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 an environment that is perpetually changing, because all other species are evolving, altering the availability of other species are evolving, altering the availability of resources and the nature of biotic interactions.” resources and the nature of biotic interactions.” Van Valen Van Valen 19731973
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 ExtinctionMice 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 23Year
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
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