Origin of species

• What is a species?• Modes of speciation• Maintenance of

species• Rate of speciation

Species & Species concepts• Biological Species:• A population or group

of populations whose have the ability to interbreed with one another in nature, producing viable offspring

• Evolutionary species: fossil record, morphology

Modes of speciation

Modes of speciation

• Allopatric speciation• Geographic isolation• Barriers:• Rivers, mountains,

Geographic isolation

Sympatric speciation

• Polyploidy• Change in

chromosome number

Adaptive RadiationMany new species

Maintenance of species

• Reproductive isolating mechanisms

• Pre-zygotic• Post-zygotic

Pre-zygotic barriers

Temporal isolation

Post-zygotic barriers

Rate of speciation

Vertical slope slow Phenotypic change, Horizontal slope fast change

Speciation event

Existing species

Extinction