CES210 Chapter Six
CES210 Chapter Six CES 210
Popular in Introduction to Conservation and Environmental Science
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This 2 page Class Notes was uploaded by Emma Eiden on Friday October 7, 2016. The Class Notes belongs to CES 210 at University of Wisconsin - Milwaukee taught by Mai Phillips in Fall 2016. Since its upload, it has received 27 views. For similar materials see Introduction to Conservation and Environmental Science in GN Natural Science at University of Wisconsin - Milwaukee.
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Date Created: 10/07/16
CES210:ConservationandEnvironmentalScience ChapterSix: Population CaseStudy:Fishing to Extinction? - Populationbiology, thescience of modeling changes in species abundance,is key to understandingthis controversy - Populationbiology allows us to identify overfishing,to modelsustainablecatch rates, and to warn abouthowquickly the species might disappearat current capturerates DYANMICSOF POPULATIONGROWTH - A 500poundfemaleBluefin can lay 30million eggs in a singlespawningseason, butfew ofthose hatchings will makeit to maturity. Ababy tunahas a less than aonein amillion chanceof survival. Ifit does liveto maturity, however,there’s almost nothingin theocean that can catch oreat it – except humans.Ordinarily thehigh fecundity ofadult females makesup forthehigh mortality among juveniles - Describing thegeneral pattern of populationgrowthis easier if wecan reduce it to a fewgeneral factors.Ecologists find it mostefficient and simplest to usesymbolicterms such as N, r, andt to refer to thesefactors Exponential growthinvolves continuouschange Exponential growthleads to crashes - Carrying capacity is theterm forthenumberorbiomassof aspecies that can be supportedin a certain area withoutdepleting resources - Shortages offoodorotherresources eventually lead to a populationcrash, orrapid dieback Logistic growthslowswith populationincrease - Logistic growthis density-dependent,meaning that thegrowthrate dependson population density.Many density-dependentfactorscan influencepopulation: overcrowdingcan increase disease rates, stress,and predation.These factors can lead to smallerbody sizeand lower fertility rates. Crowdingstress alonecan affectbirth rates. - Density-independentfactorsalso affectpopulations.Often theseare abiotic(non-living) disturbances,such as droughtorfire orhabitat destruction, which disrupt an ecosystem - R-selected species havea high reproductiverate(r) butgive little ornocare to offspring,which havehigh mortality - K-selected species growthslows as thecarrying capacity (K)oftheir environmentis approached FACTORSTHAT REGULATEPOPULATION GROWTH - To complicate it still further,wecan consider thefourfactors that contributeto r, orrate of growth.Thesefactors are Births, Immigration fromotherareas, Deaths, and Emigration to other areas Survivorshipcurves showlife histories - Several general patterns ofsurvivorshipscan beseen in this idealized figure Intrinsicand extrinsic factors are important - Factors that regular populationgrowth,primarily by affecting natality ormorality, and can be classified in different ways.They can be intrinsic (operating within individualorganismsor between organismsin thesamespecies) orextrinsic (imposedfromoutsidethepopulation). Factors can also be either biotic(caused byliving organisms)or abiotic (causedby nonliving componentsofthe environment) - In general, biotic regulatory factors tend to bedensity-dependent,whileabioticfactors tend to bedensity-independent Somepopulationfactors aredensity-independent;others are density-dependent - Density-dependentmechanismstend to reduce populationsize by decreasing natality or increasing mortality as thepopulation sizeincreases. Mostofthem are theresults of interactions between population ofa community(especially predation),butsomeof themare based on interactions within apopulation - Notall interspecific interactions are harmfulto oneof thespecies involved.Mutualism and commensalism,forinstance, are interspecific interactions that are beneficial orneutral in terms of populationgrowth Density-dependenteffects can bedramatic - Unusuallyheavy rains in the Saharain 2004created theconditions fora locust explosion. Four generations bred in rapid succession,and swarmsof insects moved outof thedesert. 28 countries in Africaandthe Mediterranean area wereafflicted. Crop losses reached 100%in someplaces and foodsupplies formillions ofpeople werethreatened. Officials at the United Nationswarned that wecould beheaded towardsanothergreat plague. Hundredsof thousands of hectares of land weretreated with pesticides, but millions of dollars of crop damagewere reported anyway CONSERVATIONBIOLOGY - A critical questionin conservationbiology is in theminimum populationsizeof arare and endangered species required forlong-term viability Island biogeographydescribes isolated populations - Island biogeographyis theidea that diversity in isolated habitats dependson rates of colonization and extinction, which depend on thesizeor isolation oran islands - Thetheory of abalance that smallpopulationsare especially likely to disappear, has been applied toexplain species dynamics in many small, isolated habitat fragments,whetheron islands ornot Conservationgenetics helps predict survivalofendangered species - Different gene typeswill bedistribution in the offspringin thesameratio in which they occurin theparents, and genetic diversity is preserved - In large population,theseconditions formaintaining genetic equilibrium are generally operative. The additionor loss ofafew individuals orthe appearance ofnew genotypes makes little differencein thetotal genepool, and genetic diversity is relatively constant.In small, isolated populations,however,immigration, mortality, mutations,orchance mating events involving only afewindividuals can greatly alter the genetic makeupof thewholepopulation. We call thegradualchanges in genefrequencies due torandom events geneticdrift. - A foundereffect ordemographicbottleneck occurs when justafew members ofa species surviveacatastrophicevent orcolonize new habitat geographically isolated fromother members ofthe samespecies Populationviability analysis calculates changes ofsurvival - Conservationbiologists usetheconcepts of island biogeography,genetic drift,and foundeffects to determine minimumviable populationsize, ornumberof individuals needed forlong-term survivalorrare and endangered species. - A meta-populationis collection of populationsthat haveregular orintermittent gene flow between geographically separateunits Additionalhelpfulterms to study:https://quizlet.com/152805324/conservation-and-environmental- science-chapter-six-population-biology-flash-cards/(copyandpaste)
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