Speciation and ExtinctionSpeciation and Extinction

BiogeographyBiogeographyOctober 29 - Nov 2October 29 - Nov 2

Speciation and ExtinctionSpeciation and Extinction

Defining a speciesDefining a species Morphological definitionMorphological definition Biological definition Biological definition SubspeciesSubspecies

Mechanisms of SpeciationMechanisms of Speciation Genetic driftGenetic drift Natural selectionNatural selection Gene flowGene flow

Types of SpeciationTypes of Speciation Allopatric speciationAllopatric speciation Sympatric speciationSympatric speciation

Other IssuesOther Issues Convergent evolutionConvergent evolution Parallel evolutionParallel evolution CoevolutionCoevolution Punctuated equilibriumPunctuated equilibrium

ExtinctionExtinction Probability of extinctionProbability of extinction Recent extinctionsRecent extinctions Fossil extinctionsFossil extinctions

Defining a SpeciesDefining a Species

MorphologicallyMorphologically Species are morphologically distinct Species are morphologically distinct

BiologicallyBiologically Reproductively isolated (geologically or biol)Reproductively isolated (geologically or biol)

SubspeciesSubspecies Populations that are morphologically (and Populations that are morphologically (and

therefore presumably) genetically distincttherefore presumably) genetically distinct

Mechanisms of SpeciationMechanisms of Speciation Genetic DriftGenetic Drift

Changes in genetic characteristics of population due Changes in genetic characteristics of population due to pure chanceto pure chance

Founder EffectFounder Effect Natural SelectionNatural Selection

Change in population (genetic/morphological) Change in population (genetic/morphological) resulting from expression of genetic characteristics by resulting from expression of genetic characteristics by individuals in population that enhances their survivalindividuals in population that enhances their survival

Gene FlowGene Flow Change in genetics of population due to introduction Change in genetics of population due to introduction

of genetic materials from outside the populationof genetic materials from outside the population

Types of SpeciationTypes of Speciation Allopatric SpeciationAllopatric Speciation

occurs when pops are occurs when pops are geographically isolated so geographically isolated so gene flow b/w pops cannot gene flow b/w pops cannot occuroccur

• Vicariance eventsVicariance events• Disperal/Founder eventsDisperal/Founder events• PeripatricPeripatric

Peripheral populations arePeripheral populations are geog. isolated from maingeog. isolated from main population and thus geneticpopulation and thus genetic divergence is accelerated divergence is accelerated (form of Adaptive Radiation)(form of Adaptive Radiation)

Types of SpeciationTypes of Speciation

Sympatric SpeciationSympatric Speciation Speciation occurring within spatially contiguous Speciation occurring within spatially contiguous

populationspopulations• ParapatricParapatric

evolutionary divergence (speciation) in populations that occupy evolutionary divergence (speciation) in populations that occupy different habitat in the same geographic area (sympatric form of different habitat in the same geographic area (sympatric form of adaptive radiation)adaptive radiation)

• Chromosomal changesChromosomal changes Polyploidy in plantsPolyploidy in plants

Other IssuesOther Issues Convergent EvolutionConvergent Evolution

Unrelated species separated geographically evolve similar traitsUnrelated species separated geographically evolve similar traits

Other IssuesOther Issues Parallel EvolutionParallel Evolution

Descendants of an ancestor now isolated evolve in a similar fashionDescendants of an ancestor now isolated evolve in a similar fashion

Other IssuesOther Issues

CoevolutionCoevolution Mutualistic associationsMutualistic associations

Punctuated EquilibriumPunctuated Equilibrium Long periods with no change followed by severe Long periods with no change followed by severe

environmental changesenvironmental changes As compared to phyletic gradualismAs compared to phyletic gradualism

ExtinctionExtinction “ “ The ultimate fate of every species is extinction.” The ultimate fate of every species is extinction.” Brown and Brown and

Lomolino 2000Lomolino 2000

RED QUEEN HYPOTHESISRED QUEEN HYPOTHESIS “ “A species must continually evolve in order to keep pace with A species must continually evolve in order to keep pace with

an environment that is perpetually changing, because all other an environment that is perpetually changing, because all other species are evolving, altering the availability of resources and species are evolving, altering the availability of resources and the nature of biotic interactions.” the nature of biotic interactions.” Van Valen 1973Van Valen 1973

The Probability of ExtinctionThe Probability of Extinction

Taxon levelTaxon level individualsindividuals subspeciessubspecies speciesspecies more inclusive taxon levelsmore inclusive taxon levels trophic cascadestrophic cascades

The Probability of ExtinctionThe Probability of Extinction

Ecological GroupsEcological Groups Large body sizeLarge body size Upper trophic levelsUpper trophic levels Highly specializedHighly specialized Specifc habitatsSpecifc habitats

The Probability of ExtinctionThe Probability of Extinction Population SizePopulation Size

Birth ratesBirth rates Death ratesDeath rates Carrying capacityCarrying capacity

Small populationsSmall populations Intrinsic demographic Intrinsic demographic

eventsevents Extrinsic ecological eventsExtrinsic ecological events

MVP = Minimum Viable MVP = Minimum Viable PopulationPopulation

The Probability of ExtinctionThe Probability of Extinction

Mice and Owl Populations

0

5,000

10,000

15,000

20,000

25,000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Year

Number of mice

0

10

20

30

40

50

60

70

80

90

100

Number of owls

(Quammen 1996: Song of the Dodo, p. 295)

Recent ExtinctionsRecent Extinctions

Passenger PigeonPassenger Pigeon

Barro Colorado IslandBarro Colorado Island

Gray WhaleGray Whale

Fossil ExtinctionsFossil Extinctions

Mass extinctionsMass extinctions Permian-Triassic (225 mybp)Permian-Triassic (225 mybp) Pleistocene megafauna (10-12K ybp)Pleistocene megafauna (10-12K ybp)

• Overkill hypothesisOverkill hypothesis• Climate hypothesisClimate hypothesis

Cretaceous-Tertiary (65 mybp)Cretaceous-Tertiary (65 mybp)

Millenium Ecosystem Assessment 2005