Biology 1001A Lecture Notes - Lecture 21: Species Problem, Reproductive Isolation, Probability Distribution

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Lecture21SpeciesConceptsandSpeciation
Whydoesitmatterhowwedefineaspecies?
● Whatdowemeanwhenwetalkaboutaspecies?
○ Example:Easterngraywolves(fromLiteracy5)Aretheyadistinctspecies,a
subspecies,orahybridoftwowolfspecies?
● Lumpingvs.Splitting
○ Lumping:Payingattentiontosimilaritiesandclassifyingtwopopulationstogether
asonespecies
○ Splitting:Payingattentiontodifferencesandsplittinguppopulationsasdistinct
species
150+yearsafterOriginofSpecies,stillnoperfectdefinitionofspecies
● Over50speciesconceptshavebeenproposed
MorphologicalSpeciesConcept:diagnosticphysicalcharacteristics
● Species=“adistinctclusterinphenotypicspace,non
overlappingwithothersuchclusters”
○ Everythinginoneclusterwouldbethesamespeciesas
everythingelseinthesamecluster
● Or,thingsthatlookthesameprobablybelongtothesame
species
LimitationsoftheMorphologicalSpeciesConcept:Howmanyspecies?
● Basesspeciesonvisiblecharacteristics
○ Sillydelineationsmayarise
● Hasproblemswithsexualdimorphism
○ Example:Femalemallardduckslookdifferentfrommalemallardducks
● Hasproblemswhenthere’svariationinphenotypeinapopulation
○ Hastroublehandlingcontinuousvariation
○ Example:Fourspidersofdifferentappearancemaybedefinedasdifferent
species
● Mayconsidertwosimilarspeciestobeone
BiologicalSpeciesConcept:reproductiveisolation&sharedgenepool
● Species=“aninterbreedingorpotentiallyinterbreedinggroupofindividuals,
reproductivelyisolatedfromothersuchgroups”
● Or,thingsthatfreelyinterbreedandproducefertileoffspringbelongtothesamespecies
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