Speciation

1
Speciation

• Species
• Types of Speciation
• Evolutionary Changes Over Time

2
Species

• Groups of interbreeding natural populations that
  are reproductively isolated from other groups
• Genetic divergence
• Gene pools accumulate differences in genetically
  separated populations
• May result from geographic barriers

3
What prevents species from interbreeding?

• Pre-zygotic barriers
• Behavioral isolation
• Recognizing specific barriers
• Temporal isolation
• Reproductive maturity at different times
• Mechanical isolation
• Incompatible structures
• Ecological isolation
• Adapted to certain microenvironments
• Gametic mortality
• Prevention of pollen tube formation

4
What prevents species from interbreeding?

• Post-zygotic barriers
• Death of zygotes
• Sterile hybrids

5
Types of Speciation

• Allopatric speciation
• Physical barriers arise which stop gene flow
  between populations
• Archipelagos island chains away from continent
• Genetic divergence within and between islands may
  lead to new episodes of allopatric speciation
• Galapagos Islands, Hawaiian Islands

6
Types of Speciation

• Sympatric speciation
• New species form within an existing population
• ex. Cichlid populations within the same lake
• Polyploidy
• Occurs mostly in plants, when offspring have more
  that 2 copies of genetic material

7
Types of Speciation

• Parapatric speciation
• Neighboring populations become distinct species
  along a common border

8
Ideas of how evolutionary changes occur over time

• Gradualism
• Small morphological changes over time
• Punctuated equilibrium
• Abrupt changes in short period of time

9
Ideas of how evolutionary changes occur over time

• Adaptive radiation
• Burst of divergences from a single lineage
• Extinction
• Total loss of a species
• Mass extinction are caused by catastrophic events
• 99 of all species that have ever lived are
  extinct