Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Chapter 16The Origin of Species1Species• The basic unit of taxonomic classification• a population that evolves independently of other populations• The biological species conceptKingdom-Phylum-Class-Order-Family-Genus-Species216.1The Biological Species ConceptBased on the observation that reproductive isolation ensures evolutionary independence Defining a species can be confusingAppearance can be misleading…•Some organisms look very similar but are different species•Some organisms look different but are the same species316.1Species416.1Fig 16.1Species516.1Fig 16.26How is reproductive isolation between species maintained?Isolating mechanisms – traits that maintain reproductive isolation• Premating isolating mechanisms•Traits or mechanisms that prevent mating between species• Postmating isolating mechanisms • mechanisms that prevent the formation of vigorous, fertile hybrids between species16.2716.2Premating Isolating Mechanisms1. Geographic isolation2. Ecological isolation3. Temporal (time-related) isolation4. Behavioral isolation5. Mechanical incompatibilities816.2Premating Isolating Mechanisms: Geographic IsolationInterbreeding is prevented because species live in different areasDoes not necessarily mean they cannot interbreedSo geographic isolation is usually considered more of a mechanism that allows new species to form916.2Premating Isolating Mechanisms: Geographic IsolationKaibab squirrel lives only on the north rim of the Grand CanyonAbert squirrel lives only on the south rim of the Grand CanyonGeographically isolated but are they a separate species?Fig 16.310Premating Isolating Mechanisms: Ecological IsolationDifferent species may occupy Different habitats within the sameGeneral areaWhite-crowned sparrow inhabitsFields and meadowsWhite-throated sparrow inhabitsDense thickets16.211Premating Isolating Mechanisms: Temporal IsolationDifferent species may breed at different timesBishop pine releases pollen in the summerMonterey pine releases pollen in early spring16.2 Fig 16.512Premating Isolating Mechanisms: Behavioral IsolationDifferent species may have different courtship signals and behaviorsColors, mating calls etc.16.2Fig 16.613Premating Isolating Mechanisms: Mechanical IsolationDiffering sexual organs may foil mating attempts16.2Fig 16.714Postmating Isolating MechanismsServe to limit hybrid offspringGametic incompatibility – sperm from one species may not be able to fertilize eggs of anotherHybrid inviability – hybrids either abort early in development due to genetic differences, or have difficulties performing tasks like carrying nest material16.215Postmating Isolating MechanismsHybrid infertility• Most commonly because due to inability of chromosomes to pair up properly during meiosis so gametes fail to develop16.2Fig 16.81616.21716.3So how do new species form??Speciation – the process by which new species formSpeciation depends on two factors•Isolation•Genetic divergenceIsolation followed by genetic divergence can occur in several different ways1816.3So how do new species form??There are two broad categories of pathways to speciationAllopatric speciation• when two populations are geographically separated from one anotherSympatric speciation• when two populations share the same geographic area1916.3Geographic separation can lead to allopatric speciation•Organisms may colonize isolated habitats•Landscape changes(rising sea levels, formation of mountain ranges, etc.) may isolate populationsGenetic differences between two isolated populations may become sufficient to prevent interbreeding2016.3Geographic separation can lead to allopatric speciationFig 16.92116.3Genetic isolation without geographic separation can lead to sympatric speciationCan occur in an area with two distinct types of habitatsBiologists are watching such an event right now in a species of fruit fly!22Genetic isolation without geographic separation can lead to sympatric speciationR. pomonella is a fruit fly that lives in hawthorn trees• Lays eggs in the fruit• Maggots hatch and eat the fruitAbout 150 years ago scientists notices that r.pomonella had started to infest apple trees (introduced from Europe)16.323Genetic isolation without geographic separation can lead to sympatric speciationtoday is appears that r.pomonella is splitting into two separate speciesOne breeds in hawthorn trees and one breeds in apple trees16.324Fig 16.1016.32516.3Genetic isolation without geographic separation can lead to sympatric speciationBut apples and hawthorns typically grow in the same areas, so how is reproductive isolation maintained??• female flies tend to lay their eggs in the same type of fruit that they developed•Males also prefer the same fruit26Under some conditions many new species may arise in a relatively short amount of time This is called adaptive radiation•Can occur when a species encounters a location that has a wide variety of habitatsEx. Ancestral silversword plants and the Hawaiian islands16.327About 30 different species of silversword plants inhabit the Hawaiian Islands and they all descended from a single ancestral speciesFig 16.1216.32816.3Under some conditions many new species may arise in a relatively short amount of time Fig 16.1129What causes extinction??Extinction is the death of all remaining members of a species99.9% of all species that have ever existed are extintThe immediate cause of extinction is almost always environmental change16.430What causes extinction??Habitat change and habitat destruction are the leading causes of extinction•Present-day habitat destruction by humans is proceeding at a rapid pace•Many biologists believe that we are in the midst of the most fast paced, widespread episode of species extinction in the history of life•As many as 50% of the species on earth face extinction as we continue to clear the rainforest16.431What causes extinction??Golden Toad•Lived only in the monteverde cloud•Has been recentlyDeclared extinctSource: Mother Nature Network16.43216.4What causes extinction??Interaction with other species can also cause extinction•Competition•Organisms compete for limited resourcespredation3316.4Some species are at a high risk
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