as weatherevents. Example:Ponderosapinetrees

  9. Density-IndependentFactors • Example:Humpbackchubfish in Colorado River.

  10. Density-DependentFactors • Density-dependentfactors: • Anyfactor in an environmentthatdepends on thenumber of members in a populationperunitarea is a density-dependentfactor. • Thesefactorsareoftenbioticfactorssuch as predation, disease, parasiteandcompetition. Predation:

  11. Density-DependentFactors • Disease: This is a density-dependentfactor. • Whenpopulationdensity is high, diseasesaretransmittedeasilyfromoneindividualtoanotherbecausecontactbetweenindividuals is morefrequent. Competition: Competitionbetweenorganisms increaseswhendensityincreases. Competition can occurwithin a speciesorbetweentwodifferent speciesthatusethesameresource.

  12. Density-DependentFactors • Parasites: • The presence of parasites is a density-dependentfactorthat can negativelyaffectpopulationgrowth at higherdensities.

  13. NIS - BIOLOGY Lecture 17 PopulationGrowth OzgurUnal

  14. PopulationGrowth Rate Checkthisout! http://www.molecularstation.com/science-videos/video/85/bacteria-growth/ How is thegrowthrate of thesebacteria? Do theygrowfastorslowby time? Howwouldyouplotthenumber of bacteria vs time?

  15. PopulationGrowth Rate Populationgrowth rate (PGR) explainshowfast a givenpopulationgrows. Whatfactors do youthinkaffectthe size of a population? • Thenatalityof a population is thebirthrate, orthenumber of individualsborn in a given time period. • Themortalityof a population is thenumber of deathsthatoccur in a given time period. • Emigrationis thetermtodescribethenumber of individualsmovingawayfrom a population. • Immigrationis thenumber of individualsmovinginto a population.

  16. PopulationGrowthModels Therearetwomathematicalmodelsusedtodescribepopulationgrowth: Exponentialgrowth model andlogisticgrowth model. ExponentialGrowth Model: Rememberthebacteriagrowth. Thegrowth rate wassmall at first, but then it increasesrapidly. Theinitialgrowth rate is smallandcalledlagphase. Exponentialgrowthoccursafterthelagphase. Similarly, a micepopulation in an areawithlargefoodsupplygrowsexponentially.

  17. ExponentialGrowth Model Thegraph of exponentialgrowth is J-shaped. The rate of growth is proportionaltothe size of thepopulation. Allpopulationsgrow exponentiallyuntilsome limitingfactorslowsthe population’sgrowth.

  18. LogisticGrowth Model Logisticgrowthoccurswhenthepopulation’sgrowthslowsorstopsafterexponentialgrowth, at thepopulation’scarryingcapacity. Manypopulationsgrowlike in this model, ratherthan exponentialgrowth. S-shapedcurve is typical forlogisticgrowth. A populationstops increasingwhennatality is lessthanmortality, orwhenemigration exceedsimmigration.

  19. LogisticGrowth Model Carryingcapacityis themaximumnumber of individuals in a speciesthat an environment can supportforthelongterm. Carryingcapacity is limited bytheenergy, wateroxygen, andnutrients.

  20. ReproductivePatterns Thelogistic model showsthenumber of individualsincreasinguntilthecarryingcapacity is reached. However, thereareadditionalfactorsthatmust be consideredforrealpopulations. Number of birthsperreproductioncycle, theagethatreproductionbegins, life span of theorganism.. • r-strategists: The rate strategy is an adaptationforliving in an environmentwherefluctuation in bioticandabioticfactorsoccur (such as availability of foodorchangingtemperature). • Example: Fruitflyorlocusts • r-strategistsusuallyhaveshort life spanandproducemanyoffsprings.

  21. ReproductivePatterns • k-strategists: Thecarryingcapacitystrategy is an adaptationforliving in environmentsthat do not fluctuatemuch. • k-strategistsaregenerallylargerorganismsthathave a long life spanandproducefewoffspring. • Theirpopulationreachesequilibrium at thecarryingcapacity. • Populations of k-strategistsusuallyarecontrolledbydnesity-dependentfactors. Populations of r-strategistsusuallyarecontrolledbydensity-independentfactorsandtheyusually do not maintain a populationnearthecarryingcapacity.

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