SpeciationSpeciationFormation of New SpeciesFormation of New Species

Formation of SpeciesFormation of Species

• Formation of Formation of new species is new species is called called speciation.speciation.

• Two or more Two or more new species new species arise from a arise from a previous previous species.species.

Darwin’s Finches of the Galapagos islands

Morphological Concept of Morphological Concept of SpeciesSpecies

– Based on Based on similar similar structures structures (morphology)(morphology)

– Older definition Older definition of species.of species.

– Not used Not used today.today.

how many species do you see?

Biological Concept of SpeciesBiological Concept of Species

– A population of A population of organisms that organisms that can successfully can successfully interbreed.interbreed.

– The same The same population population cannot interbreed cannot interbreed with other with other populations populations successfully.successfully.

LeopardsPanthera uncia

Panthera pardus

Isolating MechanismsIsolating Mechanisms• Speciation begins with separation and Speciation begins with separation and

isolation of a single population into two isolation of a single population into two separate populationsseparate populations

Geographic isolationGeographic isolation• A physical A physical

separation.separation.• Referred to as a Referred to as a

barrierbarrier– CanyonsCanyons– RiversRivers– freewaysfreeways

California Newt, 3 subspecies separated by mountains and waterways

What other types of animals might be geographically isolated?

Reproductive IsolationReproductive Isolation– Reproductive barriers prevent Reproductive barriers prevent

portions of a population from portions of a population from interbreeding.interbreeding.

– Prezygotic isolationPrezygotic isolation: sperm and : sperm and egg cannot reach each other.egg cannot reach each other.• Ecological isolationEcological isolation: same region : same region

different habitatdifferent habitat• Temporal isolationTemporal isolation: Mate during : Mate during

different seasonsdifferent seasons• Behavioral isolationBehavioral isolation: different : different

mating ritual (bird song, dance, mating ritual (bird song, dance, pheromones) pheromones)

TemporalTemporal Ecological Ecological

BehavioralBehavioral

Postzygotic IsolationPostzygotic Isolation

– Fertilization occurs but zygote does not Fertilization occurs but zygote does not survive or offspring cannot reproduce.survive or offspring cannot reproduce.

– Offspring cannot compete successfully for Offspring cannot compete successfully for resources.resources.

Horse Donkey Mule

Summary review1. What is speciation?

2. Give your own examples of geographic isolation and prezygotic isolation and explain how they can lead to speciation.

3. What is postzygotic isolation?

4. What kind of speciation is shown in the cartoons below?